Some background info. This is my first grow. I am currently using a 4x4 tent with 8 plants (4 of these plants will be moved outside in a week or two). 3 of my plants have a couple of the bottom leaves turning a yellowish green tent and have yellowish, orangish, brown spots. These plants are 23 days old and have experienced some stress over the past week. All of the plants were doing fantastic until I had to stay in the hospital for a few days and the person I left in charge of watering them only watered them once, and not a lot of water either. When I came home all the plants were dehydrated. I then overcorrected and gave them too much water. They were in jiffy pots in FoxFarm Ocean Forest. I moved them to 1-gallon fabric pots using Coast of Maine Stonington Blend 3 days ago. At first, it looked like they were recovering nicely but now I am seeing yellowing of the some of the bottom leaves and brownish yellowing spots. I just checked my PH of my water which is 5.85 and my soil which in 6.8. I have not used any fertilizer.....just well water. What should I do now?
Newbie needing help diagnosing spots on leaves!
- Thread starter Lovie
- Start date
It is almost impossible to give the plants too much water in one watering session. Let the soil dry out a bit and then resume the normal and proper watering schedule.
The problem is giving the plant too much water all the time which keeps the soil from drying out from top to bottom.
It is possible that some of the lower leaves are not recovering fully from when the plants dried out. Kind of hard to tell at this point. Might have to wait a week or so to see if the yellowing problem continues and gets worse.
Two things. The pH of the water is a tad below the recommended pH for growing in an organic/mineral based soil. The recommended number for the water is often a 6.3 pH.
Do not worry about the pH in/of the soil. More often than not if a grower starts trying to figure out what to do about soil pH numbers they end up running around in circles trying to get the number to match something or another for more than a couple of minutes.
Wait and watch what happens.
Welcome to 420Magazine my friend.Some background info. This is my first grow. I am currently using a 4x4 tent with 8 plants (4 of these plants will be moved outside in a week or two). 3 of my plants have a couple of the bottom leaves turning a yellowish green tent and have yellowish, orangish, brown spots. These plants are 23 days old and have experienced some stress over the past week. All of the plants were doing fantastic until I had to stay in the hospital for a few days and the person I left in charge of watering them only watered them once, and not a lot of water either. When I came home all the plants were dehydrated. I then overcorrected and gave them too much water. They were in jiffy pots in FoxFarm Ocean Forest. I moved them to 1-gallon fabric pots using Coast of Maine Stonington Blend 3 days ago. At first, it looked like they were recovering nicely but now I am seeing yellowing of the some of the bottom leaves and brownish yellowing spots. I just checked my PH of my water which is 5.85 and my soil which in 6.8. I have not used any fertilizer.....just well water. What should I do now?
Your girl doesn't look too bad.
That soil should feed her for a bit.
One thing to keep in mind if your leaf tips sit on top of the soil they are prone to necrosis.
If you set ph on your feed water it should be 6.3, that'll help her pick up nutrients better and improve color.
Do you have a line of nutrients for future use?
Stay safe
Bill284
- Thread starter
- #4
Thank you for your response! After I posted this I noticed my Do-Si-Do leaves appeared to be showing signs of being over-watered. I searched for signs of over-watering and found this 5 Surprising Signs of Overwatering | Grow Weed Easy and some of the pics in this article look similar to what I have going on. I have been using this soil tester as a guide. The instructions say to insert to root level. It says the moisture level for cannabis should be between 6-9. I have been waiting until the moisture level at root level is between 4-5 before giving water. However, even though the moisture level at root level may be 4-5 the bottom of the pot the moisture level is 10. My plants are currently sitting on the bottom of the tent so I was going to find something to put them on to allow air flow along the bottom. Do you have any experience using a soil tester to monitor moisture levels? If so, what are your thoughts?
Those testers are notoriously unreliable.Thank you for your response! After I posted this I noticed my Do-Si-Do leaves appeared to be showing signs of being over-watered. I searched for signs of over-watering and found this 5 Surprising Signs of Overwatering | Grow Weed Easy and some of the pics in this article look similar to what I have going on. I have been using this soil tester as a guide. The instructions say to insert to root level. It says the moisture level for cannabis should be between 6-9. I have been waiting until the moisture level at root level is between 4-5 before giving water. However, even though the moisture level at root level may be 4-5 the bottom of the pot the moisture level is 10. My plants are currently sitting on the bottom of the tent so I was going to find something to put them on to allow air flow along the bottom. Do you have any experience using a soil tester to monitor moisture levels? If so, what are your thoughts?
Your better off feeling the weight of the pot after watering.
Then monitor the weight.
When it's light and your girl gets a slight droop then feed again to run off.
Stay safe
Bill284
- Thread starter
- #6
Thank you! I am going to follow Coast of Maine Stonington Blend feeding schedule and recommend products. My next transplant my plants will be moved into 5-gallon containers. My outdoor plants will get one more transfer into 25-gallon containers so their feeding will be slightly different than my indoor plants. I read that normally well water your PH will already be in range so until last night I hadn't checked it. I am going to start adding a touch of baking soda to the water to bring the PH up before watering from now on. I figure since this soil is designed for cannabis already, I should follow their instructions.Welcome to 420Magazine my friend.
Your girl doesn't look too bad.
That soil should feed her for a bit.
One thing to keep in mind if your leaf tips sit on top of the soil they are prone to necrosis.
If you set ph on your feed water it should be 6.3, that'll help her pick up nutrients better and improve color.
Do you have a line of nutrients for future use?
Stay safe
Bill284
- Thread starter
- #7
I was under the impression when using super soil that you shouldn't water until you have run-off because it will cause leaching. Is this not correct?Those testers are notoriously unreliable.
Your better off feeling the weight of the pot after watering.
Then monitor the weight.
When it's light and your girl gets a slight droop then feed again to run off.
Stay safe
Bill284
The tap root needs something to chase.
You should water until you get a little water coming out.
Otherwise you only get water in half your pot.
Missing the rest of the roots.
A little run-off is always the best way to ensure the entire pot has moisture.
And the tap root keeps chasing moisture.
Watering the outside edges until runoff is what I've always done.
Regardless of what's in the pot.
Good for the roots.
Stay safe
Bill284
Theoretically, yes. The water would pick up soluble nutrients and carry them out the drain holes. But in a soil containing a lot of organic & composted material the micro-organisms will replace what has been drained out within a day.
Thing is that some growers figured that if coco coir or peat moss based soils had to be watered to 10% runoff then so did mineral/organics based soils. Ended up that for years that was the popular way to do it. Even in the popular "how to water a potted plant" thread the author, Emilya Green, would recommend 10%. Then over the years she started to recommend watering until the runoff would just start to happen.
- Thread starter
- #10
That makes sense. Thank you!The tap root needs something to chase.
You should water until you get a little water coming out.
Otherwise you only get water in half your pot.
Missing the rest of the roots.
A little run-off is always the best way to ensure the entire pot has moisture.
And the tap root keeps chasing moisture.
Watering the outside edges until runoff is what I've always done.
Regardless of what's in the pot.
Good for the roots.
Stay safe
Bill284
- Thread starter
- #11
As long as there is water at the bottom of the pot for the roots.
Make sure they get moisture!
Stay safe
Bill284
- Thread starter
- #13
Thanks. I am reluctant to water until run-off because the Coast of Maine feeding schedule has a note that says if you water until run-off additional nutrients will need to be added. I have not studied this enough to feel confident in knowing what to add, when, and how much. I figure this product line is designed specifically for cannabis and their botanist have conducted several field studies to come up with their feeding chart so I am going to trust it as long as everything looks good.As long as there is water at the bottom of the pot for the roots.
Make sure they get moisture!
Stay safe
Bill284
Almost all newb problems tend to stem from either over or underwatering. I'm going to post a post that I read on another site that answered a lot of questions I had but never really got a definitive answer to. The post also showed me things I had no idea were going on in the soil.
I am not the author. Read and learn.
This will be a long read based on my personal knowledge, opinions, research and others work to consolidate information for our members. I'm not presenting my opinions as facts so take from this what you like. I will be putting it in subsection format for easy reference.
First, I want to make an important point to take into consideration before reading. The tap root will grow directly downwards to the bottom of the container before spreading out.
PERCHED WATER TABLE
What is it?
The perched water table is basically the height of the saturation zone where capillary action and gravity cancel each other out. This area will be saturated with water and will be responsible most growers' issues with watering practices especially in soil grows.
WHAT IS CAPILLARY ACTION
CAPILLARY action is is the combination of the cohesive and adhesive properties of water.
In short adhesion is water clinging to the media (think of it like wicking or soaking up)
Cohesion is where the water clings to itself.
So as the water is wicked up (adhesion) it pulls more water with it through Cohesion and at the point gravity and these properties cancel each other out is the perched water table.
This perched water table will always remain the SAME HEIGHT and will always stay saturated unless taken up by the plants or evaporates when the pot dries out. No matter the container height, depth or volume of media. So, if a tall skinny container had a perched water table of 1" then a short wide one of the same media will also have a perched water table of 1". Which means the ratio of water to air in a wide pot will be higher than a tall skinny pot which will have a higher air to water ratio... keep this in mind as we get further.
Different media's have different perched water tables. A more absorbent media will have a higher perched water table than a less absorbent media... REMEMBER THIS as it makes a big difference on pot selection for your media.
DIFFERENT MEDIA
Water holding capacity is directly related to the height of the perched water table so soils with more clay or silt and less sand will have a higher perched water table than those with more sand because sand is a larger particle.
The larger the overall particles of the media the lower the perched water table and better the drainage.
By adding things like perlite or vermiculite (while vermiculite is good at absorbing water it also improves drainage so its helpful in keeping a more even level of moisture throughout the media while increasing drainage due to its size) we can lower the perched water table by reducing the wicking (adhesion) ability and creating more space between particles overall reducing the cohesion effect and in turn the height of the perched water table.
Media like peat based or coco have a much higher drainage and lower perched water table than soil and are therefore less susceptible to over watering but will require more frequent watering due to the lower water holding capacity.
Adding things like perlite or hydroton to the bottom of the pots will NOT reduce the water table but instead raise it. This is because as I said the height of the water table will not change for a given media. So, if you add things like that to the bottom you are essentially just moving the water table up.
Basically, the larger the particles IN the media the better drainage and lower the water table.
If you want to see the height of your perched water table use a clear cup with drain holes fill with media and saturate it. Wait a few hrs for drainage and then come back and look. You can see the difference in the varying media's if you want to experiment.
If you feel you have over watered or your perched water table height is too high you can simply tilt your pot on a 45 degree angle and release more water from the media as runoff. To help visualize think of it this way if you have a perched water table of 2”. You can draw an imaginary horizontal line at that height, when you tilt the pot you have less media below that line and therefore you will have less water in the pot after tilting it.
POT SIZE
I have already covered this a bit, but my opinion is if you are using a media with a higher water table you will benefit from taller narrower pots and if using a media with a lower perched water table the shorter wider ones may benefit you depending on your watering practices.
I prefer the taller over wider no matter the media as I choose to water often and have a higher air holding capacity and lower water table but that can work against you if you can't water as frequently and as plants grow it can greatly increase the frequency required as the roots will be pulling the water out of that saturation zone quickly. So, you may want to use taller pots for small plants and transplant into a wider one as they grow.
You also don't want a pot that's to tall and the top portion of the media is drying out to fast while the bottom is wet.
Let's use seedlings as an example take a solo cup or a large container... the water table will be the same height in either. I see so often ppl trying to water a tiny bit in circles or mist the surface and for lack of other words IT DRIVES ME NUTS. Why? Because the roots are so shallow they are not at risk of being over watered. Remember though, tap roots grow straight down so we need to be mindful as they grow depending on the gas exchange of the media that the majority of roots are not sitting in the saturated zone with poor gas exchange because this will cause lack of oxygen that we incorrectly refer to as overwatering which is actually the cause not the symptom.
It's important to fill containers to the top to give us a good amount of space above the perched water table that high in o2. If you fill a solo cup halfway with soil it's likely to be sitting in the saturation zone and will not do well.
Also going to make the point that plants will be most susceptible to overwatering when the roots first hit the bottom and spread out until they fill the bottom and start moving back up out of the saturation zone. So, again, it may be more beneficial to use a taller narrow pot for the early stages of growth (2-4 weeks depending on growth) and transplant into a wider pot as you go. After the transplant almost all of the roots will be above the saturation zone and it becomes much harder to over water. New roots will again work their way down into the saturation zone but you will have plenty above so it's less likely to over water and why uppotting as you go I see as a benefit instead of starting in a large wide container.
POT MATERIAL
Some prefer plastic others fabric, air pots etc.
This can affect the perched water table by evaporation as the lager the exposed surface area the more evaporation that occurs from the media in say fabric pots. This imo has a few benefits.... slightly reducing the perched water table but more so the exposure for gas exchange that's happening and that's a good thing for o2 levels in the root zone that I feel are directly related to growth rates and I'll explain why going a bit off topic for a second.
It's no coincidence that the fastest growing media's have the highest amounts of o2 and gas exchange.... for eg aeroponics have unlimited to rich o2 and water. Hydro similar with slightly less o2, soiless media's such as coco and I would possibly include peat and last soil. If you notice they are in order of growth rates and it's not hard to see the difference in their air holding capacity in that order along with the fact that larger particles also have a better gas exchange rate. This is important because the plants take in oxygen and expel co2 in the rootzone as do the microbes on top of that so good gas exchange is important for both.
Just a note... air pruning has nothing to do with the benefits of fabric pots all it does is signal the roots to grow in a different direction.
But let's get back on topic of watering and how it's affected.
TEMPERATURE AND HUMIDITY
The warmer the temps the more evaporation occurs.
The lower your humidity the more evaporation occurs
The more surface area exposed to air movement (wind) the more evaporation.
Think those don't need an explanation. But the difference in pot material coupled with these environmental factors will have an impact on your watering needs.
The temperature of the media not only affects evaporation but also directly affect the temperature of the plant and leaf temps. This has a large impact on nutrient uptake and transportation.
First let me say that this next part is opinion and I will give my reasoning for my opinions. With the exception of hydro (leaving this part out as this post is about watering not hydro) roots like to be about the same temperature as the leaves contrary to what's talked about from many prominent growers in the industry but not all like Dr.Bruce Bugbee. IMO ideal root temps are the same as ideal leaf temps and overall plant temps especially since the root temps have a large impact on the plant and leaf temps. What are ideal temps imo and many studies show that leaf temps (NOT AIR TEMPS) of around 77f are most efficient. So how does a cool rootzone impact the plants negatively? Well it's 2 fold because of the cool temps the viscosity (measument of flow rate) of the sap will decrease so its harder for the plant to move the nutrients through the plant. The other is absorption and one fact is that in a cooler rootzone the concentration of nutrients is higher (but you just said it slows absorption) well it does as the nutrients build up in the roots it can absorb less and this has a direct impact negatively on the plant. It may appear to be overwatered because the plant is now struggling to take up and use oxygen. Add that to the slowed transpiration rates and you have the same symptom many refer to overwatering which again is lack of o2. Now take a cold rootzone where the plants slow water uptake and then add the saturation zone to it and you can see the road to correction and recover is a long one and can have huge impact on growth and yields.
So, get your pots up off the floor
WET AND DRY CYCLES
in soil and peat with higher water tables or with wider pots or combination of wet and dry cycles are important. This is to allow the dry back (including the uptake of water from the saturation zone) to prevent symptoms of over watering and help with o2 levels. Remember the majority of roots will end up in the saturation zone with these media's or with wider pots. Which can become depleted of o2 quickly as gas exchange is lower in water and media made up of smaller particles. This is where pot size and shape are important for the size of plant. You have a small plant in large container and there is no way it can take up enough of the water in the saturation zone fast enough to get air exposure in a media that has low gas exchange and majority of the roots. So, it's important to choose a pot size that will allow for this. It's also why using the finger method to gauge watering is poor and lifting the pots is much better... when they are light you know they have taken up a good portion of the saturation zone and are ready to be watered again.
This is much less of an issue when using soilless like coco or peat/perlite.
I am not the author. Read and learn.
This will be a long read based on my personal knowledge, opinions, research and others work to consolidate information for our members. I'm not presenting my opinions as facts so take from this what you like. I will be putting it in subsection format for easy reference.
First, I want to make an important point to take into consideration before reading. The tap root will grow directly downwards to the bottom of the container before spreading out.
PERCHED WATER TABLE
What is it?
The perched water table is basically the height of the saturation zone where capillary action and gravity cancel each other out. This area will be saturated with water and will be responsible most growers' issues with watering practices especially in soil grows.
WHAT IS CAPILLARY ACTION
CAPILLARY action is is the combination of the cohesive and adhesive properties of water.
In short adhesion is water clinging to the media (think of it like wicking or soaking up)
Cohesion is where the water clings to itself.
So as the water is wicked up (adhesion) it pulls more water with it through Cohesion and at the point gravity and these properties cancel each other out is the perched water table.
This perched water table will always remain the SAME HEIGHT and will always stay saturated unless taken up by the plants or evaporates when the pot dries out. No matter the container height, depth or volume of media. So, if a tall skinny container had a perched water table of 1" then a short wide one of the same media will also have a perched water table of 1". Which means the ratio of water to air in a wide pot will be higher than a tall skinny pot which will have a higher air to water ratio... keep this in mind as we get further.
Different media's have different perched water tables. A more absorbent media will have a higher perched water table than a less absorbent media... REMEMBER THIS as it makes a big difference on pot selection for your media.
DIFFERENT MEDIA
Water holding capacity is directly related to the height of the perched water table so soils with more clay or silt and less sand will have a higher perched water table than those with more sand because sand is a larger particle.
The larger the overall particles of the media the lower the perched water table and better the drainage.
By adding things like perlite or vermiculite (while vermiculite is good at absorbing water it also improves drainage so its helpful in keeping a more even level of moisture throughout the media while increasing drainage due to its size) we can lower the perched water table by reducing the wicking (adhesion) ability and creating more space between particles overall reducing the cohesion effect and in turn the height of the perched water table.
Media like peat based or coco have a much higher drainage and lower perched water table than soil and are therefore less susceptible to over watering but will require more frequent watering due to the lower water holding capacity.
Adding things like perlite or hydroton to the bottom of the pots will NOT reduce the water table but instead raise it. This is because as I said the height of the water table will not change for a given media. So, if you add things like that to the bottom you are essentially just moving the water table up.
Basically, the larger the particles IN the media the better drainage and lower the water table.
If you want to see the height of your perched water table use a clear cup with drain holes fill with media and saturate it. Wait a few hrs for drainage and then come back and look. You can see the difference in the varying media's if you want to experiment.
If you feel you have over watered or your perched water table height is too high you can simply tilt your pot on a 45 degree angle and release more water from the media as runoff. To help visualize think of it this way if you have a perched water table of 2”. You can draw an imaginary horizontal line at that height, when you tilt the pot you have less media below that line and therefore you will have less water in the pot after tilting it.
POT SIZE
I have already covered this a bit, but my opinion is if you are using a media with a higher water table you will benefit from taller narrower pots and if using a media with a lower perched water table the shorter wider ones may benefit you depending on your watering practices.
I prefer the taller over wider no matter the media as I choose to water often and have a higher air holding capacity and lower water table but that can work against you if you can't water as frequently and as plants grow it can greatly increase the frequency required as the roots will be pulling the water out of that saturation zone quickly. So, you may want to use taller pots for small plants and transplant into a wider one as they grow.
You also don't want a pot that's to tall and the top portion of the media is drying out to fast while the bottom is wet.
Let's use seedlings as an example take a solo cup or a large container... the water table will be the same height in either. I see so often ppl trying to water a tiny bit in circles or mist the surface and for lack of other words IT DRIVES ME NUTS. Why? Because the roots are so shallow they are not at risk of being over watered. Remember though, tap roots grow straight down so we need to be mindful as they grow depending on the gas exchange of the media that the majority of roots are not sitting in the saturated zone with poor gas exchange because this will cause lack of oxygen that we incorrectly refer to as overwatering which is actually the cause not the symptom.
It's important to fill containers to the top to give us a good amount of space above the perched water table that high in o2. If you fill a solo cup halfway with soil it's likely to be sitting in the saturation zone and will not do well.
Also going to make the point that plants will be most susceptible to overwatering when the roots first hit the bottom and spread out until they fill the bottom and start moving back up out of the saturation zone. So, again, it may be more beneficial to use a taller narrow pot for the early stages of growth (2-4 weeks depending on growth) and transplant into a wider pot as you go. After the transplant almost all of the roots will be above the saturation zone and it becomes much harder to over water. New roots will again work their way down into the saturation zone but you will have plenty above so it's less likely to over water and why uppotting as you go I see as a benefit instead of starting in a large wide container.
POT MATERIAL
Some prefer plastic others fabric, air pots etc.
This can affect the perched water table by evaporation as the lager the exposed surface area the more evaporation that occurs from the media in say fabric pots. This imo has a few benefits.... slightly reducing the perched water table but more so the exposure for gas exchange that's happening and that's a good thing for o2 levels in the root zone that I feel are directly related to growth rates and I'll explain why going a bit off topic for a second.
It's no coincidence that the fastest growing media's have the highest amounts of o2 and gas exchange.... for eg aeroponics have unlimited to rich o2 and water. Hydro similar with slightly less o2, soiless media's such as coco and I would possibly include peat and last soil. If you notice they are in order of growth rates and it's not hard to see the difference in their air holding capacity in that order along with the fact that larger particles also have a better gas exchange rate. This is important because the plants take in oxygen and expel co2 in the rootzone as do the microbes on top of that so good gas exchange is important for both.
Just a note... air pruning has nothing to do with the benefits of fabric pots all it does is signal the roots to grow in a different direction.
But let's get back on topic of watering and how it's affected.
TEMPERATURE AND HUMIDITY
The warmer the temps the more evaporation occurs.
The lower your humidity the more evaporation occurs
The more surface area exposed to air movement (wind) the more evaporation.
Think those don't need an explanation. But the difference in pot material coupled with these environmental factors will have an impact on your watering needs.
The temperature of the media not only affects evaporation but also directly affect the temperature of the plant and leaf temps. This has a large impact on nutrient uptake and transportation.
First let me say that this next part is opinion and I will give my reasoning for my opinions. With the exception of hydro (leaving this part out as this post is about watering not hydro) roots like to be about the same temperature as the leaves contrary to what's talked about from many prominent growers in the industry but not all like Dr.Bruce Bugbee. IMO ideal root temps are the same as ideal leaf temps and overall plant temps especially since the root temps have a large impact on the plant and leaf temps. What are ideal temps imo and many studies show that leaf temps (NOT AIR TEMPS) of around 77f are most efficient. So how does a cool rootzone impact the plants negatively? Well it's 2 fold because of the cool temps the viscosity (measument of flow rate) of the sap will decrease so its harder for the plant to move the nutrients through the plant. The other is absorption and one fact is that in a cooler rootzone the concentration of nutrients is higher (but you just said it slows absorption) well it does as the nutrients build up in the roots it can absorb less and this has a direct impact negatively on the plant. It may appear to be overwatered because the plant is now struggling to take up and use oxygen. Add that to the slowed transpiration rates and you have the same symptom many refer to overwatering which again is lack of o2. Now take a cold rootzone where the plants slow water uptake and then add the saturation zone to it and you can see the road to correction and recover is a long one and can have huge impact on growth and yields.
So, get your pots up off the floor
WET AND DRY CYCLES
in soil and peat with higher water tables or with wider pots or combination of wet and dry cycles are important. This is to allow the dry back (including the uptake of water from the saturation zone) to prevent symptoms of over watering and help with o2 levels. Remember the majority of roots will end up in the saturation zone with these media's or with wider pots. Which can become depleted of o2 quickly as gas exchange is lower in water and media made up of smaller particles. This is where pot size and shape are important for the size of plant. You have a small plant in large container and there is no way it can take up enough of the water in the saturation zone fast enough to get air exposure in a media that has low gas exchange and majority of the roots. So, it's important to choose a pot size that will allow for this. It's also why using the finger method to gauge watering is poor and lifting the pots is much better... when they are light you know they have taken up a good portion of the saturation zone and are ready to be watered again.
This is much less of an issue when using soilless like coco or peat/perlite.
- Thread starter
- #15
This is awesome! Thank you. I only had a chance to skim-read this but I cannot wait for my kid to go to bed so I can sit down and fully read without being interrupted every couple of minutes!Almost all newb problems tend to stem from either over or underwatering. I'm going to post a post that I read on another site that answered a lot of questions I had but never really got a definitive answer to. The post also showed me things I had no idea were going on in the soil.
I am not the author. Read and learn.
This will be a long read based on my personal knowledge, opinions, research and others work to consolidate information for our members. I'm not presenting my opinions as facts so take from this what you like. I will be putting it in subsection format for easy reference.
First, I want to make an important point to take into consideration before reading. The tap root will grow directly downwards to the bottom of the container before spreading out.
PERCHED WATER TABLE
What is it?
The perched water table is basically the height of the saturation zone where capillary action and gravity cancel each other out. This area will be saturated with water and will be responsible most growers' issues with watering practices especially in soil grows.
WHAT IS CAPILLARY ACTION
CAPILLARY action is is the combination of the cohesive and adhesive properties of water.
In short adhesion is water clinging to the media (think of it like wicking or soaking up)
Cohesion is where the water clings to itself.
So as the water is wicked up (adhesion) it pulls more water with it through Cohesion and at the point gravity and these properties cancel each other out is the perched water table.
This perched water table will always remain the SAME HEIGHT and will always stay saturated unless taken up by the plants or evaporates when the pot dries out. No matter the container height, depth or volume of media. So, if a tall skinny container had a perched water table of 1" then a short wide one of the same media will also have a perched water table of 1". Which means the ratio of water to air in a wide pot will be higher than a tall skinny pot which will have a higher air to water ratio... keep this in mind as we get further.
Different media's have different perched water tables. A more absorbent media will have a higher perched water table than a less absorbent media... REMEMBER THIS as it makes a big difference on pot selection for your media.
DIFFERENT MEDIA
Water holding capacity is directly related to the height of the perched water table so soils with more clay or silt and less sand will have a higher perched water table than those with more sand because sand is a larger particle.
The larger the overall particles of the media the lower the perched water table and better the drainage.
By adding things like perlite or vermiculite (while vermiculite is good at absorbing water it also improves drainage so its helpful in keeping a more even level of moisture throughout the media while increasing drainage due to its size) we can lower the perched water table by reducing the wicking (adhesion) ability and creating more space between particles overall reducing the cohesion effect and in turn the height of the perched water table.
Media like peat based or coco have a much higher drainage and lower perched water table than soil and are therefore less susceptible to over watering but will require more frequent watering due to the lower water holding capacity.
Adding things like perlite or hydroton to the bottom of the pots will NOT reduce the water table but instead raise it. This is because as I said the height of the water table will not change for a given media. So, if you add things like that to the bottom you are essentially just moving the water table up.
Basically, the larger the particles IN the media the better drainage and lower the water table.
If you want to see the height of your perched water table use a clear cup with drain holes fill with media and saturate it. Wait a few hrs for drainage and then come back and look. You can see the difference in the varying media's if you want to experiment.
If you feel you have over watered or your perched water table height is too high you can simply tilt your pot on a 45 degree angle and release more water from the media as runoff. To help visualize think of it this way if you have a perched water table of 2”. You can draw an imaginary horizontal line at that height, when you tilt the pot you have less media below that line and therefore you will have less water in the pot after tilting it.
POT SIZE
I have already covered this a bit, but my opinion is if you are using a media with a higher water table you will benefit from taller narrower pots and if using a media with a lower perched water table the shorter wider ones may benefit you depending on your watering practices.
I prefer the taller over wider no matter the media as I choose to water often and have a higher air holding capacity and lower water table but that can work against you if you can't water as frequently and as plants grow it can greatly increase the frequency required as the roots will be pulling the water out of that saturation zone quickly. So, you may want to use taller pots for small plants and transplant into a wider one as they grow.
You also don't want a pot that's to tall and the top portion of the media is drying out to fast while the bottom is wet.
Let's use seedlings as an example take a solo cup or a large container... the water table will be the same height in either. I see so often ppl trying to water a tiny bit in circles or mist the surface and for lack of other words IT DRIVES ME NUTS. Why? Because the roots are so shallow they are not at risk of being over watered. Remember though, tap roots grow straight down so we need to be mindful as they grow depending on the gas exchange of the media that the majority of roots are not sitting in the saturated zone with poor gas exchange because this will cause lack of oxygen that we incorrectly refer to as overwatering which is actually the cause not the symptom.
It's important to fill containers to the top to give us a good amount of space above the perched water table that high in o2. If you fill a solo cup halfway with soil it's likely to be sitting in the saturation zone and will not do well.
Also going to make the point that plants will be most susceptible to overwatering when the roots first hit the bottom and spread out until they fill the bottom and start moving back up out of the saturation zone. So, again, it may be more beneficial to use a taller narrow pot for the early stages of growth (2-4 weeks depending on growth) and transplant into a wider pot as you go. After the transplant almost all of the roots will be above the saturation zone and it becomes much harder to over water. New roots will again work their way down into the saturation zone but you will have plenty above so it's less likely to over water and why uppotting as you go I see as a benefit instead of starting in a large wide container.
POT MATERIAL
Some prefer plastic others fabric, air pots etc.
This can affect the perched water table by evaporation as the lager the exposed surface area the more evaporation that occurs from the media in say fabric pots. This imo has a few benefits.... slightly reducing the perched water table but more so the exposure for gas exchange that's happening and that's a good thing for o2 levels in the root zone that I feel are directly related to growth rates and I'll explain why going a bit off topic for a second.
It's no coincidence that the fastest growing media's have the highest amounts of o2 and gas exchange.... for eg aeroponics have unlimited to rich o2 and water. Hydro similar with slightly less o2, soiless media's such as coco and I would possibly include peat and last soil. If you notice they are in order of growth rates and it's not hard to see the difference in their air holding capacity in that order along with the fact that larger particles also have a better gas exchange rate. This is important because the plants take in oxygen and expel co2 in the rootzone as do the microbes on top of that so good gas exchange is important for both.
Just a note... air pruning has nothing to do with the benefits of fabric pots all it does is signal the roots to grow in a different direction.
But let's get back on topic of watering and how it's affected.
TEMPERATURE AND HUMIDITY
The warmer the temps the more evaporation occurs.
The lower your humidity the more evaporation occurs
The more surface area exposed to air movement (wind) the more evaporation.
Think those don't need an explanation. But the difference in pot material coupled with these environmental factors will have an impact on your watering needs.
The temperature of the media not only affects evaporation but also directly affect the temperature of the plant and leaf temps. This has a large impact on nutrient uptake and transportation.
First let me say that this next part is opinion and I will give my reasoning for my opinions. With the exception of hydro (leaving this part out as this post is about watering not hydro) roots like to be about the same temperature as the leaves contrary to what's talked about from many prominent growers in the industry but not all like Dr.Bruce Bugbee. IMO ideal root temps are the same as ideal leaf temps and overall plant temps especially since the root temps have a large impact on the plant and leaf temps. What are ideal temps imo and many studies show that leaf temps (NOT AIR TEMPS) of around 77f are most efficient. So how does a cool rootzone impact the plants negatively? Well it's 2 fold because of the cool temps the viscosity (measument of flow rate) of the sap will decrease so its harder for the plant to move the nutrients through the plant. The other is absorption and one fact is that in a cooler rootzone the concentration of nutrients is higher (but you just said it slows absorption) well it does as the nutrients build up in the roots it can absorb less and this has a direct impact negatively on the plant. It may appear to be overwatered because the plant is now struggling to take up and use oxygen. Add that to the slowed transpiration rates and you have the same symptom many refer to overwatering which again is lack of o2. Now take a cold rootzone where the plants slow water uptake and then add the saturation zone to it and you can see the road to correction and recover is a long one and can have huge impact on growth and yields.
So, get your pots up off the floor
WET AND DRY CYCLES
in soil and peat with higher water tables or with wider pots or combination of wet and dry cycles are important. This is to allow the dry back (including the uptake of water from the saturation zone) to prevent symptoms of over watering and help with o2 levels. Remember the majority of roots will end up in the saturation zone with these media's or with wider pots. Which can become depleted of o2 quickly as gas exchange is lower in water and media made up of smaller particles. This is where pot size and shape are important for the size of plant. You have a small plant in large container and there is no way it can take up enough of the water in the saturation zone fast enough to get air exposure in a media that has low gas exchange and majority of the roots. So, it's important to choose a pot size that will allow for this. It's also why using the finger method to gauge watering is poor and lifting the pots is much better... when they are light you know they have taken up a good portion of the saturation zone and are ready to be watered again.
This is much less of an issue when using soilless like coco or peat/perlite.
- Thread starter
- #16
One last question....it may be a little off topic but from what I understand you should top your plant sometime between the 2-4 weeks old and once they have 5 or more nodes. My plants are 24 days old so the 4-week mark is approaching. Do you think it is okay to top my plants in their current condition or should I wait? Is there a point when it becomes too late to top? If so, when?
Sativa1970
Well-Known Member
You don't want to top a stressed plant. There is no plant age or size cut off point with topping a photo type. There is a point where your grow space has a size cut off since topping turns vertical into horizontal growth.
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- #18
Will the leaves that are yellowish turn back green once the plant is doing better? And should I remove the damaged leaves?
Hey Lovie, sorry nope damaged leaves do not recover, look to new growth for signs of recovery. But know in most cases (unless pests or pm, blight etc) again most cases it’s best to leave foliage intact until the plant sucks them yellow and they fall off. Those fans are nutrient storage center that the plant taps later in flower cycle. It looks unsightly to us but the plant doesn’t care, it’s easier to pull resources from the fans rather than the roots in late flower
Yep if one could figure out how to revitalize damaged leaves it would be a cash cow!
Sativa1970
Well-Known Member
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