Does PPM runoff after feeding reflect what the plant used in the previous feeding?

[InTheShed]

New grower here, in soil. Just chopped down my first plant on Tuesday. I recently got a PPM meter which I find a great tool.

Here is my question (let's assume no PPM in the water to make this easier):

If I always water in flower with 600 PPM nute solution, and this time the first runoff is 200, that seems to me that the soil retained 200 PPM of the 600 I used last time, and it used the other 400 PPM for the plant.

If the runoff was 600 PPM on the other hand, it means that none of the 600 I added last time was absorbed by the plant.

Is this correct? By way of example, if I flush with hose water at 100 PPM, first runoff won't be 100 PPM, it will be whatever is left in the soil by previous feedings. It can take 2-3x the pot volume of water to get output = input.

Therefore I can tailor each successive feeding to what the plant has been using previously. If the runoff is 200 as mentioned above, I can assume that I am slightly overfeeding it. If the runoff is 600 that means the plant is not using any nutes I give and it's time to make a serious change, either flushing or adjusting pH to correct lockout.

Is this line of thinking correct?

---------------------------------

On another topic, if you don't water to runoff, how do you know that all of your roots are getting wet? I don't understand growers who say "I fed it 1 liter with no runoff." How can you be sure every root was fed?

 

[Scientific]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

It's kind of complicated, isn't it? In an air pot and/or during hot/windy weather, how much of the water you added just evaporated? How much of the water was taken up by the plant, especially when it's transpiring heavily? What about nutrients crystalizing in air pockets or interacting with other chemicals in the soil? What about pH shifts taking place in the soil as a result of both biological (including bacteria and fungi) and non-biological activity? Go far enough down that road of trying to nail down and understand all the variables and you have the makings for a doctoral dissertation in agronomy.

It's interesting, though.

I think a practical approach is just to water (including feeding) on as consistent a basis as possible (which is easiest with coco coir, because you can literally water like clockwork and water as much as you want). Then you track pH and PPM in and out and just watch the overall trend. In my experience, it doesn't change very much.

For what it's worth, here's the last 12 days of my coco grow (there's a link below). It's a dwarf plant at the end of flowering so it doesn't need much feeding. The weather was pretty consistent the whole time, so the liters required (which were determined by actually weighing the pot), are pretty consistent too. What I think this shows is that over time you can find a volume and concentration that works and stay with it. (That said, a couple of weeks earlier I tried feeding at 500 PPM and got tip burn.)

Anyway, you happened to ask just as I'm ending an experimental coco coir grow in which I was closely tracking just what you were asking about, so I thought I'd show you my results.

Good luck, happy gardening, and please share your results if you have any brilliant insights.

 

[HigherTheHigh]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

i hope you dont mind me asking on this thread.

im growing in coco/perlite 60/40 mix, 20L pot and started feeding 2Lof just water from last saturday, today i flushed them with 32L and the end run of was 150 on 3 and 280 on another.

my water from the tap is 85-100ppm, do you think i should try get it further down or will it stay at roughly 150?

is there anyway of getting low ppm water? something i can do maby?

also im running a hydro line and there ppm is 2900, is that safe?

 

[Scientific]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Hi HTH -- Maybe cut and paste your question into a new thread here at FAQ? When you do, it would really help if you could provide all the info that's asked for in the "How to Ask for Grow Assistance" thread. In particular it would be useful to know how far along your grow is (Just starting? Flushing for harvest?), how well it has been going, etc. And of course photos really help. And if you could make your Qs a little clearer, that would help too. I'm having a really hard time trying to understand what you're asking (2900 PPM?!)

 

[InTheShed]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

It's kind of complicated, isn't it? In an air pot and/or during hot/windy weather, how much of the water you added just evaporated? How much of the water was taken up by the plant, especially when it's transpiring heavily? What about nutrients crystalizing in air pockets or interacting with other chemicals in the soil? What about pH shifts taking place in the soil as a result of both biological (including bacteria and fungi) and non-biological activity? Go far enough down that road of trying to nail down and understand all the variables and you have the makings for a doctoral dissertation in agronomy.

It's interesting, though.

I think a practical approach is just to water (including feeding) on as consistent a basis as possible (which is easiest with coco coir, because you can literally water like clockwork and water as much as you want). Then you track pH and PPM in and out and just watch the overall trend. In my experience, it doesn't change very much.

For what it's worth, here's the last 12 days of my coco grow (there's a link below). It's a dwarf plant at the end of flowering so it doesn't need much feeding. The weather was pretty consistent the whole time, so the liters required (which were determined by actually weighing the pot), are pretty consistent too. What I think this shows is that over time you can find a volume and concentration that works and stay with it. (That said, a couple of weeks earlier I tried feeding at 500 PPM and got tip burn.)

Anyway, you happened to ask just as I'm ending an experimental coco coir grow in which I was closely tracking just what you were asking about, so I thought I'd show you my results.

Good luck, happy gardening, and please share your results if you have any brilliant insights.

Excellent record keeping (as usual)! I don't think I could ever grow in coco because there are many days I just can't water. Sometimes two or three in a row.

That said, your chart shows that the runoff went to its highest number just before you flushed. Did that cause you to flush or was that all according to your schedule set beforehand?

I'm trying to be consistent but finding that two different strains at the same age are showing completely different runoff numbers, so that's why I was asking. I'm trying not to use tip-burn as an indicator alone, but to figure out what the plant needs based on the runoff.

Regarding liters of water, I've read that before and never understood the weighing thing:

For example, I put a sprout in a pot with dry soil and it weighs 10 pounds. I soak it and it weighs 14 pounds. Do I only water it when it weighs 10 pounds again, i.e. completely dry? 11 pounds? 12.5 pounds? Is there some magical percentage of its wet-weight that says water me? And as the plant grows the total weight dry will change.

I feel like I may eventually end up with a degree in agronomy!!

 

[InTheShed]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Hi HTH -- Maybe cut and paste your question into a new thread here at FAQ?

Thanks Sci! I was going to say something similar but in a much more New York way

 

[HigherTheHigh]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Thanks Sci! I was going to say something similar but in a much more New York way

what would your new york way be?

 

[Scientific]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Thanks Sci! I was going to say something similar but in a much more New York way

One of the things I like about this site is that people are nice to each other. (Plus after a long life of being direct and confrontational with people, I am slowly figuring out that being patient and diplomatic is the better way. Too soon old, too late wise...)

 

[InTheShed]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

what would your new york way be?

One of the things I like about this site is that people are nice to each other.

I would have been nice, just maybe not as helpful with the list of things to include, that's all. After all the help I've gotten on this site (including past help from you) there's no way I would have gone with "Hey buddy, get your own thread!"

 

[Scientific]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Excellent record keeping (as usual)!

Oh, that's the highly simplified version!

> I don't think I could ever grow in coco because there are many days I just can't water. Sometimes two or three in a row.

That's what's so cool about a coco drain to waste grow! (Or one of the cool things, anyway.) Because coco never saturates, there's no danger of drowning the plant. It always gets plenty of air to the roots (especially with an air pot, the other thing that I am giddy about).

Whether you water to 20% runoff or 200% runoff, it's pretty much the same. So you can just set a pump to run once or twice a day and you're good! And because it's fresh nutes, your nute balance and pH are always exactly what you want (which is a huge difference from chasing the pH all over the place in a conventional hydro grow).

> your chart shows that the runoff went to its highest number just before you flushed. Did that cause you to flush or was that all according to your schedule set beforehand?

No, I think that's just normal variability. I should have been clearer that I'm flushing because I'm ready to harvest.

> I'm trying to be consistent but finding that two different strains at the same age are showing completely different runoff numbers

From the logs that I have read here, even under identical growing conditions, different strains will grow very differently, which I guess isn't much of a surprise if one is sativa dominant and the other indica, but you see big differences even in the same strain with seeds from the same plant!

> I'm trying not to use tip-burn as an indicator alone, but to figure out what the plant needs based on the runoff.

I'm the first to agree that increasing concentration until you kill the tips of your leaves is a crappy way to monitor. My beautiful baby growing out on my deck has dead brown leaf tips from my trying to goose the concentration to 500 PPM. And I knew from a previous grow that >400 PPM was trouble with these little dwarves. But live a learn.

The safe thing to do is to use half the manufacturer's recommended dose, but then you start to wonder if you're leaving money on the table by not feeding more. I think that's why staying with one strain and taking careful notes can be a good idea--because you get to know the strain and what works best for it.

> Regarding liters of water, I've read that before and never understood the weighing thing...

Again, there are a lot of variables. I just went through the tedious and time-consuming process of weighing wet and dry every day to see how much she dried out between waterings and so how much water the plant needed at a minimum. Now that I have just about finished my experiment and become an evangelical coco grower, I realize that I can just pick a value that gives enough runoff to have some flushing action and stick with that. For this plant under these conditions, 1.5 liters a day is always enough. More would be wasteful and not have any further benefit as far as I can see.

BTW, there is a guy here who grew a nice, big plant in a tiny pot of coco just by feeding it a bunch of times a day on a timer.

I saw a video once in which the grower claimed that hands-down, drain-to-waste coco on a timer was absolutely the best way to go. I'm still not sure that it can beat having the roots constantly bathed in a nutrient bath like with full hydro, but coco is a lot less work (no pH chasing and fully automatable) and it's conceivable that an optimized coco grow could even give better results because of more O2 to the roots.

My .02. YMMV, etc. etc.

The best part of growing pot for a hobby is that when you're done, you have a bunch of high-quality pot!

 

[InTheShed]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Scientific your name suits you to a T. Your responses are so complete and well thought out they are a pleasure to read! And you really are getting this "hobby" down to a science.

As this is my first time growing I've got two different strains from the breeder to see which is the one (or neither!) to stick with g(r)oing forward. In experimenting I've tried 15 different nute strength combinations throughout the grow and I plan to narrow that down (a lot) for the next one. But as you mentioned, ramping up so slowly left me wondering if I have to go that easy next time. I have taken pretty good notes and a hell of a lot of pictures to go with them, but I'm sure there will be many mistakes on the next grow as well (maybe fewer caterpillars though!).

Alas, since I'm growing autos outside during the day and inside at night, the coco with a water pump is beyond what I can swing. Smart pots and soil/perlite is going to have to be my medium for the time being.

Thanks!

 

[Scientific]

Re: Does PPM runoff after feeding reflect what the plant used in the previous feeding

Thanks ITS. I do have a lot of fun experimenting with and learning this stuff. I had a friend in college who was an Ag major and so was able to do stuff like growing corn with exactly defined nutrients--so much so that he could see the results of just leaving out, say, cobalt. That was pretty cool. It would be fun to have those kinds of resources for a pot grow.

Be sure to post anything new, interesting, or unexpected that you learn.

Happy growing!