Continuous soil flushing by way of run off?

[NorthernCosmos]

I know some are proponents of flushing the growing medium (soil in my case) some time(s) during the grow, to wash out accumulated salts/nutes that might cause nute lock outs. The general recommendation seems to be to run 3 times the medium volume of water through the medium.

I fear that soaking the pots of soil that much would lead to them needing weeks, or at least quite a few days, to dry out again. Much to wet for too long I'd have thought. Or perhaps the 3 x volume advice is for coco and the like that has little water retention?

Then I read Old Salt (gone MIA?) mention that watering to run off would achieve much of the same, which is logical. So how about this:

Start every feeding with a bit of plain water, a fraction of the medium volume, say around 10%, let it sink in, maybe a little run off will be seen, then proceed with the nutes-mix on top of that until there's more run off, maybe 25% in total

Would this constitute a continuous flushing/cleaning of the medium, so that no huge flush is needed?

 

[Lime]

If you water to sufficient run off there is no need to flush as your doing it as you water. But if your feeding to high and don't water to sufficient runoff than you can get buildup and cause lockout. I soak my pots everytime I water i get 25% runoff which is enough to clear out old nutes and replenish with fresh nutes.

 

[NorthernCosmos]

God to hear, Lime!

I've already practiced the outlined scheme since I started growing. It just seemed the logical thing to do. I've since read much about flushing, and finally saw Old Salts comment, which prompted me to start a reality check thread.

So yeah, if the water table sinks fairly evenly through the soil, starting with a little plain water might just improve the effect of the continuous-flush-by-runoff method.

 

[VetSmoke85]

Good question. Not sure but I do have a thought on something you said.

I fear that soaking the pots of soil that much would lead to them needing weeks, or at least quite a few days, to dry out again. Much to wet for too long I'd have thought. Or perhaps the 3 x volume advice is for coco and the like that has little water retention?

If we are watering to runoff correctly then our medium is saturated to the point it cannot hold anymore water. Whether you water to 10% run off or flush 3 x the volume it will still only hold the same amount of water in the medium.

 

[Emilya Green]

I fear that soaking the pots of soil that much would lead to them needing weeks, or at least quite a few days, to dry out again. Much to wet for too long I'd have thought. Or perhaps the 3 x volume advice is for coco and the like that has little water retention?

Your fear is unfounded. Soil can only hold a set amount of water. If you water to runoff and then quit, or flush with 3x the container size and then quit, at the end the same amount of water is in the soil with each process. Also, soil does not dry out by magic or evaporation, it dries out because the plant USES the water. The rate that your container dries out is mostly dependent on the strength of your roots and nothing else.

 

[NorthernCosmos]

Edit: adding quote for context as I was Ninja'd by Emilya - this was in response to VetSmoke85.

If we are watering to runoff correctly then our medium is saturated to the point it cannot hold anymore water. Whether you water to 10% run off or flush 3 x the volume it will still only hold the same amount of water in the medium.

Well yes, that's also logical. However, I've observed that the buckets that I have soaked quite a bit for starting plants weigh a lot more than buckets in normal service with grown plants after watering, even with 25% run off. These take 2-3 weeks to become dry/light (I now soak them far less initially, and have adopted Emilya's watering scheme for seedlings started in their final container).

This could simply point to better water retention in the buckets with no root system and no plant to drink. That might make a 3 x volume flushing "safe" IF the roots (and soil structure...) and thirsty plant ensure a much faster drying than I've seen with the starter buckets. Of course there are so many variants of mediums around that they could have very different water retention...

A 3 x volume flush would be a little tedious, as I'd have to bring all that water into the room, catch the water from the flush, and carry it all away again. It's doable seeing as it would only be done once or twice in a grow, but it's not something I'm keen on on a practical/lazy basis.

Then there's this : Could it simply be better to continuously "cleanse" the medium rather than letting the salts/nutes build up over time to undesirable levels before one or two major flushings?

 

[Emilya Green]

It is a common practice to water to 20% runoff either in soil or coco, so as to never need to flush. By moving 1/5 of the container size of extra water through there each time, it is possible to keep the soil clean.

 

[NorthernCosmos]

Your fear is unfounded. Soil can only hold a set amount of water. If you water to runoff and then quit, or flush with 3x the container size and then quit, at the end the same amount of water is in the soil with each process. Also, soil does not dry out by magic or evaporation, it dries out because the plant USES the water. The rate that your container dries out is mostly dependent on the strength of your roots and nothing else.

This in just as I was typing my previous posting - Ninja'd again!

As I write above, my experience with water retention is that it's not constant and predictable. Also the slow normal watering with run off might well lead to less soaked buckets as the result is not a "swamp". I.e. I do get run off without soaking the soil to full saturation.

I know there's no magic and that the plants drink the major portion of the water - I try not to rely on magic/rumours/superstition etc. as a fairly rigid rule - this thread might be an indicator of just that

And as I typed this, another message came in:

It is a common practice to water to 20% runoff either in soil or coco, so as to never need to flush. By moving 1/5 of the container size of extra water through there each time, it is possible to keep the soil clean.

Exactly - so we're in agreement there. With the main point of the thread being Emilya approved, I see no need for the the 3 x volume flush

 

[Homer Simpson]

I find it makes a stagnant mess over time in the platter I keep my fabric pod on when I watered to run off so I stopped a few generations ago and have had absolutely no negative impact.

 

[MochaBud]

I would never, and I mean never flush my soil

I'm afraid it would clog up my pipes


On a more serious note, which is unusual for me TBH my plants set in their runoff and soak it back up, whether it's water or feed...what it doesn't soak back up stays in the old tray, and I change it out for a clean empty new one

 

[Nunyabiz]

Here's my 1cent

If you wish to use bottled nutrients then just use a quality coco mixed 30% with pumice and biochar in fabric pots.
That way if you need to flush out salts its no big deal can flush the hell out of it and go right back to normal watering/feeding next day.
Also feeding at 1/4 strength and watering 1 to 2x a day you really shouldn't have salt build up anyway.
Salt build up comes from heavy soil that allowed to dry out which leaves salt behind.

Better still, grow in large fabric pots in 100% living Organic Soil and there's nothing to flush, ever.
Keep the Living Soil moist at all times.

 

[Emilya Green]

it just depends on how you feed and if you are leaving a lot of salts in the soil. If you follow the Fox Farms feeding schedule... you will need to flush... they throw a lot of nutes at the plants. If you are feeding 1/2 or 1/4 strength you probably never will need to flush. If you are not running synthetic nutes, you don't need to flush... so it depends on a lot of things, and what works for you.

 

[bobrown14]

What are we flushing out of soil again??

I have to ask... there's a lot of myth about flushing soil.

Use the proper amount of fertilizer or go organic soil.

Problems solved.

Speaking about problems, was/is there actually a lock out happening or are we just talking theory here??

What "salts" are we flushing out?? I don't think that's even scientifically possible but here I go again. lol

OP - look up this and read about it:

"Cation Exchange Capacity" of soil.

This is how your salts or whatever fertilizers you add to your soil get chemically BOUND to soil particles and how its very close to impossible to "flush" excess out.

Again best practice is to only use what fertilizer is required and nothing more/extra that can build up.... food for thought.

 

[Emilya Green]

What are we flushing out of soil again??

I have to ask... there's a lot of myth about flushing soil.

Use the proper amount of fertilizer or go organic soil.

Problems solved.

Speaking about problems, was/is there actually a lock out happening or are we just talking theory here??

What "salts" are we flushing out?? I don't think that's even scientifically possible but here I go again. lol

OP - look up this and read about it:

"Cation Exchange Capacity" of soil.

This is how your salts or whatever fertilizers you add to your soil get chemically BOUND to soil particles and how its very close to impossible to "flush" excess out.

Again best practice is to only use what fertilizer is required and nothing more/extra that can build up.... food for thought.

Again Bob, like a broken record... go ask Fox Farms Labs (and several other nutrient manufacturers) why they recommend flushing the soil several times during the grow? When chelated nutrients break down so that they are available to the plants, the waste product of that process is salt, specifically EDTA. Salt takes up valuable spots in the cation exchange capacity and if enough salt gets locked into the soil, nutrients begin to be locked out. Salt lockouts are real, whether or not you wish to believe in them.

Luckily salts dissolve in water, and flushing the soil with 3x the container size effectively washes the salt right out of there. Flushing our soil to eliminate lockouts has been around as long as people have been growing in containers... but suddenly it is a bad idea? Sorry Bob, but your simplistic answer to just use the "proper" amount of fertilizer sounds nice, but following that methodology you are simply giving the plants just enough nutrient to live, ie., giving them a subsistence diet... and you certainly are not fertilizing them so that they grow bigger. What is the point of that level of timidity?

 

[NorthernCosmos]

Speaking about problems, was/is there actually a lock out happening or are we just talking theory here??

No specific problems, just theory.

I'm going with what appears to be the consensus and will continue to water to run off. IME, using excessive nutes gives burns, so I'm not doing that - it's not the issue here.

 

[CBD BudMan]

Looks like U're in good hands here @NorthernCosmos. I would like to add one thing. If the pot is light when U water, then the soil or medium is getting on the dry side. The dryer the soil the more runoff U'll get, even before the soil is fully saturated. When U flush using large amounts of water (like 3x, etc) more of the water is able to soak in. This "may" explain what U're noticing with ur grow. Just a thought.