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[Bluey]

I don't measure anything in runoff because I could not get consistent results, especially with pH, so gave up on that approach.

The way I do it is just increasing the frequency dependant upon how much the plant is taking up and pot size. Sure its guess work but I feed them a litre or two to soak the coco then just give a little bit to first sign of run off then stop, if taking up a lot, I'll feed more often but try and avoid runoff for most feeds. I'll only give runoff about once every 4 to 7 days but a good amount, say 20%. At those frequencies you need to watch for algal bloom on top of the coco and its easy to see the slightest color change by just moving your finger through the top ¼" of coco and looking for change. If it starts I'll reduce the frequency if feed by 1 per day. Seems to work.

Last grow plants were so large I gave them all half a gallon in the middle of the dark period also and 3 to 4 times during a 12 hour day depending on their uptake. Minimum feed was a half gallon at a time in 7.6gal pots. They each produced over a pound of great but and about ¾ of a pound of average to poor bud for processing for hash/butter. I hand watered them and that was exhausting but it made me watch them closely and it worked out great.

[Rootsruler]

I think the key to fertigation is the constant presence of nutrient in the rhizo along with being able to keep media saturation levels at a constant where the plants are able to freely do the O² exchanges they need to max the potential of the plant.

The way I understand it is that when we traditionally water our plants, the first few hours is really dedicated to the media equalizing the saturation levels through capillary action while the plant continues to do its thing with what it has within its vascular system. Once the saturation levels reach a certain point, O² exchanges become easier for the root system and performance increases but there is a time lag before the media reaches these levels whereas Fertigation essentially operates constantly at these ideal levels as long as you can keep the saturation levels at a point that allows the plant to maximize its exchanges.

The trick, from what I've observed, is in being able to determine where those levels are. I've seen some measure their runoff to see how much food the plant is taking up and adjust accordingly. Part of those adjustments are light energy and media saturation levels. This is the balancing act part that tends to keep most growers from diving into this type of irrigation strategy but I've seen the results. I'm already taking measurements so a few more to increase my yields exponentially is more than worth it.

[Gingerbeard]

Well, let us see how this goes...

[Bluey]

I use between half and about 80%. They say you can't really overwater a coco grow but you can cause problems if you keep it too wet with algae growing on top or fungus gnats, so if I get a green haze on top of the coco I back things off a bit.

From what I can gather you'd use a bit more in DWC and less in something that resembles soil.

[Gingerbeard]

Dang you all and your making me look up fertigation! I was planning on doing half my usual amount of full dose nutrient solution more frequently, this grow. Keep the coco good and wet. That's sort of fertigation, huh? Maybe quasifertigation? Is fertigation why some of you people get such big plants using half dose nutrients?

[Bluey]

I fertigate, absolutely!

[Rootsruler]

I agree with Gingerbeard and Bluey .

I like Bluey multiple feed strategy in coco. Similar to a Fertigation process. Something you may want to look into if you continue in coco. Most of the highest yields I see in coco tend to run Ferti Irrigation or some variant of it.

[Bluey]

I run just coco also and at that stage I'd be feeding them between once and twice per day and increasing to 3 possibly 4 times a day if large plants or in small pots...I call 7gal small for photos. 6 to 6.3 works for me also.

It might help if you had an EC meter to measure the amount of nutrient in your water. I find that important given the way I grow. Without it I'd be guessing.

Edit. The pH in your medium likely ran too high because you are not feeding them enough. Also give decent runoff once or twice a week, say 10 to 20% of the input on that feed.

[Gingerbeard]

I use Dynagro in coco. Try lowering your pH to 5.8 and do not worry about runoff. My 5-gallon bags take 1-gallon of full or better dose of nutrients when they get going.
Learn what your bags feel like just before and just after watering. That's a good way to tell how dry they are.

[Shenandoah]

Gingerbeard Thanks for the link, I will check it out. I figured there probably isn’t a ton I can do now, but it would be great to get better for next time!

Bluey No soil, just coco/perlite. I’ve been pH adjusting my water to between 6-6.3. I tested the runoff and it was at 6.75-6.85. I adjusted the water to 5.5 for the next waterings until the runoff was the same as the input. Only got it under control a couple of days ago.

Rootsruler I’ve been giving 1tsp/gal of nutrients. But if they’re short on nutrients, maybe I should have been feeding/watering more often?

[Rootsruler]

What was the dosage Dyna Gro recommended? Looks like they were underfed.

[Bluey]

What is your pH inputs range? Is this a soil grow or a coco grow and how did you plan to manage it given each have different pH values about 0.5 variance?

What is the ideal pH ranges for your medium?

I'd stick with one or the other for ease of management.

You have probably washed out most nitrates out of the soil with your runoff. Likely it needs feeding more often but you need to get the pH on point and I don't know how to work that out with two different mediums.

[Gingerbeard]

What you have going on is common in late-stage flowering. It is not typical, just common.
Bad news is you have all sorts of nutrient lockout issues, and it is too late to do anything about what has happened to this point. Good news is you are on track for some fine dope, seriously.
You are about to get a lot of helpful advice that may help you avoid this in the future. The pictures in the link are a lot prettier but what you have going on, they have going on, and theirs is a little more genetic and a little more on purpose.
On the same website is information on what to look for when harvest time comes.
The Cannabis Autumn Color Effect (Get Colorful Leaves!) | Grow Weed Easy

[Shenandoah]

HELP!!

Problem: first time grower here. Plants are 8 weeks old, should be harvesting in a couple weeks. About at the start of flowering they started yellowing and showing brown spots. It’s worse on the lower leaves, but the tips at the top are brown and curled also. First photos are when it started, later photos are how it looks now.

Tested the runoff pH and it was too high, so corrected that over a couple of waterings. Also moved the lights further away so they are getting around 750-800 umol. But they have continued to get more crispy.

Setup: 300W AC infinity light, fox farms 70% coco, 30% perlite, dynagrow liquid nutrients

Watering: I way over watered when they were seedlings, but I’ve tried to get it back on track. Currently giving ½ gallon every 3 days and getting about 5% runoff. Could I be giving too little water now?

Nutrients: gave 1 tsp/gal of the dynagrow- Grow until 2 weeks ago when I switched to Bloom

Temp/humidity: Temp 70-80 deg, humidity a little low at 30-40%

Any suggestions would be helpful!

[Bluey]

Here's an older article on root zone health explaining how we thought it all worked back in 2016.

https://www.cannagardening.com/articles/root-zone-temperature-and-plant-health

Dissolved 0² or DO does leave the surface water over a period of time but it can take a little while to reach equilibrium, eg. overnight, without help, eg. Stratification. It is leaving the water in the root zone though so can it still be used by the plant or soil microbes? Is it raising the 0² in the medium which in turn keeps it dissolved longer in the H²O?

CO² at the roots which is also beneficial to a healthy crop is 200 times more soluble than O² in water. That is my understanding although the above article states CO² serves no purpose for cannabis in the root zone..I'm not so sure about that.