Get Help for Cannabis Plants Problems as Quickly as Possible!

[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!

[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

[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.

[Rootsruler]

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

[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?

[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.

[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.

[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.

[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 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]

Well, let us see how this goes...

[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.

[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'm thinking of setting them up on a reservoir/auto irrigate and program in around 8 -12 feed events a day on the digital timer. I'm thinking that it would also be a good idea to give them a deep watering once a week to make sure all the media gets wet.

In veg that would mean they get a feed every 1.5 to 2 hours at lights on. Obviously the feed times will be around a minute or two per event but I'll need to stay on top of the timing and intervals as the water needs change to make sure the volumes are correct.

Bluey - I'm thinking of using the amounts of water I typically use at whatever growth stage the plant is at as a basis to determine the feed event volumes, In five 7 gal pots I was feeding around 5 - 6 gallons in veg and around 6 - 7 in flower every 3 - 4 days. If I run 8 events a day that would mean each event would use around an 1/8 of a gallon or around 480ml per event. Obviously in early veg they'll get less but, I would say after week 3 of veg, this is the volume I tend to see. I may add a few more ML per event to make up for evaporation but I think I'm pretty close.

I'll adjust as I go along but I think this would be a good way of having a threshold to start from.

What do you think?

[Bluey]

Well I feed say 3 times a day and once at night thereabouts and I was starting to get algal
growth on one of the pots.

Each feed at max they would take about 4 to 5 gal ( 5 off 7gal pots) when they were at there thirstiest, so more than 2 gal per day each. From memory a few maxxed out around 2.5 gal/day.

When I had 4 not quite so large plants (harvested about a pound each total) in 13gal pots a 25 gal reservoir would last
about 5 days max at there peak.

I automated it in minutes and adjusted the sprayers to deliver the correct amount. Sprayers would regularly block and flows would slow a tad as the week went on so I'd just give it a bit more on the timer remotely. I wouldnt do it without a drain to waste because of risk of flooding. Manually I didn't bother draining to waste, just used saucers I'd have to suck dry from time to time.

[Rootsruler]

Do you think lights out feeds are ok? I was told the plants change up processes at lights out and uptake is reduced in favor of processing the sugar that was made during lights on.

[Bluey]

I did it to stop the coco from drying out.

I'd only do it as long as you can keep humidity down. These girls had a canopy of about 9' x 6', and hardly any defol. They were big.

When I dropped temps from 23⁰C to 22⁰C in mid to late flower the water uptake dropped a lot as humidity didn't drop much as 40% was as low as I could go at those temps with 5 huge plants.

Dehumidifiers that work well at 22⁰C are very expensive, mine couldn't go below that temp without issues.