Problems with leaf edges burning

[WonderWoman]

Hi,

i'm growing in 15l bucket with hydroton at bottom and rest biobizz coco and lately, beginning at 5th week of flowering, the leaves of my plant have started to curl up on the edges and it slowly leads to the edges burning. the tips of the leaves look also burnt. it's worse on the middle/top of the plant rather than the bottom. atleast on the curling side. Bottom leaves also show these burning tips.

It looks almost identical to magnesium deficiency or heat stress although i'm certain it is not heat stress as I have my cooltube 50cm away from the highest part of the plant. It's now on 7th week of flowering and supposed to finish at 64 days but i think she will take it over 70 days as almost all hairs are still white. the colas have gotten bigger and the plant looks healthy overall expect for this curling and burning of the leaf edges and tips. But some budleaves (the small sugarleaves) have burnt tips and they curl upwards too on the edges-

I'm feeding once a day until i get 30-40% runoff. i use AN PH perfect Micro Grow Bloom with canna mono magnesium. ph is ~7 but it should be ok with these an nutrients. i think magnesium may be locked out cause of high ph but shouldnt it still be available at that ph to the plant?

i feed at 0.8ec and the runoff is 1.0.

using 2ml of grow, 4ml of micro, 6 ml of bloom and 3-4ml of magnesium / 5 liters of water.

What could be causing this?

 

[PetFlora]

Pics would help. Leaf tip brown/curling is a sign ppms are too high, however a 1/4" is ok. Back down

You may be over feeding. Get a moisture tester to check moisture ~ 3" below the surface

Also, check pH of runoff AND make sure pH meter probes are clean- buildup will affect readings. Keep pH pen in 6.5-7.0 pHed water between use

 

[firehound]

sounds like it needs water only til finish. this is a great time to drop all nutes. water only like a flush basically. hope this helps. i stop feeding at like 6 1/2 wks. plant will continue on its reserves stored in the plant

 

[WonderWoman]

I started using only ph'd water as of today and watered with 30% runoff and got 0.9 ec out.

you suppose if i continue watering like this the plant will have the nutrients she needs until I chop her?

the leaves are dark green and the plant looks overall very healthy except for those over fert symptoms.

some hairs at the more shady spots have started to turn in colour but the main cola has only white hairs.

 

[firehound]

as noted from above post says your on the 7th wk. my personal thought is that you will be fine doing like you are until you chop her. it will have a cleaner taste in the end. got any pics?

 

[Snow Crash]

To address the actual issues here...

It sounds to me like you have cation competition and a VPD issue. Leaf edge curl and burn is typically from the plants inability to effectively cool their leaf tissue temperatures through transpiration.

Potassium is the primary element for transpiration. Normally in woefully low supply in nutrient programs the competition for uptake against Calcium and Magnesium (specifically in mid to late bloom) can cause these issues after several weeks of increasing feed strengths. Coco is notorious for retaining cations, and sodium can be an issue depending on water source (softener) or additives (like sea kelp). Decreasing the amount of AN Micro in weeks 3-4 may improve the availability of the Potassium later in bloom. I use AN Big Bud Dry for a healthy boost of K during this stage and absolutely love the results.

If the temperatures are too high, and humidity too low, the leafs essentially become chapped. Vapor Pressure Deficit is an important factor to plant health and can vary in what is appropriate variety to variety. Many Cannabis growers use far too low a humidity level during flowering for fear of mold and rot setting in. I can't argue against that fear although I can say that a healthy plant is better suited to fight infection and maintaining 76f-ish temperature and a 55%-60% RH is a more ideal environment than hitting say 78-80f on the regular and keeping the RH>40%. For many people in winter the relative humidity can be very ow because the cold temperatures have frozen the water right out of the air outside.

My suggestions in the future are to reduce your EC in weeks 4-6 of flowering by 10-15% of what you ran this time around. Decrease the use of Micro considerably and increase the amount of Bloom to improve K+ availability. Maintain a healthy VPD and that should be a good start.

Root death can also cause these symptoms as the plant simply cannot uptake enough water to maintain itself. During flowering root health is not the main concern of the plant and a dwindling root zone is only capable of maintaining a certain amount of vegetation above ground. Removing some vegetation (leaf mass) after flowers have fully set is a way of lessening the load on the taxed root zone. Although, stressing your plants could be an issue so don't be too overzealous and don't prune a princess plant.

 

[RonSmooth]

You can develop heat issues due to the radiant heat. Think of a blacktop on a hot summer day. IME, heat issues like this come when the humidity is very low.

The plants will try to cool the leaves by curling them and reducing their surface area. The plants don't release water through their stomata. Transpiration is affected. This in turn affects respiration. The plant wont uptake water or any nutrients the water may carry.

I just finished a run and had this problem on a few of the plants (all the C99)

I just let them finish. My thinking was that chasing a deficiency late in flowering would probably lead to more problems than it would solve.

 

[papaduc]

Wonder Woman, I'm not having a go at you, but you really need to post pictures if you want people to give you solid constructive advice, otherwise it's shooting in the dark.

You've had problems now in every stage of growth from seedling to full flower but still haven't posted a picture to show anybody the plants. It means any advice is just roulette.

You've got to remember, your description is a diagnosis in itself. Without pictures we're going on your word of what the problem is, but if you knew that you wouldn't be here in the first place.

You might not have tip burn because you've overfed. You might have underfed and the leaves might be dying.

For example snowcrash has advised you to drop your feed back by 10-15% in the peak of flower, based on the fact you say you've got nute burn.. But that'd mean in the peak of flowering you'd be feeding about 0.6-0.7ec.. that tells me it's not burn.

And that's the problem with asking people to solve a problem they can't see.

There's no possible way to tell whether the nutrients are too strong, too weak, out of balance... or whether the heat/humidity is too high or too low.. or even whether the light is simply just a bit too close to the bud affected... without seeing the whole plant.

You might as well just read the forums as pose questions without pictures, because there's nothing anyone can do other than give you general advice.

In the meantime, like I said in your last thread - stop using mono elements. You're complicating things for yourself and replacing an already low strength balanced food, with one element. You should add magnesium as a supplement only if you need it.

Adjust your ph to 5.6 - 6.2 before you feed.

Stop watering daily to 40% run off. Even if your plants are vigorous and drinking every day, 40% is a massive waste of nutrients and water. Your plants might not even justify the pot. That's something else you can't tell without pictures.