Recurring grow problem.

Hi

I'm currently on my second grow (had to kill my first lot from overwatering+nute burn)

My setup:

Closet grow with air cooled 400w HPS, 100mm RVK fan+carbon filter, passive intake.

Using 6x3gal pots with my own compost/perlite mix.

Canna terra vega+bloom nutes.

My plants are vegging and about 3.5 weeks old from planting seed. The seeds were germinated in rockwool then transplanted into small pots (3L) then up to these big'uns about 2 days ago. They've been fed once at 25% strength. And I've been watering about once per week with PH water. My soil PH is between 6.6-6.9.

Ave temp 26-28c and humidity 30-50%.

The problem


I've noticed my plants just stop growing at this height, they seem to be really short bunchy and the growing tip is halted with spindly little leaves popping out but not growing. Some are a little droopy too.

In the photos you can see a couple of yellow lower leaves. I fed after seeing this guessing I had an N deficiency but I think I may have burnt a little (is this possible with such a small amount of nutrients). You can see some brown on the leaf tips. They feel brittle and snap when held.

I'm very confused because I've been very careful this time, not to overdo the nutes or the water and tried to keep them happy with a nice temp and air.

Any Ideas?

Thanks in advance guys!

psyfiend, do you ph after you mix your nutes or before? Do you run an osilating fan on them? Is it only affecting the top leaves? How far away is yr light?
my eyes stink, but you say those are 3 gallon pots?

Videoman, Thanks for your quick reply!

When I mix my nutes PH is about 6 so I use a little PH up to take it back to 7 then I water.

I've been running an oscillator fan for about 2 hours a day but It's harder to fit in now with the big pots.

Well the problem is that the entire plants growth is slowed down to the point of stopping. So i guess the whole plant is affected.

And, my light is 30cm from the growing tips.

Sorry dude, but I dont know metric, I'm an old fart in the states. lol
Can you give me a measurement of your grow pots, as to me, they look small, maybe its just the pic?
(A PH of 6 should be ok)
Do you let your water sit prior to using?

Sorry man, 30cm is about 12 inches which I think's a foot. My pots are 3 US gallons and 9.5 x 9.5 x 10 inches. If you ever need any conversion just type it straight in to the google search box and it'll do it for you!

I let my water sit for about 24 hours prior to mixing.

psyfiend said:

I'm very confused because I've been very careful this time, not to overdo the nutes or the water and tried to keep them happy with a nice temp and air.

Click to expand...

I'd like to know what soil mix you're using, because that may be impacting on your problems. You're not using Biobizz allmix as a soil base are you?

Anyhow, firstly, they're over-watered, secondly, they're over-fertilised, because you've misdiagnosed. Thirdly forget ph for soil - stop messing with the ph, you'll do more harm than good - soil buffers ph to an extent and as long as your water isn't overly acidic or alkaline, you shouldn't have to mess with the ph in soil grows. Ph and EC is critical for hydro, not for soil

Good quality soil should contain at least 3-4 weeks of nutrients in it and you shouldn't have to feed them anything. However, some supposedly 'high quality' soils like Biobizz allmix are notorious for Mg deficiencies, I use it and that's what I get and I suspect thats what you've got.

Don't feed any more nutrients, adhere to the correct /wet'dry watering cycle (I posted in one of Typo's threads about how to water correctly) and next feed give them 1 level teaspoon of epsom salts per 2-3 litres of water only.

If you prefer you can foliar feed 1/2 teaspoon per litre of wate for faster results but hold back on that for the moment until you've sorted your over-watering problem.

Hi there psyfiend;
As this is my first post here at rollitup I guess I'll say "hi" too.

My name is cannazine and I run a cannabis news portal based in the UK, <cannazine.co.uk>, (feel free to subscribe and say hi).

I saw your question via RSS feeds (respect to admin ) even though I was not yet a member of rollitup, nor even knew of its existence.

I rocked up to 'roll it up' via the link in the RSS news feed, joined up, and here I am with my answer to the question!

How cool is technology?

Now on to the problem.

I think your plants have stopped growing because the CO2 in the atmosphere in which they live, is depleted.

Cannabis uses carbon dioxide from the atmosphere as the actual source of the carbon it uses to build itself at cell level.

So, when the CO2 runs out, (as I believe it has in this instance), the plant stops growing.

Quickest fix is to get as much fresh air in there as possible, and she'll fire up again quickly.

But I think in the long term, you're going to have to take a look at your ventilation system sooner rather than later.

Hope this helps, and great to meet you.

cannazine

cannazine said:

I think your plants have stopped growing because the CO2 in the atmosphere in which they live, is depleted.

Cannabis uses carbon dioxide from the atmosphere as the actual source of the carbon it uses to build itself at cell level.

So, when the CO2 runs out, (as I believe it has in this instance), the plant stops growing.

Click to expand...

Hi there Cannazine, welcome to rollitup.

Lack of co2 would certainly account for the slow growth, but it doesn't account for the yellowing leaves.

Hey Cannazine welcome aboard and good call, I never thought of that! Makes sense to me though.
The yellow as far as I can tell from the pic, seems very minor.

Hey there thanks for all the response.

I have been using All mix until the final transplant when I mixed about 1 part perlite to about 6 parts Gem all purpose compost (common UK gardening compost).

I thought it looked like Mg def but I figured the soild would have enough in.

So I don't need to Ph my soil at all? Is this true?

Also I have a fan pulling the air across my light and out of the closet, maybe there's not enough air getting in. I should maybe add an intake fan.

Lol..when I came into the site it was as a guest so I didn't see any pictures. Forgive me.

The yellowing looks like it could be a little light depravation. It does seem to be shielded by the larger leaf above it.

Chances are even a light feed has caused a bit of tip/edge burn because the compost will be providing everything needed at this stage, so even a light feed can upset the applecart a little.

With a good quality compost, I normally feed only plain, unadjusted tap water for the first 3-4 pot sizes. Regular potting on provides a regular long term feed in the fresh compost used, so I find only water necessary until flowering and beyond unless extended veg times are used.

Just a personal thing and I'm sure there's lots of others using different techniques.

Regards

cannazine

babygro said:

Thirdly forget ph for soil - stop messing with the ph, you'll do more harm than good - soil buffers ph to an extent and as long as your water isn't overly acidic or alkaline, you shouldn't have to mess with the ph in soil grows. Ph and EC is critical for hydro, not for soil

Click to expand...

Babygro you cant really beleive this? Ph is the corner stone of growing an awesome crop. Ph can make or break your day. Not all people have 7.0 tap either may I remind you...hell mine is 7.9/8.0. you tryin to tell me its point less to check PH? LOL you are good people tho....i like your staright foward attitude and i look forward to your reply!

cannazine said:

The yellowing looks like it could be a little light depravation. It does seem to be shielded by the larger leaf above it

cannazine

Click to expand...

Lack of light would not cause that, why would you think that?

psyfiend said:

I have been using All mix until the final transplant when I mixed about 1 part perlite to about 6 parts Gem all purpose compost (common UK gardening compost).

I thought it looked like Mg def but I figured the soild would have enough in.

So I don't need to Ph my soil at all? Is this true?

Also I have a fan pulling the air across my light and out of the closet, maybe there's not enough air getting in. I should maybe add an intake fan.

Click to expand...

Yeah I knew it - it's that bloody Allmix! Almost definitely Mg deficiency then in my opinion. Hold fire on the epsom salts for the moment as you've repotted - don't know what nutrients your new compost contains, and it will take a little while for the plant to settle into it's new home. If it gets worse after a week or so, start giving it some epsom salts. Don't feed it any more nutrients for the moment - there should be enough in the new soil for at least 3 weeks growth.

Whats your watering schedule been like? How much water have you been giving it?

I don't buy into the lack of co2 myself (no offense Cannazine) that fan should be supplying enough co2 for the size of that plant. You will need to set up a proper intake/exhaust system though as it grows older and bigger because it will need higher levels of co2 than your current setup can provide.

Your problem at the moment is - some Mg deficiency from the allmix soil, probably over-watered and over-fertilised.

I wouldn't bother with phing the soil, as I said, soil buffers ph to a large extent and unless you've got particularly acidic or alkaline water, it won't move the ph enough to become a problem. You right to let your water stand for 24 hours though, so some of the solids can vaporise out.

Seedlessone said:

Babygro you cant really beleive this? Ph is the corner stone of growing an awesome crop. Ph can make or break your day. Not all people have 7.0 tap either may I remind you...hell mine is 7.9/8.0. you tryin to tell me its point less to check PH? LOL you are good people tho....i like your staright foward attitude and i look forward to your reply!

Click to expand...

Well I did caveat my answer with (as long as your water is not highly acidic or alkaline) and the vast majority of tap water in England (where both he and I live) is well within the correct ph range. Messing with it can cause you more problems than you solve to be honest.

As I said, soil buffers ph to a large extent (that means it takes an awful lof of acidic or aklaline or chemical nutrients to alter the ph value of the soil) and by the time it has altered the ph value its either time to repot on into fresh soil or time to harvest.

Where ph and ec values are critical is in hydro grows where there is no substrate like soil to buffer the ph and ec, and acidic/alkaline water and large quantities of chemical nutrients can change the ph and ec of the solution quite radically.

With good quality soil and good quality treated tap water there really is no reason to be fretting over ph values.

I defenitely have a hard time with that statement too, Ph comes into play in several seperate areas, Your nutes, your water, and your soil.
The best test is to test your water run off from your grow pot.
You need to PH your water, after adding yr nutes to it.
Soil should be between 6.5 and 7.5 since marijuana does not do well in acidic soil. High acidity in soil encourages the plant to be predominantly male, an undesirable trait.
One problem alot of growers encounter is adding fertilizer to there soil mix, this will almost always results in a more acidic pH.
The amount of salts produced by the breakdown of fertilizers in the soil causes the soil to become increasingly acidic and eventually the concentration of these salts in the soil will stunt the plant and cause browning out of the foliage. Also, as the plant gets older its roots become less effective in bringing food to the leaves. To avoid the accumulation of these salts in your soil and to ensure that your plant is getting all of the food it needs you can begin leaf feeding your plant at the age of about 1.5 months. Dissolve the fertilizer in warm water and spray the mixture directly onto the foliage. The leaves absorb the fertilizer into their veins. If you want to continue to put fertilizer into the soil as well as leaf feeding, be sure not to overdose your plants.

YouTube - Growing with the Stars - Arjan

I dont grow in soil so i dont really get what they are doing with the ph

Anyone out there that can explain?

videoman40 said:

I defenitely have a hard time with that statement too, Ph comes into play in several seperate areas, Your nutes, your water, and your soil.

Click to expand...

Best not to pay too much attention to anything I say then hmm? I clearly don't know what I'm talking about...

i didnt see that you said as long as your tap ph is not all outta whack you should be ok. if my ph was around 7.0 outta the tap i guess you could get away with out checking it. ive grown without use of ph meters and my whole thought on the thing is: "growing with nothing ph is like growing blind"

Nice setup psyfiend. Great feedback too. I'm also on my second grow and am experiencing 90% slow squat (indica?) growth. I always attributed lower node yellowing as normal. Your plants look great from the pictures, a little yellowing is not cause for alarm. These plants are very hardy. Good luck with the grow.