Help Diagnosing Micrgrow Issue For 1 of 2 Plants

[MidgeSmith 1,326]

Hi,

 

I wrote a few months ago as both plants - in my very restricted height microgrow (60cm from floor to ceiling) under an SF1000 light in compost and perlite, with pH adjusted water and Biobizz nutes - were losing leaves.

Fast forward to this grow.  I still can't do anything about the size of my chamber and it is kind of fun but... I upgraded to Biobizz All Mix with their nutrients and kept the light to 60% brightness max.  Now I have got the 2 plants to week 7 without much in the way of leaf problems apart from a little brown on one or two leaves of ONE plant.

The humidity in the grow room does vary between 35% - 55% which is a little low at worst, but there's little I can do apart from make sure I keep them watered and leave a moist sponge in there.

I've been using Biobizz nutes (Grow, Bloom, Topmax & Calmag) at 1/4 strength since week 3 - no pH adjustment, water pH appears to be around 7.2.  I noticed a little rusty brown on one leaf - looked like potassium deficiency to me.  I guess could have been light stress, but only on one plant and in the middle of the plant?

First 2 weeks, I only needed to water the plants once or twice, but have slowly increased this as they went into flower and now they are drinking 500ml a day.

In the last week or so, a few leaves have got brown patches and a couple have started twisting.  Seemingly random locations on the plant and the other plant has no leaf damage apart from a little yellow brown at the tips. A few days ago, I wondered if I'd let the soil get too dry, it was dry down to about 7cm (the pot is only 14cm high but wide, to maximise the little height I have) but no leaves were wilting, just this dry leaf twisting on one or two fans? So maybe the twisting is a knock-on from there?

The nutes don't seem to have stopped the browning and the tips are yellow to brown, which I suspect means that even at 1/4 strength, I haven't watered the plants often enough that the soil is depleted enough to need nutes at even 1/4 strength?

I am including photos of both plants, though note, apart from slightly yellow leaf tips, only a couple of leaves on one plant are affected currently and this has only occurred since week 2 of flowering.  I could imagine even at 50%, the 100W SF1000 at 24cm (less than the 12 inches closest for flowering at 100% power) might cause a little heat or light stress, though my hand is comfortable at leaf-top height and I don't want to turn down the light too far or prematurely as these plants only have another 3 or 4 weeks flowering to go.  I will turn them down if light is the likely culprit though.  I felt it looked like a pot deficiency, hence continuing with the nutrients.

Could you offer any indication of what the problem might be?

 

 

Edited April 24, 2021 by MidgeSmith

[KC 11,794]

The first pic looks like water has gathered on the leaf and got burnt by the light. Do you have an oscillating fan in there? Sometimes it happens when the leaves rub together. As for the tip burns that means it had been overfed at some point. You say you've been using quarter strength but how much is that exactly (ml/ltr). If the pots dry out too much that can cause problems too.

 

They don't look too bad tbf, I wouldn't panic too much.

[MidgeSmith 1,326]

12 hours ago, KC said:

Thanks for replying KC!

I do have a gentle fan on some of the time, but it is fixed and blows across the bottom of the lamp towards the exhaust.  I figured that would provide a gentle air movement in there without making them agitate too much.  The leaf movement in there is almost imperceptible.  I don't know that water could have pooled and burnt, but I guess it is possible.

 

The feed schedule I am using currently is:

1ml / 4.5L Biobizz Grow (1/4.5 strength)
4ml / 4.5L BB Bloom (1/4.5 strength)
1ml / 4.5L BB TopMax (1/4.5 strength)
0.5ml / 4.5L BB CalMag (1/4.5 strength)

I figured that was dilute enough not to cause an issue but it seems not.

I was thinking of reformulating without Calmag or Topmax (humic and fulvic acids) in case something about those is causing a lockout and maybe back the nutrients off by 50% to 1/8 strength?  They are very small plants.

Would you do a couple of feeds of just plain water to flush the soil a little or at least use up some of the remaining nutrients before moving on to a different feed routine?

 

It doesn't look too bad in the photos, I know and it is only really effecting one plant (the shorter of the two) but the march of the leaf drying and browning has sped up in the last 2 days.  It's weird it is only on one plant, the other just has the yellow tips.

Cheers again,

Midge
 

---------------------------------

The first pic looks like water has gathered on the leaf and got burnt by the light. Do you have an oscillating fan in there? Sometimes it happens when the leaves rub together. As for the tip burns that means it had been overfed at some point. You say you've been using quarter strength but how much is that exactly (ml/ltr). If the pots dry out too much that can cause problems too.

 

They don't look too bad tbf, I wouldn't panic too much.

 

[KC 11,794]

Hi,

 

You don't look like you've been feeding much at all really, but the tip burn says something happened it didn't like, maybe when they got a bit dry. I've never used calmag, you don't look like you've got calcium or mg def, have you had these without using calmag?

I think the general consensus with Biobizz is not to bother with topmax, I never used to use it when I used BB nutes. Not due to plant issues, more as it can affect the taste of the weed. 

 

I wouldn't feed plain water myself, maybe make up the feed, feed the good one, then drop a bit more water in for the second one so it gets a slightly weaker feed. 

 

Atb

[MidgeSmith 1,326]

I love this reply KC, thanks!

The reason I am pleased you said that is because I am asking for help in a couple of forums and your advice is a little different to the others, but similar to what I had started to think. I.e. don't bother with the TopMax or the CalMag (which was legacy from trying to fix a similar but more aggressive issue in a previous grow). They also suggested pH balancing the water, but from the last time I measured it, it was around 6.7 anyway, which seems reasonable while growing in soil.

What I have done this morning, prior to reading this is to run 2 litres of plain water through each pot.  Interestingly, the plant with the problems ran slightly brown water at first, then clear (only about n500ml runoff) and the healthier looking plant ran clear from the start, which would suggest a greater suspension of nutrient solution in the plant with problems.

1) My next quandry is what to do next feed though, which will probably be in 2 days time. My two thoughts are either:

A) As you say, make a feed of what I was using before (minus topmax and calmag) and give that to the healthy plant and a dilute version of it to the plant with problems:
 

1ml / 5L BBG (1/4.5 strength)
4ml / 5L BBB (1/4.5 strength)

 

or

B) Make up a weaker feed and give it to both:

0.5ml / 4.5L BBG (~1/8 strength)
2ml / 4.5 BBB (~1/8 strength)

My intuition is currently to choose A) as we know one plant is happier with the current regime than the other and so adjusting for the sick plant seems wiser than reducing the feed overall.

The reason I am finding it hard to choose whether to drop nute levels down for both is concern about those yellow tips.  2) Is there a chance that even 1/4 strength is too much for these tiny autos?

3) I am growing these two plants in wide, shallow baskets (to allow air pruning and enough substrate for some nutrient reention and growth vigour (in theory).  The same problem occurred when I was using standard taller, less wide fabric pots but... Could the problems with some leaves simply be because not all the soil is managing to get damped by the watering and a corner or side didn't get enough water, damaging a branch of the root and causing the damage on just a few leaves?

Thanks again for your suggestions!

Midge

Edited April 26, 2021 by MidgeSmith

[KC 11,794]

That's why we water to run off then let it sit in it for a bit just to soak up and get an even wetness. 

 

Beat of luck whatever you decide. 

 

Oh and no need for pH in compost

[MidgeSmith 1,326]

Just now, KC said:

That's why we water to run off then let it sit in it for a bit just to soak up and get an even wetness. 

 

Beat of luck whatever you decide. 

 

Oh and no need for pH in compost

Cheers dude!