Drying Out Damage vs Nutrient Deficiency or Lockout

I have a microgrow. Literally 60cm (2ft) tall and deep and 40cm (just over 1 ft) wide. I have a problem with the grows I have done in it. The leaves have browned off, to the point where even the sugar leaves were a dry mess. The smoke was pretty good regardless, but eh.

I have had a few conversations on forums about the problems I have had with my plants in 2 different soil media. One my own mix of compost, perlite and coco and the other BioBizz All-Mix - which I think is probably broadly similar.

I tried following Biobizz nutrient guide at 1/4 strength on one, 1.2 strength on another and eventually almost full strength. All attempts to maintain a complement of fan leaves til the end failed.

I had 2 other suspicions, the one was the level of light - ruled out now as there is little difference in the scale of the problem whether I am using 40% or 60% power and the former is cool as heck, the latter only slightly warm at cola tops.

The second suspicion was the tiny fan blowing on the plants, but I get the same result fan or not.

Suggestions from forum members included pH issues causing nutrient lockout, though other soil users said with a water pH of 7.2 this was highly unlikely (also with nutrients added, the pH is more like 6.8 - 6.4 depending on concentration). Nothing I have tried has worked consistently or improved the problem until it is non existent.

I have only used 2 strains the whole time I have been testing, Royal Dwarf and Green-O-Matic, but I haven't heard these problems in any grow-diary or report, so I am ruling it being just a type of strain expression out.

The problem starts around 3 weeks, just before flowering was clear and continued each crop. The first time all the leaves went and the plants finished early by a week or two with small buds. The last took most of the fvan leaves and some of the sugar leaves.

What about my watering schedule? Sure, any of the above problems could be present in addition, but I think there is a chance that maybe I was letting the plants dry out too much between waterings. I have been going by the 'water if the top inch or two of soil is dry' method, but I am in shallower, wider pots than normal to fit my basket, so perhaps a more frequent and thorough wetting could help? I wonder if after drying out properly, my soil isnt getting uniformly soaked and some roots / tips are feeling it? I have been using fabric smart pots.

I know there has been no drooping of leaves to suggest they were low in water, but drying out and browning is the recurring theme. Could it be watering or am I still in the dark?

Let's start here

What light, how far away from plants

Grow box RH and Temp

Sure, thanks Bob.

SF1000 (~100W) @40% Output
>22cm
50% (+/- 5%)
23C - 27C

Yer burning them up

PERIOD

Light too close

Box too hot

Can't grow weed in a 2' box.. sorry

I'm shocked you're able to keep the temperatures that low in a box that small.

First of all Bob, thanks for your thoughts, that is what I expected to read also. I have a suspicion that despite my calculations and perception of how LED lighting works, there may well be radiation damage at that distance, but I also have other ideas. The damage did coincide with a couple of things, but namely my being a bit mean on water supply.

Quite a few people grow in really small spaces, likeunder-counter fridges and PC cases with CFLs and LEDs. It appears to work reasonably well, once the method is down, according to the diaries and cases I have seen. I will move to a full-size tent at some point, but I just don't have the capability at the moment.

I average ~45 grams - per auto grow (2 dwarf plants which just meet my personal needs). The buds are nice, flavoursome and stinky, if not the densest. About 1g per Watt, which I think is ok. The buds didn't seem to suffer any damage, particularly the last time. It was just fan leaves at first and then a portion of the sugar-leaves. There was no damage at all before flowering though admittedly they put on 3 or 4 inches of height during stretch, though I continued to LSTd them.

The cola tops were still 23cm away from the light at harvest. The light has a stated minimum distance of 30cm from cola top at 100% power I believe. I am running 23cm at 40% to 50% of max power, a reduction of about 23% of height threshold, but a reduction of perhaps 60% - 50% of the power. I would have thought that would have been reasonable. The damage first occurred during early flowering when water-pickup sped up and I felt maybe some of the roots might actually be damaged by drying out too far and perhaps that damage was mapping to the leaves.

Dubanpoisoner, there seems to be very little heat generated by the LED pane really. The tent is maxing at around 2c - 5c over ambient - measured halfway up the tent. So, maybe at harvest, a few cm below the very tops of the colas. The LED is running at around 40 Watts (of its maximum 100W). I use a 12v PC case fan with kitty-litter filter during veg and currently - due to my not finding a suitable option which took up less space - a 4" Rhino Hobby filter for flowering.

So there is pretty good airflow and a small 5v fan blowing across the LED towards the extraction. At cola top, there is certainly no uncomfortable heat, only really a slight idea of barely noticeable heat on the back of my hand. Perhaps the slight breeze mitigates the heat of radiation a little, or it isn't the heat but something, as you say, to do with light proximity working against the health of the plants at that distance.

When the signs of damage did come, it came at random across all parts of the plant. Not at the top parts which I expected for light intensity / heat damage. The first grow, I lost pretty much all the leaves (or most of each to some degree) and they finished on schedule according to the breeder. The last grow the damage to the fan leaves was probably 30-40% by harvest. The three differences between the first and last crop were reducing the light level by 5%-10%, moving from my own soil mix to Biobizz All-Mix and trying to be just a little bit more generous with the water. As I say though, I did let it dry out as much as I did in the first grow, once.

I totally agree my nano scale of microgrow is not leaving much margin for error, is sub-optimal and requires some tweaking. However, it is all that I can do for now and it is keeping me going and growing. So, I am keen to experiment, even if it means turning down intensity further to say 30%. There's little to lose, except yield, in trying. I guess that is what I will do, try with the light dimmed further and see if I get annoyingly fluffy buds in comparison.

If the leaves stay healthier (for longer), with less light, I will have succeeded in proving the diagnosis of 'light level / proximity'. I was 5-10% more dimmed in the last grow compared to the first. The buds were noticeably less dense in the last grow, though bigger and heavier overall. That shouldn't be much of a surprise maturity came a lot later than in the first crop, the fan and large sugar leaves made it until 12 weeks (rather than 8 weeks in the previous grow), so there was more energy available to them overall I guess.

And as a side note... if using BioBizz All-Mix, a continuous supply of magnesium should be added to your watering / feeding schedule, (1/4 to 1/2 teaspoon per gallon)! I call it preventive medicine! Why, because it's well know fact, that if you grow in BioBizz All-Mix, you will more often than not, end up with a very bad mag deficiency! And your plants are sadly displaying that. Yeah, like everyone has told you, you have a lot of burning and overheating affecting yours plant, but you also have a very bad mag deficiency that has caused a lot of your fan leaves to dry out!

I would try a 26 watt cfl.. The plant can almost touch it w/o damage..

My guess is you have some root rot, and perhaps even bud rot going on. I don't think the light intensity is the issue, or temps. However they may have become an issue once the rot started to take over.

PJ Diaz said:

My guess is you have some root rot, and perhaps even bud rot going on. I don't think the light intensity is the issue, or temps. However they may have become an issue once the rot started to take over.

Click to expand...

Hi PJ Diaz,

thanks for the suggestion, but I the roots were fine as far as I could see. I don't run the plants very wet, my crime this time seemed to be letting them dry too far. I don't have them to show you as they were chucked a few weeks ago now, but I washed the soil off and checked them and they looked good to me. There was a single bud with a little mould in it that I only spotted once I trimmed one of the larger buds down for curing. I was surprised to see it as due to a local heatwave, the temps shot up here and the drying phase was cut short to 6 days from my usual 12...

My intuition is that you are right regarding light intensity though. With the LED dimmed to 40% there just doesn't seem to be anything like enough heat to even irritate the plants, let alone blow their leaves. I couldn't say for sure.

I think I will try the same system with plain compost and perlite next time and see what happens. It may not be the most amazing yield ever, but it will show a different set of deficiencies if it is the medium / nutrition that is a problem.

Thanks also PirateBug. I will definitely bear it in mind next time! I've had loads of advice each way, but last time I didn't add calmag and still saw some leaf damage, so I don't think I overloaded with that before (at 1/2 strength each watering).