Grow Box Plants not Growing

by Eric
(California)

I bought the Caddy, which is the cabinet with 2 LED UFOS, and a chamber with an aerated drip system, and a fogger. I got a couple nice plants, about 8" tall. They were in a starter, it's maybe rockwool? I packed them with the rockwool (they had lots of roots) into the clay balls. I washed the balls first.

I got deionized water (my home water was 500 ppm, too high). I got the hydroponic nutrient strength at 400 ppm with Moon Dust. I read lots on this, and saw lots of different recommended levels. For small plants, most recommended around 400-800 ppm. I recently put the levels up to 800. I balanced pH to somewhere around 6.5-7. Temperature has been good. Doesn't go below 70 at night, and 85 in day.

Fans are blowing in fresh air full time. Lights are on 24/7. Lights placed about 1 foot above the plants. So, there seem to be TONS of new leaves growing from the nodes, but they are kinda curling down. And the plant isn't getting taller at all. It's been over a week. Slowly, the bottom leaves have been dying. On the two plants, the lower leaves have been turning yellow.

Help! What am I doing wrong?! I covered the extra plant holes on the lid with plastic to keep the fog inside with the roots. Is this correct?

Answer: Eric- when leaves yellow, it is often because of Nitrogen deficiency. I noticed "Moon Dust" has several different products....make sure you are using one with plenty of Nitrogen (the first number in the N-P-K rating). The most appropriate product they have for your situation would be their 19-8-13 formula, although you will probably need to add a Phosphorus supplement during the fruiting/flowering stage.

When leaves at the bottom of a plant yellow and die, it is either due to under-feeding or to low light conditions. Seems like you should have enough light. Since you were only feeding at 400 ppm, I'm going to have to go with under-feeding. I am guessing you had them at 400 ppm for about two weeks or three weeks. Plants feed less under low light, and feed more under brighter lights. At 400 ppm, you were probably feeding them less than they needed under two UFO lights. Nitrogen is a mobile nutrient, and after a week or two of under-feeding, your plants decided to pull the Nitrogen out of the lower leaves and send it up to the tops of your plants (where it was desperately needed because the tops get a lot of light). This would also be the reason your plants are not getting any taller.

The moment heavy feeding plants, like tomatoes, are a few inches tall, they can take 400-500 ppm. After two weeks, this needs to be increased to 600-700 ppm. By the time they are 8 inches tall, 700-800 ppm should be fine. After that, you can slowly increase the strength of your hydroponic nutrient solution from week to week---simply keep a close eye on the tips of your leaves. At the first sign of leaf tip burn, consider this your maximum nutrient strength for your plants....and you may want to back off the nutrient strength just a little bit at this point.

Whenever you use expanded clay pellets, be sure to soak them for at least 20 minutes first. Otherwise, they do not soak up enough water initially. It is great that you are using a low TDS water source to start with. It is also good that you have covered over the unused plant holes. In my opinion, your pH is a tiny bit high. The maximum number of nutrients are available to your plants at a pH of 6.2 in soil, although hydroponic gardeners often use a slightly lower pH than soil gardeners. Try shooting for 6.0 for a while and see how that works for you.

When leaves curl down, it is caused by one of three things. One- over fertilization (which I do not believe to be the case in your situation). Two- genetics. I have grown two types of the same plant side by side before, and had one grow normally and the other grow with many of the leaves curved down. It drove me crazy, but I eventually figured out that the variety always grows that way, no matter what. Third- temperatures that are too high. This is most likely your case. Ideally, 72 to 75 degrees would be your daytime temperature in the grow box and 78-80 degrees would be the maximum hot spot temp (directly under a grow light at plant top level).

Warmer temps will stress out your plants. You may be able to pull it off (I have grown perfectly fine crops when my grow room temps have gotten up to 85 degrees before). The deciding factor may be whether or not you get mites- mites LOVE warmer garden temperatures, and when it comes to mites the difference between 72 degrees and 82 degrees is like night and day. 72 degrees- manageable and still a good crop. 82 degrees- webs and mites and dead leaves all over the place, and maybe 30% of the produce you could have gotten from your garden.

Hope this helps you out Eric, and Happy Growing!