OK, so these AK-48 plants where sprouted almost 4 weeks ago. There are five plants, which I started under four 4' 40w fluorescent tubes. When it was evident that the plants were stretching badly (growing 4" in a day and falling over), I added two additional 150w HPS bulbs and a small fan. This seemed to solve that problem. I transplanted them from their starting cups to 5 gallon buckets about a week ago. The soil is all Miracle-Gro moisture control potting soil. Except for the stretching, they have seemed extremely healthy until now. As you can see in the pictures, the edges and tips of some of the leaves have begun to yellow. The initial two sprout leaves have completely shriveled, though I assume this is normal. On all of the plants the single bottom leaf has yellowed at the tip (second and third picture). Additionally, on a couple of plants the first real (bottom-most) fan leaves have yellowed slightly at the edge (first and fourth pic). I read that this type of yellowing was sometimes a symptom of Nitrogen deficiency, especially because it was starting at the bottom and going up. So, two days ago I fed the plants with fertilizer for the first time with Miracle-Gro tomato fertilizer (18-18-21) at about 3/4 strength. Two days later the plants look the same: no better, no worse, and still growing steadily. The rest of the leaves are a healthy looking deep green. Some additional information: I have been giving them a decent amount of water every 3-4 days. The water is filtered city water, which is then left out for several days. Also, the room gets a bit warm when we have hot days, but nothing over 90 degrees or so on the worst days. A fan keeps fresh air circulating from outside. So, am I worrying over nothing or is there something I should be doing? Pictures
I hate replying to myself, but wanted to post a short update: The bottom-most leaves seem to have yellowed slightly more and I read that Nitrogen availability starts to go down at a PH of 8, so I'm wondering if the PH could have been causing what I thought was a N deficiency. I used bromothymol blue to test the PH of my tap water and it was pretty high, somewhere between 7 and 8. I don't have anything to test soil with right now, but I think it's safe to assume that it's probably high too since I've been putting this water in it for weeks. Because of this, I added sodium bisulfate to the water before watering today and brought the PH down to around a 6. I then watered fairly generously. Even if this isn't the cause of the damage I'm seeing, I think it's safe to say that the PH needs to be brought down anyway. I'll probably bring the PH of my water down to 6.5-7 from now on. I'm curious though; is the sodium bisulfate OK for cannabis or is there something else I could/should use? The only thing that worries me is that this is technically a salt. I have hydrochloric acid on hand and have heard of some people using vinegar and lemon juice. I also have some aquarium PH down, but it doesn't say what's in it. What would be best/safest to use? Would the acid end up breaking down into chlorine? I added before and after PH pictures to my imgur album. I also took some more pictures of my setup.
Im not 100% but ill try to help you out. The yellowing could have been from your PH. Try to keep your PH between 6.3 to 6.8. The tester you have is a good starting kit, but if your serious into growing, id suggest getting a digital PH meter. Also don't invest in a soil ph meter, you can determine the soil PH by measuring the runoff after you water your girl. I've never used that salt to lower PH.. but you can use the aquarium PH down instead. I've heard other users buying PH products from pet stores. I've also never used miracle grow fert, but it looks like its really high in nutes. Since you said you used 3/4 strength without any problems, id stick to it. Just keep an eye out and if it worstens, stop using and flush her. Id also make another suggestion, can't really tell, but if ur leaves are mostly rusty looking than yellowing, it could be a cal/mag deficiency, which is more common. If you think it is, a tsp of epsom salt per gallon of water should do the trick. Good luck.. she looks healthy. Sometimes you tend to do more for your plant than needed and that's when things get bad.. so if anything be patient. A yellowing leaf will always be yellow, so don't think it will heal itself. You'll want to look at other leafs next to it to see if the symptons are being transferred.
Hey shug, thanks for the advice! I'll definitely switch to the aquarium stuff next time I water; hopefully the one dose of salts won't damage anything. As far as the color, there's some very small brown spots at the very tip, but other than that it's just yellow coloration on the edges/tips. I'll try to be patient and not do anything crazy. Thanks again!