Plants not doing well with Technaflora

by Ray

I have been in hydroponics for 11 years and just made a change to BC hydroponic nutrients bloom + boost, pH 5.9, ppm 1300 (25 gal reservoir) 6" rockwool cubes on hydroton rocks, in a drip system. As soon as I made the move to bloom formula the top of the plants turned a gray, brownish color and will brake off the leafs were dry and "crisp" (on top mostly) roots look fine. I have never seen this, only thing new is the Technaflora BC products!?

Answer: Ray- there are only three things I know of that could cause crisp leaves.... one possibility is that the lights were left a little too close. To me, this would make the most sense if most of the damage is on the tops of your plants. A digital thermometer with an indoor-outdoor probe comes in handy for monitoring the "hot spot" in the garden, right underneath the light. Even at a proper distance, the heat from the light could cause damage if your oscillating fan were to quit working (or was left out of the room by accident).

One more word on light burn.... when plants are used to the light from growing under a regular two bulb fluorescent, they grow "low light" foliage used to, say, 10 watts/sq ft. When these plants are suddenly placed into a highly lit flowering area, I have had all the old leaves die as the plant replaces them with "high light" foliage better able to handle, say, 60 watts/sq ft. It's a good idea to give them several days of "transition" time from the low light environment to the high light environment to keep leaf loss and plant stress to a minimum.

The second possibility is nutrient burn. This happened to me twice over the years, in spite of the fact that I had a TDS meter. The first time, I had jumped my plants up from 700 ppm to 1200 ppm too quickly.... I should have given them a level in between for at least a week to help them transition. The second time, my TDS meter was not giving me the correct reading.... I tried to re-calibrate it, but I ended up having to buy a new one (it was toast).

If the nutrients in your reservoir were not mixed completely, you could get a reading of 1300 ppm in the top of the tank while there is a stronger concentration sitting deeper in the reservoir. Also, I always used 1200 ppm as my high limit, mostly because the strain of plant I was growing was sensitive to over-feeding. If you recently changed the type of plant you are growing, you may be inadvertently over-feeding the new plants. You did recently change the hydroponic nutrients you are using... 1300 ppm may have been OK with your old nutrients, but may be too strong a dose with your new nutrients (more nutrient availability in the new stuff).

Nutrient imbalances can occur if you keep using the same nutrient solution week after week. It may not have caused a problem with your old nutrients, but it may with your new nutrients. It is a good idea to completely dump the nutrient solution after two to three weeks of use and start fresh. In between, you can "top off" the reservoir with 1/2 strength nutrient solution.

The third possibility is a nasty one... you could have spider mites or thrips. These little bugs are so tiny, you can look directly at your plants and not even see them. They like nesting in the tops of the plants... they enjoy the heat from the lights. When they bite into your plants and suck out the sap for food, they cause tiny dead spots in the foliage. The situation can become critical in just a few short days, and can kill whole tops and leaves. The damage looks very much like fertilizer burn or temperature burn from the lights. Make sure to look at your plants very, very closely and (hopefully) eliminate this possibility.

There are a couple of other ideas I've got about your problem. Rockwool needs to be soaked with Ph adjusted water before it is used... the Ph in the rockwool itself is too alkaline for most plants, especially freshly rooted clones just getting plugged in. Your description of some of the tops appearing "grey" concerns me a little.... white mold and powdery mildew can make plant tops appear greyish, however they wouldn't cause the plant material to become brown (usually). Keep an eye on your humidity levels just to be sure... you want to stay in the 40-60% range. Cheap thermometers are available that also measure humidity and record the high and low readings of both.

In particular, humidity is a problem shortly after the lights go out for the night. As the temp drops in the grow area, the air cannot hold quite as much moisture... it ends up condensating onto the walls of the grow room and onto your plants. This is especially a problem if your plants have begun to produce large flowers, which tend to trap and hold the humidity. An extra exhaust fan would help (if this is the case), as would an extra oscillating fan inside the grow area.

You mentioned the roots still look healthy, so I would not suspect fungus gnats, wilt, pythium, or fusarium.... Just one other possibility has just occurred to me... sometimes nutrient salts can accumulate over time in the rockwool grow medium. If the plants have been growing in the same rockwool for a while now, you may want to squeeze a little water out of one of the cubes and test it with your TDS meter. It should read the same or less than the nutrients you are feeding in from the top. Otherwise, you want to flush all your rockwool with 1/4 strength hydroponic nutrient solution for at least a day.

Well, I can't think of any other possible reasons for your problem. Given your years of experience, my best guess is that 1300 ppm was just too strong of a dose for the new fertilizer. I hope this helps!

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