New and need help with burnt growth

14 years ago

I decided to give hydroponics a try and bought an ebb and flow system.

My water is very soft and PH out of the tap is right around 7. With nutrients added, it drops below 5, so I add some PH up to get it to around 5.5. Over the next day or so it creeps back up to between 6 and 6.5 and pretty much stays there. I change the water every Saturday and being my first try, I'm trying not to worry about EC levels or overthink things too much. Temperature in the grow room has been around 68-70, but started spiking to around 75 in the heat we've had the past few days. Plants are 18-24 inches away from a 400 watt MH bulb.

I'm only growing greens in my first batch, bibb lettuce, cilantro, spinach and basil. All were started in the last week of February. The spinach and basil have had absolutely no problems whatsoever. I've been harvesting the spinach for the past two weeks and basil for the past week. In the last week though, I've noticed all the new growth on the cilantro and lettuce turning black and burnt. This doesn't seem to be affecting any mature growth.

Only thing I turned up on a google search was could be a calcium uptake issue caused by temperature being too high. Does this sound right or any other possible causes I should be aware of for my next try?

Comments (5)

ethnobotany
14 years ago
Hello firstyear, welcome to the hydro section of Garden Web

Regarding the calcium uptake... that is surely not the case. If your garden is within the 72 - 82 degree range MOST of the time then you will be fine. One thing I do want to ask is the nighttime temp whenever the lights are off. What is that temp? Also, what is your humidity running at??

The only leaves that are burnt or black is the new growth??

How are your roots looking? If there is anyway you could post pictures of the plants and or the roots that would be very helpful.
firstyear
Original Author
14 years ago
Hi Ethnobotany...nighttime temperature would be just a few degrees cooler, so probably 65-70 at any time. The hydro system is in the most humid part of the house, basement room with fieldstone foundation and the utility closet. I do have an issue with algae growing on the exposed surface of the rockwool.

Only new growth is black/burnt. None of the old growth has any issues. I harvested all the lettuce last night as it was a pretty good side and was starting to have crowding issues. The roots were all white, strong and looked perfectly healthy.

I'll try to get pictures of the cilantro this evening.

Thanks.
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urbangardenfarmer
14 years ago
Hey first year, welcome. I have a couple of things that might help tweak your hydroponics.

First, if I had to guess, I would say the burnt tips are a calcium deficiency. Do you have good air movement in your garden(fans blowing on your lettuce)? Calcium is not a mobile nutrient, so if your plants can't transpire, the calcium can't make it to the tips. I see this a lot in lettuce especially.

Next time you mix your nutrients, wait an hour or so before adding any PH buffers. It takes a little while for the PH to level out. It looks to me from your numbers, that you might not need any?

Here is a link that might be useful: Lettuce tip burn
organic_oddity
14 years ago
18-24 inches for a 400 watt MH bulb I think is too close for what you are growing. 18 inches with mine (250 Watt MH) a thermometer right down by the plants was reading 90 degrees - way too hot for lettuce. It's not the grow "room" you're looking at, it's the temperature the plants are at. Recommendations I have seen suggest 1-4 feet above, but put your hand (palm side down) under the light where your plants are. If it burns - the light is too close. I have mine 36" away and that still makes them sweat a bit, 80 degrees with a fan blowing pointing up blowing over the plants and out the top. Lettuce likes it cold.
firstyear
Original Author
14 years ago
Thanks for the great advice everyone. I have a fan blowing across the greens while the lights are on. Had a bit of trouble getting good photos, but I think the temperature under the lights probably is the culprit. The spinach is bolting now as well. It didn't seem too hot at that distance when I started growing, but then the overall temperature in the room was about 10 degrees less. I think lesson learned here is to be more diligent about keeping the temperature under the lights down. I think I was focusing too much on the temperature of the roots as opposed to the growing surface.