Watering at night

16 years ago

I am using 1" rockwool starts, then transplanting directly into hydroton clay pebbles. I am growing lettuce and basil, and so far half way through the first week, they seem to be doing very well. This is my first time growing with hydroponics.

The light cycle is 18/6. I irrigate for 15 minutes every 60 minutes, because of the clay pebbles. I'm sure the rockwool never dries out, but I guess I can't wait for that b/c of the root system in the clay pebbles, but it seems to be fine so far. I am also using one drop of H2O2 35% concentrate per gallon, about every three days, so that may help with the web rockwool, I don't know. Also the entire flood tray is covered with black/white poly, only holes are there for the plant cups of course. It is pretty dark down in the flood tray so I think this is a good setup.

HERE IS MY QUESTION: As the plants begin to get bigger, I am concerned that even though I am told plants don't need the nutrition to grow at night (6 hours when light is off), I am concerned they might go for so long in those clay pebbles without water that the roots would dry up before morning. Could anyone please offer me some advice or experience they've had? Is this a valid concern or not? And would the answer be different for lettuce/basil vs. tomatos (what I want to grow next)

In the morning (~8:00 AM) before the lights turn on the temperature is about 70 or 72 deg. with humidity of around 65%. In the evening before I go to bed,(~11:00 PM) the temp. is around 82 - 84, with humidity around 50 or 55%. The light and water turns off at 3:00 AM, resumes at 9:00 AM. I am using a four foot, 4 lamp, T5 HO flourescent fixture... two 6500K and two 3000K (even though lettuce and basil don't flower I do want to grow other crops that will). The light is probably about 6 inches above the plants to allow a fan to blow across the plants 24/7.

My EC is 1.0, which is 400PPM on the 500 scale that my nutrients use (Technaflora grow/boost/Thrive alive red/magical/sugar daddy)

Thanks in advance!

Once I get going with this pretty confident I'm going to post some pictures and some notes to share.

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Comments (3)

shockingelk
16 years ago
Your roots absolutely will NOT dry out in six hours. In clay pebbles, they can go well over 24 hours without a flood and suffer no harm.

If you want unsolicited advice read on ...

Your EC of 400-500 ppm is perfect for lettuce. The limiting factor in hydro lettuce is the speed at which the plant can get calcium to the growing tips of the leaves. At higher than 500 ppm, it will grow faster than calcium can be transported and without calcium the cell walls will not farm properly causing the leaves get flimsy and "watery" at the tips.

About your flooding periods: The advantage of Ebb and Flow is that the roots are almost always exposed to the air to get the oxygen they need. Your flooding period should be no longer than it takes to get all the roots wet. For my 7 gal set-up, that is about three minutes. Your lettuce will grow better if you only flood 4 to 6 times a day.

- Erik
plantboy_grower
Original Author
16 years ago
Thanks Erik. Your reply is VERY helpful.

I had read somewhere else that when growing in clay pebbles it is important to flood very often, because the clay will dry out quickly. I even got a non-digital timer, whose smallest "on" increment is 15 minutes, because the digital timer I had bought for the task didn't have enough on/off settings for such frequent waterings throughout the day.

If I flood 6 times a day in 18 hours, that would be once every 3 hours. I suppose that it:

1) depends on how fast your plants use water available to them
2) is the rate of water use different at different cycles of the plant's life for lettuce, tomatos, etc.
3) I suppose the rockwool 1" cube holds some moisture in there for the plant during those dry spells

Thanks for the advice; I think I will try flooding 6 times a day as you suggest; should the frequency be changed at different stages of the plant's life? If this less frequent watering works, then I could use the digital timer and cut down the 15 minutes that the analog timer uses.
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shockingelk
16 years ago
Yes, different plants differ greatly on how fast they can utilize nutrients

I've had my timer at 5 minutes every three hours ever since I learned to keep the PPM low for lettuce. I now keep the PPM at 900-1100 which seems to please everything I've tried in it at every stage of growth, other than some bell peppers which I believe wanted more nutes and light (it gets only 15 - 20K Lux from floros). It's produced great jalepenos, cilantro, parsley and basil. And some strawberries I'm keeping alive for another run under the HIDs.

If everything was at thew same stage, I'd choose lower PPM for seedlings to encourage faster root growth.