I planted red baby lettuce in an indoor hydroponic system. There are two types of lightning I used for this plant, A system (a hydroponic system that uses white LED lights) and a B system (an aeroponic system that uses 52 Watt Red and Blue Grow lights). I used Air Conditioning in the room so the temperature were always around 22 Celcius degree and the relative humidity was 55-58%.

  • The A system (a hydroponic system that uses white LED lights) The rockwool are half-dipped in the system so they always wet

A system

  • The B system (an aeroponic system that uses 52 Watt Red and Blue Grow lights) The sprayer turns on every 12 minutes and it sprays for 2 minutes.

B system

I transplanted them when they were 11 days old. The AB mix fertilizer was around 600 - 680 ppm, and the light intensity was around 1000 - 2000 lux. The last time I checked the pH is around 7.0 - 7.6. When they were 14 days old, some of their leaves are dehydrated even though the rockwool was wet by the water. I changed the fertilizer afterward and now the pH was around 6.7 and the nutrition was 719 ppm.

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My assumptions regarding this problem were the lettuce plants were too young to be transplanted to a hydroponic system with fertilizers around 600 ppm. Then the pH was too high for the young leaves because the optimum pH must around 6.0 - 7.0. But I'm not sure if they were the only problem, I might miss the other factors.

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    I would borrow or rent a light meter , ideally with different spectrum capabilities, That does not look like much light. One measurement is worth many guesses and calculations. Sep 11, 2020 at 16:58

1 Answer 1


Did this system work previously? The only thing I can think of is that the cubes of rockwool are evaporating the nutrient liquid to leave behind concentrated salts around the upper roots.

To test for this, mark the location of several typically wilted plants, then slowly pour nutrient fluid over the cube to flush any excess salts out. Photograph experimental and control plants, and compare later.

Or if you dare, mark a few plants to leave alone, and rinse all the rest.

Also check root colour, if not white then there is another problem.

Note that sub-optimal conditions will significantly retard the growth even before symptoms are noticeable, so you may have to wait longer before getting a good crop.

  • When you mentioned about root colour, I noticed that some of them have red colour. Is that because of the concentrated salts around the upper roots? Sep 11, 2020 at 3:23
  • Red pigment in roots is fine, same as stalk colour. Sep 11, 2020 at 3:30

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