I started growing tomato and pepper plants in my indoor hydroponic system. The first two weeks after the transplantation all the plants were healthy, but after the second week, there hasn't been any growth.

I am:

  • watering every day in the morning
  • aerating with air pump 1/2hr before watering
  • using 4 T5 lights
  • using NPK 19:19:19, epsom salt as fertilizer in water, ppm: 1100, pH: 6.5

Please give me suggestions if I'm missing anything

Two level NFT Hydroponic close-up From the front Fertilizer bag Magnesium Sulfate

  • 2
    You asked the same question here gardening.stackexchange.com/questions/30252/… Dec 21 '16 at 7:13
  • 1
    @GrahamChiu If this question does get closed, can we replace the other question's content with this one's (or close the other one instead)? This one is much easier to answer, and it has much more useful information in it. Dec 21 '16 at 8:55
  • It's not clear to me what you're doing. Is this a run to waste, or a recirculating system? What nutrients are in the solution? How often are you applying the foliar spray to leaves? How long are the lights on for? What's the air pump being used for? How often are the roots being irrigated? What's the root temperature? Dec 21 '16 at 17:42
  • Siddu, did you mean to ask the same question twice, or were you trying to add more details to the first one and you asked another one by mistake? It's important to let us know. If all the information was meant to be in one question, I think there are things the moderators can do, or suggest, in order to keep things from getting closed. Thanks! Dec 21 '16 at 20:50
  • Shule, I'm going to vote to leave this open. I agree, the extra details are more likely to benefit the community. Closing the other as a duplicate of this makes more sense, but I don't know the procedure while this one's in the close queue. Also, maybe @Graham Chiu or someone else who has hydroponic experience could add their answer here. That would make it even better. Dec 21 '16 at 21:03

In a hydroponic grow system you have to supply all the micronutrients that the plant would normally extract from the soil. Looks like you're only providing magnesium, and nothing else for the roots. You're also giving some npk via a foliar spray but that can't make up the absence from a root supply.

In particular, calcium, boron, molybdenum, manganese, and zinc are missing from your setup, and probably others.

You need to purchase a nutrient A and B solution that you mix up to add to the water. Making your own has a high set up cost so it's better initially to purchase.

I'd also question the once a day watering. You may not be supplying enough nutrients once you get your solution right.

I have no idea what your air pump is doing. Running it for 30 mins in your solution will do nothing much.

  • Thanks for doing this. I appreciate you taking the time to add this. No matter what happens between the two questions, the community will continue to see this great answer! Dec 22 '16 at 0:44
  • Yup, you need a complete hydro fertilizer.
    – Evil Elf
    Sep 24 '20 at 11:51

I haven't done hydroponic gardening (and I don't know a terrible lot about hydroponics specifically), but from my observations of hydroponic fertilizer, it's usually very high in potassium compared to nitrogen and phosphorus. Your fertilizer has the same amount of potassium as it has nitrogen and phosphorus, and it's designed for use as a foliar spray (spraying the leaves; usually, you put hydroponic fertilizers in water to feed the roots, I believe; foliar sprays might be useful once in a while, but probably as a complement to the nutrients in the water, rather than a replacement; foliar nutrients don't go all the same places as root nutrients). I would switch fertilizers if I were you. You probably need specific levels of calcium, manganese, boron, copper, iron, zinc, and molybdenum if you're not adding them (stuff like silica, and sodium might be kind of helpful, too, in the proper amounts). Epsom salt is magnesium sulfate (so you've got magnesium and some sulfur, at least).

Also, your lights are extremely far away from your plants. How close they are makes a huge difference to their health and growth (I have used lights indoors, with soil). You want the lights as close as you can get them without burning them.

You might try Greenway Biotech's hydroponic fertilizer. I haven't tried it, but I've tried other stuff from them, and it's very good and affordable, with very fast, free shipping (like two days).

Notice the NPK values of this hydroponic tomato fertilizer (4-18-38; lots of potassium).

Notice the NPK values of this hydroponic pepper fertilizer (11-11-40; also lots of potassium). I've noticed the same trend with potassium with other hydroponic fertilizers. Anyway, you'd probably want to get something like those links offer, since it comes already equipped with a fair amount of minerals (so you won't have to get them individually). You may need other fertilizers to complement them eventually, though (e.g. one of the links suggests extra potassium nitrate for the blooming phase; you might want more of certain wavelengths of red light then, too, or lights of a lower color temperature, if you're not using LEDs; but certain wavelengths of blue light, or higher color temperatures if you're not using LEDs, are supposed to be great for leaf growth).

In your other question you showed a picture of the roots, which were kind of small and sparse. Proper levels of potassium and phosphorus are important for strong roots. Too much nitrogen can weaken roots (especially without enough potassium to balance it).

I don't know the proper amounts of all the nutrients. You'd have to ask a hydroponics enthusiast or expert about that, probably. But, I suppose those pre-mixed nutrients I mentioned above probably have the essentials.

Silica probably isn't an essential for hydroponic gardening, but it can be useful for plants. Sources include such as basalt rockdust, diatomaceous earth, etc. Rockdust tends to have a fast array of minerals; I believe some people use it for hydroponics. Sea minerals, of course, also have lots of minerals, and can give plants a quick boost (but don't overdo it as it's high in sodium). Those links just show you places that specialize in or sell the things I mentioned (if they ever get broken).

  • Thanks for your response. I'll try to change the fertilizer which is suitable for hydroponic system.
    – Sidda
    Dec 22 '16 at 14:32

Do you check the ph of the water tank? If the ph is incorrect your plants will be unable to consume the nutrients in the water. You need to have either a kit or a ph pen to check the ph of the water on a regular basis. Also ph up and ph down is crucial to a hydro setup.

Most experts tell you check the water every five days but the more often you check it the easier the maintenance is

  • I am maintaining ph 6.5 and ppm 1100.
    – Sidda
    Dec 22 '16 at 14:20

Had similar issue. Plant looks healthy, but doesn’t grow. ‘My’ problem was wrong ligh. Lot’s of light... wrong spectrum... Replaced light with broad spectrum led, that solved the problem.

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