I started these tomatoes on the soil and they were kind of crowded. I placed 2 of the largest ones in a separate container and they already have 2 tomatoes and lots of flowers, these where the others that where left. I put them in the aquaponic system a month ago, and although it has grown, it's no where near the size of the bigger ones I placed in soil. Other plants in the system are doing well ( I think :D ) 1 main difference is that the potted tomatoes get around 3 hours of direct sunlight and the aquaponics get all they're light through a grow lamp

I'm wondering if that bad start has anything to do with how things are going now.

These are the tomatoes in question, as you can see, even at that size, they can't hold up their own weight.


Here are the tomatoes that got a head start on the crowded pot that I separated.


Here are some happy plants on the system. I mention this because this leads me to think it's not some nutrient issue. The first gets the same amount of direct sunlight, and the bottom one is all by the grow light.

Happy1 Happy1

  • 1
    If they are getting different amounts of light then it is apples and oranges. Commented Jul 3, 2012 at 14:13
  • The bigger ones are getting 2-3 hours of direct sunlight. The crappy ones have a grow light on a 12 hr timer so if anything it should be the other way around shouldnt it ?
    – geermc4
    Commented Jul 4, 2012 at 4:43
  • 1
    Not necessarily the 12 hour cycle should be ideal... But if the number of photons striking receptive pigment in the chloroplasts. Ie if the grow lights aren't strong enough then you will get more energy from the sun. Commented Jul 4, 2012 at 13:35
  • :o how can i test that, this is the light amazon.com/gp/aw/d/B0031CA3OM
    – geermc4
    Commented Jul 4, 2012 at 14:55

2 Answers 2


As the conditions between the two sets of plants are totally different, it could be anything. Since the most significant difference is the light source, test that first:

  • Place one tank so at least half of it is exposed to sunlight
  • Cover the other half so it is never exposed to sunlight (a large piece of cardboard taped between the halves should do)
  • Set your grow lamp up so it lights the dark half
  • Move a set of fresh seedlings into each half (you want several to get any meaningful result)

Now they should have the same conditiions apart from the light source. Let them grow for a few weeks and you should see under which light conditions they thrive.

If it isn't that, rule out the other factors with similar tests (change only one condition at a time).

As for the question if it is too late for those tomatoes, no - they look healthy to me, so apart from growing slower, they're fine. You could move them out like the others, or just accept the slower development.


If you want tomatoes to hold their weight better, giving them potassium sulfate and rockdust (I used basalt rockdust) will greatly strengthen the stems and plants. I'm not sure that the rockdust is strictly necessary to strengthen the stems, but calcium and silica, which are in rockdust, are supposed to help with strengthening plants, along with potassium. You should notice a significant difference within a few days, for tomatoes. I've done it many times when starting tomatoes and it strengthens the stems a lot every time. If your nitrogen is high without enough potassium to compensate, that might block the potassium and make the stems softer, too. If the plants have already fallen over, giving them these nutrients will strengthen them in their position, but it won't cause them to stand up again. What you can do is replant them deeper in an upright position, after the stems have been strengthened, and then they should be in a more sturdy, tree-like position.

Softer stems doesn't necessarily mean the plants are potassium deficient, per se, but it does mean they could use more if you want stronger stems. Some varieties of tomatoes need more potassium to prevent stem problems than others.

It looks like you're using a hydroponic system. Fortunately, potassium sulfate is water soluble and should work well with hydroponics. I'm not sure about rockdust.

The problem probably isn't so much the nutrients in the system lacking as that they were started and separated. Plants are in need of more potassium when transplanted, as it helps them to absorb more water from the roots. Plus, they might have used more nutrients from the initial soil, due to lots of plants being in it.

Extra potassium is helpful during transplant time.

However, from the look of your plants, I'm thinking more potassium would probably benefit all the tomatoes, at least. They don't look bad, but they do look like they have plenty of nitrogen, and extra potassium wouldn't hurt, I'm thinking. I would use potassium sulfate, personally, as I've had good success there, but I haven't done hydroponics.

Most hydroponic NPK fertilizers are high in potassium compared to fertilizers for soil (e.g. 4-18-38 vs 18-18-21). The third number is the K, or potassium. N is nitrogen. P is phosphorus.

Potassium is even more important when light levels are low, I've noticed. Nitrogen doesn't seem in as high of demand when light levels are low. There is such a thing as too much potassium, however.

If you use rockdust, be sure to realize that it may change your pH, which affects which nutrients are most available.

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