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How to get indoor tomato seedlings to not be spindly

February 28, 2018

We started tomatoes from seeds indoors using a 5x10 seed tray and have been having problems with them leaning towards the light and being spindly. We recently got a new grow light system for them and put the light about 3 inches above the tops of the plants. They are still leaning towards the light. The temp is at a constant 75° and we used heating mats to under the trays until they first germinated. We have also been making sure the soil is kept moist and have a fan going on the seedlings. What are we doing wrong??

Comments (15)

  • zippity1

    i read tonight that lots of direct sunlight makes tomato plants "sturdier/more sturdy" wish i had known that last fall......

  • zippity1

    i also just read that epsom salts helps keep tomato plants from being spindly don't know if either of these suggestions work......

  • PRO
    The Logician LLC

    Many grow shelf systems have multiple parallel bulbs for wider light coverage. It looks like yours has a single-line of bulbs. You do need to keep the lights just above the tops of the plants, so the light angle will be severe for the outer plant rows. The seedlings look fine to me, good color.

  • daninthedirt (USDA 8a, HZ10, Cent TX, Sunset z30)

    Yes, your tray of plants looks a lot wider than your light fixture. So if you have the fixture 3 inches above some plants, it'll be a lot further from others. 3-inches is a lot. I keep mine almost touching the tops of my plants. Your plants aren't getting enough light.

    Note that these T8 systems are very much LESS bright than real sunlight. They can suffice, but barely.

    That's an epsom salt myth I hadn't yet heard. Did you know that epsom salt makes tomatoes taste like filet mignon? Seriously!!

  • tommyr_gw Zone 6

    Not enough light, also they need to be closer to the light. They are stretching to get more light.

  • funkyhat

    Light, light, light. This picture shows how quickly light intensity (PAR, photosynthetic active radiation: aka: light) drops off quickly from artificial sources. https://goo.gl/images/za4Jxe. At 24" height dead centre 302 "PAR", 24" height 4' away from centre 27 "PAR". It's hard to not provide enough light using artificial lights.

    You might find this interesting: http://www.econoluxindustries.com/Library/Library-What%20Light%20Do%20Plants%20Need.html

  • Tim in Colorado (5b)

    Follow-up question to the experts... as long as the seedlings aren't getting leggy, does it really matter if they're leaning some as shown in those pictures? Won't they just straighten up and be fine as they grow bigger and get transplanted up and then eventually moved outdoors?

    I know the amount of light is a big issue, but IF it's enough light, it doesn't really matter if it's from (somewhat of) an angle and causing the seedling to lean some, does it?

  • susanzone5 (NY)

    Put in another light fixture next to the one you have to cover the whole width of the trays..

    Place the lights no more than one inch from the plants.

    Pinch out the worst seedling in each cell, leaving only one plant to a cell. They compete with each other when close.

    Tim, leggy plants just fall over and make a mess under the lights and when planted out, they start out crooked. You can strip the lower leaves and plant outdoors deeply, but growing straight plants to begin with saves a lot of time and trouble.

  • Tim in Colorado (5b)

    There's a difference between leggy and leaning though, isn't there? I know leggy is bad (noticeably stretched out). But if it's NOT leggy and just leaning some, that should do OK, shouldn't it?

    I know that running enough light fixtures to try and get every single seedling 1" from a bulb is ideal, but that can be an awful lot of bulbs if you're growing much. I think my tomatoes and peppers did fine last year with lights more than an inch away, and the outer ones leaning some. Maybe I just got lucky, or tomatoes/peppers are more forgiving than flowers?

  • susanzone5 (NY)

    Tim...tomatoes grow roots all along the stem so you can just bury them as deep as you want. Can't do that with flowers and other veggies. (Altho you can lay cosmos seedlings down along the ground and they will root from the stem and put up a ton of flowering branches).

    I don't grow peppers so I don't know about those. I like all my seedlings to grow the right way indoors. Putting up another couple of fixtures isn't expensive, and since the light bulbs are only used for 3 months a year, they last for years.

  • authereray


    They don't look spindly to me. They will naturally lean toward the direction of the sun. Craig LeHoullier advises to turn off lights at night and turn back on in the morning.

  • floral_uk z.8/9 SW UK

    I agree. They don't look particularly badly etiolated to me.

  • lgteacher

    I don't think you're doing anything wrong. You could put them closer to the light source, but when you plant them, you're going to put them deep in the ground, so don't stress over it. If it's not too cold where you live, putting them out in natural sunlight during the day will give you more compact growth. I live in southern California where the soil temperature is still too cold to get good growth outdoors, but my seedlings go from the heat mat during the night to the outdoors during the day.

  • Shule

    Lots of light and cooler temperatures (I don't know the exact temperatures required offhand, nor for how long they're required) are supposed to help seedlings to not be spindly. Warm temperatures may be better for faster growth, however.

    If you just want a sturdy plant, give it some potassium sulfate, wood ash or something. Potassium really strengthens plants (they'll still be leggy, if they were before, though, but tough). It can help plants to stand up straight longer, too, if they haven't fallen over, yet. You probably wouldn't want to add wood ash until the plant is a certain size, unless you use it quite sparingly (diluted in water).

  • Shule

    Low phosphorus is said to help seedlings to not be spindly. I hear some commercial growers use low phosphorus during the young seedling stage.

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