Why Tomato Seedlings Become Leggy
One of the problems with growing tomato plants at this time of the season, when light levels are usually low, is that plants grow too high, too soon, searching for light and become spindly or leggy.

Here are a few tips to help prevent this happening or at least slow them down.

  • Keep plants in as much light as possible – a sheet of white paper directly behind and below helps reflect light back on them.
  • Higher temperatures, when days are warm but cloudy, will also make them become leggy. Temperature and light should go up and down together for best results.
  • Under-water rather than over-water when light levels are low because if it is too warm they will shoot up, and if it is cold they will be sat in cold, wet water overnight!
  • If they are over-watered, too warm and in low light they will also become leggy.

Phew … that sounds a bit complicated and confusing … I think I’ve just confused myself!

To put it in as few words as possible, when it’s sunny and warm, you can water them as much as you like, within reason.

When light levels are low, be a bit mean with the water.

It’s a difficult balancing act between light, warmth and water.

Of course they do need to be watered, but after a good watering (when it’s not too cold), allow the compost or soil to become just slightly damp before watering again. If the seedlings/plants start to look limp, give them a spray mist of water, then water them thoroughly again.

By allowing soil to become almost dry lets air back into the soil – roots need moisture, nutrients and oxygen.

Some Varieties Don’t Become Leggy
Tumbling Tom is a bush variety that doesn’t become leggy in low light conditions.

A lot of the dwarf varieties for windowsill growing are also OK in low light conditions. However, most tomato plants do become leggy. Red Alert will shoot up like a rocket unless kept under control!

I have found that Black Cherry is rather unusual for a tall variety because it doesn’t shoot up as much as most other tall varieties do. I guess that’s one of the advantages of growing a black variety plant that originates from a cool area of the world – Eastern Europe or Russia.

Black Cherry Tomato

Black Cherry contains lots of seeds and would be ideal as a Mum plant if you wanted to cross pollinate with another variety (see make your own hybrid).

How about Black Cherry and Chocolate Cherry … you could call it Black Chocolate!

Black Cherry is a great variety but like Sungold, it’s a bit prone to splitting if grown outside, and is exposed to rain.

Chocolate cherry has the advantage of being crack resistant and less likely to split.

If you grew Black Cherry or Chocolate Cherry last season, it would be great to hear from you – what do you think about either of these varieties?

Please leave a comment below if you would like to.

15 Responses

  1. Alison Greer
    | Reply

    Hi Nick. I am growing Ailsa Craig tomatoes in an electric propagator. They have shot up in a week and are already 20cm tall. What can I do to save them from getting any taller?

    • Nick
      | Reply

      Hi Alison,
      If the propagator is inside the house, it’s best to remove the lid and turn it off.
      Propagators are great for germinating, but as soon as seedlings appear it’s best to remove the lid and lower the temperature to prevent legginess. Also, put them in a light position on a windowsill.
      If you are germinating in a greenhouse, seedlings will only need heat during the night.
      Nick

  2. Pauline Pate
    | Reply

    Hi Nick,
    I have just read newsletter no. 10….why seedlings become leggy. Last year was my first attempt at growing tomatoes. My husband bought me a greenhouse for Christmas (something I have waited 40 years for.) I tried growing Black Cherry and some other varieties, all of which did very well. You said that Black Cherry was good because it didn’t grow too tall. Well, mine reached the roof of the greenhouse! I thought I would try an experiment and let it carry on growing. It crawled along the roof like a grapevine and I had to tie it from the beams in the roof. The amazing thing is it yielded LOADS of tomatoes. There were so many growing that I had to give a lot away to friends and family! I wish I had taken a photo of it to show you.Either it was beginners luck or it had the royal box in the greenhouse. I am growing Choc Cherry instead this year. Can this one grow outside in a grow bag?
    Your website is so helpful, I love reading it. Best regards. Pauline

    • Nick
      | Reply

      Hi Pauline,
      I’m pleased that you had such success with Black Cherry – it’s a very vigorous variety.
      The growing too tall mention was in regard to it becoming leggy as a seedling – as a mature plant it will grow as high as you wish until it is stopped as you say.
      Chocolate Cherry isn’t quite as vigorous, but has the advantage of skins that won’t crack as easily as Black Cherry. I’m growing both varieties this season in order to compare them so I hope to have more information about these lovely tomato plants and tomatoes too!
      I’m pleased that you find the website helpful!
      Best wishes,
      Nick

  3. john
    | Reply

    I do not have a green house and use my peugot partner car with back seats down( with plenty of light all round) to grow on my toms + runner beans. I know its a bit sad but I have very healthy plants??

  4. Erica
    | Reply

    Hi Nick,

    I’m a bit concerned that my Red Alert plants grown from seed are growing too tall too fast. They are now 75cm from base of plant to top of leaves – is this too tall already? They look very happy growing on my south-facing window sill & are still in 6″ pots. Should I pot them on again? I’m just hoping the weather improves soon so I can get them outside!

    Best wishes,

    Erica

    • Nick
      | Reply

      Hi Erica,
      They are taller than they should be at 75cm from soil level to top leaves. A Red Alert normally grows to about 35 to 40cm.
      We’ve had some poor light levels lately, and combined with warm indoor temperatures, will make most varieties a bit leggy.
      Pot them into a bigger pot, remove the lower leaf branch or two, and plant it “as low as it will go” in its new pot. This will create new root growth from the stem below soil level.
      Red Alert is prone to becoming leggy and I’m struggling to keep my Red Alert seedlings from shooting up like rockets!
      Best wishes,
      Nick

      • Erica
        | Reply

        Hi Nick,

        Thanks for your reply. I mistakenly put Red Alert – my seedlings are actually Sungold! Not sure why I put the wrong name… Does the advice still stand for Sungold?

        Best wishes,

        Erica

        • Nick
          | Reply

          Hi Erica,
          When plants get very tall for their position, it’s possible to allow a side shoot to grow from the first or second leaf joint, low on the plant, and have two main stems rather than just one. You can then pinch the top out of the highest stem after three trusses and then grow a further three trusses on the second stem – which is the side shoot.
          I’ll write more on this in the next newsletter but for now, take a look at this …
          https://www.tomatogrowing.co.uk/a-sucker-saves-the-day
          Regards,
          Nick

  5. Avril
    | Reply

    Hi Nick,
    Some of my tomato plants need potted on to a 5″ pot from their 3.5″ as their roots are showing at the pot holes.
    Due to this poor weather we have had for the past two weeks (especially in cold Scotland), I have had to bring them indoors, as I don’t have a heated greenhouse, and some of my tomato plants have become leggy. All my windowsills are full!
    Am I okay at this stage to plant deeper to help the legginess, or do you think I should still plant up to the seed leaves?
    This year I am growing, Sweet Million, Sungold, Tiny Tim, Polen and Zelta Gaulis (latter two from Irish Seed Savers). Any info anyone has on the latter two would be appreciated.
    I did originally try to order Scotland Yellow on two occasions, but both times ISS somehow sent me the wrong seeds. So I thought I’d give these a go and see what happens!
    As always thank you for your advice.
    Avril

    • Nick
      | Reply

      Hi Avril,
      You can remove the seed leaves and even lower leaf branches to plant as deeply as possible into the next size pot. I wish they would make pots a bit deeper!

      You’ve got one or two varieties that are unknown to me, and I expect a lot of other tomato growers too. It would be very interesting to hear how they do!

      As soon as night time temperatures are predicted to stay at around 10c for a few days, I’ll leave my largest plants out in the greenhouse/polytunnel. It’s great when the windowsills etc. can return to normal!

      Best wishes,
      Nick

  6. johann
    | Reply

    Can you grow tomatos in a dark or shaded place.? instead of giving them too much light for a too short a time??

  7. Rhys Jaggar
    | Reply

    My experiences to date this year:

    1. Shirley’s don’t become leggy but Milla definitely do.
    2. Alicante is very sensitive to temperature and/or a brief drink with coolish water (20 minutes outside in the sun caused wilting and drooping, recovered by an overnight stay in an internal cupboard at around 18 – 20C). Tumbler isn’t.

    • Nick
      | Reply

      Hi Rhys,
      Thanks for your updates – they are very interesting and helpful!
      Regards,
      Nick

  8. fred
    | Reply

    Very helpful.
    I have had occasions when my clients cant get enough yield from greenhouse tomatoes because because the internodes are to long, hence few bunches per plant.
    This will help me check out this for them

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