Tips for watering tomato seedlings

I should call this article “It’s difficult being a tomato seedling” or “how to kill your seedlings with kindness!”

It has just poked its head above soil only to find that there is very little light, it’s cold and there are still a couple of months to go before the weather is good enough to guarantee no frosts at night!

Tomato Seedlings

The worse thing for a tomato seedling is to be sat in a dish of cold water with saturated soil – especially at night when temperatures drop. Too much water takes the air out of the soil and makes it difficult for roots to grow properly.

Also, if watered heavily from above, seed compost can become compacted – a bit like a lump of mud!

To make things worse, if the seedling is fed tomato food, it will damage its sensitive roots (tomato food should only be given to established plants that are fruiting) and after a couple of weeks the poor seedling catches a fungal disease and looks near death or dies!

But the book says: “tomato plants need plenty of water and are hungry feeders!”

As a tomato plant gets older, it will need more water and food – but not when it’s young.
A tomato plant with lots of leaves and growing fruit needs a lot of water – especially if grown in a hanging basket in very warm weather. When plants are older they also need feeding regularly, especially if grown in containers where resources are limited.

However, it is generally true to say that on a scale of ten, a seedling needs one out of ten, and a fruiting  plant needs ten out of ten – of both water and food.

So keep the soil very slightly damp with seedlings and don’t feed them – seed and potting compost already contains enough food to take them through to their first transplant into an individual pot and perhaps multi-purpose compost or something similar.

Liquid seaweed extract is sometimes used on seedlings to encourage growth, but it is not essential.

If seedlings wilt give them a spray/mist with water – it’s the quickest way to revive them.

Mist Sprayer

It’s so easy to kill plants with kindness – a bit like over-feeding tropical fish!


10 Responses

  1. Jackie Argo
    | Reply

    The leaves of my tomato seedling are turning under from the tip of the leaf. They look green and healthy. I’m new at this and just don’t what to do. I put them under LED lights up to 16 hours daily. When they got their first true leaves I removed the heating pad. I have not fertilized. Any suggestions. Jackie

    • Nick
      | Reply

      If the true leaves are turning under it is because of stress. This could be over/under watering or temperature fluctuations and many other reasons too.
      You’ll probably find that the plants will settle down as they grow bigger.

  2. Will
    | Reply

    I find that it’s also very dependent on what you’re growing the tomato in. For instance, I start my tomato seeds in a coconut coir / perlite / worm cast mix that drains very well, using compressed coir pots. They dry out completely after about two to three days, meaning the seedlings must be watered at least every other day since the water just does not hang around in the pot or in the growing medium.

  3. Rachel
    | Reply

    Hi. Some people advise to keep ripening tomato plants on the dry side to intensify flavour. Do you advise this?
    Thanks Rachel

    • Nick
      | Reply

      Over watering can reduce the flavour, that’s why I like to feed little and often.

  4. Sandra
    | Reply

    Thank you! Was dithering around whether to water my seedlings-first year of growing them. I’d thought I would only water them by placing them in a tray of water, so the uptake encourages the roots downwards. Will persevere!

  5. Sue
    | Reply

    Great Site! So well laid-out and easy to understand. Thanks!
    Do you have advice for growing cucumbers?

    • Nick
      | Reply

      Hi Sue, Cucumbers like a slightly higher humidity than tomato plants but they can be grown together, in the same greenhouse.
      If there are problems, a cucumber plant will usually display them before a tomato plant, so we can use cucumber plants like a canary down the mines – if the leaves display a nutrient problem, we can adjust for the tomatoes too!

  6. Hamish Montgomerie
    | Reply

    I’ve spent years reading tomato growing books, asking advice from other allotmenteers and trawling the internet so that I can build up my own files. I still, of course, have failures but your tips are definitely the way to go to minimise my occasional tomato plant manslaughter. How I missed your site I don’t know but now that I’ve found it I’m sticking with it. Your information, advice and understanding of the little creatures is the best and clearest; thanks.

    • Nick
      | Reply

      Thank you Hamish, I’m pleased that you’ve found the website helpful!

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