If you are like me, you have a house full of plants in the spring and can’t wait for the weather to improve enough for them to go out into the greenhouse or polytunnel, or outside in the garden.

By April, some of my plants are already in the polytunnel – one’s that I’ve hardened off – but I still cover them with fleece each evening … tuck them in at bedtime!

Hardening off - Four Tomato Plants in PotsEach pot is about 16 inches across
The canes help support the bush plants when fruiting and also the fleece cover at night!

To “harden off” a tomato plant is to get it used to being outside 24/7.

  • Harden off
  • Hardening off
  • Getting plants adjusted to …
  • Getting plants conditioned to …
  • Getting plants acclimatised to … the outside!

If plants aren’t hardened off, they will suffer at night when temperatures drop, and even during the day, if in direct sunlight for more than an hour or two.

Cold Conditions
Going from a mild environment to the cold outside without becoming acclimatised first, will stress tomato plants and they’ll wilt or even stop growing altogether.

Avoid direct sun and wet leaves
To get plants acclimatised to outside conditions, start by putting them out in a shaded place for a few hours each day. They should also be sheltered from the rain because wet leaves is something to avoid.

It’s a matter of leaving them out longer each day and later in the evening to experience the drop in temperature. After a week or two of this, they should be able to cope outside overnight, if temperatures are favourable – around 8c or above.

Garden fleece
Covering with garden fleece helps protect them – they should also be kept dry – especially at this early stage.

I use garden fleece for protection against the cold and for shading my young plants from direct sunlight – it’s very useful!

Direct Sunlight
Direct sunlight on seedlings and young plants for several hours can be as harmful as frost.

Undeveloped roots
Their root area is undeveloped and they only have enough moisture available for a few hours if they are in small pots.

Also there is a huge difference in light levels from inside the house, to a bright sunny day – our eyes can compensate but a tomato plant gets blasted!

But tomato plants like full sun don’t they?
They do after they are in their final position and have developed a large enough root system to cope.

The affect of too much direct sunlight will show when:

  • New growth shrivels
  • Plants become stunted
  • Leaves curl and turn away from the sun
  • Leaves wilt

Tip: Use a sheet of garden fleece to diffuse direct sunlight on seedlings.

To sum up
Acclimatise plants gradually and resit the temptation to plant them straight out – so many plants go from a warm house or just bought at the warm garden centre – to a cold, wet and windy garden.


Choosing Tomato Plants With disease Resistance

11 Responses

  1. derek
    | Reply

    hi nick i,ve had mine out in the greenhouse now for about 3/4 weeks because they all, got to much & big for the house (90) for freinds / family they don,t seem have come on very much is this down to the weather ? i am experimenting with different varieties this year , such as orange berry,costoluto florentino,red pear , san marzan 2 ,lldi , tigerella and a couple of others any tips on these?? allso are gardiners delight heavy croping . i am giving a lot to my grandsons school for their healthy grow and eat yr 1 project thanks for any help you can give regards derek

    • Nick
      | Reply

      Hi Derek,
      Sounds like you’ve got a good variety of varieties!
      The best tip I can give you is to watch out for Blossom End Rot. The cherry toms like Ildi will be fine, but larger tomatoes will need spraying with calcium when their first green fruit appear. Chempak Calcium is very good and so is Vitalink Foliar.
      Gardener’s Delight is a heavy cropper of good size cherry tomatoes and well suited for school. It’s probably the most reliable traditional cherry variety and should be able to cope with all the attention!
      Best wishes,

  2. Mark Downing
    | Reply

    I noticed in Liddles today they had some large plastic pots for sale and also growbags for £1.20 or something ridiculous. (Although I’m a bit uneasy myself about buying peat-based products.)

    • Nick
      | Reply

      Hi Mark,
      They sell some good value stuff in Lidl – even tomato seeds!

      • jean
        | Reply

        yes I bought some from lidl, unfortunately they don’t tell you the variety. I bought a pack of six, 2 * beef, 2 * vine 2 * plum, no idea which is which and neither did any of the staff, guess I’ll find out at some point, just hope the different one don’t need special treatment.

  3. john
    | Reply

    Hi Nick

    Can I plant toms in soil used for over wintering onions – I used 3″ well mature horse manure on plot in autumn (perhaps thats why onions are going to seed?? but lovely soil)
    I shall be removing onions sood before planting toms – thanks john

    • Nick
      | Reply

      Hi John,
      Sounds like good soil but you can never be totally sure if there are any tomato-unfriendly diseases in it.
      I would take the risk though, with up to half my plants!

  4. allan
    | Reply

    thanks very much very helpful
    is that the pots you use for final potting for bush types

    • Nick
      | Reply

      Hi Al,
      I like to use the biggest and the best value large pots I can find for my Red Alerts. I also grow bush varieties in old buckets with holes in, a waste bin and even a KFC family feast container for the windowsill varieties! However, if it’s a take away, I usually have a curry!

  5. Rhys Jaggar
    | Reply

    Did my first bit yesterday – 16 plants which needed watering and stayed out for 4 hours under the car port.

    They are talking of the unimaginable heights of 18C on Monday – who knows, maybe we’ll get them out for 6 hrs then?

  6. George
    | Reply

    10/10 Good advice.

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