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!
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.
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.
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 on seedlings and young plants for several hours can be as harmful as frost.
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.