“April showers bring May flowers.”
The traditional way of telling whether soil is warm enough to start planting outdoors is (allegedly) to see whether you can stand to sit on it with a bare bottom. In this day and age, with smaller gardens and nosier neighbours, it’s probably better to rely on the weather forecast!
April is famous for its showers, but what it really brings is some very changeable weather. It can be bright and sunny one minute, enticing gardeners outside to sow seeds and plant out, and literally freezing the next. Combined with stiff breezes, it’s a trying time for plants, particularly those raised indoors.
Seedlings that you’ve been nurturing on the windowsill (or in a heated propagator, if you’ve invested in one) need to adjust to life outside if they are to survive. It’s not a ‘sink or swim’ scenario – they’ll sink. It’s not just that it’s cold at night, but the sun’s rays can be harsh and those breezes are drying. It’s an endless source of stress that, at the very least, will cause a ‘check to growth’ – a phrase that strikes fear into the heart of vegetable gardeners everywhere, as it means your final harvest will be smaller.
The solution to this problem is hardening off. This is a process somewhat mired in myth and mysticism, but it’s pretty simple really. Hardening off is simply the process of gradually introducing indoor plants to the outside world, to lessen the shock. It’s a bit like taking a child to nursery for a couple of hours the first few times, so they get used to their new world before mum disappears for a well-earned break.
So… hardening off. In some ways it’s easier if you’ve got a cold frame, which acts as a halfway house. You can pop your seedlings in there and they’ll be protected from the wind and the cold. But they won’t be protected from burning up if the sun comes out and there’s not enough ventilation and they won’t be protected from the slugs and snails that love to congregate in the nooks and crannies. A cold frame is a useful tool for hardening off, but it’s not a low-effort solution and it’s not a necessity.
Hardening off requires a little bit of planning and a glance at the weather forecast. All you need to do is take your seedlings outside for an hour, when the weather is in the Golidlocks Zone – neither too cold, too sunny, too wet nor too windy. An hour. Then you bring them back inside.
The next day, if there’s a suitable window in the weather, you put them outside for 2 hours.
Depending on how it fits into your life, the ideal way to do this is to just increase the time the seedlings spend outside by an hour every day until they’re outside all day. BUT NOT AT NIGHT. It’s still cold at night, they could get frosted. And slugs and snails prowl. Night is a dangerous time for little seedlings.
But most of us can’t manage that level of organisation and dedication, so after the first couple of days, do your best. Avoid leaving your seedlings out in torrential rain, howling gales, freezing winds and scorching sunshine, and they’ll adjust.
The ideal is then to plant them outside once the risk of frost has passed, for which – clearly – you will need a crystal ball. The middle of May is a good bet in the UK and Ireland; elsewhere check your hardiness zone for an idea of when your frost dates are. You may still find you’re caught out, and frost is predicted after you’ve planted out your tender seedlings. Or you may want to plant early, for an early harvest. In that case, it’s time to deploy the crop protection.
…a reminder that if you aren’t lucky enough to have a greenhouse you can still join in the seed sowing game… pic.twitter.com/q3GDn2Xnvt— Benjamin Ranyard (@higgledygarden) March 30, 2019
Crop protection serves two functions – protecting plants from the weather and/or pests.
Horticultural fleece is a plant blanky. You can use it to cover rows of plants to keep a light frost off them, or to protect them from marauding insects and birds. Fleece is a handy thing to have in the shed, as you can use it to cover plants at the last minute if the temperature drops unexpectedly. Fold it over, and use a double layer. (If you haven’t got any fleece, try layers of newspaper instead, but remember to remove them once the sun comes out.)
Cloches and tunnels
There’s an army of cloches and tunnels on the market, sized to protect individual plants or whole rows. Cloches normally have sides of glass or plastic; tunnels can be clear plastic or insect-proof mesh. They’ll keep a light frost off plants, but their small volume means that if they are sealed plants can quickly overheat in warm weather. Most have some sort of ventilation. Cloches offer some protection against slugs, snails and birds. You can make your own mini cloches from clear plastic bottles. Just cut the bottoms off, and pop it over your plant. Push it firmly into the soil and you’ve got a little microclimate for your plant that’s also slug and snail proof. You can remove the lid when you need ventilation.
Cold frames and mini greenhouses
Cold frames, and their larger cousins the mini
greenhouses, are freestanding. A traditional cold frame is given a permanent
position (usually by the greenhouse), but the lighter modern versions can be
moved around and used much like a tunnel. Mini greenhouses are plastic or metal
frames with shelving and either solid plastic slides or (more usually) a
removable plastic cover.
They’re great for hardening off seedlings, and extending the growing season at either end by giving plant some weather protection. But (as mentioned above), you need to be vigilant about ventilation and slugs and snails, or they become a death trap for immobile plants.
Also… something the marketing blub never mentions – mini greenhouses make great kites. Anything other than a puff of wind and you risk coming home to find them in your neighbour’s front garden. They need to be well anchored down.
Greenhouses and polytunnels
If you have the space, then of course greenhouses and polytunnels are a wonderful protective environment for your plants, and you can use it for looking after seedlings, growing early and late crops and even successfully growing plants that won’t thrive outdoors in our climate. But you can’t leave your seedlings to their own devices, even in a greenhouse or polytunnel. You need to check on them every day to ensure they’ve got enough water, open vents on sunny days to make sure they don’t overheat, and keep an eye on the weather forecast to see whether they’ll need extra protection or heat on cold nights.
April is a wonderful time, when the soil is warming up, the sun shines and plants everywhere are coming back to life after the winter. It’s time to start preparing for the warmer weather, when you can finally move all of your seedlings outside, and get outside and GROW!
This post has been produced in collaboration with Premier Polytunnels, but the words and thoughts are (as ever) my own.