Giving early seedlings a head start…

Tue, 07/02/2017 - 16:14 -- Nic Wilson

It’s the middle of February, days are lengthening and I’m contemplating using the ‘s’ word, even though that would no doubt bring on months of snow.

I can see the garden awakening: fresh yellow primroses have emerged in the lawn whilst daffodils and rhubarb are poking their noses tentatively above the ground. On the kitchen table, seed packets are balanced in precarious piles and every instinct is to start sowing – in drills, pots and modules.  

But such a keen attitude can have its drawbacks. If the soil is too cold (below 7°C for many seeds), germination won’t occur. By using cloches, mulches or starting seedlings off in pots, modules and seed trays in a growhouse, it’s possible to extend the growing season and increase productivity in the garden and allotment.

Laying a fleece sheet over vegetable beds can increase soil temperatures by 2 or even 3°C, enabling earlier sowing. The fleece can then be left in situ whilst seedlings are growing, protecting them from cold temperatures and birds. Once warmer weather returns, the fleece should be removed to avoid problems with disease or plants overheating. Alternatively, seeds can be sown in a seedling cloche or under a grow tunnel with a fleece cover. This creates a micro-climate (warming soil by up to 10°C) to encourage better germination and seedling growth. Bell cloches can also be used to protect larger plants as they act like mini-greenhouses, warming the air around the plant. Tomatoes, peppers, aubergines and courgettes can be planted out earlier in a bell cloche, so seeds can be sown a few weeks early too.

With all of these methods, the fleece or cloche should be in place for a week or two before sowing to warm the soil in advance. Seeds can then be sown a couple of weeks earlier than in open ground. Crops should be ready to harvest up to four weeks before uncovered plants. Make sure that fleeces and cloches are securely fastened to the ground to avoid them blowing away in high winds. Weeds and slugs can also be a problem as they appreciate the micro-climate created, so it’s a good idea to check plants regularly and remove any unwanted visitors. When removing crop protection later in the season, it is important to harden plants off by opening the sides of cloches or removing fleece sheets for a few hours each day over a week before removing protection completely. As the growing season draws to a close, crop protection can be reused to hasten fruit ripening and protect crops into autumn and over winter.

So, most importantly, which seeds can be sown outside this month under fleece, plastic or glass? In milder areas of the UK suitable vegetables include early carrots (eg. ‘Nantes 2’), early beetroot (eg. ‘Bolthardy’), early peas (eg. ‘Feltham First’), broad beans, lettuce, radish, spinach, salad rocket and spring onions. In colder areas it might be better to wait until the end of the month, depending on local temperatures and weather conditions. So if the desire to start sowing is getting the better of you, harness that enthusiasm and increase the productivity of your plot with a fleece, cloche or growhouse. Once the first seeds are sown, the gardening year begins in earnest and the promise of spring (there, I’ve said it) is just around the corner.

By Nic Wilson

Nic Wilson is a garden designer, garden writer and enthusiastic home grower (especially of more unusual fruit, vegetables and herbs). She enjoys volunteering in her local community garden and experimenting in the kitchen with crops from her garden, allotment and the hedgerows.