Autumn in the polytunnel is a time for planting for the winter and hungry gap, as well as for harvesting melons and other autumnal treats. To make the most of growing under cover through winter, you should be sowing nearly as many seeds as you were in spring. It’s also time to check your cover for damage and to give it a quick clean if algae has built up in the damp weather, to let as much light as possible get in during the winter.
Planting for autumn
Tunnel winter crops need to be sown by the middle of September at the very latest. Here are some potential winter tunnel crops to consider, which are all likely to survive right through until spring: celery, chard, chicory, Chinese cabbage, carrots, cauliflowers, corn salad, beetroots, endive, lettuces (all kinds), mizuna, winter peas, parsley, autumn-sown broad beans, radishes, rocket and spinach.
Planting to meet the hungry gap can also take place at this time of year, but getting the timing right is tricky; you need the plants to establish properly before the light levels drop so that they are ready to take off again in the spring, but a little too early and they will crop before you really need them.
Timing is very much dependant on your local climate and particularly the number of sunny days you receive in winter, so note down your planting dates and a few remarks about the winter weather. This will help you develop the expertise to master the trick of producing spring onions while you are waiting for early japanese onions outdoors, overwintering broad beans while your neighbours are anxiously waiting for their first plants to germinate, and armfuls of kohl rabi and baby carrots for fresh buttered vegetables… to go with your astonishingly early potatoes!
Inspect the entire tunnel cover, and fix anything that flaps by using repair tape on both sides of the cover. Clear away summer crops to make way for winter planting and clip up unwanted string supports with clothes pegs. As soil becomes vacant, top-dress with 7.5cm (3″) of compost. Keep the doors open all day and keep a close eye out for moulds and fungi, especially on blight-prone plants such as tomatoes – which should have their tops nipped out towards the end of September to prevent any more fruit trusses from forming. Top-dress any bare soil with compost. Bring pot-grown herbs such as basil into the tunnel to extend their season. If your local climate is too cool to do so outside, some early potatoes can be planted in soil beds or deep pots to provide a crop of new potatoes for the table at Christmas.
As temperatures fall so does the tunnel’s requirement for water, so do not forget to adjust any automatic watering systems. In any season the best time of day for watering is first thing in the morning, but this is particularly important in autumn because there is a higher risk of fungi and moulds attacking plants.
Globe artichokes (second flowering), peppers and chilli peppers (taken red), tomatoes, basil, physalis, melons, watermelons, cucumbers, courgettes, aubergines, celeriac (does well with longer growing season), celery, fennel, primocaine raspberries, monster-sized onions, French and runner beans. If the weather outside is less than ideal pumpkins should be brought in and left for 7-10 days to cure the skins; onions dry well on the staging and can be stored over the winter in strings hanging from the crop bars.