In December daylight levels are at their lowest ebb, and even if you’ve gone to the trouble of installing a heater you won’t see a huge difference in the growth rate of your polytunnel plants. However, another thing you won’t see is frost damage, even without the protection of a fleece cloche. In an unheated polytunnel frost protection is essential and without it the plants you could be harvesting this month may not have survived even thus far, let alone through the coming months.
Now is when you can really begin to see the difference between the polytunnel beds and those outside. Inside the polytunnel, you could have fat, juicy lettuces, beetroot, mizuna and mustard greens, radish, pak choi and more – but you won’t find any of those outside at this time of year! This is what polytunnel growing is all about. It’s easy enough to grow vegetables of all kinds outside during the summer, but to have your very own walk-in larder of fresh, organic vegetables at this time of year is downright special. When, for instance, did you last pick a salad in December? If you don’t have a polytunnel, you would probably have needed to live somewhere far south of the UK to do so – but if you have a polytunnel, you could live in the north of Scotland and still be able to pick lettuce right the way through the winter.
Broad beans and peas sown earlier may be taller than 30cm by now, and it could be difficult to cover them with fleece if frosts threaten. While winter varieties of both are hardy enough to withstand sub-zero temperatures, if a cold snap is set to continue you may nevertheless need to provide some additional protection. Even if the low temperature doesn’t kill them, it will cause them to droop. When it warms up again they will brighten up and carry on, but If frosts continue for too long the stems can fold over, creating a kink from which they are unlikely to recover. To help prevent this, tie broad beans up to strings or bamboo canes. Peas normally use their tendrils to hang on to things, but the cold may make them slacken their grip, and unless you tie them in place they may keel over and die.
It’s quite possible that peas will flower and even produce pods in December. If this happens, remove (and eat!) them to prevent the plant getting the message that it’s all over. They will then continue to pod in the spring.
If you need to water, try to do so early in the day. Avoid wetting the leaf surfaces, as on overcast days the polytunnel will stay very cool and evaporation is at a minimum. If the leaves are still wet when night comes, this could result in frost damage.
Tips this month apply for the entire winter period:
Keep everything well ventilated: whenever it’s possible, open the doors for a few hours even on overcast, cool days. Only if it’s really cold should the polytunnel remain closed all day. Don’t forget to close them again well before it gets dark, as once it does so the temperature will plummet.
Clear up debris regularly and often. Left alone it will quickly become a source of mould, a habitat for pests, or both!
Don’t neglect watering. Even though plants require far less water during the winter the beds shouldn’t dry out.
Coriander, grapevines - November and December are both recommended for planting grapevines as while they are dormant they can be pruned without damaging the plant.
Beetroot, cabbage, carrot, cauliflower, celeriac, celery, chard, coriander, daikon, fennel, kohlrabi, lettuce, pak choi, pepper, radish, potatoes, rocket, spinach, spring onions, turnip.
Celery will probably become poor towards the end of the month. However, and as it’s unlikely you have anything to plant in its place, just leave it. Once spring begins to warm things up it will become productive again for a while before finally bolting.
Please see our Top Of The Crops for a list of over 80 Vegetables, Fruits, Herbs and Spices, Flowers and Exotics.