Still jobs to do in the December polytunnel
Short days and cold weather can mean that little gets done in the polytunnel in December, but there’s no harm in taking things easy for a few weeks. There are jobs that can be done, of course, but every gardener needs a break. If you leave most of the work for this month until January, little will suffer, but do take a regular walk around to harvest crops and to check that nothing needs immediate care. It’s a great time to do a bit of armchair gardening too – reflect on the past year in the polytunnel, browse through some seed catalogues and start to draw up plans for the year ahead. Of course, if the sun shines and the polytunnel beckons, get out there and enjoy some winter gardening.
Weather report
December can be cold, wet and windy. Daytime temperatures might struggle to get above freezing and the days are so short that there hardly seems time to do anything in the polytunnel. Block draughts under doors and keep growing crops as warm as possible. The shortest day will pass by at the end of the month and new enthusiasm will build as the days start drawing out.
December jobs in brief
Plant out peas and beans
Plant a few early potatoes
Clear the last of the summer crops
Clean up and prune grape vines
Check the structure and make repairs
Order seeds
Think about fittings and fixtures
Wash pots
Look after the soil
Keep harvesting
Time to sow
Broad beans
Mangetout peas
Winter lettuce
Mizuna, mibuna, rocket
December sowing
This isn’t the best month for sowing crops: days are short, light levels are low and soil temperatures can often be below the level that is required for growth. Having said that, it’s always worth sowing a few salad leaves if spring crops are in short supply.
• Try sowing mizuna, mibuna and rocket in large pots rather than in the ground. Bring the pots into the house until the seeds germinate. After germination, move the pots back out to the polytunnel, with an extra layer of fleece on top. There should be plenty of pickings in a few weeks’ time.
• It’s still worth trying a sowing of mangetout peas this month. Sow plenty of seed, as some will not germinate. There should be plenty of plants to go out in late January or February.
How cold is cold?
Temperatures usually drop significantly in December and for the next couple of months growth will slow right down, or stop altogether. Plants can’t grow at temperatures below 5˚C/41˚F and if they freeze solid, some of the less hardy ones won’t survive. Polytunnel crops have the benefit of raised daytime temperatures on bright days. This will keep soil temperatures higher than those outdoors, but nights can drop below 0˚C/32˚F. It’s worth investing in a maximum and minimum thermometer, which will give some idea of the temperature swings that plants in the polytunnel have to cope with. You can buffer them from the worst effects a little by using fleece, or cloches, as an extra layer of protection.
Top Tip
I only use fleece in this way during really cold spells. Most plants should be pretty hardy at this end of the year and it is best to remove extra coverings if temperatures are above 0˚C/32˚F. This allows more light and air to reach plants, which means fewer problems with moulds and mildews.
Peas and beans
Mangetout peas and broad beans, sown in pots, will be ready for planting out when 5–8cm/2–3in tall. Dig a trench to a spade’s depth and half fill this with compost from the garden heap. Fill the rest of the trench with soil. Place plants at the same depth at which they grew in the pot and don’t bury any stem as this may lead to rot. Set a double row of peas 15cm/6in apart with approximately 5cm/2in between plants. If seeds were multiple-sown in pots, it is possible to loosen the compost and shuffle the plants apart to the correct spacing. Having said that, this isn’t a precise science and mangetout peas do very well at closer spacings if that’s how they work out.
Broad beans should be planted in a double row 20cm/8in apart with 15cm/6in between plants. This is slightly closer than they might be outdoors, but it seems to suit the conditions in a polytunnel.
If the soil is acid, scatter hydrated lime or wood ash along the row, taking care not to get any on the leaves of small plants. This will also help to keep any active slugs and snails at bay.
Top Tip
Plant broad beans as close to a door as possible. This gives flowers the best chance of pollination in early spring. Peas are self-fertile and the first flowers don’t need any help with pollination. They grow quite tall, however, so place them where they won’t overshadow low-growing crops.
If you decide that there isn’t room in the polytunnel for a crop of broad beans, it’s still worth raising young plants in pots from an autumn sowing. You can plant these out in the garden and they will often crop better than ones that are direct sown outdoors. Just make sure to cover the row with a cloche, so that they don’t suffer too much of a shock in the move from the tunnel to the great outdoors.
Planting broad beans
Extra early potatoes
Some people get great results from planting first early potatoes in a polytunnel in December. This is only really an option for areas where a mild winter is the norm, but it can be worth having a go. Plant the sprouted seed potatoes 15cm/6in deep and 30cm/12in apart, in a soil enriched with plenty of compost. Nothing much will happen for a few weeks, but once the first shoots start to emerge keep a close eye on things. Always cover emerging leaves with extra layers of fleece – double or triple thickness may be required. If nights are really cold, cover each plant with a cardboard box. If days are cold as well, place a large clear plastic tub over every plant. Light levels might be reduced slightly, but this is less of a problem than frozen foliage. Potato leaves will discolour if they are lightly frosted, but a hard freeze can kill the growing plants outright. Adequate covering should avoid this problem and the reward will be an extra early crop next spring.
Carrots
If you sowed carrots in a pot in October or November, these should be well up by now. Don’t thin the seedlings, even if they seem crowded. Slugs will eat some, some may just wilt, but the survivors will grow to cram the pot with tasty little roots.
Kohl rabi
Seed sown in late October will have produced small seedlings. These will be ready for planting out now. Growth can be very slow during the winter, but it is still worth getting small plants into the border: they will have a chance to become established before putting on growth next year.
Tomatoes and peppers
All the other summer crops will be long gone, but in a good year a few tomatoes and peppers can hang on until December in an unheated polytunnel. It might even be possible to pick the last cherry tomatoes for Christmas dinner, but it isn’t really worth hanging on to diseased plants just for a handful of fruit.
It’s best to clear any remaining tomato and pepper plants in early December, especially if they have been grown in the border. This gives the soil a chance to recover before you plant out another year’s tomatoes and peppers. Pick any ripe and unripe fruit and spread this out on a sunny window ledge. Be scrupulous about removing any fallen leaves and fruit. Dig lots of good compost into the empty bed and keep this damp so that microbes can do their work – the border should be healthy and ready for planting in the spring.
Top Tip
Try not to pass any problems on to the next generation: plan to grow next year’s tomato crop in a different part of the polytunnel.
‘Bendigo’ peppers still ripening
Clear all fallen leaves from vines and pick free any leaves that haven’t fallen. Some may stick against the polythene. Check the vine at the same time and cut away any diseased or damaged sections. Prune this year’s side shoots back to leave one fat bud. Fruit will form next year on the new growth. Vines can take quite a hard pruning and they will bounce back with vigour next year.
Some people prefer to untie vines from supports and to lay them down on the ground for the winter. This can be fiddly, if not extremely difficult, to do. Provided the vine is held away from the polythene, and provided you check it over and prune it back, it doesn’t have to be moved.
Remove last leaves from a grape vine
Look after the structure
This may seem repetitive, but if you maintain the structure of the polytunnel well it will last for years. The winter months usually see most damage, so repetitive checks and repairs are just the thing (see Part 6).
• Check all polythene regularly, especially at corners and where it crosses the framework. Repair any rips before they spread.
• Check catches and hinges on doors, so that these don’t break off and flap loose in a winter storm.
• If an elderly polytunnel has wooden door frames which go down into the ground, check that these haven’t rotted through over the years. For a quick repair, knock a strong post in and fix the old frame to this.
Top Tip
If the structure suffers from prevailing winds that blow directly in through the door, it may be worth rehanging the door from the other side of the frame.
Order seeds
Early December is a good time to send off for seed catalogues. Get a few, as this will give a wider choice. Once someone is on the distribution list, companies usually send catalogues out automatically in subsequent years.
It’s worth taking the time to sit down and work out what to grow next year: what to buy as plants and what to grow from seed. Consider factors like disease resistance, vigour and size. This should be a pleasant job, so don’t rush! Ideally, seed orders should be sent off before the end of the year. This gives you the best choice of varieties – some may sell out if you leave ordering too late – but in practice, in January you will still be in plenty of time to get your order in.
Extra fittings?
December is a quiet time to review the polytunnel and assess what might be useful in the year ahead. Is there enough bench space? Would shelves be useful, or would they get in the way? What about a watering system? Or soil-warming cables? Then there are paths and raised beds . . .
Don’t rush into making expensive decisions, but do look into anything that might make the workload easier.
• Shelves can be hung from the polytunnel framework.
• It’s a good idea to dig out paths and add the extra topsoil to the borders. Back sufferers will appreciate the raised beds.
• Soil won’t fall on to paths if it is held back behind planks of wood.
• A board across a couple of boxes, or bins, makes a quick bench that can be moved as needed.
Wash those dirty pots!
A year’s worth of sowing and potting on will leave behind a pile of dirty pots. To minimize the possibility of disease being carried through to next year’s sowings, all tubs, trays and pots should be washed. Some people are organized enough to scrub each pot as it empties and, since damp compost lifts off the inside of a pot much more easily than compost that has been left to dry on for several months, this is the ideal thing to do. More people make a pile of dirty pots and vow they will deal with them at a later time. Look on December as that time arriving! Fill a large bucket, or even a wheelbarrow, with warm water and an environmentally friendly washing liquid. Add some algae remover, or Citrox, or tea tree oil. Then find a nice sunny spot in the garden, sit down and start to scrub. A washing-up brush works well for getting into the corners and removing all debris.
Spread the washed pots out on the ground and hose them off with clean water. Once they are dry pots can be stacked and stored in boxes. They will be clean, disease and pest free, and all ready for the growing year to come.
Soil health
Gardeners expect a lot from the patch of earth inside a polytunnel. It gets little rest and is often expected to crop on a year-round basis. This may work out extremely well for the first year, but fertility will decrease and pest and disease problems increase over subsequent years, unless you take some action. Some people choose to grow only in growbags and containers, so that the compost can be changed with each crop. Others dig out and replace the border soil every few years, which seems like an awful lot of work. The best option is to look after the beds that are there and keep them in good condition so that they can crop well without any change of soil (see Part 6).
December is the perfect time to get things sorted. Clear any debris and remove any diseased material before adding anything that might cover the problem up. Borders in a polytunnel can become covered in a green crust during the winter months; this is most common on wet heavy soil. Riffle around plants, with gloved fingers or a hoe, to break up the surface and help the soil to ‘breathe’.
Adding well-made compost can restore vigour to old beds and will often help sort out disease problems too. A layer of seaweed, applied as mulch in December, can work wonders. Well-rotted manure will replace lost nutrients and the border will be all ready for planting out in the spring.
Pile fresh manure in a corner of the polytunnel. It will generate heat as it rots and, after this process is finished, it can be spread around over the soil.
Enjoy the December harvest
Last peppers
Last tomatoes
Salad leaves
Lettuce
Fennel
Beetroot
Turnip
Oriental greens
Spinach
Chard
Kohl rabi
Potatoes
Kale
Pak choi
Swiss chard
Some harvesting hints
• Harvest cut-and-come-again crops regularly to keep them producing and preferably pick while the taste is still sweet.
• Winter lettuce, mibuna, mizuna, land cress, lamb’s lettuce, mustard greens, rocket, purslane, etc., can all provide plenty of picking for winter salads.
• If you sowed pak choi in August, it can stand well into December, but not much longer, so pick and use plants now.
• Make sure you lift any late-cropping potatoes and get all small tubers out of the ground. The earliest new potatoes can be planted this month and it’s not worth risking the spread of disease to next year’s crop.
• Fennel bulbs may not reach the size of summer ones, but they taste wonderful when picked fresh in December, as do small tasty beetroot and spinach leaves.
• Keep harvesting and be patient: small things will come into their own as the days start to lengthen again.
