Undercover: December 2011

Published: 11:53AM Nov 3rd, 2011
By: Sue Stickland

Harvest and clear late autumn crops before they succumb to cold or disease. Florence fennel is a real fresh crisp treat in December, but will not stand temperatures much below freezing. Spring onions are hardy, but the foliage is susceptible to fungal diseases in the cold and damp. Second crop potatoes are best harvested before the skins start to toughen and while they still have a good ‘new potato’ flavour. I usually grow these from spring seed potatoes, which I keep ticking over in a cool light place before planting in pots under cover in mid-August

Undercover: December 2011

All of this year”s shoots should be cut back to within one or two buds of the main stem.

December jobs

•    Clear autumn crops
•    Prepare beds for spring sowing and planting
•    Give extra protection to overwintering crops if necessary
•    Open doors and vents when conditions allow
•    Prune grapevines


Fennel, beetroot, turnips, spinach, chard, spring onions, lettuce, chicory, endive, Chinese cabbage, pak choi, oriental salad leaves, rocket, landcress, second cropping potatoes.

Give extra protection

A polytunnel or greenhouse will keep off a few degrees of frost, but if temperatures go much lower some plants will benefit from an extra insulating layer. The options are:

•    Covering crops temporarily with fleece on cold nights
•    Insulating the whole structure on the inside with bubble polythene or thick fleece
•    Making a warmer section inside – screen off part of a greenhouse or put a cold frame or small temporary ‘tent’ type greenhouse inside a polytunnel

Protect with fleece

Fleece works best for winter salads and leafy vegetables because you can remove it during the day unless the weather is very cold, so allowing in plenty of air and light. Raise it off the plants on hoops if you can. Many crops would survive without it, but the additional protection helps to ensure a continual harvest. Fleece varies in thickness, measured by weight in grams per square metre: ordinary garden fleece (17g) is said to keep off frost at temperatures down to minus 2-3ËšC (28-27F); winter weight (30g) fleece similarly down to minus 5-6ËšC (23-21F). Add its effect to the benefits already provided by the tunnel, and you will see how cosy your plants can be.

The disadvantage of permanent winter insulation is that it reduces the light getting to the plants, even during mild spells. However, it can be very effective for overwintering tender herbs and exotic crops which are not actively growing. Autumn planted peas, beans, onion sets and other vegetables which usually survive outside should need no extra protection.

Winter watering

Only water if the weather is mild and plants are actively growing – wet can be as much a cause of winter losses as the cold. Salads grown in containers and evergreen herbs in pots are most likely to need emergency watering. Keep a small water butt or large watering can full of water inside the greenhouse or tunnel, as supplies outside are likely to be icy cold.

Ventilation is still important, however. Open doors or vents for a few hours each day unless conditions are very windy or cold – this not only helps avoid fungal disease but also prevents plants from getting too ‘soft’ and vulnerable – there may be lower temperatures to come.

Prepare beds

Once space becomes available, prepare beds for spring and summer crops or green manures. Beds under cover are used more intensively than those outside, each usually producing at least two crops a year, so extra feeding is necessary.

I fork in well-rotted manure for tomatoes, early potatoes and other greedy vegetables, and use garden compost for less vigorous growers such as salads and beans. Afterwards, make sure that the soil is moist, then cover it – with a mulch of straw, for example, or sheet of black plastic – to prevent it drying out.

Prune vines

Don’t forget to prune vines planted under cover this month if you haven’t already done so – leave it any later and their sap may have started to rise, causing cuts to ‘bleed’.

On established plants, prune back all shoots that have grown this summer back to one inch (or one or two buds) – you should be left with the thick main stem or ‘rod’ containing knobbly ‘spurs’. It may look sparse now, but it will produce prolific new growth in spring.

Clear away all dead leaves and prunings, as these can harbour overwintering pests and diseases.

Planning ahead

Even if the weather doesn’t allow outdoor jobs, you can escape from the house by doing some under-cover fixing and constructing which will save you time in the spring rush.

Catalogues can give you ideas for improvements (Harrod Horticultural: www.harrodhorticultural.com and Two Wests & Elliot: www.twowests.co.uk are two of the most comprehensive). If your budget is limited, translate them into DIY versions or put a few items on your Christmas list.

•    Shelves on the gable end of a greenhouse or hung from the polytunnel framework can keep seedlings near to the light and out of the way of slugs and mice. They are traditionally the place for pots of early strawberries.

•    Struts and brackets can give you sturdy tying points for canes and strings, just where you want them.

•    If you find watering a chore, look into automatic watering systems while you have plenty of time to consider the options.

•    Fitting automatic vent openers can help your greenhouse get sufficient air even if you are away from home.

Successes and failures

Before being seduced by next year’s seed catalogues, sort leftover seeds and note your successes and failures, gluts and famines. Were there times when beds were empty or when you were overwhelmed with produce? Which crops weren’t worthwhile? Are there different ones that you would like to try?

In my polytunnel, for example, I intend to cut down on the number of tomatoes I grow and at the same time nurture a few February-sown plants of an early variety – I want a longer harvest of fresh fruit and less processing and freezing. I might use the space to try something more unusual in the same plant family, such as a tomatillo or cape gooseberry, or to ensure success of a crop such as butternut squash which normally struggles outside.

I’m also learning lessons from the past two harsh winters which have devastated overwintering brassicas, and I’m adding some low-growing kales to my range of autumn planted crops.

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