Undercover: February 2012

Plant potatoes

Planting early potatoes undercover now can give you a delicious crop of small new tubers in May/June – the time when they are most expensive in the shops. Space them closely (about 30-40cm/12-15in) apart each way) as you will be harvesting them before they need earthing up; alternatively plant them singly in large pots. Read more on this starting on page 64.

Leafy harvests

With this month’s stronger sunlight and longer days, overwintering leafy crops should start to re-grow and give some welcome leafy harvests. Pull out lurking weeds and remove any dying or diseased leaves. Start watering regularly but carefully – direct water at the base of the plants and avoid splashing the leaves. Open vents and doors for a few hours every day unless it is dull and cold or very windy – this helps avoid fungal diseases and weak lank growth.

Harvest now: Spinach, chard, oriental leaves, spring greens.

Advance warming

If your seed compost is stored in a cold shed, fill pots and trays and bring them into the greenhouse or tunnel for a few days before sowing. Cover them with clear polythene to trap the heat and moisture, replacing it after sowing until the very first shoots start to appear.

Early peas and beans

Autumn-sown peas and broad beans should put on a spurt of growth this month, but if they failed to overwinter, there is still time to sow for an early crop. Sugar peas give the quickest harvest because they do not have to fill out before you pick:

●     Choose an early dwarf variety.

●     Pregerminate the seeds on moist paper towel in a warm place until the first tiny roots appear.

●     Beware of mice – set traps, or sow pregerminated seeds in pots out of their reach. Plant when seedlings are a few inches tall.

●     The crop is unlikely to be finished before June, so make sure that it is not in the way of summer crops.

Pollinate peaches

If the weather is mild, peaches and nectarines grown under cover may start to flower – well before most pollinating insects are about. You can transfer the pollen yourself by gently pushing a soft paint brush into the centre of one flower and then the next to help the fruit set. Go round them every couple of days while the flowers are still opening.

At this time of year, a greenhouse or polytunnel can help slash garden costs. You can start off plants that you would normally have to buy ready-grown, both saving money and getting much more choice of varieties. The reliable results make better use of expensive seed, and of course you get extra early harvests, at a time when produce costs more in the shops.

The gardening catalogues are full of seed-sowing aids, but what do you need to buy and where can you improvise? The main essentials are pots, trays and modules (sometimes called ‘plug trays’), sowing compost, a good watering can and – if you are starting off tender plants at this time of year – some way of providing a little extra heat.

Seed and potting composts

Both ‘seed’ and, ‘multi-purpose’ composts are suitable for sowing most vegetable seeds. Seed composts should be finely milled and contain low levels of nutrients – they are good for tiny seeds and ones (such as basil) that don’t like lots of nutrients, but seedlings must be pricked out into a stronger compost at an early stage. Multi-purpose compost is best for filling modules, as it should contain enough nutrients to support growing seedlings. I find it worth buying a proprietary compost for seed sowing. The labelling on the bags should tell you if the compost is suitable and how much peat it contains. I only buy peat-free composts for environmental reasons, but brands differ widely in performance: two that have done well in trials are Vital Earth and New Horizon.

DIY sowing composts must have a good structure – a mix of fine and coarse particles which hold both enough air and enough water for seedling roots – and this is where most DIY mixes fail. Potentially they could also contain weed seeds and disease organisms that harm young seedlings. Nevertheless, sieved leafmould on its own or mixed with 25% sharp sand can give good results for seed sowing. For filling modules or pricking out young seedlings, where more nutrients are needed, add materials such as soil, garden compost or worm compost; try out different proportions for different situations.

Water

Any old watering can will do, but a good head or ‘rose’ is important. A flat head turned upwards usually gives the gentlest spray. You can buy good quality ones which fit most watering cans.

Extra heat

Tender crops such as tomatoes and peppers sown this month need temperatures of around 20C (68F) to germinate and – equally important – the young seedlings need a light, warm place to grow on. At less than 15C (59F) they may survive but will not grow, and become prone to disease.

If electricity is available, a heated propagator is one of the most economic ways of raising the temperature. You can buy ready-made ones with integral heat mats and tall lids which give room for young plants to grow, or save money by buying a heating cable and making up the framework and cover yourself. A cheaper alternative might be to raise seedlings in the house, where light rather than temperature is usually the limiting factor. Then you need ‘grow lights’ which emit the correct spectrum of light for young plants. You can buy complete units with a base which will sit neatly indoors or buy the light units with cable and set up your own.

DIY seeds can be germinated on a warm windowsill, but seedlings nearly always get leggy searching for more light. For best results, rotate them frequently and take them out temporarily to the greenhouse on warm sunny days.

A low-tech solution for inside a tunnel or greenhouse is a hotbed – made Victorian-style with fresh horse manure and straw in a pit, or by building up a fresh compost heap all in one go. Cover the top with a thin layer of soil before standing plant trays on top.