Make the most of the first sunny day to give your greenhouse a good clean if you plan to start sowing seeds soon.

A clean greenhouse means plants will be less vulnerable to pests and diseases and, if you zap them now, your undercover growing area won't become a breeding ground for nuisances.

Before you start, take out as much as you can and turn off the power to electric points, covering them to stop any water splashing them.

The best tools for cleaning the outside are a good hose and a long-handled soft-bristled brush for tackling the roof glass, using a large sponge. Give it a good rub to remove algae and, if panes overlap, use an old plant label to ease out the dirt and then rinse the area with a hose. Replace cracked or broken panes or get a professional to do it if you don't feel confident.

Clear greenhouse gutters, removing soggy leaves and debris which could end up in water butts or block your drains. Get a long-handled brush to get rid of the rubbish before it enters the downpipes.

Once the greenhouse is empty, give the floor a really good sweep and get rid of clutter like broken pots, out-of-date feeds and other junk.

Wipe down surfaces with a scouring sponge and wash flower pots and seed trays with disinfectant before thoroughly rinsing and returning to their place in the greenhouse.

Horticulturist Frances Tophill, co-presenter of ITV's Love Your Garden and guest speaker at the forthcoming Edible Garden Show in Warwickshire, says: "The art of a good greenhouse is to have a more or less constant temperature.

"In the winter, a heater might be required or a little bubble wrap on the glass. Plants will suffer most if their foliage is in direct contact with the cold glass, so move them away during the winter months."

The warmth provided in a greenhouse will help a multitude of insects to overwinter in the warm and come back with gusto in the spring to attack your plants.

"To avoid that happening, give your greenhouse a big winter clean-up, paying particular attention to any standing water where larvae may well be multiplying."

Now is the time to think about growing your early vegetables.

"Early carrots and parsnips (make sure you use one that is canker resistant) are ideal to start in February," says Tophill. "It's also a great time to start your garlic and small onions or shallots. If you have the luxury of a greenhouse then now is the time for growing all your tomatoes, peppers and aubergines.

"Also grow radishes, brassicas and all your peas, including late sweet peas. Now is also the time to get that summer bedding going. So start sowing cleome, dahlias, ricinus (castor oil plant), snapdragons and cerinthe."

Many plants just need the protection of a frost-free environment to germinate, so can be grown in a non-heated greenhouse or in a cold frame.

"Some seeds actually need a period of intense cold known as stratification before they will germinate. So it is all a matter of looking at your seeds, reading the packets carefully and treating them accordingly.

"If you only have a non-heated greenhouse, I always find a windowsill in the kitchen works a treat!"

:: The Edible Garden Show, Stoneleigh Park, Warwickshire, runs from March 11-13. Visit www.theediblegardenshow.co.uk

BEST OF THE BUNCH - Helleborus

Their fragile-looking nodding flowers give a touch of elegance to the winter and spring garden, brightening up beds and borders in a range of colours from pure white through to deep purple, pink, cream, yellow, and red flowers. These graceful perennials like damp, shady spots in the garden and look fantastic planted in borders with snowdrops, erythronium, primula, pulmonaria and tiarella. The most popular helleborus is H. orientalis and its colourful hybrids. They flower in early spring, around the period of Lent, and are often known as Lenten hellebores or Lenten roses. They are ideal for bringing early colour to shady herbaceous borders and areas between deciduous shrubs and under trees. Plant them in heavy, rich, limey soil that won't dry out in summer months. Their leaves die down in June or July, after which the plants should be kept cool and shaded until they begin to grow again in early spring.

GOOD ENOUGH TO EAT - Planting rhubarb

Rhubarb isn't technically a fruit, as it's the stems we eat, but it has now been lumped into that category because we generally have it in puddings - pies and crumbles, fools and jams. Whatever your opinion on its category, this is a plant that is really easy to grow even if you just want a few stems. Plant dormant crowns in late autumn or early spring in heavy soil with plenty of added organic matter, preferably in full sun so the stems will become redder and sweeter. Plants should be 3ft apart. Remove any flowering stems which appear in summer, cutting them out as close to the base as you can, then remove dead leaves when the foliage dies down in autumn, adding general-purpose fertiliser to the soil and mulching liberally. If you want to force rhubarb for earlier stems, cover a well-established crown with a rhubarb forcing pot or upturned dusbin in mid January or early February and cover the ground around it with straw for insulation. A few weeks later, long stems with pale leaves should appear and they can be harvested until the end of March. Then uncover the plant to let it develop naturally and don't force the same crown every year.

WHAT TO DO THIS WEEK

:: Water trees, shrubs and climbers in containers if the weather is dry or windy, especially evergreens.

:: Prick out or pot up pelargonium seedlings that have grown from seeds sown last month.

:: Apply a top dressing of gravel or chippings to the rockery to suppress weeds and ensure alpines don't become waterlogged.

:: Bring strawberries in containers into the greenhouse for early fruit.

:: Prune half-hardy fuchsias being kept under cover as soon as the pink 'eyes', or embryo shoots, appear.

:: Sow seeds of tomatoes for growing in a cool greenhouse.

:: Clip faded flowers on winter-flowering heathers.

:: Cut back deciduous ceanothus, buddleias, lavatera and caryopteris quite drastically.

:: Prune later-flowering shrubs now if you want to reduce their size.

:: Lift and divide overcrowded winter aconites.

:: Dig out persistent lawn weeds such as dandelions with a daisy grubber or sharp transplanting trowel.