FOR gardeners with a heated greenhouse the next few weeks are a time of peak activity. The first sowings of tomatoes must be made, together with those of sweet peppers, aubergines, as well as lettuce for growing on in a cold frame.

Summer bedding plants like fibrous rooted begonias, lobelia, impatiens and petunias must be sown immediately if they are to make substantial enough plants for planting outdoors in late May and early June. Maintain a constant temperature of around 60F in a propagator and ensure that emerging seedlings are afforded maximum light.

Over-wintered geraniums and regal pelargoniums can be rejuvenated by knocking them out of their pots, shaking them free from all soil and re-potting in good fresh compost. Those that are to be grown as pot plants or for bedding can be cut to within a couple of inches of the base and allowed to break naturally to form compact plants.

Tall, lanky individuals and those intended as a source of cutting material only need to be tied up and given a good watering. In a week or two, fresh young growth will emerge from the old leaf joints and these shoots can be used for cuttings.

Dahlia tubers can be taken out of storage and started into growth. If they have been packed away in trays of moist peat all you need to do is water them thoroughly and bring them out into the light and warmth.

In a very short time, strong green shoots will be produced and these can be taken as cuttings when between three and four inches long. Remove the cuttings at a leaf joint and insert them in a tray in an equal parts mixture of soil-less compost and perlite. Given a little warmth they will root very quickly.

Early flowering chrysanthemums can be treated in a similar manner. Being almost hardy, these can tolerate much cooler conditions than dahlias.

Parsnips must be sown as soon as soil conditions are favourable because they require a long growing season if they are to produce a worthwhile crop. While old varieties like Hollow Crown and Tender and True give satisfactory results, there is much to be gained from trying a modern kind like White Gem.

Both White Gem and a recently introduced variety called Avonresister are heavy yielding varieties with considerable resistance to the brown rot or canker which regularly spoils the roots of many more traditional kinds.

Seeds of broad beans, round seeded peas and early carrots can also be made if the weather permits and the soil is workable. There is little to be gained by sowing seeds into a cold clay soil with the threat of heavy rain to follow.

Philip Swindells

WHAT'S NEW

Thermidrome is a high yielding, frost resistant variety of garlic.

Lianne is the latest butterhead lettuce for greenhouse cultivation.

Taffeta Mixed are an F1 strain of semi-trailing begonias for containers, window boxes or hanging baskets.

Q I have bought some begonia tubers, but I am not sure which way up I should plant them. Please advise?

A Begonias are always planted with the smooth curved side downwards. The fibrous part should be uppermost and just beneath compost level.

Q My gardenia has suddenly lost all its leaves. What could be the problem?

A The most usual one is dryness at the roots, although a draught from the window will produce the same results. Gardenias should always be kept really damp but not waterlogged.

Q What is the difference between longpod and windsor broad bean varieties?

A The longpods are generally hardier and suitable for early sowings. They are reliable, but not of as good quality as the windsors, which are less resilient and usually sown later