For me, bumble-bees and ladybirds are not the only signs of spring. The arrival of the first seed-trays on our ample windowsills indicates that the seed-sowing season has begun. Trays containing seeds of zonal pelargoniums have appeared in the spare bedroom this weekend, while a small propagating tray is now occupying a prime site on the dining room windowsill.

Within a matter of weeks there will be fierce competition for space throughout the house, with even the boy's bedroom window sills temporarily taken over by germinating seedlings.

Although windowsills are good places to germinate seeds, they do have some drawbacks. The overnight temperature next to the glass, even if it's double glazed, is several degrees lower than the temperature in the middle of the room (you can measure it if you don't believe me, the difference is quite marked). If that's too cold for your seeds then they will suffer and you might have to move them further into the room on really cold nights. Conversely, during sunny weather, south-facing sills can heat up rapidly, drying out compost and preventing seeds from germinating.

Once the seeds have germinated, even on the brightest sill there is not quite enough light for them to grow as they would in a greenhouse. Seedlings grow constantly towards the light, so pots and trays must be turned at least once or twice daily to prevent the tiny plants from becoming lop-sided and leggy.

Another way of stopping them from becoming too straggly is to stroke them - brushing your hand lightly over the top of the growing seedlings two or three times a day will strengthen the stems considerably.

Jobs for this week...

Prune greenhouse and conservatory climbers such as plumbago and passion flower. Cut out any weak growths and shorten side shoots by about two thirds. Tie in all the main stems firmly.

Sprout seed potatoes before planting, by placing them in trays (eyes uppermost) in a cold greenhouse or frost-proof shed.

Make a first sowing of leeks, in trays, in the greenhouse or on the windowsill.