New beginnings: Alleviate the gloom of January by ordering beautiful new seeds for your garden

Seed catalogues provide comfortable reading in the drab days of January. My order goes off next week. Top of the list is Ammi visnaga (Thompson & Morgan £1.99). On New Year's Day, I was pulling their skeletons from the flower border, the whole crop bleached cream, the stems still strong, though bent to the ground by the snow, the flat umbrella flower heads still structurally perfect. Of all the annuals I grew last year, this was the best. It was still looking terrific, even in November.

Why does it seem better to me than its cousin, Ammi majus? Partly, it's the foliage, which is much more feathery, as good as fennel in that respect. It made, at least with us, a taller, bulkier plant than Ammi majus, and the flower heads were more densely constructed, the baby florets packed tightly into elegant domes. It's not showy – the flower heads are a soft greenish-white – but it's a superb filler, airily elegant beside the chunkier, meatier strap foliage of agapanthus, which was often flowering with it. I'm hooked. This is not a plant I now want to be without.

And with my new greenhouse, raising annual flowers has become easier than ever. I don't have a propagator, or anything fancy like that, but there's no doubt that seedlings grow more steadily in the bright, all-round light of the greenhouse than they did either in the cold frame, or on the kitchen windowsill. Indoors, seedlings get leggy very quickly. In a greenhouse, set high on a shelf close to the glass roof, they do not.

Encouraged by the new possibilities the greenhouse offered, I grew vast quantities of annuals last season and intend to do so again, though I won't be doing so many tobacco plants. Last year, I grew three different kinds and because I potted up all the seedlings into their own 5cm (3in) pots, there was a stage when the entire greenhouse seemed to be taken over by them. They were the first seeds I sowed (on 14 Feb), a pot of 'Fragrant Cloud', a pot of N. sylvestris and a pot of N. mutabilis.

As the name suggests, 'Fragrant Cloud' (T & M £1.99) is a sweetly-scented tobacco plant. It has white flowers and grows to a good height – about 90cm (3ft). But after the first flush of flower it gave up, while N. mutabilis went on for the whole summer and autumn. N. mutabilis (T & M 99p) makes a much bigger plant, too leafy in its early stages as all tobacco plants are, but throwing up a huge flowering stem of small white flowers that turn pink as they age. It was my chief filler last summer, but I'm not repeating it. At the back of the border, the effect of the flowers was curiously insubstantial. This year, Ammi visnaga will be in charge.

Though I generally sow A. majus at the beginning of September (that way, you get bigger, earlier-flowering plants to set out the following year) I sowed A. visnaga in the spring. But I did not sow direct into the ground, as the instructions on the packet suggested. As usual, I sowed in a pot and later, pricked out the seedlings into their own individual containers. It's the best way to get decent plants.

The right compost matters, too. The RHS's house mag, The Garden, this month reported on a trial which indicates that it has not been as easy as campaigners had hoped to find a reliable substitute for peat. Seed germination in coir compost was "erratic with low counts of small and medium seeds". Germination in compost based on wood fibre was even worse, as the texture was coarse and watering more difficult to manage because the compost drained so quickly.

You may feel you'd do better to make your own, as all gardeners once did. My Gardeners' Dictionary (George Johnson 1886) suggests that all you need is "strong, tenacious loam, half-rotten leaf-mould, heath-soil, horse manure, cow manure, charcoal and wood ashes, bone-dust, sharp sand, burnt turf and moss, well-scalded". It's a more complicated mix than even Heston Blumenthal would suggest.

I chug along on various kinds of multipurpose compost, relying on a few simple principles to make up for the composts' deficiencies. First: there's no point in sowing too early. Many annuals are not hardy and cannot be set out while frosts are still lurking. They won't improve while they are hanging around under cover, longing to spread their roots. A few annuals are tough enough to withstand the risk of chilly nights. Cornflowers and English marigolds are usually the first things I plant out.

Second: the smaller the seed, the less weight it needs on its head after you have sown it. The fine seed of nicotiana doesn't need to be covered at all. Fill a pot with compost, smooth off the top, water it and sow the seed on the surface. Cover the pot with a pane of glass to stop the compost drying out. With nicotianas, germination takes from one to three weeks, depending on the surrounding warmth. Faster is not in itself better.

Third: seedlings like a calm, smooth progression through life. Abrupt changes in temperature or lack of moisture can check their growth. All plants will do their best to live, however crass we are at looking after them, but weak, needy plants are more prone to disease.

Large seeds, such as those of the annual climbers cobaea and ipomoea (morning glory) are easy to deal with. You can poke a single seed on edge into a 5cm (3in) pot and leave it to do its thing. Some people soak the seed for a couple of hours before planting. I never have. Germination of either of these plants can take up to a month, but they are not difficult to grow.

My mistake with morning glory was to choose a mixture. Most of the resulting plants seemed to be white and looked exactly like bindweed. I like to grow morning glories up the south wall of the house where they mix with roses, vines and wisteria. But that's exactly where bindweed has long been a problem, its roots firmly entrenched under the slabs of the adjoining terrace. Last summer, pretending to be morning glory, bindweed did far too well. This year I've reverted to the old-fashioned, sky-coloured morning glory called 'Heavenly Blue' (T & M £1.99). 'Star of Yelta' (T & M £2.69), a much richer, deeper blue, is equally lovely.

Thompson & Morgan, Poplar Lane, Ipswich, Suffolk IP8 3BU, 0844 573 1818, thompson-morgan.com