In the garden: Sow your biennials now

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The foxglove, Digitalis purpurea, is one of the showiest of our native flowers and one of the few that also make an exceptional border plant. It will happily self-sow when the seeds are left to ripen along the stem, and its beautiful purple spires, popping up around the garden, add an element of surprise and spontaneity to more permanent planting schemes. But, to use these plants to their full potential, starting new ones from seed and planting them out where you choose is usually most effective.

As biennials, foxgloves naturally germinate from fresh seed during the remainder of one season, building up enough energy to flower (and die) the next; consequently, starting your seeds off in June usually results in the biggest specimens the following year. In nature, they're colonisers of woodland clearings, so their seeds need light as a sign that con-ditions are right to germinate.

Because of this they must be surface-sown and I like to do it thinly, on shallow trays of John Innes Seed compost, which are watered well beforehand. After sowing, I cover them with horticultural fleece, which seems to help keep the humidity up without allowing the trays to get soggy. They're quite easy to germinate and the environment of a closed cold frame is usually most effective, but be careful not to over-water, which can cause damping-off diseases.

Once the seed leaves have fully developed, seedlings need to be pricked out, by carefully lifting each tiny plant and placing them individually into a cell pack. My favourite tool for this job is a well-sharpened pencil and I love the precise, repetitive, almost surgical work, which I find best accompanied by Test Match Special. In the time spent listening to the English batsmen face a few overs, a tray of 80 inexpensive baby plants can be propagated.

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The plug trays have a further period of growing on and hardening off, by gradually opening up the cold frame for longer periods, slowly introducing these pampered babies to the elements. Once they've filled their plug trays, they can either be grown on in pots or lined out in the spaces that tend to be opening up in the vegetable garden at that time of year. They can then be carefully lifted and moved to the borders in the autumn and any excess plants can be used as cut flowers the following year.

Last year, we grew a lot of Pam's Choice foxgloves, beautiful, contrasty things reaching about 5ft high, with stout spires of creamy-white flowers whose throats are attractively painted in the deepest burgundy. These plants are flowering rather nicely now at Gravetye, in combination with a cornflower called Blue Boy. Equally successful has been the Suttons Apricot foxglove, whose vertical accents contrast most effectively with the more horizontal effects of Ammi majus that were autumn-sown to obtain early flowering.

Many other biennials and perennials can be easily grown from seed now, and our sowing list for June is quite long. Among them, I'm quite fond of Echium russicum, available from Moles Seeds (www.molesseeds.co.uk; 01206 213213); it's fully hardy and bears 3ft-tall, wine-red spikes. Aquilegias are also important to sow now, being a reliable source of colour for this time of year.

The deep-purple-and-white cultivar William Guinness is excellent, but my favourite is Aquilegia chrysantha Yellow Star, a beautiful lemon colour with very long spurs, giving the plant an elegant demeanour. It also has a pleasant fragrance and makes a good cut flower when only half open.

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However, what really distinguishes Yellow Star is its prolonged flowering season. I find it combines well with the late tulip Blue Aimable and the Allium Purple Sensation. The Aquilegia will continue to flower long after those have finished, but the colour combination can be prolonged by pairing it with a later-flowering Allium cristophii and maroon Cirsium rivulare Atropurpureum.