Now's the moment to pick your plants for the summer - will it be fuchsia, a trailing helichrysum, or a delicate-petalled lobelia?

Top job for the month

For the past month, our local garden centre (the peerless Groves in Bridport) has displayed shelves and shelves of baby bedding starter plants at £1.15 each. That's because May marks the moment of the great switchover from spring displays to summer ones. Out with the tulips. In with the fuchsias. Or the petunias. Or the begonias. Cruising up and down the shelves at Groves, it was easy to see which plants were the favourites, round here at any rate. Silver helichrysum is more popular than gold. White and blue petunias shift faster than pink or red ones. Lobelias disappear from the shelves almost as soon as they are put there.

The idea behind the baby plants is that you buy them cheap and small and spend time growing them on yourself. It's getting a bit late for that, but all the classic ingredients that you need to fill a summer pot will still be available now, just bigger and more expensive. It's the most important job to do this month: set up the show in pots or windowboxes that you'll be looking at for the rest of summer.

The bigger the pot, the easier it will be to keep. But if you don't have the strength or inclination to cope with big pots, use small ones in clusters, planting just one ingredient in each pot, then shuffling them about (as the season progresses you can use different ingredients) to make a good show. Anyone who has been to Great Dixter in Sussex will know how successful this approach can be. The superb displays by the porch are made up of masses of smallish pots, each containing its own star plant.

To make up a pot you need trailers, some kind of centrepiece to give height and thirdly, what I think of as stuffing, the plants that you use in the mid-ground to give your pot a generous, well-filled look. For good reason, helichrysum with felted leaves in silver or gold, is one of the most popular trailers. It's a great survivor, and weaves about in a pot very effectively, but be prepared to prune it. Nepeta hederacea is softer, less stiff and cascades very prettily out over the edge of a pot or windowbox. I scarcely ever get further than lobelia: dark-blue lobelia with white petunias, pale-blue lobelias with the scented leaf geranium 'Pink Capitatum' and silvery Lotus berthelotii.

Fuchsias do wonderfully well in pots and can give you a centrepiece or do a trailing act. 'Mission Bells' has always done well for me. The growth is upright and bushy, it is strong growing and easy to propagate, and the single flowers are scarlet and rich purple. 'Brutus' has the same good qualities, but the flowers are a brighter red.

'Checkerboard' I've now lost, but grew for several seasons in a pot, underplanted with pale diascias and trailing blue lobelias. The growth of this fuchsia is markedly upright, which is an advantage in a pot, as you can plant other things right up to its main stem. It makes a good standard, but if you have a standard fuchsia in a pot, it needs to be in a sheltered position. Its top-heaviness can be dangerous in a gale. If you use a heavy loam-based compost in your pot, you offset this problem. The pot itself becomes more stable. I much prefer loam-based composts; they are more nourishing than the light, no-soil types.

'Mission Bells', red and purple 'Voodoo' and the salmon-pink double 'Beauty of Exeter' raised in 1890, make equally good standards. The best time to start training one is the end of summer, rather than spring. If you start in spring, you have to spend a great deal of time nipping out flower buds to persuade the plant to concentrate on leaf and stem growth.

Fuchsias tailor their ways of growing and flowering according to the length of the day. When days are short, that is in autumn and spring, they make vegetative growth. When the days get longer and the fuchsias can depend on at least 12 hours of daylight, they start getting their flower buds into action.

Scented-leaved geraniums and fuchsias in pots are old faithfuls, because gardeners know they will cheerfully adapt to life in reduced circumstances. And fuchsias are particular favourites because they can go up or down. The ones I've just mentioned are all upright, but the Groves favourite was a trailing fuchsia, the double 'Bella Rosella' with frilly flowers in two-tone pink.

With an upright fuchsia such as 'Voodoo' you might use blue daisy-flowered felicias as fillers. The variegated felicia is showier than the standard green-leaved kind, but I have not found it as free-flowering. The finely-divided grey leaves of Senecio viravira, as graceful as a fern, is another useful prop in pots. Leafy bulk is what makes pots look luxuriant. The flowers then have something to display themselves against, like jewels on velvet. This senecio looks excellent with tender, lush-leaved fuchsias such as 'Thalia' or 'Gartenmeister Bonstedt'.

The right proportion between size of pot and the plant in it is vital. A top-heavy fuchsia in a too-small pot looks and feels uncomfortable. As a rough guide, plants, when fully grown, should be about one-and-a-half times the height of the container. Balance – that is, checking that one plant does not swamp all the others – is important, too. Helichrysum sometimes needs watching in this respect. The fine-leaved Helichrysum microphylla is easier to manage than the big-leaved ones. But both the gold and the lime-coloured helichrysums are excellent in shade, better there than in sun, where the foliage tends to burn.

Find time to

Stake perennials before they get too big. Brushwood is the most elegant solution – but it is not so easy to get hold of in urban areas as it is in the country.

Use linking stakes, bamboo canes, or prunings from dogwood or willow to bend over into an approximation of a lobster pot, through which the new shots of perennials can grow.

Harden-off annuals that you have been growing from seed, so that they acclimatise to cooler temperatures before you plant them out permanently. A cold frame is ideal for this.

Think about

Making successional sowings of vegetables such as endive, lettuce, spinach, turnip, radish, and maincrop peas.

Earthing up early potatoes as their shoots come through the ground.

Mulching fruit trees before the ground dries out too much. The mulch will have the effect of suppressing the growth of weeds round the tree and will retain moisture round the roots.