Suddenly it's summer and you've got a riot on your hands

Clematis is roaring up the pergola, hostas are as big as Savoy cabbages. It's time to reassess the garden

The garden has exploded. Roses that were still hanging around in mid May wondering whether it was going to be worth while to leaf up are now in bloom. The hostas are as big as Savoy cabbages (but not quite as beautiful). Viticella clematis are roaring up the poles of the pergola. Nought to 90 in a week. That might not be a unique selling point in a BMW but it is an extraordinary performance for a garden.

Gardeners are always telling each other what a weird season it has been. The thing is that each year the weirdness takes a different form. Last summer there was the drought. We remember the downside of that. But there have been benefits, too. The blossom on fruit trees, wisterias, ceanothus and other flowering shrubs this spring has been brilliant. That must have something to do with the way the wood was ripened in last summer's heat.

Long, cold, slow starts to the flowering year, as we have had this year, make a nonsense of the rulebook. New gardeners desperately want rules to help them make sense of what they need to do in the garden. But rules aren't as important as principles. If you understand the principle of why you shouldn't set out tomato plants or bedding plants too early in the year, then you know when you need to bend the general rule that they go out at the end of May.

This year they didn't. I am still planting petunias and lobelias and potting up geraniums to stand outside the back door and this is in the south west, where I generally expect to be a month ahead of the rest of the country. Most years, tomato plants and other tender material are out in the garden by the beginning of May. Now we have to hope that we get an extra month of warmth tagged on at the end of summer to make up for the month we have missed in front.

The speed of growth over the last two weeks has meant that the gaps I thought I had for plants that have been waiting in the wings have suddenly closed up. I have wasted a good deal of time when I could have been attacking bindweed, mooning about with various pots - an extra peony, a romneya, a very pretty variegated myrtle - trying to find space for them.

This is not the recommended way to go about things, but mooning can be oddly productive. You suddenly get fresh ideas about ways of combining plants. Or you suddenly realise, as I realised this morning, that it is time for something to go. In my case it is a Ceanothus 'Autumnal Blue'. It is one of the evergreen kinds, generally less hardy than the deciduous ones.

It has got so big that its head pokes well above the parapet of sheltering shrubs that stand between it and the northeast wind. It suffered badly during the winter and is being very slow to reclothe itself. It is, anyway, now out of scale with its surroundings. I should have pruned it harder. Late flowering ceanothus such as this (it flowers in July, August and September) respond well to hard pruning in April. The spring flowering evergreen ceanothus such as 'Blue Mound', C. veitchianus and 'Puget's Blue' should be pruned when they have finished flowering.

The little myrtle, which I'm going to go on calling myrtle even though the botanists have now shifted it to another family (they call it Luma apiculata rather than Myrtus apiculata) is a variegated one called 'Glanleam Gold', which was found off the west coast of Ireland, on Valentia Island, just south of Dingle Bay.

'Glanleam Gold' is an evergreen and each of its tiny leaves is edged with an irregular creamy margin. At the moment it is dense and bushy and I hope to keep it that way, by some judicious pruning in March and April. It starts to flower in September and continues through until October. The flowers seem mostly to be bosses of white stamens, rather than petals. They have a spicy smell. Unfortunately, this species is slightly more tender than the common myrtle, Myrtus communis. I shall keep my fingers crossed that we don't immediately get another winter as savage as the last.

Gambling, though, is part of the fun of gardening. If winters were always harsh, as they might be further up country, then I would be a fool to fall for myrtle. But I am not sufficiently dismayed by the losses of last winter, which were considerable, to stick to planting only safe bets. You learn a great deal from winters such as the one we have just had. All my hebes perished, but the huge spurge, Euphorbia mellifera, said to be tender, waltzed through without a hiccup.

The myrtle is part of a drive (if I'm honest, more of a drift) towards strengthening the performance of the garden in late summer. My obsession with tulips and a growing, extremely dangerous, interest in columbines, means that there is far too much happening in May and June and not enough in August and September.

The romneya is also supposed to help prop up the garden in late summer. (I've tried it four times before in different positions and each time, have lost it. Normally, after that number of losses, I would give up, but romneya, the Californian tree poppy, is such a fabulous thing, with its huge, white papery flowers and beautifully cut glaucous leaves, I'm having another go.

Part of the problem here is finding a place that is sufficiently light and well-drained. Romneya likes masses of sun and the potential of plenty of space. If well suited, it is a runner. I've never had that luck. Oh, to be able to curse your romneya for running. Because it gets tall (6- 8ft), it can't go too far forward in a planting. It also hates being disturbed, so this is not a plant you can afford to make a mistake with, in terms of its position in the garden.

What will go with the romneya, while it is deciding whether to die? I fancy the dark-leaved cow parsley, Anthriscus syvlvestris 'Ravenswing'. This might seem an odd choice when the lanes all around (and swathes of the garden) are already covered in cow parsley. But 'Ravenswing' has foliage that early in the season is dark and sumptuous. Then it collapses, like its wild relative. With it, perhaps another cow parsleyish thing, actually a type of chervil, Chaerophyllum hirsutum roseum, with lilac-mauve flowers.

In the foreground, perhaps some Jacob's ladder. Again, it is the foliage that draws me towards this plant. Bright, juicy, vivid, the ferny leaves are made up of small leaflets neatly paired along the stem. The one I have is the wild Polemonium caeruleum but there are excellent fancy forms such as 'Sonia's Bluebell' sold at Glebe Cottage Plants. This has paler blue flowers and darker, more bronzed foliage than mine.

To contrast with the Jacob's ladder in the foreground, I would bring in more sisyrinchium, which gives you upright sword-shaped iris leaves, in places where irises wouldn't be happy. I am very fond of the small cream-striped sisyrinchium called S. striatum 'Aunt May'. Clever Aunt May to have spotted it and sent it round her friends. It is just coming into flower now, pale creamy flowers on top of stiff, fan-like foliage, no more than a foot high.

Carol Klein's nursery, Glebe Cottage Plants is at Pixie Lane, Warkleigh, Umberleigh, Devon EX37 9DH (01769 540554). The garden will be open for the National Gardens Scheme on Sunday 28 July (2-5pm). Admission pounds 1.50. Plants can be sent mail order. Send pounds 1.50 for a catalogue