The June borders at Crathes Castle, Scotland, provide a pleasing mix of hues

In a sudden rush, British gardens have just passed Midsummer Day. They are curiously ahead and behind their usual selves. The warm April accelerated much that we associate with June and July. Penstemons, heleniums and day lilies are flowering well in advance of the customary season. The grey, cold phase in May then held back plants we associate with early June. The roses are already losing their first flush but I still have full flower on paeonies, admittedly in shade, and some of the sun roses, or helianthemums, are still a carpet of colour.

What are we to make of it all? So much thought and advice go into planting plans but the results seem to be surprising us. Borders are supposed to be a carefully planned harmony of colour, merging one soft shade with another. I welcome the chaos because I have always been suspicious of detailed plans that tell us exactly what to put where. The warmer weather now makes wonderful fun of them.

Who can be sure nowadays that their blue delphiniums will merge delicately with tall white Crambe cordifolia or that their deep blue veronicas will wait obligingly for the pale yellow flowers on their daisy-flowered anthemis? As this century was beginning, I heard an impassioned lecturer claiming that the careful combination of colours would be the next new frontier for gardeners. It was not exactly new but the millennial weather has torn up its rules. Variable seasons stop us controlling what this lecturer kept describing as absolutely crucial.

Does seasonal confusion matter if nature’s colours seldom clash or conflict? I think they do but less than we are all taught to believe. Purple-magenta and scarlet are not the most pleasing of neighbours. Magenta and orange or scarlet and yellow are another matter. I therefore work to a broad general rule. I like to limit the general colours in a big planting, rather than worry about each shade’s closest neighbour. Erratic seasonal weather is then less of a problem, as it only retards or advances flowers from a broadly similar range.

My aim is not to have a one-colour bed, a red border or a blue haze. It is simply to concentrate the range a little and exclude the stale colours of pink-purple or purple-violet. They are surprisingly popular with advocates of big drifts of perennials, interplanted with ornamental grasses. I find them deadening and I used to marvel at their presence in so many of the borders planted by Graham Thomas, former adviser to the National Trust.

Clear blues, yellows, reds and pinks are so much more beguiling. Here, the seasonal confusion is not a problem if you simply plan to work with this general range, more or less at ease with one another when they flower. The exciting change is not the new timing. It is that the new range of choice as new varieties come to the fore, refuting those who think that flower-gardening is living only in the same old past.

A good new plant is like a new tube of paint in one’s paintbox. I bless the day that we found tall blue Salvia uliginosa or realised that Aster Little Carlow is the most electrifying blue among the healthy types of Michaelmas daisy. So many of the crocosmias have proved hardy in modern winters and changed the look of borders in July. I have been slow to wake up to the exceptional vigour and clarity of colour in red Crocosmia Emberglow or yellow Norwich Canary. They are best in sun where the soil is not too dry and dusty but they really intensify the effect in the next month or so.

Plant hunters, too, continue to enrich us and stop us falling back on the outdated planting plans in books. In the days of Gertrude Jekyll, Britain’s queen of colour-planning, nobody had introduced the pale yellow hollyhock called Alcea rugosa. It came in about 20 years ago from collections in the Far East and has proved extremely easy to grow. The old girl would have loved it, especially as it stops at a height of about 4ft and does not need staking. It is also better able to shake off attacks of rust on its lower leaves, the besetting disease of the taller hollyhocks that we have grown for centuries.

I suspect that there is so much more to find in the lower levels of herbaceous plants that grow wild in China or parts of north Turkey near the Black Sea. Collectors here began by looking especially for shrubs or rare bulbs. Border plants were less in their sights and we have so much more to learn.

Meanwhile, new variations turn up at random in gardens or are cleverly bred by selection and hybridisation. Quite the best family in my borders this weekend are the campanulas in their many shades of blue and deep violet. So many of them are excellently equipped for our new dry summers. The good old Campanula lactiflora has really proved its worth recently because it has such chunky roots and can draw and store water so effectively in a tough, hot year. It is now one of my first tips for anyone with a new garden that needs border plants with height.