How to ensure a garden keeps flowering into ‘old age’

The pacing of our lives and gardens is moving in tandem. Vita Sackville-West, queen of the great Sissinghurst garden, once compared the seasons to the stages of a human life. Spring was childhood and so forth, but in September old age began, at which point she considered it too horrible to go on. Genes permitting, it is now an active pleasure for many of us. The pensioner revolution has been matched by a horticultural one. To judge from last year, the best in the garden is still to come.

I keep on urging you to plan for a flowery autumn. Last year the weather gods listened and extended the season into the third week in November. They have been in kindly form for most of this year, so I expect them to prolong our pleasure and give two months more in which it will still be easy to fill a flower arrangement from the garden without going to the shops.

Like most other elderly beauties, the garden needs a makeover. Clear out the worst in order to see the best. Dead-head everything you missed while on holiday and be sure to cut back any sprawling hardy geraniums which have become a tangle of dying stems. In general, you cannot cut back a border’s previous stars too hard. If you still have tall plants like verbascums, campanulas or thalictrums looking drab and dirty, cut them right down to a basal cluster of leaves and remove them from the sightline. They respond by sprouting healthily at their base. Quite often I see gardens in September whose keen owners have been taking an ill-advised break. They have left dirty deadheads on the summer’s white daisy-flowered leucanthemums and are tolerating plumes of brown on their shrubby buddleias. Dirty buddleias are a missed opportunity. If they are deadheaded promptly, most of them will flower again on shorter stems from the axils of their leaves. It is worth setting about them this weekend in order to have a second season.

After a similar deadheading and cutting back, give all bedding plants a drenching with Miracle-Gro. Most of them will then jump back into life and repeat their flowering in October. When sharp frosts used to begin earlier, the chances of October flowers on antirrhinum, phlox, salpiglossis and every kind of petunia were quite slim. Now they are there for the having if you do not let the bedding plants of summer run to seed. I still have excellent flowers on the universal pansies of late spring, plants which I picked up as a discarded lot for £1. They have been cut back and stuffed full of chemicals. They have responded with Olympic zing.

Ceratostigma’s blue flowers are unsurpassed and as a bonus they attract the best butterflies of autumn

The next step is to be sure you have an iconic plant. In any sunny bit of the garden it has to be the brilliant blue-flowered pseudo-plumbago, Ceratostigma willmottianum. In the 1960s, books were still wary that it might not survive winters in England. Since then, it has survived more than 50. When it eventually drops its leaves, it is best not to cut back the wiry stems until April. Treated in that way it is certainly hardy. It is also topical. The blue flowers are unsurpassed and as a bonus they attract the best butterflies of autumn. Red admirals love them, but so do those glorious migrants, the painted ladies. They are very much the butterflies of the moment. They migrate by the tens of thousands into Britain from north Africa where their emergence in big groups in springtime is one of the wondrous sights of nature. They then fly north at heights of up to 30,000ft, pouring into Britain in complete disregard for border controls and “targets”. Until recently, scientists thought that they never bred in England and that a proportion of them flew back to north Africa in order to reproduce. That theory has now been disproved. Painted ladies sometimes breed in Britain. This month they will be sitting on our ceratostigmas, where they feed and fan their wings, a living reproach to fears that England will be worse if it is “overrun”. The Painted Lady should be adopted as a symbol by those in Britain, more than 16m, who did not vote for Brexit.

Butterflies are less interested by dahlias, but we disagree. I am having a great dahlia year both at home and in the long borders in Oxford. Again, judicious feeding is part of the reason, daily deadheading another. It is fun to take off dahlia deadheads, fat and squishy, before going off to work. I have scores of buds still waiting to open on my beloved pale cream-yellow Cameo, on pink Bracken Ballerina and an excellent first timer in my garden, Brian’s Dream. It is classed as a small decorative, but its flowers are perfectly rounded and as tight as a pompon in a good shade of white, beautifully flushed with lavender-pink in the centre. It is no use going to a store and buying plants of red Dahlia Bishop of Llandaff as if they are special. Dahlia breeders continue to multiply the range and shapes on offer and it is far better to order from a specialist in early spring. Dahlias are listed in the RHS Plantfinder now that it is no longer limited only to hardy plants. One place to check out is Gilberts Nursery near Romsey, Hampshire, an interesting general nursery with a fine display field of dahlia varieties by the hundred, which is open this month to visitors (gilbertsnursery.co.uk).

Otherwise, keep your eyes open, identify and imitate other gardens’ autumn perennial winners and comb the better catalogues. Asters abound, even under the three new names, including Symphyotrichum, which wretched botanists are trying to impose on them. Fortunately, blue aconitums are still aconitums and Japanese anemones are still anemones, though their second names are becoming a battlefield. Even the good old Lady Gilmour is reclassified as “ambiguous” or “misapplied”. However, nobody has yet renamed the excellent family of toad lilies, or tricyrtis, a group where autumn’s cognoscenti now shop with discrimination. They are enchanting small plants with spotted flowers, usually in white or purple, as late as October and they thrive in shade which is not too dry. In a shaded bed in London they ought to be excellent so long as they are not beset by tree roots. Snails and slugs love them, so year-round pelleting is essential. They are one of the stars which take the edge off those chilly thoughts about autumn and old age.

Photographs: Alamy