The magnificent swallowtail butterfly landed nearby on a blue spike of Echium candicans and began making its way round the inflorescence, delicately ascending the spiral staircases of tiny flowers. I watched for ages as it inspected each ‘stair’ for nectar as it went. This rapturous event occurred exactly a year ago, in a garden on the Ligurian coast, but, as my camera had been to hand, that swallowtail and its echium lodged themselves first in my computer as the desktop ‘wallpaper’ and then in my memory. The object of the exercise was to remind me to plant more things for butterflies in future.

Now, I see in numerous reports that British butterfly populations are plummeting, as indeed they are in the rest of Europe. This is especially so in eastern Europe, where the Brian Aldridge effect of traditional husbandry being replaced by the industrialised farming methods of the West is rapidly diminishing all aspects of wildlife. It is time to act.

It is easy to plant for the ‘end product’ the adult butterfly because so many lovely garden flowers appeal to them. Among these are echiums, of course, plus lavenders, wallflowers, stocks, marigolds, arabis, aubrietas, scabious, thymes, verbenas, hyssop, centranthus, sedums, thrift, ox-eye daisies, teasels, echinacea, michaelmas daisies and good old buddlejas. Not always so easy to remember is the parallel need to plant (or rather, leave alone) a rough area with ideal food plants for the caterpillars: common nettles, thistles, sorrels and wild mustards, to name a few.

Right on cue, Buddlejas, a new book by David Stuart (Timber Press, £25) has just arrived, revealing the buddleja tribe to be more varied than I guessed. True, as a genus they are a rather untidy crew, but they’re suited to rougher areas of the garden, and some are lovely enough to take pride of place in a mixed border or beside a gravelled drive. Mr Stuart has grown the lot over many years in the National Collection at Longstock Park in Hampshire.

From his recommendations, I am tempted to get hold of B. x weyeriana Honeycomb, which bears silvery stems covered in little gold-amber golf balls. It ‘outperforms its B. x weyeriana stablemates in several ways,’ says Mr Stuart. ‘It is a strong grower, it has better leaf colour, its flowers are fragrant, and it is easier to grow.’ Rich magenta B. davidii Royal Red looks as exotic as sari silk and grows strongly (rapidly reaching 15ft) but, like other davidiis, it responds well to hard pruning in spring. I find the white-flowered varieties less appealing as the ‘clean’ effect of the white is entirely lost as soon as the flowers start to fade. B. colvilei Kewensis, on the other hand, is a connoisseur’s plant of clustered crimson bells, freely produced if it is grown somewhere sheltered from winter winds and chills.

Easy work can be made of pruning buddlejas and other later-flowering shrubs now, with a really good pair of loppers (long-handled pruners). The ones I usually reach for are Felco 21: lightweight but strong and well balanced. For many years, I have also used a pair made by Sandvik which, at about £40 per pair, are two-thirds of the price of Felco’s, but are excellent quality (as you’d expect of Scandinavians, who know all about forestry) and with superb shock absorption, which is essential if you have a lot of pruning to do.

One thing I tackled recently with gusto was an overgrown run of star jasmine, Trachelosper-mum jasminoides. This lovely twining evergreen, with shiny, elliptical leaves, can take several years to get going, but if it likes its location (plenty of sun, freely draining soil), it eventually romps away. I had ignored it for such a long time that when I recently looked up, I was horrified to find it had clambered two storeys and was about to start pushing the tiles off the roof. Its whippy stems are like waxed, brown bootlaces; they look innocuous, but can insinuate themselves and cause damage, although they are very amenable to training. I have hard-pruned some back to a grim looking skeleton as an experiment, to see whether I can retrain it into something like the luxuriant walls of greenery that feature in the gardens of Fernando Caruncho, Spain’s leading garden designer. Regularly sheared, star jasmine can be as neatly trim as a prize poodle at Crufts, and still spangle all over with tiny white flowers, deeply fragrant as evening descends.