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October brings a haze of daisies to the garden but is no longer the month in which most of us begin to pull the plantings apart. As our gardens’ show went on last year until mid November I have been banking on it doing so again. In spring I doubled up on hardy chrysanthemums as part of my prolonged game plan and now have so many flowers that I can hardly house them all. Blue-flowered Aster amellus King George is about to hit its peak. It remains one of the best of the late varieties of Michaelmas daisy and has no serious trouble from mildew. I am reckoning on another month of homegrown cut flowers.

In mid September, I studied the gardens at Coton Manor, Northamptonshire, about which I wrote last week. Their mastermind, Susie Pasley Tyler, explained to me that she regarded October as her main month for moving, replanting and changing her borders’ design. Her words struck a chord. In the past two years the English weather has remained so mild into November that plants continue to grow on and develop more roots for another six weeks. We should take advantage of this extra season. Without it, I used to wait until November and promise myself that my misplaced offenders would be divided and moved after I had cut off their dead top growth. This promise was not always kept and the move often waited until February. So did new planting, a traditional part of the early spring rush.

Helianthus Lemon Queen © Jonathan Buckley/Gap Photos

These habits need reform. New border plants, bought and planted out now, will have established themselves far better than spring-planted ones by the time the great growth spurt of summer 2017 begins. I also expect them to be cheaper. The fall in sterling will soon be stretching the many garden centres which buy in most of their plants ready-grown from Europe and sell them on to us at retail prices. Lists from top wholesalers, such as Rijnbeek in the Netherlands, have held prices of their pot-grown perennials for the past two years, but British gardening customers cannot escape some post-Brexit damage. They are as exposed to the currency as wine drinkers. My pocket calculator has been coming up with scary figures for a new border to be planted with pot-grown perennials by the square metre. If they are already in British nurseries at end-of-season prices, I would rather buy them now than wait for another 12 per cent to squeeze them in British retail catalogues next year.

Monarda Gardenview Scarlet © Clive Nichols/Getty Images

In October, early replanters can also see what they are doing. Some of the best late summer and autumn plants are strong runners. Unless they are divided and curbed, they force out lesser beauties. While they still have late flowers and leaves, their full dimensions show up much more clearly than when they are a bafflingly dull mat cut down to ground level. In high summer my recent winners have been varieties of new and improved monarda in shades of pink, white and violet-purple. The family lost popularity when mildew began to decimate its members in the growing season. However, the brilliant red Monarda Gardenview Scarlet resists mildew and has now been joined by specially bred varieties such as Pink Supreme and Squaw. They give a bright, disease-free lift to a border, but they run around as proof of their new vigour, especially if the soil is damp. In October their dying stems are still visible and I can contain them and split them accurately as I never can in midwinter.

Aster amellus King George © Martin Hughes-Jones/Alamy

The tall, yellow, daisy-flowered Helianthus Lemon Queen has had a magnificent late run this year, enjoying the calm of a late Indian summer. In return it has run sideways, taking up far more space than could be guessed from its winter-dormant mats of hard knotted roots. As it goes over, I intend to reduce it along with any over-exuberant hardy geraniums, excessively matted day lilies and every Michaelmas daisy which has reverted and become small-flowered. In recent years I have been vowing to tie bits of scarlet string on to the stems of all asters which have gone wild and lost their size of flower. I then forget to tag them, but not because asters have been split up botanically and given impossible names such as eurybia and symphyotrichum. I simply forget the job. If I attack the culprits while they still have flowers, I can be rid of the right ones for good.

Monarda Pink Supreme © John Glover/Alamy

When the space is cleared, better replacements can go in at once. Some of them will be divisions off existing plants, cut with a sharp spade, if possible without uprooting and disturbing the rest of their parent plants. Others will be newly bought nursery plants, waiting to hand in pots. Others will be plants already growing in the wrong place. Have no scruples about lifting them entirely in October, even in full leaf, and dropping them into their new home. Early morning dews are keeping them damp but if the weather sets fair and dry, water each plant to be moved very thoroughly on the day before you intend to lift it. Pre-watering is more effective than watering a dried-out removal after replanting. The green to growth can be shortened by at least half to reduce the stress.

Phlox Dusterlohe © Martin Hughes-Jones/Alamy

In August the blot on my best border was a clump of strongly coloured solidago, the good old goldenrod. I am unsure how this vivid yellow mistake had intruded, but today it is coming straight up and out. Into the hole will go more of the excellent deep purple-violet Phlox Dusterlohe, which I described buying on a whim in the Lake District in June. It has turned out to be an excellent plant, vigorous, long lasting and even producing some late flower heads so that I can see that I am moving the right plant. Spare the rod and spoil the border, but I know that I will miss the chance if I wait until winter as the books tell me. That goldenrod will then hide, cut down in the crowd.

Those of you who open your gardens to visitors know how arbitrary most of the moving dates given in garden books really are. To sustain the impact for visitors, plants have to be switched throughout the borders’ season. This practice began in the best amateur gardens, but it now ought to spread in a small way to the rest of us. When dying lupins offend you in July, pluck them out, pot them up in a big black plastic pot and keep them out of sight until early spring. Move some tall pot-grown lilies into the gap and then pull their pot out too and move in pot-grown asters for a final fling. There is something theatrical about the best plantings and gardens. Start to move the stage effects before those boring old dictionaries tell you. In our new climatic pattern the show must still go on.

Photographs: Clive Nichols/Getty Images; Martin Hughes-Jones/Alamy; John Glover/Alamy; Jonathan Buckley/Gap Photos

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