Oxfordshire residents are well placed to see a wide range of these September sparklers because there is world-famous autumn border at Waterperry Gardens, near Wheatley, full of late-summer asters or Michaelmas daisies. More importantly Waterperry grow and sell a whole range for the gardener and these plants are in short supply in most garden centres, purely because they are difficult to transport on Danish trolleys.

When the garden centre and the plastic pot revolutionised nursery practice in the 1960s, effectively seeing off bare-root mail order, the Michaelmas daisy lost favour because it wasn’t possible to grow them in pots successfully. A way was eventually found, but when the trend for buying plants in flower arrived the aster slid even further because it was one of those plants that just looked like a bent stick in a pot. Blooms of Bressingham, who listed over a hundred species and cultivars in their 1939 list, were selling just five in their 1990 mail order catalogue. Varieties could easily have been lost, but for a few dedicated gardens and growers and Waterperry have played their part along with Paul Picton, at Old Court Nurseries in Colwall, who is almost solely responsible for keeping them in the public eye when they were at their lowest ebb. At Waterperry, it’s possible to see lines of herbaceous plants of all types laid out in the garden, all well-labelled, and that gives the gardener an exceptional opportunity to discover excellent plants. A Waterperry plant races away too, because it’s grown in good compost. September is an excellent time to plant new asters: the soil is still warm enough to encourage root development. However dividing asters (or any other late-flowering perennial) should wait until next spring. By then all autumn-flowering plants have had enough time to replenish their food reserves. Catch them just as they start to race way and they will hardly notice.

To generalise, North American asters can be subdivided between New England asters (Aster novae-angliae) and New York asters (A. novi-belgii). Both are shallow-rooted so they need moisture, but the New York asters are miffier. They go down with mildew much more readily than the others. New England asters tend to flower in late summer and early autumn, pleasing the butterflies. They tend to be strong, with woody stems tightly packed together and they often shed foliage so it’s worth placing them behind something else to hide the ragged stems. Excellent varieties include ‘Harrington’s Pink’, ‘Barr’s Violet’ and the bright cerise-pink (but very hard to place) ‘Andenken an Alma Pötschke’. These sun-loving varieties don’t need regular division, so they persist in gardens for years. There are far more New York asters and they are more diverse, varying in height and colour, but tending to flower later.

However they often disappear in gardens if left undivided — although varieties vary. When dividing always select the outer pieces of all asters, they are more vigorous. Good taller varieties include the double blue ‘Marie Ballard’, the double pale-pink ‘Fellowship’ and the shorter purple-red ‘Jenny’. If you love asters the A. cordifolius hybrid, ‘Little Carlow’ will give you a haze of blue.

In October, I am doing a one-day, plant-led course on Eco Friendly Gardens at Waterperry Gardens between 10.30am and 3.30pm. This costs £45, including tea/coffee with 25 per cent discount on a light lunch, (telephone 01844 339254 or see the website www.waterperrygardens.co.uk). Other courses are also available.