Asters are the starts of autumn, says Val Bourne

I woke up this morning to a crisp September day with clear light and a heavy dew. The garden gleamed and after June and most of July's extreme heat, August's damp mugginess and that period of easterly winds that's left my garden looking ragged, I'm glad to welcome calmer autumn days to encourage those jewel-box flowers, the asters.

Asters need a sunny position like all daisies, but many also need moist, fertile soil. The most demanding when it comes to moisture are the two North American species Aster novae-angliae (commonly called the New England asters) and Aster novi-belgii (the New York asters). If moisture is lacking, both can suffer from leaf drop and mildew, although New York asters are the most prone.

There are many varieties of these and my own favourites are the soft-pink Harrington's Pink', the rich-violet Mistress Quickly', the soft-pink, late double Fellowship' and the bold cerise-pink Andenken an Alma Ptschke'.

However if your soil is drier there are several excellent asters that don't suffer from mildew and they often flower earlier too.

Aster x frikartii Mnch' has the longest flowering season of any aster, from July until September. It has large, lavender-blue flowers with slender, linear petals plus handsome, dark-green foliage.

I also rate varieties of Aster amellus, a floppy Italian species perfect for the front of the sunny border. The best varieties are the purple-blue King George' and Violet Queen', now dubbed Veilchenkningen'.

Use clear blue asters because they glow in evening light. The tall, black-leaved Aster laevis Calliope' and the shorter small-flowered Little Carlow' are both excellent evening stars.

Waterperry Gardens, near Wheatley, has a huge border full of asters and it grows and sells many varieties, raising them traditionally in outdoor beds.

It is holding a Michaelmas Daisy weekend on September 23 and 24, between 10am and 4.30pm daily.

There's a charity plant sale on Saturday and throughout the weekend there'll be country craft demonstrations.

Waterperry will also donate 25 pence to the gardeners' charity Perennial for every perennial sold during September.

Although Waterperry is undoubtedly splendid during late-summer and autumn, it is worth visiting throughout the year.

The gardens have a dedicated, small team led by Bryn Davies, pictured above in the Formal Garden.

Here a classic Elizabethan knot garden formed by red berberis, plain-green and variegated box has been planted up with with airy, white cosmos and pink gaura.

It is easy to lose yourself for an afternoon at Waterperry and the excellent tea shop, which serves home-cooked food and cakes, makes any visit pleasurable.

Kingston Bagpuize House, five miles west of Abingdon, celebrates its 60th year of opening for The National Garden's Scheme on September 17, and there will be a special ceremony and tree planting. This interesting garden is open from 2pm until 5pm and there are teas and plants on offer.