In the Garden: Tis the season for Michaelmas
Some early asters have been in flower for weeks but the main group of this wonderful, late-season plant are not far behind. The flower colours of asters, or Michaelmas daisies as they are widely known, are perfect for autumn.
The range of smoky reds, blues, purples and pinks makes an excellent contrast with the yellow and brown colours of most trees and shrubs as their leaves change colour.
There are several kinds of asters, the largest derived from North American species, some smaller ones from Europe.
The American kinds, the New England asters and the New York asters, also have some shorter varieties that have been selected, such as the very popular 'Professor Anton Kippenberg', a reliable short plant with denim-blue flowers, and 'Jenny' has rich pink-red flowers.
Varieties based on the Italian aster, Aster amellus, are mildew-proof and smaller in size but flower from late summer to autumn, such as 'King George' and 'Monch', both blue.
There are scores of varieties, but some well-known kinds include: 'Andeken an Alma Potchske', pink; 'Harrington's Pink', light pink; 'Barr's Violet', violet-blue; 'Ada Ballard', lavender; 'Royal Velvet', violet-purple; and 'Ernest Ballard' which is deep red.
All of these are quite large, to 1.2m and more, and carry masses of daisy flowers at the top of the flower shoots.
The asters are completely hardy and will grow in cold areas.
The big American kinds suffer from mildew in dry years and where they are grown in soil that is too well-drained. While they need soil that drains, they like moist, fertile soil in full sunshine.
If they dry out in summer, the leaves of the New York varieties especially will be affected by mildew, and leaf spots can be a problem if the soil is too wet.
But most gardens with good fertile soil suit them fine. If the plants suffer, they should be moved to other areas that might be more suitable.
Try to find a place that suits them well and then leave them be to make a good-sized clump. Divide the clump every few years if it gets too big or congested.
If the ground is fertile, do not over-feed the plants. Too much feeding, especially with manure, increases disease problems and causes the plants to be too vigorous and need staking. But these plants can look just as attractive with a few flower stems leaning out of the clump, especially in an informal setting.
Q One of our trees is infested with vine weevils and they are attracting wasps. We have removed as many as we can and used a spray but usually another batch appears the following day. The wasps appear very enticed by them. What could be causing them to attach to this particular tree, which is a sally, and how do we keep them away? We have issues with some of our pots having vine weevil larvae in them.
A It sounds more likely an infestation of dark greenfly, which is common on willow. The wasps collect sweet honeydew from the greenfly for food. Winter cold is likely to finish them off. If you use half unsterilised garden soil and half compost, you will have very few vine weevil larvae - or apply Nemasys, the nematode parasite.
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