ET

Thorny problems: bud blast (Filed: 01/09/2001)

Helen Yemm on banned insecticides, perennial problems and succulent babies

Chemical reactions

I have been trying to buy a systemic insecticide to spray the leafhopper that is spreading "bud blast" on my rhododendrons. I was told that all systemic insecticides have been "banned by Brussels". Can you suggest a suitable alternative? A C Long, Virginia Water, Surrey

FIRST, it is not strictly the case that all systemic insecticides have been "banned by Brussels". Rules on garden chemicals are being tightened in Britain and the EU. Chemical companies are forced to carry out more extensive tests to comply with the new regulations.

These huge, multinational chemical companies see the gardening market as relatively small, so investment in research is not deemed to be worth the return. Broadly speaking, these chemicals have been taken off the market for economic reasons, not health and safety ones.

Many gardeners have been buying up all available stocks of systemic chemicals, but this is only a short-term answer to their problem of hard-to-treat garden pests.

Imidacloprid (as in Pest Free), which was introduced relatively recently, is the one systemic insecticide available. It is suitable only for ornamental plants in containers.

It seems that we will have to learn to live with those garden pests that are hard to eradicate using contact insecticides, such as BugClear. Removal of the blackened buds on your rhododendrons is your best treatment for bud blast. It is depressing - but it will probably force us to be much "greener" gardeners.

Acorn attack

I have noticed that many oak trees have acorns that are deformed. Have you any idea what causes this? M Tasker, Budleigh Salterton, Devon

The prickly, deformed acorns you have noticed are called "knopper" galls, and each one houses the larvae of an insect called the acorn cup gall wasp. I once had a garden overhung by an afflicted oak, and the presence of the galls made walking barefoot on the lawn unpleasant - almost as unpleasant as hand-weeding near a holly hedge.

Knopper galls were first noticed about 40 years ago and are now quite common in the South. They are relatively harmless, and the wasp/gall population seems to fluctuate from year to year, along with the acorn count. I am told there is no need to panic about them.

What is a perennial?

I bought a tray of gazanias and, when I consulted my plant encyclopaedia, it said they were "a perennial grown as an annual". What does that mean and how should I look after them in winter if I want to grow them as perennials? P Gildon, by email

This subject is complicated. A perennial is a plant that comes up year after year which, in this country, means that it has to be frost tolerant. While shrubs and trees are technically perennial, the term is generally applied only to herbaceous (non-woody stemmed) plants, such as lupins, phlox and so on.

Perennials are a diverse bunch. Some set seed and can be propagated in the "normal" way - lupins, for example - while many others have to be propagated vegetatively - as with Geranium 'Anne Folkard'. Some perennials die down and disappear completely during the winter; others maintain a rosette of foliage.

Annuals, as the name implies, complete their whole growing cycle in one year. Some, known as hardy annuals, germinate in autumn (love-in-a-mist), come through the winter as tiny seedlings, grow, flower and make seed rapidly the next season. Others (petunias) have to be sown in spring indoors and planted out in late spring.

What you have acquired is a perennial that comes from a warmer climate than ours (in this case South Africa), is not frost tolerant and cannot be relied upon to go through the British winter and come out the other side smiling. Hence the "grown as an annual" tag.

There are many other summer dazzlers like this - well-known examples are pelargoniums, salvias and the more upright osteospermums (the ones that lie along the ground are hardier and are more likely to survive here, given well-drained soil).

To sum up: it is probably not worth the fuss of giving these plants protection, although you might be lucky if we have a mild, dry winter and you have a sheltered garden. So enjoy your gazanias while summer lasts.

Succulent discovery

I bought what I think is an echeveria at a plant sale (it was sold as a cactus). It had an orange flower and now has lots of "babies" around the stem base. What do I do now? J Pretty, by email

The rather fashionable echeverias come from semi-desert areas of Central and South America and their fleshy leaves do look rather cactus-like, but they are more accurately called "succulents".

They are not frost hardy, and can survive outside in the drier months here, preferably in pots on slug- and snail-free patios and terraces, and given an occasional liquid feed. In the cooler months of winter, they should be brought indoors (a light, frost-free windowsill is fine), and kept very dry.

Your "babies" - properly called offsets - should be separated from their parent gently and pressed lightly into their own pots of gritty compost.

This operation is best carried out at the start of the growing season, but you could try to separate one or two now. They may make roots and become viable plants before the winter slows down their growth.

If they fail, try again next spring. If other readers want succulent babies, too, www.crocus.co.uk can deliver a potted echeveria to your door. Visit its website or call customer services on 01344 629629.

-- Anonymous, September 03, 2001