A Question of Sex.

Byline: Peter Surridge

ANSWERING gardening questions is a little like being an agony aunt. It's not so much "My boyfriend wants me to . . ."

as "How can I get my apple tree pregnant?"

Sex plays a critical role in the garden. It decides which pests prosper, which weeds spread and how many fruits a tree will bear.

Take these two fruit questions I received recently.

Q: A friend says that apple trees need a crab apple tree somewhere nearby for pollination to take place. Is that true?

A: Many kinds of fruit tree need pollen to be transferred - by insects in search of nectar - from another variety in blossom at the same time. Only then will fruit set plentifully. These are called "self-sterile". In the case of self-sterile apples, pollination can be encouraged by other cultivated varieties or by crab apple trees, which are closely related. In some cases two other varieties are necessary.

However, many modern varieties can provide suitable pollen for themselves. They are known as "self-fertile" and are the best kinds to buy if you want to grow only one apple tree. Among the most reliable, especially for the north, are James Grieve or the excellent new Scrumptious (pictured), both available by mail order from Highfield Nurseries, of Whitminster, Glos GL2 7PL (01452-740266).

The same problem arose for another reader with a different fruit tree:

Q: We bought a damson tree six years ago. It is growing well and produces a snowstorm of blossom - but no fruit. Is this because it is alone and not self-fertilising? If that is so, will I have to buy another?

A: There are two possible causes of your damson problem: frost on the blossoms or self-sterility. The second is more likely and means, as you surmise, that a second tree is needed for pollination. This can be complex because you must choose a tree which flowers at the same time. It would be easier to plant a self-fertile variety such as Merryweather or Shropshire Prune.

Sex is not always responsible for the spread of weeds. Although seed production is a sexual process, some weeds spread by runners, called stolons, or by roots, as this reader found:

Q: A weed with small, bright blue flowers seemed attractive when it appeared beneath my rose arches in spring. I thought, "What nice ground cover!" But it isn't - it's invasive, creeping on to the lawn and, when we pull it up, leaving areas bare of grass.

Why has the weed come so suddenly and how can I kill it without harming other plants?

A: The weed sounds like a species of speedwell, which can be very invasive. It should be possible to trace all the roots and remove it with an old knife or hand fork. If it can be sprayed without the spray touching other plants, then try a proprietary weedkiller containing glyphosate.

Other gardening queries in recent weeks have included these:

Q: I am enclosing a few leaves of my gooseberry bush which have been badly eaten. I have searched my gardening books and cannot find an illustration. I hope it does not mean burning the bushes, but spraying could do the trick next year.

A: Your gooseberries have been attacked by the larvae of sawflies. Next year, check the foliage weekly from May for any sign of insect eggs and destroy them. If caterpillars are seen - which is not easy, because they are usually green - spray immediately with a non-persistent contact insecticide such as malathion and repeat weekly as long as the caterpillars are still evident.

Q: In spring I planted expensive gladioli corms but they have not come up. What has gone wrong?

A: The corms may have been planted too deep but probably rotted in damp soil made even wetter by that notoriously rainy spring - the wettest on record. In future plant corms 8cm (3in) deep, in a part of the garden where the soil drains quickly, or with 5cm (2in) of horticultural gravel or gritty sand underneath each corm to improve drainage.

Q: I purchased a pair of bonsai trees while on holiday earlier this year. Although they have continued to flourish I am a little concerned as to how they will cope with the coming autumn and winter.

A: The care of bonsai trees can be a fairly complex business. You need to know the species, whether they are hardy or are best kept indoors in winter, whether the leaves are likely to fall naturally and several other points. I suggest you consult a good book on the subject such as the "Complete Book of Bonsai" by Harry Tomlinson (Dorling Kindersley) to identify your species in the first instance.

Q: I have taken cuttings of some shrubs - weigela, rosemary and others - which are being kept in pots in a cool conservatory. When should I plant them in the garden?

A: Cutting take at this time of year may take several months to root properly so keep them cool in your conservatory until next April before moving them to a sheltered position outside. Plant them out when the roots are growing strongly - check by knocking the rootball out of the pot or waiting until roots show through the hole in the base.

CAPTION(S):

BEARING FRUIT: The selfpollinating apple Scrumptious