THE evening primroses arrived from nowhere. The first plant grew by accident, the seed presumably blown in the wind or dropped by a bird, or perhaps trodden in on a country boot. There were no plants in neighbouring gardens and the nearest patch in the wild was perhaps half a mile away.

Whatever the happy chance, the oenothera had sown itself in the wild garden where it was able to grow unhindered fully 5ft high and spread its own seed far and wide. A year later a rose bed was well nigh eclipsed in an ocean of green and yellow that lasted throughout the summer, there were evening primroses among the vegetables, in the fruit garden and even in a garden frame.

They spread next door where my kindly old neighbours were both mystified and delighted.

After running riot for several years, the interlopers had to be rigorously controlled in an effort to confine them to permitted quarters. The hoe has restored the rose bed to the roses. Even so, the inevitable has happened and yet more neighbours wonder where their evening primroses have sprung from!

The evening primrose is a plant that comes into its own in a summer with lovely, long, warm, heady evenings when the flowers open and positively glow and the scent wafts throughout the garden. Some of the many species of the oenothera tribe (there are more than a hundred) have the heaviest of sweet scents on the darkest of nights when the flowers are pollinated by moths. Each flower lasts only a short time but another takes its place immediately in a succession of bloom that will last from June to October. Few garden plants have a season of bloom that lasts so long.

Plant height varies. There are ground-hugging types with huge flowers and a good many that stand no more than a foot or two high. The giants, perfect for the back of a border, tend to be the garden escapes that come in again from the wild.

Mine, I am sure, is none other than oenothera biennis, the most familiar of the species, a biennial which once established in a suitable site is never likely to leave, self-sowing so readily that it may cover a large patch of ground with flattened rosettes of leaves in the first year, sprouting its tower of pale yellow bloom in the second.

Many gardeners advise sowing in shady spots but the tree primrose, as it used to be called, actually does best in a sunny site in a light and easily drained soil. The plant actually originates from the dry and waste spaces of North America and sinks a strong taproot deep into the soil which makes it a plant that is apt to withstand dry conditions.

Few of us really appreciate the fact but our long and light summer evenings are the envy of people from warmer countries where the temperature may be high but darkness tends to fall like a stone at around about teatime. We should make more of this and exploit flowers that are at their best in this twilight zone.

I have been fascinated in recent years by the return to fashion of night scented stock. Some of the modem versions are bright and cheerful in colours that range from deep mauve through pink to yellow and cream which makes a big change from the usual night-scented stock which, although with a superb scent, often looks rather insipid in a dusty lilac shade.

It is to be hoped, however, that the search for a more attractive daylight look does not lead to a diminution of that glorious nighttime scent.

There are not all that many of the true evening plants that only release their scent at the end of the day in order to attract the night-flying insects that pollinate them. Nicotianas are among the most popular, especially the taller varieties (some of the bedding types have little or no scent) but we can be more adventurous and look to night-scented jasmine, the Mexican orange blossom, honeysuckles, wisterias, lilacs, and others.