Fast plants: A guide for impatient gardeners: 4: Welcome invaders

LARGE clumps make new gardens look established in a single season, so it is worth choosing a few expendable plants to gallop over the ground among the rarer perennials that take longer to mature. Important plants tend to look thin in their early years unless they have been set extravagantly close together. The gallopers are cheap, one plant will often cover a yard or more of ground in a summer, and they are the sort of things that gardeners with mature plantings will gladly give away.

Some of them are thugs, but plants that are described as 'invasive' are not always as threatening as they sound because anything that will cover a yard square in a season can be valuable in the right place. The comfreys (Symphytum) are colonisers on a grand scale. In a flowerbed among choice perennials their behaviour is less than desirable because one scrap of root from this flowering herb can cover a couple of yards in a season. Once introduced, it is almost impossible to eradicate and can only be frightened off by repeated poisonings. But the flowers of Symphytum caucasicum are bluer than the best postcard summer sea and the leaves are packed so densely on the ground that they smother all weeds. If the plant is cut down after flowering, it will bloom again later in the summer. Out now, it rivals the forget-me-nots, and its intense colour is a tonic in cold springs. On a bank where nothing else will grow, or under a tree in dry shade, comfrey can be an unbeatable ally.

Tellima grandiflora is another plant for impossible conditions which will grow into a large mat in a season. Its flowers are green and its leaves are evergreen, so it will not shout for attention as the comfrey might seem to do, but like the comfrey it will thrive in shady places or among the roots of trees.

The hardy geraniums, or cranesbills, are good value anywhere. In new gardens they are useful spreaders to use while waiting for rarer plants to grow. The pink geranium known as endressii 'Wargrave' will flower off and on from May to October above neat green leaves. As with most hardy geraniums it will spread quickly into a weed-proof clump. Planted among peonies, which are slow to develop, 'Wargrave' can be a great help, provided it is not allowed to take over. The way to stop this is to dig it up every spring and divide it before replanting. Where there is room, it and the rest of the cranesbills can be allowed to ramp, but they are hard work to dig out once they have put down roots. Polite cranesbills are 'Johnson's Blue' and 'Ann Folkard'. These do not root from spreading stems as do some of the more invasive forms. 'Ann Folkard' is a dashing colour combination of magenta flowers over lime-green leaves and 'Johnson's Blue' is soft and true.

In a sunny place, a good choice for those in a hurry is Anthemis cupaniana. This has feathery, silvery leaves covered in marguerite-sized daisies. It flowers better and stays tidier if divided every year and then replanted. But as it will spread into a mat more than two yards in length and breadth in the course of a summer, most gardeners will want to check its spread, and it is, anyway, easy to dig out. In cold wet places Anthemis cupaniana may disappear in winter, but any plant that grows at such a rate earns its keep in a season and will make new beds look furnished in no time at all.

(Photograph omitted)