Country & Garden: It's good to know there's something you can rely on

IF THERE is one feature of a plant which we gardeners like more than another, it is the propensity to flower for months on end. We will forgive a plant a lot if it is prepared to oblige us in this way. It is so much easier to paint convincing garden pictures if there is a plant that can anchor a scheme, acting, as it were, as a rock in a stream of ever-changing, swirling colour.

Late April or early May, depending on the season, sees the first unfolding of the flowers of the shrubby potentillas (mostly varieties of Potentilla fruticosa): these are plants with the capacity to flower for almost half the year, without fail and regardless of weather conditions or circumstances. That is some achievement.

Potentillas are closely related to species roses, and have similar single, five-petalled, saucer-shaped flowers, measuring up to 4cm across and ranging in colour (depending on variety) from pure, chilly white through all the yellows and orange, to deep scarlet. Whatever the colour of the petals, all these flowers have yellow bosses of stamens. The flowers are held above small, palmate leaves, consisting of five narrow leaflets, not unlike little hairy fingers. The plants are usually rounded shrubs, clothed to the ground, and excellent weed-smotherers.

If the shrubby potentilla combines so many virtues, why is it that one hesitates for a nanosecond before filling the garden borders with these amenable plants? Surely only a deep-seated wilfulness or ingratitude could stay one's hand?

I am perfectly willing to plead to wilfulness, but I do still have a reservation (well, two in fact) about potentillas. Neither is so serious as to make me banish them from the garden, but both encourage me to take care how I place them.

The first reservation is that the potentilla has a prim habit, as if it had never been able to bring itself to kick over the traces. It is so blooming well-behaved, it's unreal. It never sends out an inconvenient shoot, or dies off unexpectedly, or looks anything but completely in control. It is a plant that lives within its limitations, never apparently yearning to be variegated in leaf, or double in flower. The only adventurous aspect to it is the way it will occasionally produce a seedling with a differently coloured flower, causing sharp-eyed nurserymen to pounce on it, name it, and send it out into the world to general acclaim.

The second slight misgiving I have is that, over the years, a number of seedlings have been raised which have orange or scarlet flowers. The most famous is probably "Red Ace", but there are also varieties with names such as "Tangerine", "Sunset" and "Royal Flush". These are fine plants in their way, but put them into a sunny spot and their petals will fade in colour as surely as if they were curtains hanging in a south-facing window. Yet, if you plant these in a shaded position, the flowers will be much less abundantly borne, and a sparsely flowering bush of a plant that does not anyway bear flowers densely, is hardly a heart-warming sight.

I have come to the conclusion that the solution is to plant these shrubs in very light dappled shade, such as that cast by a birch tree, like the cut-leaved Betula pendula "Laciniata", so that some of the worst glare of the sun is mitigated but there is still plenty of light filtering through.

Although it does not worry me, not everyone is enamoured of the rather domey habit of these shrubs, either. If that is the case, plant them in front of more informally shaped shrubs which have similar, smallish leaves, so that the specific habit of the potentilla is lost, rather than accentuated. Suitable shrubs might be daphnes, genistas and most cytisus.

Having said all this, I admit that there are one or two truly first-rate potentillas which I would genuinely recommend to anyone. The first is "Primrose Beauty" which combines intensely hairy, silver-green leaves with pale, clean, lemon yellow flowers. The combination is a winning one in a sunny place, among artemisias, dianthus, santolinas and the like. And, for a more dwarf plant to go in an alpine bed or rocky outcrop, I suggest "Princess", which has pale pink flowers and a more ground-hugging inclination.

I THOUGHT Independent readers would be interested to know (and I am sure that she won't tell you) that Anna Pavord won the Walter Blom Trophy at the Royal Horticultural Society's Westminster Show on 27 April. This trophy is awarded to the winner of the class for a vase of nine tulip blooms, in this case "Prinses Irene". Which shows that she can grow them, as well as write about them.