How to rescue a rockery

"Our rockery is a large, arc-shaped arrangement, 24 paces long and about 6ft wide, humped up in the middle to between 2ft and 4ft high. It is made with largish chunks of sandstone rock and we think it was built at the same time as the house (1904 Edwardian semi). It must, anyway, be at least 70 years old. It forms a barrier between the front path and the gate, and the rest of the front garden. The whole front garden adjoins our neighbour's. There is no wall or fence, just a joint flower bed with some rather limp rosest, but the rockery curves round to complete a semicircle in our neighbour's garden.

We get a lot of rain. We are on the 500ft contour. The prevailing wind is from the south west and it is not without reason that Burnley has a wind farm. The rockery, being humped up, faces all ways, and the slugs hunt in packs.

Over the years we have tried some replanting, but the rockery is undermined by moles, all the bulbs are eaten by mice and our attempts to brighten things up have failed. We have aubrieta, saxifrage and lungwort, but after spring everything reverts to green.

We would like to extend the flowering season, brighten the rockery and restore it to its former glory, but we don't know where to start or what to plant. Anything that isn't rampant seems to fail. We get quite despondent."

Keith and Judith Hartley's Edwardian semi faces out over the sweeping slopes of Queen's Park in Burnley, Lancashire. It's a splendidly civic part of town: hefty park railings are of green-painted cast iron, with gates bearing brightly painted coats of arms, and the houses down the road were once lived in by the park superintendent, the chief of police and the chief of the fire brigade.

The rockery - the cause of their despair - is the dominant feature of the front garden, common to the two semis, curving in a wide arc to follow the line of the path from the gate to the two front doors. The mirror layout of the front gardens is charming, each of them marked out in the far corner by a huge, sentinel copper beech. The size of the trees suggests that they must have been planted when the gardens were first made.

When the Hartleys moved in, 30 years ago, their neighbours were three spinster sisters, the first owners of the next-door house. They told the Hartleys that Fred Loads, the founder of the BBC's Gardener's Question Time, had had something to do with the rockery. Could he have built it? Possibly, though if he did (he worked for a time in Burnley's Parks Department) the rockery can't be the same age as the houses. Fred Loads was born only the year before they were built.

If he did make it, then the rockery is more likely to date from the Thirties, which would fit with the craze for all things alpine at that time. Or he may have been called in then to refurbish a rockery originally laid out when the house was built. I slightly favour the first theory. The curving shape would have been part of the original layout, but you would expect it to have been, in 1904, a flat bed crammed with bedding plants, planted in formal ribbons with contrasting borders.

The humped shape of the rockery is an advantage, in gardening terms, as it creates two completely different planting areas: one sunny, facing south and west, one chillier and shadier, facing north and east.

But the general effect at present is too homogeneous, and Mrs Hartley's attempts to break up the swathes of saxifrage (a white-flowered, mossy type) and lungwort (not, she says, a particularly exciting one) have failed. The rockery needs defining.

One option she had thought of was to transplant some dwarf conifers growing in tubs in the back garden into the rockery at the front. The conifers include a fine, small pine, Pinus mugo, but I thought they would be better left where they are. In open ground, they would grow faster than they have in their tubs and would soon be out of scale with the relatively narrow contours of the rockery.

More could be made of the rocks, which have become almost completely covered by big mats of saxifrage and alyssum. As Mrs Hartley said in her letter, these were hefty chunks of sandstone, very handsome, and they had gathered some wonderful mosses and lichens. Uncovered a little, they would sing out and mark off various pockets of planting between them.

This done, Mrs Hartley would then have to harden her heart and jettison some plants that she has too much of - and also cut back severely some of those, such as the alyssum, that have become straggly and are overlying their neighbours. When she put in new plants, they should go into bare ground, well forked over, with no other neighbours likely to swamp them in infancy.

Although the humped shape of the rockery would suggest that it has excellent drainage, the Hartleys said that they got lots of rain. I would take the precaution of digging in some extra grit while planting, together with some bonemeal for long-term feeding. Alpine plants wouldn't mind the cold of the 500ft contour. They are used to that. The most important thing is to give them sufficient air space while they are getting established.

What new plants should the Hartleys try? One of their aims is to extend the season of colour on the rockery. Alpine plants, by nature, tend to peak in the spring, and it is always difficult, without introducing bedding plants, to get a rockery to perform throughout July and August. September is not so difficult, because by then you can reach for cyclamen, such as marble-leaved C hederifolium, and colchicums.

I would choose two sets of completely different plants, to reflect the two differing habitats. On the north-east side, the Hartleys could use a collection of small ferns, cyclamen, the marble-leaved arum, A italicum pictum, and small species crocus, such as C tommasinianus (especially `Barr's Purple'). I, too, suffer from mice gobbling my crocus, and find the best way is to plant the corms in 5in pots (they can be planted quite close), then staple Netlon or some such plastic mesh over the top and sink the pot and its contents into the ground. Not too deep, for crocus hate lots of earth on their heads. Then you can leave them to multiply in peace.

It wouldn't be worthwhile, in this situation, to plant tiny alpines, such as the special saxifrages that never get bigger than a 10p piece. They'd get lost in the hurly-burly.

Judith Hartley is a gardener of the most endearing kind, who would manage to smuggle a couple of pots back from a plant sale even if you tied both hands behind her back. But she'd only make herself miserable if she planted her rockery with the the erythroniums and trilliums that she dreams of. They are plants of acid woodland and couldn't be expected to give of their best here, even if they weren't throttled by the alyssum and lungwort.

Other plants to extend the flowering season on the north-east side would be violas such as the superb blue `Ardross Gem' and smudgy mauve `Haslemere'. The slugs would like them, too, and being an organic gardener, Mrs Hartley is loath to use pellets. Crushed eggshell or sharp grit round the plants might provide a little protection. Yellow and orange Welsh poppies (Meconopsis cambrica) should be immune, as would the fine giant purple-leaved bugle. February-flowering Cyclamen coum would give colour early in the year, chequerboard colchicums at the end of the season.

For the sunny side, I would try dianthus (with extra grit), species tulips, dwarf campanulas such as C cochleariifolia (fairy thimbles), diascias, Spanish daisy (Erigeron karvinskianus), sedums, dwarf iris and small aquilegias such as A flabellata.

My way home from the Hartleys led over the tough high moors of the south Pennines. Although the thaw had started, huge snowdrifts mounded up on either side like frozen waves. At the peak of this bleakness a small sign announcing a nursery, Slack Top Alpines, loomed up through the fog. That would be a good place for Mrs Hartley to acquire new plants, I thought. If they can take the vicissitudes of life on Slack Top, they sure as hell can survive anything that Burnley could throw at them.