Gardening: The plants that come in from the cold

From dahlias to geraniums, now is the time to prepare for frost. But which warm-weather plants can you leave to brave the winter outside, and which should you lift and store indoors?

There are still some exquisites who sneer at dahlias, thinking them gross and vulgar. But now that they have appeared in full, shining splendour on the front of the latest edition of the glossy Gardens Illustrated, surely their apotheosis is complete? Like aspidistras and giant marrows, they have a touch of the music hall about them, and even their most ardent devotees have to admit that there are some sulphurously evil yellows among the dahlia tribe. But there are also some gorgeous terracottas, such as the swirling, sunny 'Hamari Gold' and the neat, rich flowers of 'David Howard', set against dark bronze foliage.

I can scarcely remember a year when dahlias have looked better. September, with its still, sunny days, suited them perfectly. There were no high winds to snap them from their supports, no heavy downpours to melt the petals into mush. The beautiful dark-leaved 'Grenadier' is the best thing in our garden at the moment. It has the same foliage as the red-flowered 'Bishop of Llandaff', but the flowers are double, beautifully formed and without the Bishop's distracting eye.

As anyone who listens to Gardener's Question Time knows, there's a splendid mystique attached to dahlias: the disbudding, the lifting, the storing, the dusting with flowers of sulphur. It all sounds so reasonable, but with us the storing tends to be followed by the things GQT doesn't talk about: the shrivelling; the eating by mice. These kinds of problems forced us to reappraise the purist approach, and now we leave the tubers in the ground, well mulched with beech leaves.

There are disasters associated with this course of action, too, but not so many as when we used to lift dahlias. There were some exceptionally cold spells last winter and we lost three plants, including the fine, spiky red cactus dahlia 'Alva's Doris'.

But leaving dahlia tubers in the ground is an option only if you live in the relatively mild south or west of the country. Any day now the dahlia roadshow is going to be brought to an abrupt end by frost. What do you do then if you live in a chilly area?

First, cut down the blackened stems, leaving about 6in intact, and ease the tubers gently out of the soil with a fork. Shake off any soil - lifting is much easier if the soil is relatively dry - and label the tubers as you lift. By next May, when you come to plant, all the tubers will look exactly the same and, without labels, colour co-ordination will be a lottery.

Stand the tubers upside down to drain any moisture away from inside the hollow stems. They should dry off within a fortnight. Then trim off the stems and stack the tubers in wooden apple boxes lined with newspaper. When the box is full, cover the tubers with compost, chipped bark or Vermiculite that you have dampened very slightly. Stack the boxes in a dry, cool and frost-free place. Set mousetraps nearby. I find chocolate a good bait for mice.

Dahlias are not the only plants that, in cold areas, need special treatment to get through the winter. Perennial tropaeolums, nasturtium-flowered climbers such as Tropaeolum tuberosum 'Ken Aslet', also grow from tubers that will rot and melt if they are left in the ground through a severe winter. The tubers are yellow, marbled with purple, much more interesting than a dahlia's.

The trumpet flower is red on the outside, yellow inside, held elegantly on a long stem. The leaves are good, too, greyish-green and lobed. In fact, the only problem with this climber is its tender disposition. But its home is South America - Columbia, Ecuador, Peru - so it is not surprising that it doesn't like our winters.

When frost has knocked back the foliage, cut off the dead stems at the base of the plant, clear them away, and lift the tuber carefully with a fork. Brush off as much soil as you can before drying it off gently in a warm place such as an airing-cupboard. Then clean up the tuber, getting rid of any last bits of soil or dried-off root before storing it in a dry, frost-free place until planting-time next spring.

Geraniums are also now growing in borrowed time, but here you need to act before the first frost, rather than after. Left to themselves in a frost-free situation such as a conservatory, geraniums never become dormant. They just go on growing. If they are growing outside in pots, you have two options: either overwinter the whole plant, or take cuttings and overwinter those rather than the parent. If you've got room you can do both.

If you want to take cuttings, do it before you lift the plants, choosing healthy side shoots and cutting them just above a leaf joint. A cutting about 3in long is ideal. Choose shoots with no flower buds if you can. If you can't, trim off the flower buds along with the lowest leaves. Then trim each cutting to just below a leaf joint and stick all the cuttings round the edge of a 5in pot of compost. Do not cover. Let the pot soak in a saucer of water until the compost is damp but not saturated. Keep the cuttings somewhere light and frost-free over winter.

Keeping the plants themselves is a bulkier business, and the method you use depends on the resources available. If you've got a light porch or conservatory, you can just bring the geraniums in, still in their pots, and overwinter them undisturbed. Cut down on the watering, so that the plants just tick over, otherwise they will get very big and leggy. Take off dead leaves and flower heads which might otherwise turn mouldy.

If you don't have that option, lift the plants before the frost gets them, shake the soil from the roots and cut the stems down to about 4in. Get rid of any leaves that are left on these stems. Then cut back the roots by about a third. Line an apple box with newspaper and half fill it with old compost (the contents of a used Growbag are ideal, if you have one) or coir. Stack the cut-down plants in the box, close but not quite touching. Tip some more compost round them and firm it gently down. Water the compost and leave it to drain, before storing the box somewhere light and frost-free.

When the cut-down plants begin to resprout, you can use the new growth to make more cuttings. Then, when frost-free times begin to loom again over the horizon, you can pot up the plants and give them more encouragement to grow.

But that all seems a very long way away. Meanwhile, I've got another overwintering problem to solve. The front border is edged with clumps of fat, fleshy, succulent echeverias, as big as cabbages. Somehow, I have to ease these out of the ground and get them into pots for the winter, but without breaking any of their juicy, spoon-shaped leaves. And what am I going to do with the baby echeverias that are clustered like bantam chicks under the mother plant's great skirts? Leave them attached, or break them off and pot them up separately? My instinct is to leave them be until spring.

weekend work

Finish planting spring bedding plants such as wallflowers, polyanthus and forget-me-nots. These last make an excellent undercarpet for tulips, especially the dark mahogany 'Abu Hassan' or the lily-flowered 'White Triumphator'. Water the plants in well. September has been very dry in most parts and wallflowers, generally uprooted from open ground for sale, will need help in settling into new quarters.

Clean up the ground between strawberry rows, getting rid of weeds and unwanted plants that have rooted themselves. Mulch between the rows with well-rotted compost or manure. Lilies are best planted in early October as soon as this year's growth has died down. The problem is getting hold of them. It suits suppliers better to dish them out in spring. The martagon lily is a hardy, lime tolerant basal-rooting species that will thrive in sun or shade. Plant the bulbs about four inches deep and nine inches apart on a sprinkle of sharp sand to deter underground slugs.

Mulch in spring with compost or leaf mould. The ordinary martagon has dirty purple flowers with ginger anthers, but there is also a lovely white form. L. pyrenaicum is another basal rooting lily tolerant of lime, with greenish yellow flowers spotted with black.

Gather late ripening apples and pears and store them in a cool, dry place. you can keep them in polythene bags with a few holes. I stick to wooden trays and newspaper.

Think about planting more fruit trees. The best specimens are likely to be grown in the open ground and will be lifted for delivery after leaf fall, usually from the first week in November. Cordon-trained apples are ideal for small gardens and make good screens between one part of the garden and another.

Cut back the dying stems of herbaceous perennials and compost them. Do not cut back penstemons. These should be left until March. Cutting back will encourage young growth which could get clobbered by frost.

cuttings

Derek Longden, of Worthing, writes in response to my piece about places to sit in the garden (Independent, 12 July). "I was dismayed to read you have covered your new sitting-out space with beach pebbles. I believe that the foreshore is owned by the local authority and that therefore it is no more acceptable to collect pebbles for one's terrace than it would be to take plants from the public gardens or to steal books from the library ... On noting your success, readers who may not be fastidious about their sources of supply, will be inspired and encouraged to do similar work on their own property ... I should be glad if you would please warn your readers accordingly."

I am at fault for assuming that readers would not take the phrase "beach pebbles" as literally as Mr Longden. No. I have not been shovelling up the Chesil foreshore. The pebbles were delivered in sacks from our local gravel merchant. The technical description for the stuff we used is 10/6 grade pea gravel, available at pounds 3.65 a 40kg sack.

Zooming up in a lift recently, I met Chris Brickell, editor of Dorling Kindersley's trio of essential reference books, the latest being the fine A-Z Encyclopaedia of Garden Plants (pounds 55). He was off to China, plant-hunting. Plenty of good plants there, he said, that gardeners elsewhere have yet to set eyes on. But it's more of a challenge now to find plants that are both unknown and easy to grow outside their natural habitats. A new book by Brenda McLean, a Fellow at the University of Liverpool, tells the story of an entrepreneur who operated in the golden age of plant collecting: Arthur Bulley (1861-1942) was a Liverpool cotton broker who paid legendary plant-hunters from Sikkim, China and Burma.

Bulley, a philanthropist and active Fabian, established many of these rare plants in his garden on the Wirral, which was always open to the public. Later, he established a nursery to supply as cheaply as possible the plants that he grew in the garden. It is now the University of Liverpool's Botanic Garden.

Bulley, who subscribed to the first Everest expedition, was adept at getting his collectors into the most difficult parts of the world. These included Bhutan, where he sent the young Roland Cooper. Bulley wrote direct to the Maharaja of Bhutan, requesting permission for Cooper to collect in his country, telling him it was "a service to mankind to get the fine things there must be on the Bhutan Himalaya into the gardens of the world". The Maharajah assented and got an Inverness plaid rug for his troubles.

Ms McLean's book, A Pioneering Plantsman, draws on contemporary journals and gives an insight into the great collectors. It is the latest in the series of books on the collectors, spon- sored by the Royal Botanic Gardens, Kew, the Royal Botanic Garden, Edinburgh, and the Stationery Office who publish it, at pounds 29.