Gardening in the 21st century

Nowhere are the effects of soaring temperatures and dwindling water supplies more obvious than in our gardens. Are we just going to have to watch them dry up and die? Or will we adapt to Mediterranean conditions? Anna Pavord explains how much the green-fingered can gain from some blue-sky thinking

Gardeners (and there are 27 million of us in the UK) have a vested interest in our climate, and vivid memories of the cataclysms that have been unleashed on our beloved gardens. In the 1960s, millions of supposedly hardy plants died in the savage winter of 1962-3. The 1970s were marked by the extraordinary drought of 1976, when plantsmen bailed out their weekly bath water to save rare rhododendrons. In the 1980s we had the great gale that felled an estimated 15 million trees in southern Britain alone.

Those of us in the West Country, which had escaped the worst effects of the 1987 storm, had our own replay in 1990. I remember roaring encouragement to the great beech trees in our garden, a lunatic, powerless figure wearing the tin hat my father had as an ARP warden in the last war, shouting at them to hang on. Why the hat? Because flying slates and bits of our neighbour's greenhouse were skimming through the air like slingshot.

In 2000 and 2001, the threat was not drought, but flooding. Rivers could no longer contain prolonged and torrential rain, burst their banks and stormed through homes, leaving gardens buried under sludge and mud.

These events are unsettling and always have been. Gilbert White, the great 18th-century naturalist of Selborne in Hampshire, wrote of the "amazing and portentous" summer of 1783, a season of "horrible phaenomena" such as meteors, thunderstorms, and a weird smoky fog that lasted from 23 June to 20 July.

"The sun, at noon," he wrote, "looked as blank as a clouded moon... but was particularly lurid and blood-coloured at rising and setting. All the time the heat was so intense that butchers' meat could hardly be eaten on the day after it was killed; and the flies swarmed so in the lanes and hedges that they rendered the horses half frantic." In the following summer, Selborne was hit by hailstones three inches across which broke the windows of White's house as well as all the glass in his cold frames. They were followed by floods so violent that the lane to Alton was blocked by falling rocks, some of them weighing two tons apiece.

These events, though recurrent, will always be seen as extraordinary and memorable. More insidious are slow changes to climate. The central England temperature record, which collates information from several sites in Britain (some records date back to 1659), shows that the average temperature in central England rose by 0.7C between 1750 (which marks the beginning of the Industrial Revolution in this country) and 1900. It went up by another 1C in the 20th century; two-thirds of that rise happening from the 1970s onwards. Five of the six warmest years since 1659 have been 1989, 1990, 1995, 1997 and 1999.

As temperatures have gone up, so frosts have decreased. Gardeners of the 1880s could expect at least 55 frosty days in their gardens in central England. A hundred years later, there were just 35. So are we going to see olive groves in Oxfordshire, peaches in Peebles? Will the plants of Tresco in the Scilly Isles (already blooming happily in the gardens of Tunbridge Wells), charge on up to Teeside? Much depends which climate scenario you fancy. UKCIP (the UK Climate Impacts Programme, funded by Defra and based at Oxford University) has developed four climate models. In the worst-case scenario, temperatures increase by 2-3C in winter and 2.5-5C in summer and rainfall decreases by up to 10 per cent. Levels of CO ₂ are already rising at a rate of 1 per cent per year.

As always, these scenarios put us at the centre of the picture. Because we depend on oxygen to survive, we see an increase in carbon dioxide as a threatening prospect. Plants have an alternative view. They thrive on the stuff. Photosynthesis - the process that drives plant growth - depends on a fusion of carbon dioxide, which the leaves absorb from the atmosphere, and water-borne nutrients, which the roots gather from the soil. Sunlight provides the energy and we benefit from the oxygen that the plant releases as a waste product. But the whole process is carefully weighed against temperature and day length. Some plants, such as garlic, will never continue to grow after the longest day, no matter how warm the summers become, or how extended the growing season. Their clocks are set and regulated by a particular gene, and at a certain point, they stop ticking.

But commercial growers have known for years that if they increase the levels of carbon dioxide in their greenhouses, they will get better crops of some flowers and vegetables. Doubling the CO ₂ can increase carrot yields by 50 per cent, provided they have everything else they need. Under this regime, roses bear more buds than normal and bloom earlier. A Forestry Commission bulletin suggested recently that tree growth in the UK may increase by 40 per cent as extra CO ₂ in the atmosphere allows trees to photosynthesise more efficiently.

But only if, and it's a big if, they have enough to drink. That is, in large part, our responsibility. We are shockingly selfish in our use of water - topping-up water features and swimming pools, watering lawns (which they very rarely need), showering twice a day, turning on the washing machine for a single shirt. Consider the poor trees. As the water table drops, their roots can't find what they absolutely must have. Being tuned in to their environment in a way that we are not, they desperately try to cut consumption, drop all their leaves and stand stark naked in August, as they did in the summer of 1976.

Provided there is sufficient water for them to draw on, a 1C increase in the mean temperature will also suit many plants. It gives them a longer growing season: as much as three weeks in the South-east, 10 days in the cooler North-west. Since the mid-1960s, Mary Manning has been recording the first flowering date of plants in her garden in East Anglia. Forty years ago, aconite flowered around 11 January, hazel around 3 February. Now, both tend to flower in mid-December. But for most gardeners, this season has been different: a long, cold haul through February and March has set flowering clocks back to a more normal pattern.

If the UKCIP models are accurate, wine-growers at least will have something to celebrate. Buds will burst from the vines a couple of weeks earlier than they do at present, giving growers a better chance of ripening their crops in autumn. But I'm not expecting us to produce our own chablis or press extra virgin oil from our own olive groves.

It's not that olive trees can't grow in this country; they can and do. Reads Nursery in Loddon, Norfolk, sells a couple of hundred of them every year. In the Chelsea Physic Garden, London, there's an olive tree that is already 30ft across, probably planted sometime in the 1880s. But the garden is very sheltered, and the tree is tucked away in the warmest place by the glasshouses, on very well-drained, sandy soil.

London, though, is a heat island, wrapped in wasted central heating and car fumes, insulated by heat-absorbing tarmac and concrete. The temperatures there bear little relation to what's going on in the rest of the country. Gardeners in Sussex may be shivering in a climate 13C lower than that in Notting Hill.

Then there's the critical question of winter wet. Mediterranean plants die here, not because they are cold (so is France, away from the coast) but because they are wet at the roots. They rot, rather than freeze. All the UKCIP scenarios predict wetter, even if warmer, winters. Only on well-drained soil, such as the gardeners have at the Chelsea Physic Garden, do tender Mediterranean plants have a chance of surviving.

Gardeners in this country now have access to about 70,000 different kinds of plants (our native flora numbers a measly 1,500 species), but growing exotics is not a new thing. Lord Burghley, Queen Elizabeth I's chancellor, was at it way back in 1561. "If the prise be not too much," he wrote to Thomas Windebank in Paris, "I pray you procure for me a Lemon, a Pomegranate and a myrtle tree."

A hundred years later, the diarist Samuel Pepys went off to see oranges growing in Hackney. He ate one while the gardener wasn't looking. That was in 1666, two years before the coldest period ever recorded in England. Then, for 21 years, frosts came in August, and winters lasted for eight months. In the winter of 1683-4, the river Thames was frozen solid from November until April. That year, the diarist John Evelyn noted that there had been severe damage to "sipris" (cypress) trees.

Despite a trend towards global warming, there will still be sudden frosts in this country which will have a devastating effect on tender plants such as trendy tree ferns and bananas. On two successive nights in the 1990s, the gardeners at Crathes Castle in Scotland recorded temperatures of minus 22C, which caused the worst damage in living memory to the plants growing in the sheltered walled garden there.

And Mike Nelhams, head gardener at the famous garden on the island of Tresco, will never forget the destruction caused by the January frosts of 1987, when 80 per cent of his rare plants were killed. Tresco, until then a frost-free paradise of tropical, Mediterranean and Australasian plants, was hit by temperatures of minus 25C. Even long-established plants, such as the Norfolk island pines 80ft high, were massacred. Just one blip like that, even if it runs counter to a well-established trend, can mean death for marginal plants.

Self-preservation, not altruism, is at the centre of our concerns about global warming. Plants are exquisitely adaptive creatures, and will survive things that we cannot. Largely they are destroyed, not by climate change but by human greed. When we have gone they can once again get on with what they were doing for a hundred million years, before we ever arrived on the scene.

For a comprehensive survey, read Gardening in the Global Greenhouse, which documents the likely impact of climate change on gardens in the UK by Richard Bisgrove and Paul Hadley of the School of Plant Sciences at the University of Reading. It is available free from UKCIP, Union House, 12-16 St Michael's St, Oxford OX1 2DU (01865 432 076)

Dig it: 20 great exotic plants, fruits and flowers to grow

Chosen by the Royal Botanic Garden, Edinburgh

Here are 20 exotic non-native plants that can now be grown more easily outdoors in the UK. They are all subject to local conditions, and, as a rule of thumb, the further north we travel the more challenging it is to find success with many of them. In general, this selection prefers warm, sheltered areas in fertile soil, with a fair degree of sunshine and good drainage.

Anyone who decides they want to grow these plants would be well advised to take a few cuttings - or divide and separate - in the summer or late autumn and over winter keep the young plants in a greenhouse or conservatory, where it is warm, so all need not be lost if the garden plant does not survive the winter months.

This is not a definitive list of what to put in your garden. These are suggestions for gardeners interested in experimenting with new plants. Remember, for example, the variety on offer from plant families: other species and varieties of the same genus may be better suited to individual garden environments. Some of those mentioned are considered by many to require heated glass. However, in milder regions, particularly in southern Britain and coastal areas, gardeners should be willing to try new challenges.

Climate change offers the opportunity to experiment with new plants which, until recently, we would not have expected to see growing outdoors in the British Isles. Gardening should always be regarded as something of an adventure and this is particularly true when working with tender exotics.

All the plants below are available from suppliers in the British Isles. More information can be found in the Royal Horticultural Society (RHS) Plantfinder - www.rhs.org.uk . Those marked AGM have received and Award of Garden Merit from the RHS.

1 Olive tree

Olea europaea (AGM)

What is it?

The olive is native to the Mediterranean. It may have been grown in Crete as long ago as 3500BC. At the ancient Olympic Games, winners received an olive branch. Olive oil is still used for medical and religious purposes and has been proved to be good for health.

What conditions does it need?

The olive requires a long, hot growing season to ripen the fruit. The tree can withstand temperatures down to about minus 5C.

When and where in my garden should I plant it?

The olive is an evergreen tree that can grow to be 10m tall, with a sizeable root spread. Some can live as long as 500 years. Plant olives in a sunny area of your garden or in a large container.

How do I look after it?

Olive trees can thrive on well-drained soil up to pH8.5 and are tolerant of mild saline conditions. Deep watering once a month should normally be enough.

How long before I am pressing my own olive oil?

It could fruit well after a period of about 15 years.

2 Banana

Musa basjoo

What is it?

The banana hails from Asia and produces pale-yellow or cream flowers in summer.

What conditions does it need?

It can be grown in all but the coldest upland regions, if it is given winter protection. Well-drained soil with high organic content is ideal. Regular watering is essential and a liquid feed is needed every week during the growing season.

When and where in my garden do I plant it?

Plant it in the sunniest spot available.

How do I look after it?

The plantwill even grow from below the ground each year if the trunk is protected with straw and a plastic wrap during the winter.

How long before I am eating bananas?

Small bananas will grow, but these are unpalatable. This is more of an architectural plant.

3 Kiwi fruit

Actinidia deliciosa 'Hayward', or the self-fertile 'Blake'.

What is it?

Native to China, it is also called the Chinese gooseberry. The name " kiwi fruit" was coined by growers in New Zealand.

What conditions does it need?

As sunny a position as possible.

When and where in my garden do I plant it?

Sow seeds in containers under glass in autumn or spring. Plant in rich compost on a south-facing wall. It is an energetic climber and can be trained.

How do I look after it?

The kiwi can withstand low temperatures, although it will not prosper in late spring frosts. Old wood should be pruned when buds appear. At home in well-drained, deep, fertile soil and should be watered well in the summer.

How long before I have fruit?

The kiwi can fruit in the UK, but it needs a warm summer.

4 Tea

Camellia sinensis

What is it?

The plant behind your daily cuppa, but it is difficult to obtain and challenging to grow. What's more, a huge selection of other camellia species is available in the British Isles. Camellia tsaii, for example, is very similar and holds an AGM.

What conditions does it need?

Moist, acidic soils that are rich in organic matter.

When and where in my garden do I plant it?

This is well suited as a border plant. It will not thrive if the soil is too alkaline. Can also be grown in containers. Do not plant too deep.

How do I look after it?

The plant should be watered well in summer. Protect in periods of hard frost and when growth starts in spring.

How long before I am drinking my own tea?

Probably a long time, if ever. But you will enjoy the blooms.

5 Oleander

Nerium oleander

What is it?

This evergreen is found from the Mediterranean to China. Flowers range from red to lilac, pink, apricot and white.

What conditions does it need?

A hot, dry site with free-draining soil.

When and where in my garden do I plant it?

You can plant oleander as an informal hedge or as a specimen plant on a patio.

How do I look after it?

It stands heat and drought but is poisonous.

6 Echeveria

Echeveria gibbiflora "Metallica"

What is it?

A Mexican cactus with rounded, metallic leaves that are usually purplish-pink.

What conditions does it need?

Plant where it can benefit from the sun. Apply gritty free-draining compost.

When and where do I plant it?

Compact species can be used as annuals in carpet bedding.

How do I look after it?

Lay pots on their side to prevent them getting too wet in the winter.

7 Gardenia

Gardenia augusta

What is it?

An evergreen shrub that grows and spreads to around two metres. It bears fragrant white to ivory flowers.

What conditions does it need?

It prefers neutral to acid soils, which should be moist but well drained. Feed regularly.

How do I look after it?

Regular watering is required. Prune once flowering has finished - and keep watering even after blooming.

8 Century plant

Agave americana (AGM)

What is it?

The agave will look familiar to anyone who has holidayed on the Mediterranean. Agave americana originates from Mexico and has succulent grey-green leaves that can reach two metres in length.

What conditions does it need?

Grows quite quickly in summer if well watered, and is very heat resistant. But beware; it may take time to recover from frost damage. It prefers slightly acidic soil but can stand poor soil and drought.

When and where in my garden do I plant it?

The agave requires a very well-drained soil and a sunny position, and can make a wonderful focal point as a patio pot-plant. It is possible to grow from seed; sow in a greenhouse or on a warm windowsill in spring. The seed normally germinates in about 12 weeks. When seedlings are big enough to handle, they can be placed in individual pots and nurtured indoors until ready to go outside.

How do I look after it?

Water regularly in summer and apply a low-nitrogen fertiliser. Don't risk painful injuries from the spiny thorns of the agave: wear stout gloves when handling!

9 Mimosa

Acacia dealbata (AGM)

What is it?

This mimosa has fern-like leaves and produces fragrant yellow flowers.

What conditions does it need?

Does well in free-draining soil.

When and where do I plant it?

Use as a wall shrub, south-facing, in moderately fertile, neutral to acid soil.

How do I look after it?

Don't prune too severely. Lag the bottom metre with straw in winter.

10 Grevillea

Grevillea 'Canberra Gem' (AGM) or Grevillea robusta (AGM)

What is it?

The grevillea is native to Australasia and found in woodland and more open areas. This evergreen has needle-like or, sometimes, broader leaves. The flowers vary in shape and colour - 'Canberra Gem' produces red flowers, while Grevillea robusta (silky oak) offers a show of yellow.

What conditions does it need?

It grows in acid to neutral soil. Some species will tolerate temperatures as low as minus 7C.

Where in my garden do I plant it?

At a sheltered south-facing wall or in a shrub border.

How do I look after it?

Grow it in acid to neutral, moderately fertile soil, in full sun. As this is another plant that can aggravate skin allergies, gloves are advised.

11 Bower plant

Pandorea jasminoides, Pandorea jasminoides 'Rosea Superba' (AGM)

What is it?

A striking climber, with fragrant flowers, originating from Australasia. The Pandorea jasminoides 'Rosea Superba' variety produces large pink tubular flowers with purple-spotted, deep pink throats.

What conditions does it need?

Grow in fertile, moist, but well-drained soil in full sun.

When and where in my garden do I plant it?

Grow this vigorous climber against a south-facing wall - or consider a pergola.

How do I look after it?

Described as "frost tender" but may be fine down to 0C - mulch in the winter to protect the base of the plant. Feed well after the last frost to encourage new growth. During the growing period, water moderately and feed monthly.

12 Rose of China

Hibiscus rosa-sinensis 'Cooperi'

What is it?

Part of a large family of plants to be found in tropical and sub-tropical regions, Hibiscus rosa-sinesis flowers in a variety of colours. The 'Cooperi' is a compact variety with marbled green and white - sometimes tinged with pink - leaves and red flowers. It can grow to around 2m in height.

What conditions does it need?

Humus-rich, moist, well-drained soil. Needs a long summer to be seen at its best.

When and where in my garden do I plant it?

A good border plant, the hibiscus is also well suited to a container.

How do I look after it?

In frost-prone areas, bring inside to overwinter.

13 Angels' trumpets

Brugmansia x candida 'Grand Marnier' (AGM)

What is it?

This garden hybrid produces apricot-coloured trumpet-shaped flowers.

What conditions does it need?

Grow in as sunny an area as possible. Prefers fertile, moist, free-draining soil, mulch over winter and feed heavily in the spring to encourage new growth.

When and where in my garden do I plant it?

In borders or pots.

How do I look after it?

Keep your children away from it - it's highly toxic if ingested.

14 Begonia

Begonia sutherlandii (AGM)

What is it?

It's tuberous, single-flowered and from Southern Africa. Its leaves often havered veins.

What conditions does it need?

Prefers full shade to partial shade or partial sun; soil should be moist.

When and where do I plant it?

Does well in borders andwindow boxes.

How do I look after it?

Free-draining soil in the sun, tolerates light shade. Don't over-water. Feed in summer.

15 Bougainvillea

Bougainvillea glabra (AGM)

What is it?

A colourful tropical plant with white to magenta flowers.

What conditions does it need?

Fertile well-drained soil in the sun.

When and where in my garden do I plant it?

Plant by a south-facing wall - or consider a pergola. Can also be planted in a pot.

How do I look after it?

Be careful not to over-water. Ensure that it is dry in the winter, and feed in the spring.

16 Queen's tears

Billbergia nutans

What is it?

An epiphytic bromeliad, also known as the "Friendship Plant".

What conditions does it need?

It will tolerate frost to minus 5C.

When and where do I plant it?

It grows on other plants, without feeding from them, or can be planted in humus-rich soil close to water.

How do I look after it?

Cover with straw in winter in colder regions.

17 Zantedeschia

Zantedeschia elliottiana

What is it?

A moisture-loving plant, suited to pond margins or pots.

What conditions does it need?

Requires fertile, well-drained soil and is hardy to minus 5C. Plant in acidic soil that is moist.

When and where in my garden do I plant it?

Will overwinter in sheltered sunny sites, particularly against a wall.

How do I look after it?

Mulch in winter with compost, and feed well in spring to encourage new growth. Or lift the tubers and store dry over winter and replant in the spring.

18 Clivia

Clivia miniata (AGM)

What is it?

A magnificent South African plant with yellow, red or orange flowers.

What conditions does it need?

Hardy to 0C if dry.

When and where do I plant it?

Best grown in a pot and taken inside in winter. In hot climates it will grow in a border. Acid soil; very forgiving of neglect.

How do I look after it?

Water regularly; can withstand drought.

19 Mother-of-pearl plant

Graptopetalum paraguayense

What is it?

A silvery succulent originating from Mexico and the south-west of the USA. A clump-forming perennial, it flowers in the late winter and early spring.

What conditions does it need?

Moderately free-draining soil.

Where in my garden do I plant it?

Try planting it in a crevice of a wall so that the rosette grows vertically and tight to the wall, shedding the rain and avoiding rotting during the winter.

How do I look after it?

To keep it dry in the winter, cover with half of a plastic bottle.

20 Chinese lantern

Ziziphus jujube

What is it?

Jujube is known as being both a delicious edible fruit and a Chinese herbal remedy.

What conditions does it need?

This plant can grow in light, medium and heavy soils, but it does need good drainage to thrive and will not grow if it is placed anywhere that is in the shade. It can tolerate both times of low rainfall and temperatures as low as minus 5C, if the soil is very free-draining.

When and where in my garden do I plant it?

Suitable as a free-standing plant or as a wall shrub.

How do I look after it?

Remove winter damage in the spring.