Club Tropicana

Climate change is already affecting British gardens: the growing season is a month longer than it was a hundred years ago. So, with rising temperatures, drier summers and fewer frosts, what can we expect? Kim Wilde on the exotic plants that are set to change our landscape.

The earth’s climate is changing. And the warming observed over the past 50 years, most scientists agree, is largely due to increased greenhouse gases (carbon dioxide being the main one) in the atmosphere. The primary culprit is human activity: the burning of fossil fuels and deforestation. But climate change has occurred many times during the earth’s history. Indeed, the current phase is part of a gradual warming that has been going on for 150 years. What is so alarming is the speed at which it is happening. The average temperature in Britain is increasing so fast that, in climate terms, gardens are moving south at the rate of 12 metres a day. A study by the UK Climate Impacts Programme, involving the Royal Horticultural Society (RHS) and the National Trust, predicts that, by 2080, the average annual temperature in the UK could increase by between 2C and 4.5C, resulting in waterlogged winters and summer droughts.

Weather patterns are likely to become more erratic: more bouts of torrential rain, temperature extremes and storms. Snow will become so rare that Christmas card companies will have to rethink their festive themes. Even in the Scottish Highlands, snowfall will decrease by as much as 60% over the next 80 years. There will be a significant increase in pests and diseases due to mild weather and reduced frosts.

This may appear to conflict with the widespread snowfall and Siberian winds of the winter just gone. But it doesn’t. “You will still get natural variations on a year-to-year basis,” says a spokesman at the meteorological office. “Climate change projections are for the next 100 years, but we are seeing global warming now. When you look at the records of the growing season compared with 100 years ago, it’s now a month longer. Changes in rainfall are visible, too, but there is natural variability and that tends to confuse the issue.”

Climate change will have a major impact on the way we design gardens: milder winters will allow a greater range of tender species to be grown outside, such as citrus fruits, bananas and bougainvillea. But lawns and traditional herbaceous borders will struggle in drought conditions. Indeed, Andrew Colquhoun, head of the RHS, advises gardeners in the south of England to give up on lawns altogether. Plants that love cool weather, such as snowdrops, rhododendron and many conifers, will suffer. But plant growth, which depends on carbon dioxide (for photosynthesis), will increase by as much as 50%, leading to the production of more flowers and fruit.

For gardeners, then, there is as much good news as bad. The way we could benefit from the potentially devastating effects of global warming reminds me of a tactless joke: a doctor asks his patient if he wants the good news or the bad news. “Give me the bad news,” says the patient. “We have to amputate your feet,” says the doctor. “What’s the good news?” asks the patient. “The guy in the next bed wants to buy your slippers.”

So, it’s goodbye to England’s green and pleasant land, and hello Chteau Kilmarnock. Here are the plants you can expect to see more of on our new, balmy isle. Most of them (bar the banana) can already be grown successfully in most parts of the country, given a sunny, sheltered spot.

Salvia uliginosa (bog sage)
This tall herbaceous perennial will grow up to 2m. It originates from South America and has loose spires of azure flowers from late summer to autumn. It needs moist but well-drained, fertile soil, a sunny, sheltered position, and may survive the winter outside in milder areas. Protect underground shoots in winter with a light mulch. It has survived without protection in recent years at Cragside, Northumberland.

Phoenix canariensis (Canary Island date palm)
A tropical, evergreen giant with trunk patterned by old leaf scars. It can reach 18m and has leaves that grow up to 5m long on mature plants. Large, pendant sprays of tiny yellowish flowers may be produced in summer, and small yellowish fruits on mature plants in autumn and winter. It can either be grown in a container or planted out in fertile, moist, well-drained soil. This palm prefers full sun and protection from cold winds, though it can withstand wind in milder coastal areas. Protect young plants from collecting water at their centre by wrapping up the leaves with raffia or string in winter. Protect from frost by wrapping in several layers of horticultural fleece or sacking.

Agave americana (century plant)
Viciously toothed, with sharp needle-like tips and rigid, grey-green, fleshy leaves, Agave americana is not a plant you want in the garden if children are around.

Native to North America, it can grow up to 3m high in the wild, reaching 2m here if grown outside and happy. Agaves don’t like cold, damp winters, and if water gets into the crown and freezes, the plant will become mushy and die. Plant at an angle so water can more easily drain away. Agaves need perfect drainage and good air movement. Grow in well-drained, sandy soil in full sun, and protect in winter by covering in plastic or with an umbrella, ensuring ventilation is good. Alternatively, grow in pots and overwinter in a dry, frost-free place.

Its common name, century plant, refers to its habit of flowering once every 100 years, after which the plant begins to die and a profusion of juvenile plants form at its base. Don’t worry, though: it’s unlikely to flower in this country.

An alternative is Agave salmiana var.ferox which is much greener, and more tolerant of the wet.

Olea europaea (olive)
This evergreen tree has narrow grey-green foliage, rough grey bark and an extremely elegant habit. It is hardy from London southwards, or in any warm microclimate in a sunny position. In the UK, it usually flowers between late May and mid-July, and the varieties recommended below will produce a surprisingly large amount of olives from late October to early December. They are tolerant of poor soil and will do well in a coastal garden, producing best results in a sunny, shelteredspot with fairly fertile, free-draining soil.

Olives also do well in containers; use a soil-based compost (such as John Innes No 3), incorporating plenty of grit. Use a general-purpose liquid feed in early spring and again in midsummer. Olive trees will tolerate cold and frost, but not prolonged winter wet. Protect container-grown plants by ensuring sharp drainage, cover the base of containers with a double layer of bubblewrap to protect from hard frost, and mulch with some large cobbles to keep off the worst of the winter rain. Olives are best pruned in late spring and early summer.

The varieties recommended for the UK, ‘Leccino’ (‘Leccio’) and ‘Frantoio’, are typical of northern Tuscany, and are selected for their tolerance of cold. These are black olives – green olives tend to be less suitable since they are of southern Mediterranean and north African origin.

Hedychium (ginger lilies)
Ginger lilies are an ideal choice for those wanting a tropical look. These rhizomatous perennials come in an array of sizes and habits with white, yellow, orange or red flowers, which are often fragrant. Plants should be grown in moist but free-draining soil, in sun or partial shade. As gingers are heavy feeders, well-rotted manure and liquid feeds should be added through the growing season. Mulch with straw or chipped bark in winter. Hedychium gardnerianum is one of the tallest gingers (2m), with deliciously scented, bright yellow flowers and orange stamens in late summer. Also recommended for the UK: H. coccineum ‘Tara’ (bright orange flowers) and H. densiflorum .

Melianthus major (honey bush)
This plant has fabulous grey-green to bright blue-green foliage on thick stems, and smells of peanuts. It comes from South Africa, so is not reliably hardy in the coldest counties. Treat this evergreen shrub as herbaceous, cutting it right back at the end of winter. It tolerates coastal sites, but needs protection from cold, drying winds and winter wet. Grow in a warm position in well-drained soil, and mulch lightly in winter. Use a soil-based compost if growing in a container, and expect it to reach a height of 1.2m, though in the ground it can reach 2.4m x 2m.

Musa basjoo (banana)
The dramatic, arching leaves of these tropical plants have been seen in Cornish gardens for more than a century, and can reach 6m or more. The plant is best grown in sunny, sheltered positions to prevent the wind from shredding its fragile foliage. Leaves are blackened by the first hard frost, but the rootstock seems hardy in much of the UK, even without protection. Stems, however, will need some looking after in cooler climates – in autumn, cut the leaves off and place a wide drainpipe over the stem, then fill it with straw and place a tile on top. It is not self-fertile, so two plants would be needed for cross-pollination if you want any chance of bananas. Plant in any soil, in sun or shade, adding plenty of organic matter, and use high-nitrogen feeds.

Ficus carica (fig)
The best variety of fig to grow in the UK is ‘Brown Turkey’, which produces a heavy crop of large, pear-shaped, dark purple-skinned fruit that are very sweet and succulent. To grow figs outside, plant in early spring against a south-facing wall and train as a fan.

Their strong roots will need confining, as they are capable of destroying underground pipes and foundations, and the plant will grow bigger and bigger at the expense of fruit. Confine your fig by making a “wall” around the roots consisting of four upended paving stones, no smaller than 45cm. Each should sit just higher than the surface of the soil. Put a 20cm layer of tightly packed broken bricks at the base for drainage, or plant in a large tub that can be sunk into the earth up to its rim. Figs are also ideal for containers on a patio or terrace (use John Innes No 3). Repot every autumn and overwinter in the shed.

All cultivated varieties are self-pollinating, so you need buy only one plant to ensure fruit. During the growing season, watering is essential. In spring, apply a light organic dressing of Growmore and spread an organic mulch over the soil surface. In June, encourage more fruit by pinching out young shoots so that only five leaves remain. Also recommended for the UK is ‘White Marseilles’

Winners and losers in climate change

On the way in
  • Protea This half-hardy plant needs a sheltered spot. Already grown in the West Country, Channel Islands and south-west Scotland.
  • Kiwi fruit ( Actinidia deliciosa ) Sun-loving species such as this, apricots, citrus fruits and pomegranate, will flourish as our climate warms up.
  • Red passionflower ( Passiflora racemosa ) P. caerulea and P.c. ‘Constance Elliott’ are currently the only reliably hardy passionflowers in this country.
  • Italian cypress ( Cupressus sempervirens ) Mediterranean plants such as these, able to withstand summer drought, might be better for hedges than native English plants.
  • Silver wattle ( Acacia dealbata ) Particularly tolerant of drought conditions.
  • Grape ( Vitis ) Grape cultivation could extend as far north as Scotland during the second half of the 21st century.
On the way out
  • Fescue grasses(currently used for lawns). This standard feature of the English garden will die off in summer and need mowing throughout winter.
  • Primula These cool-loving plants will struggle in the south.
  • Snowdrops ( Galanthus nivalis ). These classic late winter bulbs need the cold to trigger growth.
  • Delphinium and lupins Will be confined to the north and west of England.
  • Beech ( Fagus sylvatica ) Shallow-rooted beech is dying due to summer drought.
  • Fruiting trees and bushes such as cherry and blackcurrant, which need cold for formation of buds, will suffer. Commercially grown fruit in East Anglia is already being affected.