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Modern gardening with a tropical twist

The Walled Garden at Wisley. Credit: Clay Perry

Jim Gardiner, Curator of RHS Garden Wisley, reports below on sub-tropical survivors for permanent planting.

Meteorological records have been kept at RHS Garden Wisley since 1904 and show that temperatures vary between 30ºC (86ºF) and -10ºC (14ºF). The hottest day on record saw temperatures of 35.4ºC (96ºF) in August 1990. In January 1981 -15ºC (5ºF) was recorded, the coldest on record. June and July are the sunniest months, with an average of 199 hours of sunshine. An all time high of 294 hours was recorded in June 1997, with 227 hours during June 2001. The long term average rainfall is 652mm (26in) per year, though in 2000 it was 958.9mm (38in).

Walled Garden (west)

The 3m (10ft) high walls that enclose the Walled Garden (west), create a microclimate enabling tender and subtropical plants to survive year round outside. Over 30 percent of the permanent plants are tender e.g. palms (including Brahea armata), ferns (including Dicksonia antarctica) and bananas (including the half-hardy Musa basjoo).

Redesigned and planted in 2001, with the support of Witan Investment plc, this garden illustrates how to mix hardy and tender plants from around the world in a modern setting. All plants are left out over winter although some of the more tender exotics, such as bananas, are carefully wrapped to shield them from the worst of the weather and excessive winter wet.

Selected plant list

Canna ‘Rosemond Coles’
Cordyline australis ‘Red Robin’
Cordyline australis ‘Torbay Green’
Cordyline indivisa
Dicksonia antarctica
Dregea sinensis
Eryngium pandanifolium
Erythrina crista-galli
Ficus carica
Lomatia ferruginea
Musa basjoo
Mutisia ilicifolia
Phormium tenax
‘Yellow Wave’
Solanum laciniatum
Tetrapanax papyrifera
Trachycarpus fortunei

Find out more about Wisley

Bananas

One of the hardiest species to grow outside is Musa basjoo but other bananas also have potential, e.g. Musa sikkimensis and Musa lasiocarpa.

Small plants can be brought inside and overwintered in a conservatory or frost-free glasshouse, but larger plants will need to be protected in situ.

Form a cage of chicken wire around the stem and pack with dry straw. Top with a cap of polystyrene to keep rain out of the crown. Finally, wrap with fleece to keep out the wind. Unwrap plants by May.

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Tree ferns

Hardiness increases with age so young tree ferns are more vulnerable to cold. To be safe, they should be overwintered in a frost-free glasshouse.

Most of the plant’s roots are concentrated in the trunk which should be kept moist. Keep the growing point frost-free – fronds can be sacrificed.

In mild winters plants can survive outdoors with little protection. As a minimum, pack the crown with straw and cap with polystyrene. Remove after the last frosts. In colder winters also wrap the trunk with fleece and mulch the roots.