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Exotic Foliage Plants in a Cool Climate

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Contents

Introduction

I am fascinated by the idea of growing plants that give the impression of belonging in the tropics, despite our relatively cold climate and (possibly worse for plant survival) damp winters.

Other pages discuss bamboos, palms, plants which look as if they belong in a desert and plants with exotic flowers. This page concentrates on plants whose foliage appears to belong in a tropical jungle, yet are sufficiently hardy to withstand a British winter outdoors.

Exotic looking foliage plants, in my opinion, must have large leaves, preferably but not necessarily glossy. Plants which have large leaves in nearly all cases grow naturally in a woodland environment where they are sheltered from strong winds which would damage the foliage. Many of them are consequently able to withstand a certain amount of shade, but there are exceptions. Some which tolerate shade in their natural environment need full sun in temperate latitudes to compensate for lower overall light levels and lower temperatures. There are a few which can withstand strong winds, fortunately, and can be used to protect the others.

The separate page on my tiniest garden just discusses what I have actually tried and am considering doing. Here I discuss more generally the concepts involved. I will, as far as I can, also discuss some plants that I have tried, heard of or seen, and which seem possibly suitable for the purpose.

Some people reading this page seem (from messages sent to me) to be under the impression that I am growing all these plants. That is not the case. I am actually growing at present only a very small selection, just those described on the page entitled my tiniest garden.

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Ailanthus altissima

The Tree of Heaven can grow to eighty feet high and fifty feet across if allowed to do so, but to get the full exotic effect it is better to treat it as explained for the Paulownia. Its pinnate leaves will then achieve three feet in length each year. It is also deciduous, and is fully hardy.

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Ferula communis

The giant fennel is related to the edible form, but is far larger. The huge finely divided leaves appear in January in Britain, making a total contrast to the solid leaves of most of the other species mentioned. Tallish early bulbs can grow through it at this stage. When several years old in early summer it sends up a ten foot stem with a spreading panicle of yellow-green flowers. Its great disadvantage is that after flowering it dies back completely, leaving a gap for six months (or may die completely), so there is a need for something late developing to be grown close to it to fill the empty space. It is frequently treated as just a foliage plant, in which case it is enhanced by removing the flowering stem as soon as it appears. It likes a fertile, well-drained soil in full sun.

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Gunnera manicata

The "giant rhubarb" is reputed to be the only native Brazilian plant able to survive in the open in Britain. It requires plenty of space, plenty of moisture, plenty of food, protection from strong winds and, in most areas of Britain, a little protection from severe frost by covering the crowns with its own dead leaves plus some bracken or straw in winter. It is possible to stand upright under a single leaf and shelter from the rain - I know this is true because I have done it in a public garden in Devon. Far from glossy, its bright green leaves are extremely coarse and hairy. It will grow 6-10 feet tall or more (that is the length of the leaf stems) and at least as much across. Leaves can be as much as nine feet across, even in Britain. The leaves will grow larger if the strange looking flower spike is removed at an early stage, but some growers prefer to retain it. I have now been growing it for several years, but despite putting it in a boggy area (with pond liner 2-3 feet beneath it) it has remained much smaller than described above (but still impressive and plenty big enough for my small garden). I probably don't give it enough food or water to satisfy it.

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Hosta

Hosta sieboldiana
There is a bewildering variety of hosta species and hybrids available in many different colours and sizes, but I think this one (and its variety "Elegans") is the only widely available one that really deserves a place in the exotic garden. Its leaves are the biggest of any, and their glaucous colour (more pronounced in "Elegans") makes a nice contrast with most of the other plants discussed. The size of the leaves is very dependent on growing conditions. Hostas reputedly need very damp soil, but are in fact surprisingly drought tolerant. However, for the largest leaves it must have ample supplies of both food and water, and a mature plant can then sometimes produce leaves as much as two feet long. With poor conditions they may be well under half that.

Many of the plants discussed here are prone to slug damage, but hostas are well known to be a slug's idea of heaven, so protective measures are essential.

Hosta "Sundance"
This is a new American variety which I have not yet seen. It is said to have leaves at least as large as those of the above.

Hosta "Sum and Substance"
This horribly named variety is another I have not seen. It has similar sized leaves to the others mentioned, in this case yellowish green.

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Mahonia

Mahonia japonica
The mahonias are all evergreen shrubs, the better ones for our purpose all having long pinnate leaves with spiny edged glossy leaflets like large, flattened holly leaves. They also all have yellow flowers, the better one's again having in common that the flowers appear in long racemes in late autumn and winter. This species has leaves up to 18 inches long and 10 inch long fragrant flower racemes. It will grow up to 6 feet tall and 10 feet across.

Mahonia x lindsayae
This species has leaves up to two feet long, with some of the broad leaflets turning red in winter. The lemon yellow flower racemes can be a foot in length. It grows to eight feet high and across. It is a little less hardy than M. japonica.

Mahonia lomarifolia
A more upright shrub than the others, growing to 10 feet high and six across, this is reckoned by many to be the most elegant mahonia. It also has two foot leaves, but the fragrant flower racemes are smaller at eight inches long. It is said to be a little tender, but I have as yet had no problems, leaving it unprotected through several winters. I find its main flowering period is in December, just about sometimes extending to early January. The one problem I have found, which probably applies to all mahonias, is that when weeding nearby the fallen leaves remind me they have extremely sharp spines!

Mahonia x media
This cross between M. japonica and M. lomarifolia has leaves to 18 inches long and flower racemes of 10-14 inches. It will grow 15 feet high and 12 across. There are many varieties of this species. "Lionel Fortescue" is notable for having 16 inch upright racemes of flowers.

Mahonia nervosa
In contrast to the others mentioned, this is a dwarf suckering shrub only 18 inches high and three feet across. Nevertheless it still has two foot long leaves, sometimes turning red-purple in winter. It does not flower until late spring, when the racemes are eight inches long.

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Melianthus major

In its native South Africa the honey bush is a shrub from 6 to 10 feet high and 3 to 10 feet across, but in our colder climate it is (according to books and experts) cut to the ground by frost each winter, and the root needs some protection from both cold and excessive wet. Treated as a herbaceous perennial in this way it normally grows about four feet tall and two across. It has glaucous pinnate leaves up to 20 inches long, consisting of numerous long, sharply toothed leaflets. It needs a moist but well-drained soil in full sun. I find that in about half the winters the growing shoots at the ends of the branches survive happily, and if left will flower in their second year. However, I do not find the flowers particularly impressive and the bare stems from last year look rather straggly and ugly, so I cut them back hard in spring anyway. I have never bothered with any protection.

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Miscanthus sacchariflorus

The graceful Amur silver grass makes a great contrast to the wide leaves of the preceding plants, but looks just as exotic as a result of its height. Not every lawn has grass growing ten feet tall! This species rarely flowers, but the leaves remain fresh well into winter, although they sometimes turn bronze coloured in hard weather. It spreads slowly, so its roots will need cutting back once every few years to contain it.

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Musa basjoo

The Japanese banana is said to be the only banana which can survive (with some protection) in the open through a typical British winter. The leaves are destroyed by the first hard frost of autumn, but the roots will survive and sprout again the following spring, especially if they are protected with a thick mulch of dry bracken or straw. The stem as well can be preserved if it is given sufficient protection. The recommended method is to cut it down to about four feet high and remove the dead leaves, put a chimney pot over it (they can be quite decorative in their own right!) and stuff it with dry straw or bracken, then cover it to keep out the rain (but see next paragraph). In the spring the inner part of the stem will sprout again, making a plant that gets slowly bigger each year. They can in this way be brought to flowering size, but the fruits are inedible. (WARNING - straw can be a problem anywhere in the garden if it carries residual herbicides from earlier spraying of the cereal crop that produced it.) If the plant is cut to the ground each year, it will slowly spread by suckering, and it can be propagated in this way. When in full swing it grows at a prodigious rate and needs enormous quantities of food (mainly nitrogen) and water to keep it going. It must, however, be sheltered from strong winds which will otherwise shred the huge leaves.

I have now grown the plant for several years, and do not follow this advice precisely. The first problem is that a chimney pot can cost as much as the plant (more than twice as much for a really decorative one). The second problem is that a standard British chimney pot has an internal diameter of 9 inches, but my plant has become a clump several feet across, excluding the leaves. That isn't a very good fit!. Advice from the nursery is to use pieces of flue liner instead, stacked on top of each other, but that is still much too narrow. I have the good fortune to have a son-in-law who made me a wooden box, 20 inches square and four feet high, which I used instead for the 1998-99 winter (the plant's first), but it was too small in all directions for a second time.

What I have done most years instead, and recommend as a suitable method, is to wrap two-foot wide bubble wrap around the clump, then stuff it tightly with straw, ensuring that there is plenty of straw between the outermost stems and the bubble wrap. Then put another lot of bubble wrap vertically above the first, and again stuff it with straw. This was repeated for a third level, giving a tower just over five feet tall (allowing for some overlap, essential for wind and rain-proofing). Finally I put two pieces of bubble wrap at right angles to each other over the top and down the sides to make a rain-proof lid, and sealed all the edges with sticky tape to keep it in place. The only problem with this, apart from the time it takes to put in place, is that the sticky tape doesn't last the winter, especially in wet weather, so some netting tied over the top is a very useful addition.

Another approach taken by a Norfolk grower is to put four wooden pallets on edge around the clump, stuff with straw, then another set of four on top, etc., to whatever height is necessary to cover the stem, then use a piece of roofing felt as a lid. He finds this very effective, but it takes up more space than my bubble wrap method (which I don't have available), and I suspect it also looks worse, but it would be easier to put together, and pallets held together with string are more wind-resistant than my bubble wrap and sticky tape setup.

Some years recently, having difficulty getting at the ever-increasing clump to wrap it, I have merely wrapped the lower part of the stems, leaving the top open, or even left the whole thing unprotected. In 2005, using this method (just straw at the bottom), I found two stems with almost fully developed flower buds survived undamaged and consequently flowered non-stop from early June until frost in November.

A second point which has emerged from experience is what to do about the offsets. I didn't expect to get any until the main stem had died, either from frost, or less likely following flowering, but only four months after planting it already had four, one of which was then almost as big as the original was when I planted it (about two feet high). The nursery advised me that if the offsets are left on (also protected if possible) this will produce a clump of plants with a greater density of foliage but smaller leaves; two advantages to this are that the stems will tend to protect each other from wind, and the smaller leaves will be less prone to wind damage. If the offsets are removed they can be used for propagation, and the single stem remaining will grow taller and produce larger leaves. Since my plant does suffer significant wind damage, I protected the offsets while leaving them on, but may one day try to propagate one of them, keeping it indoors over winter, at some stage.

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Paulownia tomentosa

The deciduous foxglove tree will grow to nearly fifty feet high and 35 feet across if allowed to do so. It also produces sprays of pink, scented flowers (which look very much like foxgloves) before the leaves appear in spring. Grown like this it is a very attractive tree (if you have room for it), but it can be made to look much more exotic by keeping it smaller and sacrificing the flowers. If it is cut to the ground early each spring and fed well it will grow eight feet high and across by late summer, and its soft, lobed, green leaves will be up to two feet across. If it is cut further to restrict it to a single stem, the leaves can grow even bigger.

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Phormium

Phormium tenax
The New Zealand flax is a must for any exotic garden in cool temperate climates. When I first saw it, a very well-grown specimen in Kew Gardens, some years ago I could hardly believe my eyes. I hadn't heard of it before, and my first impression was of a giant iris, with eight foot long sword like deep green leaves towering way above my head. The dull red-brown flowers gave away the fact that it was not an iris, but on a ten foot stem take nothing away from the impact of the plant. It does not normally need winter protection in Britain. I now have one, not quite that big but still impressive. Since planting it I have heard that splitting it up or removing it is likely to require the services of a mechanical digger!

There is a number of varieties with different red, pink or purple coloured and variegated leaves. They are all somewhat smaller and less hardy than the type.

Phormium cookianum
Occurring in a number of varieties, this is a smaller, more brightly coloured phormium with drooping leaves. It is less hardy than Phormium tenax, but will still survive outdoors in most parts of Britain with some protection. While it does not have the major impact of its larger relative, it is still a very attractive plant with a different part to play in the overall scheme. Hybrids between the two species are available, intermediate in both size and hardiness.

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Rheum palmatum

The ornamental rhubarbs make a good substitute for Gunnera manicata if you don't have room for the latter or if your garden is too cold for it. There are several species, mostly with leaves like the edible variety but bigger and more attractive. Palmatum, as the name implies, has divided leaves, shaped like huge maple leaves. Varieties Atrosanguinium and Purpureum (I'm not sure if they are different, or just different names for the same thing) have the added attraction of red stems, red young leaves (two feet to two foot six inches long and across when mature) and red flowers in a 6 foot tall panicle. Variety Tanguticum is tinged with purple and can have white, pink or red flowers, but its main advantage is that it continues to produce fresh leaves later in the season than the others. Other species of rheum tend to be somewhat smaller. All the rheums are fully hardy in Britain, and need a deep, rich, reasonably well-drained soil.

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Rodgersia

Rodgersia aesculifolia
There are several species of rodgersias which all require a moist, humus-rich, acid soil, have astilbe-like flowers, grow to about three feet tall, and spread by creeping rhizomes, but they contrast strongly with each other in leaf form. In this species the leaves are like horse chestnut leaves with a bronze shade, five-lobed and 18 inches across. The flowers can be ivory or pale pink.

Rodgersia pinnata superba
This is quite similar to R. aesculifolia, but the leaves are very bronze when young. The flowers are bright pink.

Rodgersia podophylla
Again having bronze young leaves, in this case they are star shaped and up to two feet across. If grown in full sun the leaves turn purplish in summer. The flowers are creamy coloured, but are less readily produced than in the other species.

Rodgersia tabularis
The pale green circular leaves of this plant are a great contrast to the other rodgersias. They normally grow two feet across, but can be as much as three. The ivory coloured flower spikes go up to five feet.

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Veratrum

Veratrum nigrum
This is one of three species of veratrum, all of which require constant summer moisture and dappled shade. They do not like too much summer heat nor water-logged soil, but like plenty of organic matter in a deep fertile soil. The main attraction of all three is the large corrugated ovate leaves. This species grows 4 feet high and 3 across, and in summer sends up a tall spike carrying numerous attractive purple-black flowers which add to the exotic effect. They resent disturbance, and cannot be expected to flower or produce the best foliage until two years after planting. They are hardy, but the young shoots can be damaged by frost in very cold districts unless some protection is given.

Veratrum album
This is very similar to V. nigrum, perhaps not quite so tall, but the flowers are white outside and green inside.

Veratrum viride
This is as tall as V. nigrum but only half as wide. Its flowers are yellow-green. The leaves are hairy when young and grow to about a foot long (longer than the other two species).

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Other plants

These additional plants are also appropriate. I will include more descriptive information on them when I have time, but I thought I might as well give the simple list now as it might be of use to someone:

Lysichiton (2 species and a hybrid)
Eucomis (several species)
Ligularia
Kniphofia caulescens (some description on the page about my own garden)
Kniphofia northiae
Sarracenia flava "Maxima"
Hedera canariensis
Hedera colchica and varieties "Dentata", "Dentata Variegata", "Sulphur Heart"
Ferns (Dicksonia antarctica, Osmunda regalis, Asplenium)

[Probably more to come]

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