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Exotic plants in a cool climate

This section has become so large that I have now devoted a separate page to it.


Flowers in winter

In addition to my attempt to defy the climate by growing apparently sub-tropical plants, I also aim to have plenty of flowers in the open garden in mid-winter, despite the ice and snow. Again the method is basically choice of plants, and it is surprising how many are available. Rather than risk making this page too large, I have started developing a separate page for this topic.


General culture

Pests and diseases

This page has again become too large, so this section is now on a separate page. It currently deals with slugs and cats, but many other topics are planned, when I have time.


Soil improvement

Clay soils

Clay soils are among the most intractable for cultivation in their natural state, but have the potential of being one of the most fertile. Clay consists of extremely small particles which stick closely together when wet, excluding the air which plant roots need. This compacted mass then becomes extremely hard when it dries out. Whether wet or dry, it is almost or completely impervious to water, causing waterlogging or flooding in wet weather. In spring it is very slow to warm up, shortening the growing season significantly compared with lighter soils with similar climate. As if this were not enough, wet clay is not only very difficult to work, but doing so makes it worse by pressing the particles even closer together. Cultivation of clay soil is thus very difficult, and can only be carried out when the soil is moderately moist but not wet.

The prime objective in cultivating clay must be to separate the tiny particles to allow air and water to percolate through it. A good way to achieve this temporarily is to leave the surface roughly dug in autumn so that winter frosts can penetrate. This process breaks up the large masses into small pieces which are easy to work and easy for plant roots, air and water to penetrate, but unfortunately the effects are very temporary. Walking on the ground, or simply exposure to normal rainfall, soon causes it to stick together again, unless action is taken to prevent it.

The appropriate action is to incorporate some material that will keep the small lumps apart. Sharp grit is ideal and permanent, with sharp horticultural sand a good second best, but soft builder's sand or sand off a beach is useless because the grains are too rounded. The other material which should be worked in at least annually is some kind of humus (three-quarter rotted vegetable material) - home-made garden compost is ideal. This not only separates the particles of clay but also incorporates its own air, adds plant nutrients, helps to retain both water and any added fertilisers and provides a home and food for the myriad soil micro-organisms that are continuously at work converting soil minerals into forms that plant roots can absorb.

Making leaf mould and garden compost

All soils need to contain humus if they are to grow quality plants other than those adapted to desert conditions, and most would be improved by adding to the natural humus content, peaty soils being the exception. Light, sandy or stony soils are unable to retain much water, but added humus corrects this deficiency, albeit only for a short time because it rots away very quickly in this environment and so needs constant replacement. Clay soils have no problem holding water, but are very heavy and lack the air which is essential to healthy roots - again humus is (part of) the answer, holding the clay particles apart and incorporating air in its own structure. Humus material rots away more slowly in clay than in sand, but it does still get used up, needing replacement. In both clay and sandy soils, it is simply impossible to incorporate too much humus - the more there is, the healthier almost all plants will be.

Many commercial products are available to gardeners for this purpose, but can be quite expensive, and a lucky few have access to quantities of animal manures. For the rest of us, the cheapest and best humus sources available are leaf mould and garden compost.

Leaf mould is made simply by stacking piles of fallen leaves from deciduous trees and leaving them to slowly rot for 12 to 18 months. Smaller quantities are better enclosed in a black plastic bag, and should have water added to ensure they are thoroughly soaked. "Experts" tell us that it is also necessary in this case to make some holes in the bag to admit air, but I find there is enough air trapped between the leaves to make this unnecessary. The resulting material is just about the perfect material for soil improvement, either dug in or spread on the surface as a weed-free and weed suppressing mulch.

Garden compost is almost as easy to make and matures faster. It is helpful, and not difficult, to understand the process of converting vegetable waste material into useful compost. The raw material consists of a mixture of soft, growing plant cells containing considerable quantities of water and nitrogen compounds, and tougher, usually drier more woody material from the older growth, especially twigs, bark, dried out stems of herbaceous plants, etc. Any vegetable matter, including moderate quantities of shredded cardboard and newspaper, can be included. Animal wastes such as meat and bones should be avoided, not because they won't make decent compost but because their presence will encourage unpleasant smells and scavenging animals such as rats.

For the material to rot properly it needs air, moisture and warmth to promote the rapid growth of the bacteria and fungi that do most of the work. The more woody material also needs nitrogen in compound form (that in the air is no use). Soft material such as fresh weeds, grass clippings, etc. contain all they need at first, but quickly become consolidated so as to exclude air, resulting in a slimy, smelly mess, insufficiently decomposed to be good quality compost. Woody material, on the other hand, because it consists of hard pieces, incorporates plenty of air but is short of both moisture and nitrogen. The answer is to ensure that the two types of material are well mixed together. Additional moisture will be needed in warm dry weather, but protection from excess rain is needed at colder times since too much water will exclude air, and the bacteria will drown. Insulation is also necessary in cold weather.

If you don't have enough soft material to balance the woody stuff (and this is normal, because it takes a lot of grass, etc. to provide enough nitrogen to rot shredded twigs), an activator can be used. There are proprietary mixtures available commercially for this purpose, but animal manure is ideal, especially poultry manure which is too strong to use directly on the garden. Another readily available and very effective activator, if you collect it for the purpose instead of flushing it away, is urine (described by one BBC gardening expert as "recycled beer"). Some proprietrary mixtures claim to contain the necessary bacteria, and some gardeners add soil to the heap to provide them, but in fact the normal use of weeds, etc. will contain quite sufficient bacteria and fungi without deliberately adding them.

Many different styles of container are available commercially, and various designs have been published for home-made versions. The essentials are adequate protection from drying out in hot weather, protection from excessive wet and wind in cold weather, adequate air and the right mix of material. It is also necessary for success to ensure that the container is big enough to provide sufficient heating during the early stages of decomposition. A heap less than 3 feet cube (i.e. 27 cubic feet) is not really big enough. More than 4 feet cube (64 cubic feet) will be too difficult to fill and handle for most people. The container should have provision for turning over the material once or twice during the process, so as to re-incorporate air and mix the drier, cooler material from the outside with that in the moister, warmer centre. When I have time I will describe several designs which are easily made from cheap materials.

Many people worry that by making and using compost they will be spreading weeds from seeds and persistent roots around their garden. However, few seeds or roots will survive the high temperatures generated in a well-made compost heap in its first couple of weeks. To play safe, I always leave particularly pernicious roots, such as field bindweed (Convolvulus arvensis), to dry out for a few days before putting them in the heap. If the final product is used for digging into the soil, rather than as a mulch, this also drastically reduces the germination of any remaining weed seeds. Since it is not particularly good as a mulch anyway, this is no hardship.


Handy tip: To tell a wanted plant from a weed, pull it up. If it grows again, it's a weed. [Sent in to BBC Radio 2 by a listener]


My own garden

I live in a typical British edge of town suburb, with a small garden behind the house and a much smaller one at the front. The whole site is only 24 feet wide, and the front of the house is only about 16 feet from the public footpath at the side of the road outside. The rear garden is about 65 feet long.



The situation here from a climatic viewpoint is fairly but not extremely harsh by British standards. We are located on top of the Chiltern hills at an altitude of just over 500 feet above sea level. Although this is not a great height, it leaves us very exposed to wind. There is nothing higher between us and the north pole, while due east there are some hills of similar height in north east Germany, but nothing significantly higher this side of the Urals. There are closer hills to the south (about 40 miles) and the west (about 6 miles), but neither close enough nor high enough to provide real shelter.

I understand that in the USA there are standard hardiness zones. In these terms I am told the whole of Britain is in zone 8 of the USDA classification. Apparently this refers to the US Department of Agriculture system, based on average annual minimum temperature. Under this system, zone 8a corresponds to 10F to 15F (-12C to -9C) and zone 8b is 15F to 20F (-9C to -7C). I don't know until I check, but I would guess we are just about on the borderline between 8a and 8b here. Of course these are just averages. In a bad winter temperatures can go much lower, night after night for weeks.

Temperatures here are not normally extremely high or low by British standards, but the variation between summer and winter is; the difference between the average summer temperature and the average winter temperature is higher in Bedfordshire than anywhere else in Britain. Average annual rainfall is about 25 inches, low by British standards.



The Chiltern hills are chalk, but our part of them is covered by a layer of "clay-with-flints" (the very descriptive geological term), which is very heavy and slightly acid. The flints mean that it is impossible to dig with a spade and difficult even with a fork. It retains water reasonably well, is easily waterlogged in winter, very sticky and impossible to work unless fairly dry, but bakes hard (comparable to digging concrete) and develops deep cracks as it shrinks in warm dry weather every summer. It is also very slow to warm up in spring, so the growing season always starts later than normal for our latitude in Britain. The one good thing is that nutrients are not easily leached out by heavy rain, as they would be in a lighter soil.

I'm told that with the addition of plenty of grit and heavy annual dressings of organic matter it eventually becomes a very rich soil, but I wouldn't know - I've only been here 39 years!


The tiniest garden

My main interest at present is in trying (when I have time) to develop the tiny front garden. This discussion of an attempt to bring the tropics to a cold climate is now on a separate page (last updated 11th May 1998 - I hope to update it shortly).


Wildlife garden

With a few exceptions, I try to encourage wildlife to live in, or at least visit, my garden, and have been hoping for some time to develop an area specifically for that purpose. The prime requirement of a wildlife garden is undoubtedly a pond, but although the approximate site has been decided, the hole remains undug. The small "wildlife "area itself is more convincing - not that I have done anything special to promote it, but we now have a small colony of gatekeeper butterflies (Pyronia tithonus, also known as the hedge brown), not normally found in urban areas, but which like to breed in tall, wild grasses; this was part of the vegetable plot, intended to be partly dug out for the pond, but we have "temporarily" renamed it!

Quite apart from having a special wildlife area, I try to minimise the use of sprays, choose plants with wildlife benefits (such as buddleia and a small patch of nettles to attract butterflies) and avoid excessive tidiness so small creatures have somewhere to hide from predators and to hibernate in winter. We have a bird table and hanging bird feeders which attract quite a variety of birds, and we also put food on the ground for those species which insist on feeding there. I intend soon to put a short account of the wildlife I have found in the garden on my wildlife page.


Suppliers I have used (successfully):

Architectural Plants, Cooks Farm, Nuthurst, Horsham, West Sussex, RH13 6LH (phone 01403 891772) - Specialise in exotic-looking "architectural" plants such as hardy palms, yuccas, agaves, bamboos, "hardy" bananas, etc. - the sight of their nursery is an inspiration, and they readily replaced a plant which failed, even though the failure was caused by a wet summer, not any fault of theirs.
Burncoose & South Down Nurseries, Gwennap, Redruth, Cornwall, TR16 6BJ (phone 01209 861112) - suppliers of unusual plants.
Jungle Giants, Burford House Gardens, Tenbury Wells, Worcestershire, WR15 8HQ. (phone 01584 819885, fax 01584 819779, email - Specialise in bamboos. When they inadvertantly supplied me with the wrong species they went to great lengths to replace it and to compensate me for a season's lost growing time - the personal service (and the plant quality) could not be better.
Paradise Centre, Twinstead Road, Lamarsh, Bures, Suffolk, CO8 5EX (phone 01787 269449) - Growers of unusual bulbs/tuberous plants
Broadleigh Gardens, Bishops Hull, Taunton, Somerset, TA4 1AE. (phone 01823 286231) - Specialists in small bulbs.

I'm sure there are others just as good.


Plant names

The naming of plants has always been a source of difficulty in terms of communication, because the same plant is given different names in different places even within one country, more so between countries with a common or similar language (e.g. UK and USA), and obviously much more so between countries speaking completely different languages.

In theory this difficulty is solved by the use of scientific, Latin-based names using the system devised by Linnaeus. The way this system has been developed in recent years unfortunately means it is failing to achieve this objective.

The problem seems to be that it is being used for two quite different and incompatible purposes. The application of the system in actually deciding what name shall be given to a species has been hijacked by taxonomists whose only purpose is to use it to define the relationships between species by allocating them to genera reflected in the name, attempting to keep this up to date with the latest scientific thinking, and in cases of dispute over the correct name for a genus relying purely on "who thought of it first" - the oldest name wins, regardless of how widely a particular name is used.

The serious fault in this, in my opinion, is that the objective of ease of communication of identity of a species is being totally ignored. For this purpose the prime requirement is stability. Once a name has been established in general use for a species, it should be retained permanently, regardless of changing views on which species are really related and so belong in the same genus. There is a need, therefore, for two different international systems, one for use by taxonomists, which can be safely ignored by everyone else, and one for use by the rest of the world for purposes of simply identifying which species we are talking about in an unambiguous manner. There is no harm in them both being based on the same system and having names in common, providing everyone involved with buying, selling and growing plants, and in advising about them, uses the stable system, and the taxonomists keep their unstable system to themselves. Like legal homosexuality under current British law, the taxonomists' system should be confined to "consenting adults in private"!


Gardening organisations I am a member of

Henry Doubleday Research Association
Friends of Royal Botanic Gardens, Kew
Royal Horticultural Society



Plant databases

I have tried each of these very briefly. I was not terribly impressed by any of them. I tried searching first for the dragon arum, Dracunculus vulgaris - none of them gave me anything relevant. The Home Arts site came up with the herb Dill - I have no idea why. Time Life was extremely slow to come up at all, and I gave up waiting for the search - and this at a time (Saturday morning, GMT) when the net is usually quite quiet, as other sites confirmed. Except on Time-Life, I also tried the Queen palm Syagrus, but again obtained no hits, and this time the Plant Tracker site came up with 6 different species of Saussurea! The problem seems to be that the number of plants on each database is only about 1,000 to 3,000, which may seem a lot until you compare it with The RHS "A-Z Encyclopedia of Garden Plants", a book with details of 15,000 plants and 6,000 photographs - and it is not comprehensive.

Garden Encyclopedia
Time Life Electronic Encyclopedia
HomeArts Plant Encyclopedia
The Plant Tracker


General gardening links - Wrexham (north Wales) based specialists in rare bulbs
Royal Botanic Gardens, Kew
The GardenWeb Advice forums, exchanges, botanical glossary, plant dictonary, and more
My exotics page has a number of relevant links on that topic.
My garden pests and diseases page has a very useful link for biological controls.
Emily Compost is easy to navigate and has lots of useful tips and information. Somewhat American biased, but not intentionally and not so much as to be a put-off for Europeans (unlike some).
Lou Smith's Winter Hill Plants is a nursery site specialising in exotic, rare and unusual plants in the UK available via mail order. It gives quite a bit of useful information as well as being a source of hard-to-find seeds and plants.
Garden Forever is an American site giving lots of advice on many different aspects of gardening, with special attention to how to avoid injury and how to make gardening easier.


City Farmer's Urban Agricultural Notes

Gardens to Visit
Missouri Botanic Gardens
New York Botanic Gardens
Royal Botanic Gardens, Kew
National Trust


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This page last updated 21st April 2011