Plants for Problem Places: CLAY SOIL
by
Graham Rice
Solving the problem with plants
*****
Published by
Log Tavern Press
at Smashwords
Plants for Problem Places: Clay Soil
Copyright © Graham Rice 2010
ISBN: 978-0-9829373-1-0
UK Edition: Version 1.0
Cover Image ©judywhite/GardenPhotos.com
Artwork by David Henderson
All rights reserved. Without limiting the rights under copyright reserved above, no part of this publication may be reproduced, stored in or introduced into a retrieval system, or transmitted, in any form, or by any means (electronic, mechanical, photocopying, recording, or otherwise) without the prior written permission of both the copyright owner and the above publisher of this book.
Smashwords Edition License Notes
This ebook is licensed for your personal enjoyment only. This ebook may not be re-sold or given away to other people. If you would like to share this book with another person, please purchase an additional copy for each person you share it with. If you're reading this book and did not purchase it, or it was not purchased for your use only, then you should return to Smashwords.com and purchase your own copy. Thank you for respecting the author's work.
* * * * *
About Graham Rice
* Acclaimed expert on plants and gardening
* Former gardening columnist of The Observer and of London’s Evening Standard
* Trained at the Royal Botanic Gardens at Kew, London
* Author of over twenty books, including the four for the Royal Horticultural Society
* Writes for The Guardian, The Daily Telegraph, The Garden and Amateur Gardening and has written for BBC Gardeners World, Garden News, BBC Gardens Illustrated and magazines and publications around the world
* Winner of six awards for writing about plants and gardens
* Chelsea Flower Show judge
*****
Praise for the print edition of Plants for Problem Places
“You can give up your home and move to a better garden site, or turn your liabilities into assets. Graham Rice makes a case for the latter in this delightfully written, well-organised primer... Should lighten the spirits of those disheartened by vexing gardens.” Linda Yang, New York Times
“This is a wonderful little book that is the ultimate guide to knowing what to plant… The author is a great help, often giving exact cultivars of plants that will work for your problem spot. Seems to me any book by Graham Rice is amazingly researched and written in a sprightly style that's easy to read yet wonderfully instructive. Good for beginners as well as advanced gardeners.” Gardening Girl, amazon.com Customer Review
‘Advice is put over simply and unpretentiously.’ Garden Answers magazine
‘Throughout, one hears the voice of experience bringing confidence in the advice.’ The Garden magazine
*****
About this book
* Analyzes the problem of clay soil
* Suggests proven ways to improve clay soil
* Recommends and describes the best trees, shrubs, climbers, hedging, perennials, bulbs and annuals to grow in clay soil
****
Plants for Problem Places: CLAY SOIL
Contents
Plants for Problem Places - Series introduction
Thinking about the problem of clay soil
Solving the problem of clay soil - by choosing the right plants
Climbers
and wall shrubs
Shrubs
Recommended mail order suppliers
Plants for Problem Places - Series Introduction
We all have problems. It’s an illusion to think that somewhere there’s a person with a problem-free life. And the dream of one day being rid of our troubles is exactly that: a dream. A dream which will not lead to a state of perfect happiness but to a constant, niggling dissatisfaction with life which threatens our peace of mind. The trick is to acknowledge that our lives will never be perfect and then to get on with the fun.
And there’s no such thing as a problem-free garden. Every garden has its difficulties, and if we think that with just one new technique, one more adjustment to the design, or one more new plant it can be made perfect, then we will be striving constantly for the unattainable. Rather, we must realise that for example, we will never be able to grow swathes of rhododendrons on chalky soil. Instead, we should enjoy all the wonderful plants that will give us please in our particular situation.
So the eBooks in this series are about paying attention to reality, about looking at the inevitable problems that face every gardener, about thinking constructively on how to alleviate those problems, and then choosing the right plants to give us lasting enjoyment. This eBook, on clay soils, is the first.
I’m focusing on the factors which gardeners see as problems. First I discuss the nature of the problem, to enhance our understanding of our situation - and in one or two cases this means pointing out that, in truth, the problem is really more of an opportunity: gardeners with wet soil may not be able to grow rock plants, but they can easily enjoy the wonders of ligularias and bog primulas. Secondly, I describe how the problem can be alleviated to enable as wide a range of plants to be grown as possible. Then, finally, there are the plants themselves.
Each chapter of recommended plants is divided up by plant type: usually trees, vines, shrubs, hedges, perennials, bulbs and annuals. The most suitable plants are described in detail and I often suggest specific varieties. Then I follow with another batch of recommendations to expand the choice. Heights and hardiness zones are, of course, noted. At the end is a list of mail suppliers that I can recommend – from personal experience.
Remember, there is no garden problem so intractable that we must be totally defeated. Even the most impossible situations can be improved so that we can grow a good range of attractive plants. It may be that we cannot easily grow our special favourites but new favourites will emerge. And although we must strive for the perfect, we must also be pleased with everything that is possible.
Plants for Problem Places: Clay Soil
Thinking about the problem of clay soil
Clay really can be a problem. There’s no getting around it with encouraging remarks to turn what seems a problem into an advantage as is clearly true with some other problem places, like shade. Clay is a problem that needs solving. Clay is heavy, wet, sticky and often totally unworkable; it’s cold in spring, it rots delicate plants very efficiently and adds dead weights to the gardener’s boots.
But - and I have to say it - there are advantages too. Except in dry summers clay soils don’t suffer from drought, they retain a reserve of plant foods and can be turned into very fertile soils.
The difficulties come about as a direct result of the composition of the soil. The particles that make up clay soil are very small indeed, the smallest found in mineral soils. The result is that, unlike the more granular sandy and gravely soils, they bind together into a cohesive mass helped by the water that they retain in the tiny spaces between the particles.
If you take a jar of grit and add some water very slowly, all that happens is that the water fills up the spaces - you can watch it happen. Even if you stir in the water, there is little in the way of physical change that takes place. When eventually it dries out the grit will still look much the same.
If, on the other hand, you do the same with clay (or flour which behaves in the same way) it looks quite different. If you start with dry clay the water will not even sink in to begin with, it simply rests in droplets on the surface and will need stirring to encourage it to mix. It will then change from a powder to a thick paste and then to a cream as you add more water and stir. Leave it to dry out and it is quite likely to set rock solid. Unlike sand or grit it changes in form noticeably as water is added and as it dries.
Clay soils behave in a similar way. When very dry they tend to set hard and the rain runs off without soaking in. As the rain does eventually penetrate, the soil becomes sticky and malleable until eventually it turns quite greasy. Then, when it dries out, it’s likely to set very hard and shrink to leave cracks through which the rain runs without soaking in. At this stage you would expect many plants to wilt and die but, although the soil seems to be bone dry, there is still water being held by the soil particles which the plants can use.
These particular properties of clay soils create problems for the plants and the gardener. So much water is retained in the soil and for so long that plants have to be able to tolerate these damp conditions for long periods, often with little air to help compensate. They also have to be able to tolerate the cracking which develops as they dry.
Clay is a problem for the gardener too, as only when the soil is fairly dry can it be dug or worked in other ways and this means that cultivation is more dependent on the weather than with other soils. Of course this means that improving clay soil is also more difficult as this has to be done at just the right time.
There are advantages though. The fact that clay soils are basically water retentive makes them a good basis for growing many plants if they can be improved to make them more workable. And because of their chemical structure they also retain their plant foods for much longer than other soils, so that plants have more opportunity to use these nutrients before they’re leached away by rain. Fertilizer applications are not wasted and the nutrients released by organic matter as it rots are used efficiently.
Clay soils can be acid or alkaline so a soil test is helpful if the plants in neighbouring gardens don’t give you a clue; but they are also more stable in their acidity and alkalinity and less easy to change.
Improving clay soil
There are a number of ways that the problem of clay soil can be alleviated and one way it can be solved - by moving house! But assuming that you don’t wish to move away there are still ways you can make your soil easier to live with.
The first is to improve the drainage of the soil. On clay soils it’s often easier to drain only the surface layers than to attempt a full scale drainage operation and systems to achieve this are now available. But drainage is only part of the solution. It’s all very well to have the means in place by which surplus water can be conducted away to a drain or soakaway but if the soil is still hanging on to it, there is little point. So the soil itself needs attention, too.
Digging is the first thing to think about but not necessarily the first thing to actually do! On a clay soil digging is a long and arduous job and needs to be started early in the autumn if you are to complete a reasonable amount in any one season without ending up in hospital. This is especially true as - I have to confess - I’m going to recommend old fashioned double digging if you want to do the job properly. This involves not only turning over the top layer of soil but the lower one too. Even in an established garden this may never have been done and the lower level could be very hard and compact, not to say infertile, too.
When you start to dig you may well find that below about one spade’s depth the soil deteriorates noticeably owing to lack of aeration and cultivation and it’s important to ensure that this relatively infertile subsoil is not mixed with the more fertile topsoil during digging. It’s also important to start the job when the soil is reasonably dry, and to curb your understandable enthusiasm for this delightful occupation when the soil is wet.
At this point you are doubtless expecting me to suggest that you add more organic matter than you’ve ever seen in your life. Well, you’re getting the right idea and this will be very helpful. As you’re going to be using a fair amount, this organic matter had better be the cheapest available. In different parts of the country, different materials will prove the most economical. Composted pine bark, natural cedar or other wood mulch, spent mushroom compost, in some areas even peat moss bought in bulk may be the best buy. Making large quantities of your own compost always pays but check local suppliers of mulch and topsoil for what they have available.
If the soil is not too wet or rock hard you will be able to fork your organic matter into the bottom layer - which is far more effective than spreading it in a layer on the forked soil. This does depend on the organic matter being fairly friable too. Compost and especially manure can be rather lumpy. It’s always suggested that the top layer be left rough for winter frosts to help break down the lumps and notwithstanding the scepticism of many this does actually happen. So if you can improve the subsoil as you dig in autumn and early winter, then leave it rough over the winter and in spring fork more organic matter into the topsoil, you’ll have the ideal thorough preparation.
‘But what about grit?’ I hear you cry. This can help, too, and if you want to do the job properly it can be forked into both layers at the appropriate stage with the organic matter - in effect creating a border of potting compost. But please make sure you use grit and not builders’ sand which is quite useless by comparison.
You will find that adding all this material often increases the height of borders and to reduce this accumulation you may need to remove some of the subsoil whilst digging. The other alternative is to raise the beds slightly and this can have a very beneficial effect on the drainage and provide the opportunity to create a special soil mix for the top layer. This is likely to be the only way of growing plants needing free drainage, like alpines, on clay soil.
Some soils are so sticky that they’re very difficult to dig and, of course, many gardeners don’t have the inclination or the physical fitness to do a great deal of heavy digging. In such circumstances another approach is necessary. Organic matter spread on the surface can, over the years, have a very beneficial effect and garden compost, bark, peat moss, mulch, mushroom compost and other materials have been used successfully. They’re simply spread on the surface in spring when the soil is moist, left in place all summer and forked into the surface in the autumn to be replaced by another layer. This method can be used in conjunction with chemical soil treatments.
As well as organic matter and grit there are chemical materials that can be added to clay soils to improve them. Lime is the most commonly used and can be very helpful. It works by chemically encouraging the soil particles to gather together into groups to make larger particles or crumbs - flocculate is the technical term. These have larger spaces between them through which air can circulate and water drain away. Lime works well but whether you use it depends largely on the existing pH level of your soil and on the plants you want to grow. If your soil is acid and you want to keep it that way then using lime would be a mistake as it would if your clay soil is already fairly limy.
Many branded clay curing products are available and the one thing they have in common is that they’re expensive and if they work at all it’s only for a limited period. Generally you would be far better off spending the same amount of money on a few bags of organic matter or on paying someone to do the digging for you. But in a small garden where other methods are more difficult to apply these products can be useful. I suggest that you buy just one pack and try it out before spending too much.
Solving the problem of clay soil - by choosing the right plants
Trees for clay soil
Aesculus (Horse chestnut) As I look out of my window there are three large horse chestnut trees in the school grounds that border the garden. They’re stunning when they flower in spring. But they all flower at slightly different times and the flower spikes on one are more impressive than those on the others. All were doubtless raised from seed and the natural variation is coming out. So, to be sure of a good form, choose a named variety of horse chestnut.
The Indian horse chestnut is especially impressive and the best of these is undoubtedly A. indica ‘Sydney Pearce’ with long flower spikes in white with yellow markings and a pink tint. If you prefer to avoid the nuisance of the large chestnuts littering the ground in the autumn then plant A. hippocastanum ‘Baumannii’ with double white flowers which are sterile and so produce no nuts.
These are very substantial trees but for something a little smaller try the red buckeye, A. pavia, with crimson flowers or A. x mutabilis which is sometimes little more than a large shrub with red and yellow flowers.
Malus (Flowering crab apples) Excellent small garden trees, the crab apples give you at least two seasons of display - the flowers in spring and the fruits in the autumn. Generally they make small- to medium-sized trees, sometimes with rather tangled growth and have the excellent capacity to pollinate fruiting apples while serving their decorative purpose.
‘John Downie’ is universally regarded as the most impressive variety with white flowers and large slightly conical, orange fruits with paler streaks on trees with a conveniently upright habit. On top of its other advantages the large fruits also make good crab apple jelly. Unfortunately, it is susceptible to disease.
‘Golden Hornet’ has bright yellow fruits which are less edible but last well and although the tree spreads in the end it starts off with fairly compact growth. Sugar Tyme (‘Sutyzam’) has fragrant white flowers followed by scarlet fruits and is unusually disease-resistant.
My favourite, I have to say, is M. x robusta in its red form, ‘Red Sentinel’, and this makes a noticeably spreading tree with pinkish flowers and scarlet fruits which seem to be left till the last of all by marauding birds. The mass of red crab apples amongst the twiggy branches is most pleasing on a cold sunny winter’s day.
Ostrya (Ironwood, hop hornbeam) Closely related to the more familiar hornbeam, Carpinus betulus, these are similarly subtle in their appeal. Catkins in the spring, hop-like fruits later in the year and yellow autumn colour combined with an attractive shape make them very appealing in a restrained way.
The American ironwood, O. virginiana (50ft/15m), seems to be least cultivated in spite of its attractive pyramidal form and good autumn colour. Ostrya carpinifolia (70ft/21m - eventually) is seen more often and I especially like its spring catkins and the hop-like fruits which are about 2in (5cm) long.
And try these trees for clay soil
Acer rubrum (Red maple) An impresive maple with wonderful autumn colour. ‘Scarlet Sentinel’ is narrower, and half the height. 70ft/21m.
Alnus incana ‘Laciniata’ (Cut leaved alder) Slender alder with finely cut leaves and yellow spring catkins. 18ft/5.5m.
Carpinus betulus ‘Fastigiata’ (Hornbeam) Upright habit and striking branch structure; yellow-orange autumn colour. 20ft/6m.
Eucalyptus gunnii (Eucalyptus) Unusually vigorous; pretty grey evergreen leaves. Probably the hardiest of all the eucalyptus. 45ft/14m.
Fraxinus americana (American ash) Fast growing, relatively upright tree with impressive yellow or purple autumn colour. 80ft/24m.
Laburnum x watereri ‘Vossii’ (Golden chain tree) Bright yellow flowers hanging in streams up to 2ft/60cm long in late spring. 20ft/6m.
Populus x jackii ‘Aurora’ (Variegated poplar) Heart-shaped foliage coloured green, pink, cream and white. Not too spreading in growth. 30ft/9m.
Prunus ‘Spire’ (Flowering cherry) Pink flowers followed by fiery orange and red autumn colour; slender, vase-like habit. 25ft/7.5m.
Salix babylonica ‘Tortuosa’ (Twisted willow) Contorted willow with upright growth and attractive twisted stems, especially impressive in winter. 30ft/9m.
Sorbus americana (American mountain ash, dogberry) Flat heads of white flowers followed by clusters of red berries and yellow or red autumn colour. 18ft/5.5m .
Vines and wall shrubs for clay soil
Jasminum nudiflorum (Winter jasmine)
One of the most dependable of winter flowering climbers (although it’s more of a scrambler, really), the buttercup yellow flowers of winter jasmine sparkle in a waterfall of winter colour – even in shady situations. The main stems need tying in to a trellis or wires, then each year’s new shoots trail down attractively and are lined with flowers. Ideal for cutting for the house, they bring a little sunshine to winter evergreens, and may often start to open in December. Where the stems touch the ground they take root so you will usually have plants to give away. 6-10ft/1.8-3m.