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Climate and Soil conditions

There are many reasons for success or failure in establishing a garden and so often it is a combination of conditions rather than one single reason for failure of plants to thrive. Unless we are growing in protected environments, such as greenhouses and polytunnels, there is little we can do about the climate and it is therefore important to understand broadly the conditions we are likely to encounter through the various seasons. Much of this has to be learned through trial and error but hopefully the following pages will help to reduce the ‘error’ factor. There has always been fairly clear definition of hardy, half-hardy and tender plants, but more and more we are tempted to push the boundaries by growing varieties from all over the world originating from extreme climates and expecting them to thrive. It is very important to ensure that the framework of your garden, such as hedges, trees and all the structural planting should be of the type able to thrive in your climate. By all means take some risks with your planting but not with structural elements of the garden. A good example may be to plant Ilex crenata for a tough small evergreen hedge rather than rely on Rosemary which, even if only one or two plants suffer, the whole hedge will be spoilt. You can replace the odd Rosemary if it fails within the borders but a hedge is ruined by the gaps and varying sizes of plants.

One very simple way to get an idea of what will survive in your garden is to look around at the natural vegetation and other gardens in the area. Willows and Birch trees and Sedges will indicate possible wet areas, whilst Elder, Yew, Thorn and Beech are a fair guide to well drained land. The presence of Rhododendrons, Azaleas, Camellias and Pieris are an indication that the soil is of an acid type, that is, free of lime. However, before planting anything in your garden I strongly advise that you learn a little about the soil conditions. First of all dig a hole at least 2ft if possible 3ft and study the soil profile.

Heavy soils: Heavy clay soils are considered often to be the most difficult, but at least they hold on to nutrients and can be improved. Main problems are waterlogging in the winter and cracking up due to drying out in the summer. Incorporation of
plenty of organic matter, such as mushroom compost or leaf mould, will help retain moisture in summer and make the soil easier to work. Incorporating sharp grit will also break up heavy clay soil but will not necessarily solve drainage problems. It is often thought that on poorly drained soils larger holes needs to be dug out with drainage material put at the bottom. This does not solve a drainage problem, it will simply act as a sump as the water has no means of escape. In this case drainage should be put in to carry the water away from the planting site or choose plants which will tolerate waterlogging in winter.

A mulch every late winter/early spring will also improve heavy soil conditions as well as suppressing weeds and retaining moisture in the summer. The worms will, over time, take the mulch down into the topsoil. Another problem on heavy soils, in particular, is compaction. Either surface compaction or a hard pan several inches, or sometimes a foot or so below the surface. The causes of sub-surface compaction are often due to mechanical means caused by either regular ploughing or rotavating to the same depth or as often found on new developments the ground has been compacted by construction machinery and a layer of topsoil has been placed on top causing major problems for later. This will be discovered when digging your soil profile pit and it is vital that compaction should be eased before planting, by either deep digging or with a mechanical digger or sub-soiler. Surface compaction, i.e. capping, is less of a problem to overcome. The main cause of this is over-cultivation which breaks down the soil texture into very fine a particles which when wet form a porridge-like consistency with no air pockets, then when it dries out it becomes more like concrete than good garden soil. Regular mulching and incorporation of organic matter, mushroom or garden compost, will help in these circumstances, as will incorporation of grit or sharp sand.

On heavy soils damage can be caused by cultivation and walking on the ground in wet conditions. Try to keep off the garden when the ground is wet, but if it is absolutely necessary then I suggest working from a sheet of ply board, laid on the ground to to avoid compaction of the soil. Roses are particularly good on heavy soils providing the drainage is adequate. Silver leafed plants such as Lavender and Artemisia are less easy to grow on heavy soils.

Light soils: Although the antithesis of heavy clay, similar treatment in the form of incorporation of organic matter, e.g. mushroom or garden compost, is needed here as the main problem is normally lack of moisture retention. Because water runs through light sandy soils very easily nutrients are also leached out quite quickly so your plants will need more food as well as water. The advantage of light soils is that they do not cap or pan easily so there is little likelihood of compaction problems and they can be cultivated in most weather conditions throughout the year. They also warm up early in the year providing early growth to your plants. In the past peat has been used in large quantities to increase the moisture retention in light soils but I would avoid the use of peat for soil conditioning as it is a natural and non-renewable resource. There are plenty of alternatives for soil conditioning such as garden compost, composted bark and mushroom compost. It is best to find a compost which is readily available in your area and cheap enough to be used liberally.

Mediterranean plants, such as Rosemary, Lavender, Salvia and Cistus thrive on light, well drained soils. If you must grow Roses in light sandy conditions then a species Rose will do better than the hybrids. Rosa virginiana and Rosa nitida are particularly good with simple single pink flower, good hips and excellent autumn colour and disease free.

Useful tip on all soils: In dry weather light hoeing of the surface to form a fine tilth about a centimetre thick will act as a mulch reducing moisture loss during the summer as well as getting rid of weed seedlings. It is common practice on poor soils, whether heavy or light to bring in good quality top soil. Wherever possible I recommend that existing soil should be improved rather than replaced.

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