I have been writing for self build magazine for some time now but if you are building and at present your garden looks something like the picture above then this magazine and its website should prove really useful.
Some previous articles are available online.
This piece was on soil types and was published in 2007
Nowadays, most people’s first steps when planning a garden involve a visit to a garden centre. In this supermarket for the garden, you are likely to encounter a bewildering array of soil enrichers, soil testing kits and more to help you to understand the type of earth you have and how to enhance or adapt plants better to a soil to which they are quite unaccustomed.
Beginning with trying to explain what plants grow can grow where is almost creating a set of rules, quite the wrong course of action. The key to growing plants well in varying weathers or soil is to understand them and their origins, their homes and where or what conditions they prefer.
In truly understanding what soil actually is it’s important to appreciate that mineral or inorganic particles, vegetable or organic matter (humus), air and water are all a part of what we call soil. Because the ‘soil’ contains some physical characteristics of the parent material and contains trace elements resulting from rock erosion, the type of rock from which it was eroded will often determine if the soil is free draining or waterlogged, alkali or acid.
Climate is another important influence, in four main ways: chemical and physical weathering of mineral parent material, the glacial or fluvial or Aeolian movement of parent materials, development of the soil profile by internal soil processes and finally the erosion or physical removal of soil. The relative importance of each of these varies from region to region.
Using the ‘pH scale’ which is graded from one to fourteen, where one is almost car battery acid and fourteen more like caustic soda as a rough guide, peat is around 4.5 – 4.8pH and compost (or lime treated peat) 5.3 – 5.6pH. The optimum is 6.0 for peat and 6.7 for a mineral rich mix. Using this knowledge we can work out acidity levels, which in turn guides us towards what plants we can grow.
Despite our knowledge of the effects of pH, we still don’t fully understand why plants find it difficult to grow in acid soils. Toxicity results from the loss through leaching of valuable nutrients such as magnesium and potassium, and increased plant availability of iron and aluminium. This in turn disables the micro organisms and thus growth is prevented or severely retarded.
Ericaceous or acid loving plants include Azaleas, Rhododendrons, Pieris and some varieties of heathers, most other plants prefer a more alkaline situation.
Great Soil Groups
There are ten main Great Soil Groups occurring in Ireland. These are the Brown Earths, Podzols, Brown Podzolics, Grey Brown Podzolics and Blanket Peats (zonal soils), the Gleys and Basin Peats the Rendzinas, Regosols and Lithosols.
BROWN EARTHS (11 & 22) are relatively mature, well-drained, mineral soils with a rather uniform profile, which have not been extensively leached or degraded. Most Brown Earths occur on lime-deficient parent materials, and are, therefore, acid in nature; these are called Acid Brown Earths. These soils, in general, possess medium textures of sandy loam, loam or sandy clay loam and are often relatively low in nutrients but respond well to nourishing.
BROWN PODZOLIC (28 & 39) soils have a surface layer containing organic matter mixed with mineral material. These soils are characterised by higher iron contents in their subsoil. Their low nutrient status is easily overcome by the addition of lime and fertiliser.
GLEYS (showing “blue till” caused by de-oxygenated material, 20 & 10) are soils showing the effects of poor drainage and have developed as a result of permanent or intermittent water logging. This may be due to a high water table, to a ‘perched’ water table caused by the impervious nature of the soil itself, or to seepage of runoff from slopes. Most gleys have poor physical conditions, resulting in restricted growth in spring and autumn.
GREY BROWN PODZOLIC soils are usually formed from a calcium based parent material, which counteracts the effects of leaching. The lighter texture Grey Brown Podzolics are good all-purpose soils, while the heavier textured types respond well to the addition of manure. Very little of this type occurs in NI, it is more wide spread in ROI.
LITHOSOLS (use lithosol image in folder) are shallow, stony soils, usually overlying solid or shattered bedrock. It is soil in the early stages of being formed. They are often associated with podzols at higher elevations. Generally such soil areas have bare rock outcropping at frequent intervals and many also have steep slopes. They require a lot of top soil to cover and/or the removal of rock.
PODZOLS (8) are generally poor soils, depleted of nutrients by heavy rainfall leaching through an organic layer (the podzolisation process). They need a lot of lime and fertiliser and are usually found in hill and mountain areas.
RENDZINAS are shallow soils, usually not more than 50 cm deep, whose patent material contains over 40% carbonates. The surface layer is very dark in colour, with a neutral or alkaline pH. Rare in NI, more common in ROI.
REGOSOLS (32) are soils which show no distinct layer development. The texture can vary between sands and clays, depending on the material from which they are derived. They may be acid or alkaline for the same reason.
PEATS (40) are characterised by their high organic content, over 30%, and by being at least 30 cm in depth. Two basically different types, blanket and basin peat, occur in the country.
BLANKET PEAT typically found in the West of Ireland and all upland areas because of the high rainfall and humidity. They are poor draining and relatively shallow.
BASIN PEAT was formed in lake basins, hollows and river valleys, or where the sub-soil is sufficiently impermeable to give a high water table. Deeper than blanket peat.
RAISED BOG usually consists of a basal layer of fen or woody fen, overlain by a layer of acid peat. In their natural state, raised bog peats vary from about three to ten meters in depth. When drained and reclaimed, basin peats can have a wide range of use.
(CP 16 8A and 8B Blanket peat)
Adapted from Teagasc Project Report 4104
The Eyes have it
Time spent just looking at your soil is a much better use of it than heading off to the garden centre. The biggest curse for most of us in this green and pleasant land is drainage, identified by a combination of texture and colour. As a rule of thumb, hard layers and grey/blue soil (concrete block colour), indicates water logging. This might not be obvious at surface level so to find out dig a few three-foot deep holes, fill with water and if drained within an hour, rather than taking twenty-four, your problems should be nil.
Well-drained soils have an organic dark brown/ black (compost/ bark) colour and water should continue to flow down easily through the three-foot depth.
Knowing the soil type is the first step, finding out what plants like to grow in it means more investigation in the best tradition of the plant hunters of the past.
Handsome is as Handsome does
In 1775 Drs Fothergill and Pittcairn went to the Swiss Alps in search of curious plants, in the company of a third Scot, Thomas Blaikie. Blaikie brought back 440 various types of seeds and plants, but it was the Doctors who stole the limelight for founding the first alpine plants collection. The rock garden had been invented.
According to the Collins Dictionary, (paperback edition), the definition of alpine is: adj 1 of high mountains. 2. Alpine of the Alps n 3 a plant grown on or native to mountains.
With particular reference to definition 3, the real truth is that the gentlemen made their new plants suit the region rather than changing the region for the plants. This was why the plant finding expeditions continued and were continually funded by the rich and famous who wanted to be the first, and only if possible, to have such rarities growing in their gardens.
Some people think that you can’t plant here, or there, because of the rocks or the soil, or because they live on a mountainside for example. The truth is, as the two Doctors and their gardener friend Blaikie discovered, you can grow any plant anywhere you want and in or on any place you want, the plant must simply like their new home!
Learning the lie of the Land
But how do you adapt a plant to grow in your garden? Recently I went to view a garden in The West of Ireland. The client, expecting the garden to have an acid based soil, planted fine specimens of ericaceous plants. The results were horrific. The garden soil did not have a bog like pH, the top soil had been brought from somewhere else by the developer and was just ordinary top soil, as I know it. The only solution was to start again from scratch.
Because the soil in Dublin is alkaline, when we want to have a Pieris ‘forest flame’ on the patio we take some peat (or ericaceous compost) and put the plant in a pot. If you want to make it look as if it’s growing in the ground then in theory you bury the pot. Taking this a stage further, if you wish a large array of acid loving plants then a bigger ‘container’ is required.
Easier by far is to make an ericaceous bed. This sounds simple – the work is not, unless you have a son, as my Father would say! Assuming some mature specimen plants are included, I suggest that a pit of approximately 1.5 metres should be dug; the width depends on the amount of plants. “The bigger the better” is the golden rule here as the plant really needs to feel like it has just returned to its new cosy home. The hole is then lined with a semi permeable membrane. This allows full penetration by water, like tea bag, but retains all of your ‘new soil’. There are variations of the black liner but be careful not to take the cheaper alternative as you do not want this to break down below ground level. Ensure also to buy extra and overlap this over the edges of the hole created.
The new soil should be made by mixing three parts raw peat: two parts coarse horticultural sand: one part loam: ¼ lb four to six month slow release or base fertiliser. These are the ingredients for the John Innes composts that we see in plastic bags in garden centres. Anne Ashbury in her book “Gardening on a Higher Level”, (first published 1969), tells us that this would have been bought in its raw state and mixed by hand.
When in situ, cut off the plastic approximately 10 centimetres below the surface so that when the rest of the planting is done and mulched over it will all look even.
There are many soil enrichers and tonics that can be bought to add to your soil, but assuming you have followed my steps, no other maintenance or additives are really required outside of the usual garden maintenance such as top dressing with a slow release feed (four to six month only), weeding and mulching.
Most topsoil is neutral/slightly alkali to begin with, but if you need to alter yours, the ingredients are: seven parts loam: three parts peat: two parts coarse sand: ¼ lb four to six month slow release fertiliser and ¾ oz chalk. Again bags or pre made mixes are available if you don’t feel like getting stuck in.
Beware of following old wives tales or accepting offers of free manure when making your bed. The slow release fertiliser should provide all the nutrients needed and are a more controlled way of ensuring that equal amounts are distributed through all plants to maintain a delicate balance. C.E. Lucas in his 1956 publication tells us that “since plants imbibe their food through their roots, this enquiry should be the first and constant concern of the gardener, to an extent far greater than most of us realise. Earth is the mother of all and her children’s health depends on her own.” He goes on to say that you should “understand your soil and keep it in good heart and sweet temper. This is the beginning of wisdom.”
The best advice I can give is to ask for as much of it as possible! You don’t have to act upon it, but if you do seek professional help, never forget that cheaper can be often more tearful than cheerful. Quality lasts longer, and only use qualified staff who are members of registered and internationally recognised trade associations.
To Have and to Hold
The aftercare on a creation like this is based on understanding and no one rule will suit all. Like humans, plants will become unwell unless they have the right intake of vitamins and nutrients. A chlorosis or yellowing of the foliage may result from the lacking of a particular element or nutrient. The type of chlorosis tells us what in particular is deficient and then we can begin to understand whether the problem is one of soil type, drainage etc. One antidote is super feeds or various other quick fixes, but unless you deal with the underlying problem then it will recur.
Pre 1990 garden literature held that the gardens of bog land regions held acid soils whilst those in the Dublin/ Belfast region had more lime like alkaline soil. The rapid growth of the construction industry has changed Ireland to the point that this rule does not necessarily apply, it is now no longer possible to generalise all gardens by region. New ‘estates’ now mean something terribly different to that of the 1800’s, and for some developers the landscape is their last and least concern.
To convert a soil from acid to lime-like forever, and vice versa, or to allow opposites into the garden, requires that the plant be adapted to its new home. Attempts are often made to replicate the original rock garden, but rarely properly, and although the horticultural definition of a weed is ‘a plant growing in the wrong place’, more often the plant is put where it is not suited. As we have seen, it’s possible to create the right environment for anything from a single plant to a group or for an entire garden, mainly by adapting the soil.
The same reasoning applies to coastal gardens. In January 1927 H. H. Thomas wrote in the preface to his publication, “An Easy Guide to Gardening”, that it was “not a guide to easy gardening, but an easy guide to gardening”! (Read it twice). “Gardening is easy if you take the pains and use common sense, but not otherwise” and he goes on to say “on such a foundation, success beyond all expectation can be built.” The point is you can have the finest garden anywhere in the world, as long as you know what you are doing, have the ability to do it and carry it through. Whether bog, mountain, coast or pasture, the golden rule is planning and preparation. Fail to prepare – prepare to fail.
Prepared in association with Peter Donegan Landscaping Ltd., Bettyville, Ballyboughal, Co Dublin 01-807-8712 mobile: 087-659-4688 www.doneganlandscaping.com
Soil & Environment: Northern Ireland publ DANI, Agri-Food & Biosciences Institute, Belfast 9025-5355 www.afbini.gov.uk ISBN 0 85389 699 2