SOIL

Soil

The fertile soil that plants grow in has developed over many years through the action of the weather, insects and the incorporation of organic material, and in our gardens we have to supplement that work if we want to obtain the best from our plants. 

One thing that all Gardeners need to know about is the soil type they have, whether it is acid or alkaline, clay or sandy, or if they are lucky enough to have inherited fairly deep fertile loam. This is important since it has a significant impact upon what we can grow in our gardens.

pH

pH refers to the chemical composition of soil, whether it is acid, neutral, or alkaline. pH test kits are stocked by most good garden centres, and can even be ordered via mail order. 

A pH of 1-5 is generally accepted to be acid, a pH 7 (6-8) neutral, and pH 9-14 alkaline.

Rhododendrons, Magnolias, Gentians and many other plants will not grow in soil containing Lime (Alkaline Soil Types). Indeed some people choose where they live because of their preference for growing plants that will only grow in acid soil (ph 1-5)

Some plants prefer an alkaline soil to thrive (ph 9-14). 
Lime tends to combine with essential chemical nutrients making them unavailable to many plants, and only plants that are adapted to such conditions will thrive. 

Excepting lime intolerant plants, which require acid soil conditions, almost all plants will grow in a neutral soil (ph 6-8). Chemical neutrality means that, if present, essential nutrients will be available to support plant growth.  

There are one or two points to remember when seeking to improve the soil: - 

Never use mushroom compost to improve acid soil if you wish to grow azaleas, rhododendrons, pieris, gentians, or any other lime intolerant plants, for mushroom compost contains lime. 

Organic material will always be the best solution to both improving soil condition and improving nutrient content. Organic material breaks down slowly and releases its nutrients over time, it creates an open structure allowing the soil to breathe, and it actively promotes a living soil, where beneficial humus-forming bacteria, fungi, and other valuable forms of life like worms will thrive. 

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Sandy Soils

Sandy soils tend to be very free draining, and this can cause severe drought problems for plants.

Not only does moisture disappear, but because of the free draining nature of sandy soils, the nutrients that our plants need to thrive are also washed away, leading to poor and impoverished soil.

With the watering restrictions we now have to observe in the UK and elsewhere, it would be impossible to replace the water that naturally drains away from our soils as the water table falls. Thus we have to either work with the soil we have inherited by planting adapted or drought tolerant plant species, or do something to improve the soil and its ability to retain moisture and nutrients, however improving one's soil is not for the feint-hearted.

I have always sought to improve my soil by adding organic matter to it no matter what the soil type. But to achieve any real benefit in sandy soils, improving the moisture retention of sandy soils requires serious effort. It is of no use to add compost to the top 8 inches (20cm) of soil and think that the job has been done. In fact to do so can be positively harmful, since plants that would have sent roots downwards to find water will send their roots into the top 8in (20cm) using what water is available at that level, and then suffer the consequences of drought when the moisture at that level has gone.

When taking on a new garden, or a garden where I can start from scratch, I always aim to incorporate as much organic material as possible into the top 3 ft (1m) of my garden, even under the lawn, placing the majority of the compost as deep as possible. Inevitably when the soil is returned the soil level is substantially higher than it was before, however, with time and the breakdown of the added material the soil quickly returns to a more normal level. Having prepared my garden in this way, it only requires that new organic material is added to the top layers where the action of worms, and drainage through the soil will wash humus and minute organic particles further downwards, improving and replenishing the organic content at lower levels.

To fully appreciate the nature of sandy soils, try filling a container with marbles (representing grains of sand) and then fill the container with water (filling up the spaces between the marbles). When the marbles and water are separated, the volume of water remaining will give an idea of exactly how much space is available within a sandy soil to accommodate newly added compost as it is broken down into humus and smaller pieces of organic material. 

It is not recommended that anyone digs a trench of any depth unless they take safety precautions, a sudden collapse of the proposed flower bed could prove dangerous, if not fatal. 

In Summary:- 

Sandy soil requires a lot of improving if you are to grow the plants that you want, having due regard for the changing climate in the UK, with record breaking daytime temperatures, lack of rainfall and lower water tables at these times. The extent to which you improve your soil depends upon how much you are willing to spend, how big your garden is, and how far you are prepared to go in putting the required effort into doing what is needed. 

For the lazy gardener on a budget, it will probably be easier to work with plants that are either adapted to dry conditions, or are drought tolerant.

Grape Vines are adapted to drought conditions and will put down roots of up to 70ft (20m), and more in search of the water and the nutrients they need. Provide grape vines with a pergola-like structure, and tie the new growth into the pergola until the vines are mature and they will provide a self supporting canopy that will provide shade both for the garden and those who simply want to enjoy their gardens. Add into the equation, beautiful pendant clusters of grapes that can either be used for brewing one's own or eating dependant upon the variety grown.

Many of the common garden plants we grow in the UK will put down tap roots that seek out the moisture they need, e.g. Lupins & Oriental Poppies for example. Alternatively you may like to rely upon bulbs, tubers, corms and rhizomes, many of which need a wet spell to plump them up ready for flowering, and yet need a summer dry spell to make them thrive, Tulips are a good example. Dahlias originate in the drier areas of Mexico, and if the correct cultivars are grown, you will enjoy continuous blooms from the beginning of the season and until the end. 

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Clay Soils

Clay is a wonderful base for a garden soil, rich in nutrients, and moisture retentive too. Clay usually comprises extremely fine particles bound by natural salts. The many reference books tell me that Clay was formed by many thousands of years of glacial action grinding large rocks into a very fine powder. Let it go dry and it sets like concrete, and I do not exaggerate. At times I have had to take a pick-axe to clay soils simply to make an impression.

We have all been there, taking on a new garden that was laid to lawn by the builders to make the sale, the building rubble, wall ties, and unwanted wood all buried beneath, and yet we hope to have the best garden ever within a few weeks of moving into our new home. 

The building site when prepared probably consisted of felling trees, digging foundations and then putting up the home you purchased. Underneath the garden there will possibly be the remnants of tree root systems, all the rubbish that the builders could not be bothered to remove, and solid clay all disguised by an imported lawn laid on the bare clay.

Effectively trying to grow plants on solid clay is analogous to farmers who plant wheat on fields that for too long have been treated with contempt. The substrate that wheat grows on is like concrete, and the roots of the plant offer nothing more that a hold-fast like algae in the sea. The wheat only grows because it is artificially fed the nutrients it needs to grow. 

Do not dispare. If you know what you are dealing with, you can have a good garden. But again it takes some work.

Understanding your clay soil.

Take a sample of your soil, mix it with water, and view the cloudy mixture. Now add some lime ( I use builders lime), now watch how the particles join together and the cloudiness disappears. The process is called flocculation. The lime binds the fine clay particles together and the cloudiness disappears.

The bonding of fine particles of clay is not simply dependant upon a chemical cause, it can be achieved trough organic means too. Yet in my experience the fastest way to achieve the binding of fine clay particles is the addition of lime. Yes the addition of lime locks up many plant nutrients, but if the soil is bonded like concrete, roots would never reach those essential chemicals which are needed for growth. Indeed the roots would never penetrate the soil at all. I do not exaggerate when I say that a pick axe is needed to dig the garden if the soil has not been cultivated.

As with a sandy soil, I always work to make the top 3ft (1m) fertile.

I have read all the books, all of which inform that we should not disturb the underlying medium. We should not dig up the solid clay that underlies our garden.  I disagree with that advice.

My previous garden was in Mid-Suffolk, I inherited a garden that dated from the 1500's and yet there was less than 8 in (20cm) of top soil. Nothing would grow, despite sea-shells and everything else that had been added to the soil.

I dug deep (3' 6"), and I added lime to the underlying yellowish clay [a whole bag to 15ft x 3ft x 3ft 6in]. I added as much organic content as possible (a nearby conifer had been felled and shredded), and without waiting, I replanted the plants that had been removed, and added many including Dahlia 'Bishop of Landaff'

I watered with Miracle Grow and was amazed at the transformation. Where only weeds would try to survive, and I mean try, I now had luxuriant growth from all my required plantings, plus self-seeding from not only the plants I had planted myself, but violets, and other plants of merit.

The only drawback was that the woodchips from the conifer, which I had added to the soil, had not yet broken down and made the soil very porous, and thus the soil was freely draining and dry.

You may not appreciate my joy at being able to pull up weeds with their roots intact, nor the fact that many plants including ceanothus self seeded and grew, until you try to grow something in solid, dry, concrete-like clay.

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Humus

A good garden soil is one that is mature and contains humus. Humus is the brownish substance formed by dead bacteria that live naturally in our soils. It binds fine clay and chalk particles, it coats sand grains, and allows the soil to breathe.

Humus is produced when there is enough organic material in the soil to allow the necessary bacteria to feed and rapidly multiply.

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Compost

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