The Soil in Your Garden

The Soil in your Garden.

As summer fades and we enter into autumn and winter planting it is probably an excellent time to consider the soil in your garden and its role in the success or failure of your plants.
It is essential to the success of your garden that you understand your soil.
As gardeners we like to grow a wide range of plants, many more than those plants which occur naturally in the patch of earth in which we garden.
If our plants are to thrive we need to understand their needs and provide them with the correct environment in which to grow.

If we look at a cross section of soil, it consists of two layers – top soil which comprises the nutrients and organic matter and the subsoil, which is devoid of both these elements.
Topsoil varies in depth from centimetres to a metre or more. The subsoil is hard, difficult to dig and often paler in colour.
All soils are made up of the same basic ingredients, sand, clay, silt and loam.
The proportions in which these occur in your soil determine the type of soil you have.

Sandy soil is granular and has a gritty texture. The particles are large and of an irregular shape and it falls apart when balled up in your hand.
It is easy to dig, free draining and quick to warm up in the spring.
Because of its free draining nature it does not hold water for very long and is therefore prone to drought.
Nutrients leach very quickly from sandy soils which can leave them impoverished.

Clay soils have very tiny particles which pack together tightly excluding air and making the soil sticky and difficult to work, they can be rolled in the hand to form a ball.
Drainage is poor and clay soils are often waterlogged, making them slow to warm up in spring, in summer they bake hard, crack badly and form large lumps.

Silty soil is usually fertile, falls between clay and sand particle size and compacts easily. It is a free draining soil type.

Loam contains clay, sand and silt particles blended in combination with humus, in a balance which supplies plants with the air and fertile soil best suited to their needs. Moisture retentive and well drained, loamy soils warm up quickly in spring and are easy to work.

Once you have established your soil type you can begin to take steps to improve the condition of the soil.
Gypsum (calcium sulphate) can be used to break up clay by a process called flocculation, tiny particles form into larger particles which cause lumps to crumble and improve the friability of the soil.
This effect sometimes lasts for only 1-2 years.
The most effective long term solution to the problem of clay soils is to incorporate as much organic matter as possible into the soil
The addition of bulky organic matter will help clay soils open up, drain more efficiently and improve the uptake of nutrients.
Similarly the retention of both water and nutrients is improved on sandy and silty soils by adding humus.

Well rotted stable manure, sheep manure, cow manure and compost contain plant food and add valuable humus to the soil.
Mulch such as pea straw, which is constantly replenished as it decays, will also improve the friability of your soil
Leaf mould is a good soil conditioner although low in food value.
Growing a green manure crop is an excellent way to introduce a substantial amount of organic matter into the soil.
Healthy soil contains millions of microscopic bacteria, fungi and earthworms that are constantly breaking down humus and providing the food that plants need. The other vital ingredients are water, which dissolves these nutrients, and air, without which soil organisms would die.

Soil pH

As both very acid and very alkaline soils lock away nutrients, it is important to
establish the pH of your soil as this can have a direct impact on how successfully
your plants grow.
pH is the measurement of its acidity or alkalinity and is determined by the amount of
lime it contains. This has an effect on the uptake of nutrients and also on the species
of plants which can be grown successfully.
Soil acidity is measured on a scale which ranges from 1 which is extremely acid, to
14 which is extremely alkaline.
Each unit change in the pH scale is a tenfold difference in acidity or alkalinity.
As an example a soil with a Ph of 8 is ten times more alkaline than soil with a pH of
7
A pH of 7 is neutral and somewhere close to this level is best for growing vegetables.
Most ornamental plants grow best where the pH is somewhere between 5.5 and 7.5.
Lime hating plants such as rhododendrons and azaleas prefer a lower pH while lime
lovers such as bearded iris and brassicas grow best in soil with a pH above 7.0
Measuring the acidity or alkalinity of your soil involves taking several samples from
around your garden and testing with a small inexpensive soil testing kit which is
readily available.
Plants and weeds that do well in your garden can be an indicator of soil pH.
Rhododendrons, azaleas, sorrel and plantain thrive in acid
soil. The presence of sorrel is often a good indicator that soil is acid.
Lime lovers like bearded iris, poppies, clematis and brassicas thrive in alkaline soil.

Changing Soil pH
It is quite a simple matter to make soil more alkaline, ie raise its pH by adding lime,
(calcium hydroxide) dolomite, (dolomitic limestone) or wood ashes.
To increase soil acidity is less straightforward, the addition of animal manures, leaf
mould, sawdust and peatmoss will all help to acidify the soil.
The addition of powdered sulphur at the rate of 1.2oz sulphur per square metre should reduce acidity by 1.0 point.
Iron deficiency (Iron chlorosis) is the result of high pH soils reducing the availability
of iron to plants. Leaves which become pale green or turn yellow and have leaf veins which remain green indicate iron deficiency. The use of iron chelates will alleviate this problem.

Plant nutrients.
Plants require a whole range of mineral nutrients to sustain healthy growth.
Most soils contain a reasonable range of them, however it is possible for soils to be deficient in some nutrients, which affects growth and performance.
This often becomes apparent once plants are established and failure to thrive or unhealthy foliage indicates that all is not well.
It is helpful to know something about the most significant of these in order to identify possible deficiencies in your soil
Most of the major element deficiencies show on the old or lower leaves of the plant.
Minor element deficiencies usually appear on the newer leaves towards the tips.

Essential Plant Nutrients
Calcium (Ca)
Magnesium (Mg)
Nitrogen (N)
Phosphorus (P)
Potassium (Potash) (K)
Sulphur (S)

Trace Elements
Boron (B)
Chlorine (Cl)
Copper (Cu)
Iron (Fe)
Manganese (Mn)
Molybdenum (Mo)
Zinc (Zn)

Nitrogen
Essential for the formation of protein and chlorophyll and responsible for vigour and
size of leaves and stems.
Imparts dark green colour to plants.
The soil in its natural state has very little nitrogen available to plants, most of the
nitrogen is present in the organic matter in the soil, so the total amount of nitrogen in
in the soil is dependant on the organic matter.
Nitrogen deficiency causes stunting, harder stems and mature leaves which become
Chlorotic (yellowish) progressing from light green to yellow.

Sources of Nitrogen
Fresh Manure… rich in uric acid… a potent form of nitrogen which can easily burn plant tissue.
Aged manure…well rotted 2-3 years old.
Nitrogen content is variable and dependant on age and method of storage.
All these forms of nitrogen must be broken down by nitrifying bacteria before the plant is able to use them.
Nitrifying bacteria are most active in moist aerated soils, wet and water logged soils do not contain sufficient oxygen to supply the needs of the bacteria.
Legumes…(peas, beans, clover etc) with the help of soil bacteria are able to fix nitrogen on nodules on their roots.
Soils in which these crops have recently grown are particularly rich in nitrogen.
Blood and bone
Dynamic Lifter and similar compound fertilisers, (check the formula on the packet)
are a good source.
Sulphate of Ammonia (ammonium sulphate)… use carefully as it can burn soft tissue.
Nitrogen given in conjunction with added potash gives a balance which is necessary for growth. Compound fertilisers, (check the formula on the packet) are a good source.

Phosphorus

Important for strong root growth ( essential for root vegetables) energy storage and
seed production and is involved in the transfer of hereditary traits.
Vigorous seedlings, promotes rapid development of roots in young plants… any
seedbed should have an ample supply of phosphates.
Symptoms of deficiency include stunted growth, low drought tolerance, weak root systems, poor seedling growth and lack of response to other fertilisers.
Sources of Phosphorus
Bone or fishmeal
Superphosphate.
Organic matter in the soil is an important source of phosphorus and aeration and moisture are important for microbiological breakdown of organic matter, an important source of phosphorus.

Potassium (potash)

Necessary for the well balanced growth of leaves and stems, water uptake and photosynthesis.
Production of flowers and fruit…plants which fail to flower properly can often be induced to do so by the addition of potash.
Potash deficiency is characterized by scorched leaf margins and sometimes a reddish tint to leaves, poor flowering, fruiting and berrying, winter damage and frost damage.
Highly soluble, so well drained sandy soils are often deficient, however moisture is needed in order for potassium to move to the roots for uptake
Uptake of potassium is affected more than most other nutrients by poor aeration.
Sources of Potash
Wood ash in generous amounts
Seaweed based fertilisers
Compound fertilisers, e.g. tomato plant food.

Magnesium

This element is an essential part of the chlorophyll molecule and aids in the
absorption of other nutrients, it is also important for seed production.
Magnesium deficiency shows in the older leaves which become red-brown,
green at the tips and lower central vein areas and there is often early leaf fall.
The most common source of magnesium is dolomitic limestone which neutralizes soil
acidity while providing calcium and magnesium.
Magnesium Sulphate can be applied to the soil or used as a foliar spray.

Calcium

Stimulates root and shoot development, influences yield by reducing soil acidity,
maintains the integrity of cell membranes and is necessary for nitrogen fixation by
legumes.
Deficiencies of calcium are associated with soil acidification, poor root growth and growing tips.
As most calcium deficient soils are acidic, liming is an efficient method of adding calcium. Both garden lime and and dolomite are reliable sources .

Sulphur

Essential for nitrogen fixation by legumes, necessary for chlorophyll formation and as a constituent of the organic compounds that give odours to onions, garlic and mustard.
Deficiency shows up as pale green young leaves, thin stems and spindly growth. Sources of sulphur are animal manures and organic matter in the soil.