Prepping your Soil
In an
ideal world, the winter would be the ideal time for digging over the garden. So
the elements have a chance to work on the soil before cultivation begins again
in the spring. It is during this digging that you can do much to improve
difficult soils. ‘Difficult’ means those that may be hard to work with or those
that, because of their poor structure, are either too wet or too dry for good
plant growth, or lacking in essential humus or organic matter.
Soils can
be divided into four main types: clays, sands, chalk soils and loams. Loams
come midway between clays and sands. They are usually easy to work and provide
ideal conditions for plants. Clay, sand and chalk each have special characteristics
that can make them difficult soils and it may take several years to turn them
into easily-managed growing mediums.
CLAY Soil
Clay is
commonly known as a heavy soil because it is very hard to cultivate – both to
dig and to prepare for seed sowing or planting in the spring. Because of its
chemical composition it has a very dense structure and is able to hold large
amounts of water. It is therefore a very wet and sticky soil and takes a
long time to dry out and warm up in the spring.
During
wet weather and in autumn and winter, clay soils can become waterlogged and
this will affect the health of plants. When a soil is holding too much water
the oxygen supply to the plants’ roots is reduced and if this condition
continues over too long a period the plants may die. In hot weather during
spring and summer, clay soils can become as hard as rock; because as they dry
out, the clay particles shrink, making cultivation almost impossible.
Opening up clay soils
Dig clay
soils in early to mid winter (November to mid December) so that frosts can
break them down throughout the winter. Frosts will make a heavy soil more
crumbly and therefore far easier to cultivate in the spring. You can also make
a clay soil more crumbly, and take out most of the stickiness, by applying a
top dressing of sharp sand and horticultural gypsum (sulphate of lime)
immediately after digging. Let it lie on the surface over the winter, during
which time it will be washed into the topsoil by rain.
Apply Gypsum fairly generously each year, at a rate of about 500g-1kg per sq m
(1-2 lb. per sq yd.).
Hydrated
lime has a similar effect to gypsum. Again it can be applied as a top dressing
after digging. Apply it as evenly as possible. Generally an application every
two or three years is adequate for most crops.
It is
interesting to note that, though gypsum improves the soil without raising the
pH level (increasing alkalinity), hydrated lime raises the pH as well. Both
cause flocculation (create a good crumb structure), thus improving the soil texture,
drainage and aeration.
During
the actual digging, incorporate as much organic matter as possible to ‘open up’
the soil and to prevent it forming into large clods. This should give better
drainage of surplus water and improve aeration. There are various types of
organic matter that are suitable, such as well-rotted farmyard or horse manure,
garden compost, peat, leaf mould, spent hops, bracken, straw, composted seaweed
and composted sawdust. Try to apply at least one barrow load per square metre
or yard. It is best to double dig clay soil as this will enable you to get the
organic matter down into the lower soil.
When double digging remember to keep
the soil in its proper layers; in other words, never mix topsoil with subsoil.
Do not
apply lime and manure at the same time, but leave an interval of two or three
months between applications. If you are digging in organic material in the
autumn, then scatter the lime over the soil surface in early spring.
Spring is
also the time to apply a general-purpose fertilizer prior to sowing and
planting. It is not much use applying this in the autumn or winter, as most of
the plant foods will have been washed too far down in the soil to be of use to
the plants when they are needed.
SANDY Soils
Sandy
soils are the opposite of clays. They are generally known as ‘light’ soils
because they are easy to work. Sand has a gritty texture, consisting mostly of
grains of silica that are chemically stable. So, unlike clays, the soil
particles do not stick together and the soils are very loose in structure.
Because
of this loose structure, sandy soils are incapable of holding much water. They
warm up quickly in spring, but during dry weather they can dry out very rapidly
and cause plants to wilt or die through lack of moisture. Again, because of
their loose structure and chemical stability, sandy soils cannot hold much
plant food and are therefore said to be ‘hungry’ soils.
Feeding sandy soils
It is not
necessary to dig sandy soils as early as heavy clay types, but even so, digging
should still be completed well before sowing and planting time in the spring.
Ordinary single digging to the depth of a spade should be sufficient.
However,
in some sandy soils, an iron pan can form in the lower soil that may be
impermeable to air and moisture, and therefore harmful to plants in that it
prevents surplus water draining away. An iron pan is a rock-hard layer of soil
that, as the name implies, contains a large quantity of iron. Sandy soils
naturally contain a large amount of this element that, over the years, is
leached (by rain) into the lower soil where it cements sand particles together.
If you discover an iron pan, you would do best to break it up by double digging
the site. Thereafter you can carry out ordinary single digging as it will
probably be many years before a pan forms again.
The main
consideration in improving sandy soils is to incorporate as much organic matter
as possible to supply humus. Most sandy soils are seriously lacking in humus
and so have a very poor structure, the soil being unable to hold water and
plant foods. The humus acts as a sponge and ensures adequate moisture during
dry periods. Apply plenty of organic matter every year (provided this ties in
with the cropping programme) for it quickly disappears in this type of soil.
Also apply a general-purpose fertilizer in spring, prior to sowing and
planting.
CHALK Soil
In some
respects chalk soils are similar to sands. If you have only a thin layer of
soil overlying chalk you will often be faced with lack of moisture during dry
weather due to the percolation of water down through the chalk out of reach of
plant roots. Such a soil will also be lacking in humus and plant foods. An
additional problem with chalk soils is high alkalinity that can cause many
plants to show symptoms of chlorosis (dwarfing of the plant and yellowing of
the leaves). This occurs because the plants are not obtaining sufficient iron
from the soil; iron is rendered unavailable to plants in conditions of high
alkalinity. Roses, many soft and top fruits, hydrangeas and ericaceous plants
(such as rhododendrons, azaleas and heathers, etc.) are prone to chlorosis.
Soils
over limestone should be treated as chalk soils; it is often forgotten that
chalk is a pure form of limestone.
Improving chalk soils
Chalk
soils (especially thin soils overlying solid chalk) need plentiful additions of
organic matter; on some types it is almost impossible to apply too much. On
such a site you would do best to dig as deeply as possible each year –
preferably double digging. This will enable you to get organic matter well down
into the soil, so that, over a number of years, you gradually increase the
depth of suitable growing soil. Also add organic matter to the topsoil – mix it
well in if possible. Any of the kinds of organic matter suggested for clay
soils can be used, but very acid materials (such as peat and leaf moulds) are
particularly suitable as they help to reduce alkalinity – if only very
slightly.
Alkalinity
can be reduced by incorporating flowers of sulphur into the soil, but very
large applications are necessary to do any good; you would need to use about
500g-1kg per sq m (1-2 lb. per sq yd.).
As with
chalk and sand, apply a general-purpose fertilizer in spring before you begin
to sow or plant.
