To have healthy plants they need not only protection against diseases and pests but also to grow in soil with the appropriate nutrients for their needs. Different soils have different properties and so the advice we give to gardeners can depend on the type of soil the garden has.

Although at first sight your garden soil would appear to be solid and robust, it is in fact a fragile living environment that must, at the very least, be protected and wherever possible improved by certain rules of good soil cultivation.

The very worst situation is directly after the builders have left the site of a newly-built house where the soil has been moved, mixed and compacted. The best types of soil will normally be the dark fertile top-soil (loam). Compaction is a problem that must always be addressed to ensure that there is no ‘pan’ or layer of compacted soil. This will prevent water from draining away and plant roots from penetrating it in dry spells in their search for water.

‘Pans’ can show their effects many years after planting and lead to the death of plants and drying out of lawns.


Cultivating the soil to a depth of 50cm by double digging will take care of most of these problems. Adding well-rotted farmyard manure, spent mushroom compost or other proprietory pre-planting organic material, will help improve the soil by holding in moisture and providing some plant foods. The procedure for double digging is as follows:
  1. Dig a trench one spade or fork deep and 70cm wide. Store the soil to fill the final trench.
  2. Fork over the base of the trench, adding compost or manure.
  3. Dig and throw forward the next 70cm mixing in organic material, so creating the next trench.
  4. Repeat until the entire plot has been dug and fill in the last trench with the soil from the first.


Double digging is achieved by using a digging spade or fork but with care the hire of a mini – digger can prove an effortless way of soil preparation, particularly if large areas are to be prepared. Whether using a fork and spade or mini-digger the following rules should be followed:
  1. Never attempt to prepare the soil when very wet or frozen.
  2. Always attempt to keep the fertile top -soil on the top and the sub-soil below.
  3. Add good quantities of organic material.
  4. Dig deep if ‘pans’ are suspected.
  5. On very wet soils consider additional drainage.
  6. When possible, prepare in autumn to leave winter weather to naturally break down the soil surface.
  7. Always try to work off a board when digging to prevent compaction.


It is worth salvaging bricks and rubble as soil preparation progresses as they can be used for hardcore, under paths or even for surfacing the path. Odd pieces of timber may be useful for edging borders or producing temporary supports for banks and other constructions.


Weeds, in particular perennial types, should be removed as seen by digging out or by using a weedkiller. Dandelions, Couch grass (Twitch), Ground Elder and Docks are among the worst. If the area is covered by grass or turf it may be worth considering removing it as thin turf and storing in a stack in one corner of the garden. By stacking them roots upwards in a tidy square heap they will soon rot down into top-soil that can be used later.



There are a number of plants that will only tolerate an acid soil and therefore before planting starts it is important to test to find out the amount of acidity present. This is best done by carrying out a soil test to determine the level of pH in the soil. Commercially produced soil test kits are readily available. Take soil samples, using a hand trowel, in a line diagonally across the area to be tested at 2m intervals and 15cm deep. Bring these samples together in a plastic bag or bucket, avoid contact with your hands to prevent contamination. Simply follow the directions on the soil test kit and the pH content can be decided by comparing the sample with the colour chart supplied.



Fertilisers can be broken down into two groups; inorganic and organic.


These are either manufactured commercially from a chemical process or mined. Modern fertilisers are formulated into compounds that over a period of time release a balanced amount of Nitrogen, Phosphorus and Potassium. There are straight fertilisers that supply one of the elements only and these can be used to correct any specific deficiency. They are applied as a dry powder or in granulated from during the spring at the manufacturers recommended rate. Some act quickly, others have a slow -release formulation releasing small amounts over a long period. Some can be applied as both a dry or liquid fertiliser with the liquids applied from late spring to early summer. Applying at the correct time is important to avoid wastage and damage.


These are derived from once living vegetable or animal material such as bonemeal and fish, blood and bone. In the main they are slow acting so careful consideration to the date of application is important. On some soils it may be necessary to apply a specific fertiliser to correct a deficiency within the soil. Some specific plants need tailored cocktails of fertilisers – roses are a good example.

Applying fertiliser

The most popular way of feeding is by liquid fertiliser diluted into water, as directed on the packet. This is applied directly to the roots, and most healthy plants will benefit from being fed every two weeks during summer and perhaps once a month during winter. For small quantities of plants, liquid fertilisers marketed specially for house plants are ideal, since they are easy to dilute into small cans. For people with many house plants, containers and outdoor plants, the general purpose fertilisers such as Miracle-Gro are more versatile. It is best to make up a large watering can of fertiliser, then fill a smaller can from it.

Some fertilisers can also be absorbed through the leaves, a process known as foliar feeding. This can be applied through a sprayer or mister and is ideal for plants that need feeding during winter when the roots are less active, and for epiphytic plants such as bromeliads and orchids, which, because they naturally grow in trees, have small root systems and are more used to obtaining nourishment via their foliage.

Slow release fertilisers are ideal for busy people. These are added as tablets or sticks and gradually release nutrients over a period of three to six months.

It is worthwhile opting for a versatile, general purpose liquid fertiliser that can double as a foliar feed.
It is usually bad practice to feed a plant whose roots are bone dry and there is also little to be gained by feeding the roots of a sick plant. Some people mistakenly believe that they are applying a tonic, but sick roots will not be able to take up the fertiliser, which hangs around in the compost doing more harm than good. A weak foliar feed would be better.


Green manures improve soil fertility and increase humus content. They improve the structure of the soil and can prevent soil erosion during heavy rain or dry, hot summers, so are an excellent way of improving soil quality of a plot between crops. Green manures are fast-growing plants sown to cover bare soil. Often used in the vegetable garden, their foliage smothers weeds and their roots prevent soil erosion. When dug into the ground while still green, they return valuable nutrients to the soil and improve soil structure, meaning any empty plot of poor soil could benefit from a crop before being planted out. They are usually sown in late summer or autumn and mop up any nutrients, preventing them being washed away by winter rain. When dug in the following spring, they release these nutrients back into the soil. Winter grazing rye and winter tares are hardy green manures that will carry on growing all winter before being incorporated back into the soil in spring.

Green manures can also be used to cover bare patches of soil in the spaces between crops, or during intervals between one crop and the next. Fast-growing mustard sown before mid-September can be incorporated in October, for example, or the frosted remains left as mulch. Summer-grown green manures such as buckwheat and fenugreek form dense foliage that will effectively suppress weeds.

Green manures belonging to the pea and bean family (legumes) have the additional capacity of storing (fixing) nitrogen from the air to their root nodules, but only in summer. Nitrogen is a valuable plant nutrient.

Other benefits of green manures include protection of the soil surface from compaction by rain and shelter for beneficial insects such as ground beetles.

Using green manure

Sow seeds in rows, or broadcast them across the soil and rake into the surface. Once the land is needed for cropping, chop the foliage down and leave it to wilt. Dig the plants and foliage into the top 25cm (10″) of soil. After digging in, the site should be left for two weeks or more before sowing or planting out as decaying green materials can hamper plant growth.


A dense carpet of green makes a perfect environment for slugs and snails, so control measures may be needed after green manuring.

Decaying green manures can suppress plant growth, so allow at least two weeks between incorporation and planting or sowing.

Club root can be a problem with green manures in the cabbage family, such as mustard.

For more information, please visit one of our Garden Centres and speak to a member of our friendly and knowledgable plant team.