As we have seen, the soil teems with life, but it is doubtful if any of us appreciate its true worth. It is the gardener’s stock in hand, and as Sir Albert Howard, a pioneer conservationist, some decades ago once wrote, “a fertile soil means healthy crops, healthy livestock, healthy human beings and a healthy nation.”

a small pile of manure

It is therefore imperative that we keep the soil in a really good healthy condition, building it up and replacing those nutrients removed by growing plants. The aim should be to keep the soil.

Quick acting fertilizers will certainly speed growth but they will do little to benefit the ground or replace feeding matter which plants have used. The law of return should be followed, for it is nature’s way. It implies growth and decay—the passing back into the soil what has been taken out.

The Importance of Compost Heap

That is, using organic matter from vegetable animal and human waste. This is why a compost heap should be regarded as essential. Where space is very limited a bin can be used and properly made, the compost will be sweet and odorless.

Actively decaying humus-forming, organic matter works wonders for all soils. As food for the various forms of soil life it is digested and broken down.


In the garden we can open up and feed the soil with compost and manure. Farm and poultry manure although not always easy to obtain, are often offered in processed form and sold in bags at garden centers and stores.

It is not advisable to dig in fresh strawy manure because it usually has a denitrifying effect on the soil—wait until the straw is broken down. It should be kept in heaps until the straw has shortened and breaks easily by which time there will be no ‘smell.’ Place the heap in a sheltered position and cover it to stop rain leaching out plant foods.

Farm Animal Manure

Mixed farmyard manure can be used for all purposes but horse or stable manure is considered to be of higher quality, although its nutrient value depends on how the animals were fed.

Cow and pig manures are heavier and therefore particularly useful on light sandy soils. Sheep and goat manures are reckoned to be richer in nitrogen. When so few of us can keep animals, it is fortunate that there are quite a lot of good substitutes available.


Seaweed has long been known to benefit the soil rendering the poorest soils fertile. It can be dug into the ground up until three months of sowing or planting and also added to the compost heap.

Dried and powdered forms are now offered under proprietary names. These can be forked into the surface during autumn and winter.

Sewage Sludge

Sewage sludge improves the physical condition of the soil rather than supplying a great deal of feeding matter. It is valuable for adding to the compost heap.

Spent Hops

Spent hops are useful for digging in. They help to retain soil moisture as well as supplying nitrogen. The bag analysis will show whether potash or phosphates have been added.

Poultry Manure

Poultry manure has its uses. It can be worked into the compost heap or dug in, in the usual way. It is now possible to obtain dried poultry manure for working into the top 5 cm (2 inch) of soil in the spring.

Pigeon Manure

Pigeon manure from lofts can be used in the same way as poultry manure, but it should not be added to seed compost.

Bark Fiber

Bark fiber is an excellent soil improver. Somewhat similar to leaf mold in appearance, it is an attractive light brown color and a useful alternative to peat.

Easy and clean to handle, it is cheaper than leaf mold, lasts longer in the soil and its ‘aroma’ tends to keep away soil pests. As it does not pack down or form lumps, it allows roots the air and moisture they need for free development.

Bark fiber lightens heavy soils and gives more bulk to light ground, enabling it to hold moisture. Used as a mulch, it prevents the surface soil from crusting in dry weather and suppresses weed growth, while it can be added to potting composts with advantage.

Green Manuring

healthy looking plants growing

Green manuring is a method of increasing soil fertility in the garden, usually resulting in heavier crops of good flavored vegetables. Green manure plants are among the best natural soil conditioners. They improve the soil’s texture and make it easier for nutrients to be absorbed by the plants.

Green manure can be said to grow humus, which prevents plant foods from being washed out, and in the case of legumes they increase soil nitrogen without causing soft leafy growth.

If the green manure crop is well worked in, in naturally clay soil, it will break down quite fast and render the soil easier to work. It also tends to increase a plant’s resistance to pests and diseases.

While it is possible to use certain annual weeds, such as groundsel, as a green manure crop, and many of them are really fast growing plants, some are liable to seed when quite small and a continual crop of self-sown weeds is a nuisance.

Whenever a piece of ground can be allowed to lie fallow for a period of six weeks or more, the site can be dug or hoed deeply and sown with quick growing seeds of plants that make ample foliage.

These include peas, beans, lupins and tares, all of which add nitrogen to the soil. In, addition, flower and vegetable seeds, surplus to your needs, also make first class green manure if the plants are dug in at the peak of their leafy growth.


Mustard is one of the best plants to build up fertility in land that has been stripped of its top soil by building operations. One should avoid using mustard where club root has crippled a recently harvested crop, since it belongs to the order Cruciferae, and is liable to be attacked by this disorder.


Sunflowers are highly recommended if the land is not being used for several months in early summer. This crop must be dug in before the stems become too tough, otherwise they will take a long time to decay.

The blue field lupin, Lupinus angustifolius, and the white flowering form, have often been used as green manure crops. They are quick growing and ideal for sowing from late April to July.

Dig them in as soon as their flower spikes can be seen and while the stems are still fairly soft. It is helpful first to knock down the growths, before chopping them up and putting them in the trench as digging proceeds. Any plants not dug in can go on to the compost heap.

Winter Tares

Winter tares are often sown in late summer, but they are equally suitable for sowing in April or early May. They can then be dug in during August and September.


Buckwheat, Fagopyrum esculentum, is another useful green manure crop. The large seeds are best sown in rows 30 cm (1 ft) apart.

One ounce of seed sows approximately 30 m (100 ft) row. Sown from April onwards growth becomes very leafy, so much so that all except the coarser, more persistent weeds, such as ground elder, are smothered.

Crimson Clover

Crimson clover, Trifolium incarnatum, is best grown as an annual and if left, it will grow 50-60 cm (20-24 inch) high. As a bonus it will be of use to bees which never fail to find and regularly attend plants in flower.

Sow the seed in April making sure the site is not lacking in lime. Growth is usually quick and once the flowers begin to fade, break down the stems and dig in the plants.

Another way of using crimson clover is to sow it in August or early September after a crop such as potatoes have been lifted.

Whatever green manure crop you decide upon, every endeavor should be made to take out deep-rooted persistent weeds such as couch grass, ground elder, convolvulus, thistles and docks before turning in the sown crop.

Organic Fertilizers

Apart from the bulky and green manures, there are quite a number of organic fertilizers which can be used with perfect safety and which will build up strong healthy growth. Among these are the following which can be used on all soils.

Bone Meal

Bone meal slowly provides phosphates and is used for a very wide range of plants. It is best applied in autumn or winter.

Bone Flour

Bone flour is quicker acting but its value is more quickly exhausted.

Dried Blood

Dried blood is rich in nitrogen but expensive.

Hoof and Horn Meal

Hoof and horn meal, also expensive, provides nitrogen fairly slowly and is used in potting mixtures.

Hop manure provides bulk and is useful for working into the ground in the early spring.

Leaf Mold/Leaf Soil

Leaf mold or leaf soil has little feeding value, but is a useful source of humus. It lightens heavy soil and helps to retain moisture in light ground. Oak or beech leaf mold is the best.

Fish Meal

Fish meal is useful for supplying nitrogen, phosphates and trace elements.

Liquid Manure

Liquid manure has many bases, varying from the liquid left after soaking a bag of manure in water to a variety of named proprietary brands.


Peat has little feeding value but provides bulk, darkening and warming the soil. It can be used with success when making up seed beds and for mulching and digging in, while it is an important ingredient in seed sowing and other composts.


Soot provides nitrogen, and soot water can be applied with advantage to many plants.

Wood Ash

Wood ashes contain potash which varies according to the quality of the wood. The ash must be kept under cover for if left exposed to the elements, its value is less.


Sawdust is a cheap, useful source of humus but rots very slowly. It is best spread 15-20 cm (6-8 inch) on spare ground and mixed with a sprinkling of sulphate of ammonia to quicken decomposition. Leave it for four or five months before digging it in.

All fertilizers depend on the amount of nitrogen, potassium or phosphate they contain to do their work. Farmyard manure has equal, though tiny, quantities of all three, its chief value being its bulk. Organic fertilizers release their nutrients rather slowly.

Inorganic Fertilizers

flower grown using organic fertilizers

The point often stressed about inorganic or artificial fertilizers is that they are quick acting. Most of them are easy to handle and completely free from the pests that some animal manures contain. But they are not long lasting, and they do little or nothing to improve the soil structure or supply ‘bulk.’

Most need handling carefully to make sure that not too much is applied, while in some cases they cause discoloration of the foliage if they touch it. Their chief value is in supplementing food already in the soil or where quick results are required.

A number of inorganic fertilizers are readily available. Nitrate of soda and nitrate of chalk both supply nitrogen fairly quickly. Superphosphate supplies phosphorus and is fast acting.


Kainit is a good means of providing potash although sulphate of potash is better, and benefits growth longer.

Muriate of Potash

Muriate of potash is sometimes used but is not so pure and could have harmful effects if used too freely.

Nitrate of Potash

Nitrate of potash and potash nitrate supply both nitrogen and potash, and do this quite rapidly.

Sulphate of Ammonia

Sulphate of ammonia is one of the cheaper forms of nitrogenous fertilizers. It is not readily washed away in the soil and can be mixed with superphosphates and sulphate of potash: as a spring dressing it releases nitrogen steadily. It is best kept off the foliage.

Whichever of these fertilizers is used, be careful to apply it at the rate indicated on the container, for too much may do much harm. Many compound fertilizers are available under proprietary names and usually the manufacturers provide a full analysis of the constituents.

Trace Elements

Besides nitrogen, phosphorus and potash the other main elements required by plants are calcium, magnesium and sulphur. Magnesium is a mobile nutrient like nitrogen and phosphorus. When a deficiency occurs it appears first in the old leaves since these yield up their stock to the younger leaves.

Since magnesium is an essential component of chlorophyll, a deficiency results not unnaturally, in chlorosis, or a yellowing of the leaves between deep green veins. Calcium is necessary to bind the cells of the plant together.

This may be the reason why calcium deficiency causes poor bud development and the death of the root tips, since cell division is most active in these regions. With calcium deficiency the young leaves may become distorted, the tips hooked back and the margins curled and ragged.

Scorching may also occur and the root system is poorly developed and often appears gelatinous. Symptoms vary according to the level of deficiency and with the species involved.

Sulphur is necessary for the formation of proteins, vitamins and enzymes. Its absence results in reduced shoot growth. The leaves may be tinted or yellowed, the stems stiff, woody and thin.

Small quantities of other chemicals are also required and these are referred to as trace elements. Trace elements are needed by plants, animals and man in a number of ways—quite how many, nobody knows.

But there is one way in which trace elements are known to be essential, and that is in forming part of the enzymes which initiate and control many of the processes vital to the plant.

One of these is the use of carbon produced by photosynthesis to help make fats and sugars. In seaweed fertilizers they are present in beneficial proportions. This is important because it can be dangerous to give an overdose of a particular trace element. Excellent commercially prepared seaweed fertilizers are available.

The following are the main trace elements which play an important role in maintaining balanced, healthy growth.


Iron plays a crucial role in chlorophyll formation. Most growers are familiar with iron deficiency and they have been helped to combat it by seaweed fertilizers complexed with iron.

It appears as severe chlorosis, young growth being the worst affected. Deficiencies are common in soils of a high lime content where it is referred to as ‘lime induced chlorosis.’


Boron deficiency is not common but its lack may result in several disorders involving disintegration of plant tissue. In many cases the stem and root tip dies.


The other trace elements required are manganese, copper, molybdenum and zinc.

Foliar Feeding

Although the long accepted way of feeding plants has been through their roots, foliar feeding is an alternative method by which nutrients are supplied to the plant via the leaves.

There appears to be no conclusive evidence as to the manner in which nutrients enter the leaf, although it is thought to be possible by two routes: through the imperforated cuticle or through the breaks (stomata) in the cuticle.

epidermal cells on a leaf

The upper and lower surfaces of a leaf are covered with single layers of flattened epidermal cells. The main purpose of these cells is protection.

The epidermis is so thin that transpiration can take place through it, but before the leaf is very old, a layer of a substance called cutin forms over the surface of the leaf and prevents further transpiration.

This continuous covering of cutin, which is a resistant fatty material, renders the outer walls of the leaves more or less water-and gas-tight. Very often the cuticle is coated with wax, which increases this water and gas resistance.

This wax is present to a high degree in evergreens and gives these leaves their characteristic shiny appearance, much valued in ornamental gardens.

It is believed that plant nutrients sprayed on to the leaf might be absorbed to some extent through this protective layer—first the wax, then the cuticle, and then the epidermal cells.

This could occur by diffusion if this protective layer is slightly porous. But it is more likely that nutrients are absorbed through natural breaks in the leaf.

The most common of these are the stomata, which are slit-like openings between two guard cells. The guard cells enable the stomata to be opened and closed.

The purpose of the stomata is gaseous interchange; carbon dioxide finds its way into the leaf and oxygen finds its way out via the stomata. It has been suggested that the plant nutrients could find their way into the leaf through the stomata, but there is one obstacle in the path of this argument.

That is, the guard cells which surround the stomata are so shaped as to make the entry of drops of water impossible unless forced in under pressure. If the plant nutrients were being absorbed by the stomata, then anything which reduced the size of the water droplets should increase the absorption of the foliar nutrients.

There are other natural openings in the leaf, for example the hydathodes which are water secreting glands and present on the edges and tips of the leaves.

However, these are not present as frequently as stomata, and not in sufficient quantities to be the route for the considerable absorption of foliar sprays that takes place.

Absorption rates are greater for young leaves than older leaves and usually, absorption is greater on the underside of the leaf than on the exposed surface.

Foliar feeds have a wide and diverse range of activities. They increase yield, improve quality, increase resistance to pests and diseases and extend the storage life of crops.


Moisture is essential if the living soil is to function properly. Growing plants need water for it acts as a carrier of nutrients throughout their structure. Since it is lost in transpiration into the atmosphere, it must be regularly replaced.

If, however, too much water is present, air is expelled from the soil which becomes sour. The roots are then unable to breath and cease to function, gradually rotting away.

For proper growth, the top soil must, by cultivation, be made moisture retentive and yet allow excess water to drain away. This involves a knowledge of the type of soil we have.

When the soil is gravelly or sandy, we can, by adding humus-forming organic matter, help it to hold moisture. The subsoil which receives moisture from the top soil, must itself drain efficiently, otherwise saturation and flooding may result.

This could mean draining the site by underground pipes or breaking up the hard layer or ‘pan’ of sub-soil which prevents moisture escaping.

When it becomes necessary to water growing crops during the exceptional conditions caused by very dry weather, it is advisable to give a few really heavy soakings rather than frequent dribbling, which simply bring the fibrous roots to the surface where they may be damaged by the sun’s heat.

Remember that plants can only use the foods in the soil if they are dissolved in water, which must be applied when the soil is moist, otherwise dry concentrated fertilizers around the roots may drain them of moisture, causing a severe check or even death through dehydration.