Ultimate Soil Test

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DIY Raised Beds

Good soil know-how and preparation makes or breaks a garden, here’s how to make sure your soil passes the fertility test

The starting point in getting your head around fertilisers is that there are three main chemical plant foods and each has a specific and distinct influence on all plant life. It improves the water-holding capacity of the soil and for plants that means the garden is more able to withstand water restrictions and anything else nature throws at it. Different types of plants, require different fertiliser treatments. Think of it as the equlivent of the ‘food pyramid’ used in human food – you need a bit of everything to be and stay healthy.

The three main elements required by plants are nitrogen, phosphorus, and potash. Nitrogen builds energy and leaves; phosphorus stimulates fruiting, flowering, and seeding; while potash puts fiber and strength into the framework of the plant, while it also regulates the manufacture of plant nutrients in the leaves. This means a leaf-producer such as lettuce or lawn requires treatments different from that supplied to a seed pod crop like beans, or to a flower crop like zinnias or dahlias. Appreciation of this fundamental fact will make the use of fertilisers easy to understand, and successful for home gardening.

It is not wise to use only sulphate of ammonia, for instance, as an all-purpose fertiliser – but sulphate of ammonia, at the same time, is invaluable, apart from its use as the main fertiliser for all leaf crops, particularly in the vegetable garden, as top-dressing for some crops as they come to fruit. It supplies that extra energy which the plant, already rooted in the other elements, needs at fruiting and flowering time; it is quickly soluble; and the hose will take it straight down to the roots, for immediate use by the plant.

The three main elements, come principally from the following sources:

Nitrogen: Sulphate of ammonia; nitrate of soda; and, to a lesser extent, dried blood, bone dust, and blood and bone.
Phosphorus: Superphosphate, bone dust, and blood and bone.
Potash: Chloride or muriate of potash, and sulphate of potash.

What Are Trace Elements?

There are also many “trace” elements in the soil, in minute quantities, which are vital to plant life; and a deficiency in any of them can adversely affect a crop. Most poor soil types are lacking one or more of these elements; and if your garden will not respond to ordinary cultivation treatment — if manure or compost and fertiliser does not give you the result you expected it might pay you to get “trace” fertilising compounds. They contain magnesium, molybdenum, copper, zinc, boron, cobalt, and other elements needed by plant life.

Humus Made Easy

Humus provides the vital other half of the fertiliser story. Humus is the name given to the organic matter in the soil, without which healthy plant life is impossible. It is represented generally by animal manure, vegetable compost, and “green” crops dug into the ground to increase its fertility. Humus is essential to the soil; and it is worse than useless to expect the starved ground to recover and produce crops on chemical fertilisers alone. It is like feeding a snake-oil tonic to a starved baby. Humus is the first essential, and the rest follows. In the increasing scarcity, in cities, of animal manure, compost is the effective answer; and the story of compost, and how to make it, is really important to understand.
The whole story of soil fertility, in essence, is a balance of the elements which make for plant nutrition. It is not good gardening to use great quantities of animal manure alone – because manure lacks many mineral elements necessary for successful gardening and manure, alone, is likely to produce excessive plant and leaf growth, with poor flower or pod production.

Both phosphate and potash are essential to supplement — but if you have animal manure add a mixture of four parts superphosphate and one part sulphate of potash, you’ll have almost everything your soil will need.

Compost Everything

In cities, compost must be the basis of good gardening — compost, plus complete fertiliser. Complete fertiliser, is generally recommended for use in preparing all vegetable and flower beds and spreading 10 cm of compost (or old manure) with a handful of complete fertiliser to a square meter. Complete fertaliser contains a blending of many chemical elements and plants rooted in it, with compost have all the essentials of good growth.

Poultry manure also is a valuable fertilising agency, but it should be used sparingly, if it is used fresh, in quantities it can generate great heat, and may harm root growth which it meets. Use it lightly, when digging it in; although it can safely be used much more freely when spread on the surface.

The initial feeding of the soil, prior to planting, should be supplemented, in all good gardening, with surface feeding where required, as the plants grow – fertiliser being dissolved in water, and applied to the soil surrounding the plants; or (more simply), spread on the ground and watered. Liquid fertiliser feeding should always be done on moist soil—it should never be applied to dry ground and it is advisable generally to moisten the soil with the hose prior to its use.
With many vegetable crops, particularly the leaf things such as cabbage and lettuce, this surface feeding is concentrated in sulphate of ammonia; applied either in liquid form or dry.

In the flower garden, however, where almost all of the production is toward flowers, as distinct from leaves or fruit, surface feeding is not so frequently employed; although all flower crops, as they come into bud, will welcome a surface dressing of complete fertiliser, either liquid or dry, well watered in. A second similar treatment can be given a month later.

Don’t Waste Fertilisers

Modern experience proves that it is wasteful to broadcast fertiliser when the planting is to be made in rows, It is far better, in preparing the ground, to add the manure or compost, and the lime, first; and then, after the ground is leveled, to cut shallow trenches, about six inches deep, along the lines of the rows, and to spread the fertiliser along the bottom of each trench. It is then immediately available to the young roots, as they grow. It is important to remember, however, that this fertiliser must be at least a couple of inches below the level of any seedling roots, at the time of planting. If the young
roots touch the fertiliser, it will burn them.


Lime is not only an essential element in conditioning soil; it is also a plant food which is absorbed by some garden plants to a possibly greater degree than any other nutrient. There are, however, a few things which will not tolerate lime about their roots – principally azaleas, camellias, rhododendrons and oleanders (ferns, too); while a few vegetables, particularly strawberries, tomatoes, and potatoes, are better without lime—except in heavily-acid soils. As a general rule, use lime as part of your general soil preparation; spreading it at the rate of a handful per meter square.

It was the usual practice until recently, to spread the lime on broken ground, and to leave it for a week or two before
digging in the manure or compost. That is still, probably the best thing to do; although in normal home gardening you can if you wish to make one job of it – spreading the lime and the compost or manure, and digging in at one operation. If you do, and probably, in any case, it pays to water the soil immediately, to assist the absorption of the lime into the soil.

Green Manuring

This means growing a crop of green stuff rich in nitrogen, and digging it into the soil just before it commences to set seed. It is a great soil enricher, particularly; in light, sandy ground; farmers also habitually plant a crop of lupins or field peas and plough in the crop while it is in flower. Until recently lupins and peas were generally the only crops planted for this purpose; but soil chemists now recommend also, for home gardens, a seed mixture of wheat and vetches, broadcast with superphosphate; and then raked or spaded in, about 10 cm deep.

The growing crop is later dug in while it is still green; and before any seed-setting shows. This green manuring in itself will not build sandy soils up to full fertility, but it adds much and a normal digging in of old manure or compost, with a complete fertiliser, a fortnight later, will be followed by growth beyond that which normally would have occurred. Every home garden benefits if any area not otherwise used during autumn and winter is put under a green crop at the beginning of autumn, and dug in before the spring planting begins.

Soil Acidity

It is important to appreciate that heavy and continuous feeding of chemical fertilisers into any soil, particularly sulphate of ammonia, sets up in the soil a condition of possibly acute acidity, which many plants resent.
Some few crops (azaleas, rhododendrons, and camellias, among the flowers; and parsley, potatoes, strawberries, sweet potatoes and tomatoes) might welcome this acid condition; but it would be fatal to crops such as onions, parsnips, beetroot, asparagus, and others. It is important, except in exceptional circumstances, to dress with lime any bed which during the previous season, received heavy and continuous feeding with sulphate of ammonia. The best way to check your soil acidity before applying any soil treatment is to purchase a simple soil test kit. These kits are very easy to use and are vital to knowing and managing the health of your soil.

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