Soil Conditioners

Liming: If the soil becomes too acidic, then in order to plant species that prefer slightly alkaline conditions for growth, it is necessary to lime the soil. The lime will help break down the organic matter in the soil. Worms love alkaline soil and will draw down the mulch and further improve it. Acid soils are referred to as ‘sour’ and alkaline ones as ‘sweet’. Limestone needs to be treated before it can be used in the garden to improve the soil.

How do you test your soil for alkalinity and acidity? Use a soil testing kit to determine the alkalinity of the soil. Take a sample of soil and add the indicator supplied in the kit. The colour that you see can be matched against a chart to determine the soil pH.

Buy ground limestone and use it quite generously, about a handful per square metre of soil. Another way to sweeten the soil is with dolomite, which contains calcium and magnesium. Dolomite is a very good medium for sweetening the soil, but it takes some time to do so.

If you are in a hurry to reduce the acidity of the soil, use builders lime or hydrated lime. This lime is prepared by heating limestone and cooling it, then slaking and grinding it. The powder is much finer than other limes. Spread the lime on the surface at about the same rate as before. Do not dig it into the soil, the rain will take it in for you. This lime is very readily available to plants, but it you will need replenish it more than other limes.

Another source of calcium used in the garden is gypsum (calcium sulphate). It is like a plaster of paris and has a brown colouration. Gypsum doesn’t alter the pH of the soil, and in very alkaline clay soil, will make the soil slightly more acidic. Rather, gypsum is used to help break up clay soil.

Seaweed concentrate is an excellent soil conditioner. It contains alginates and thus improves the soil structure. Use seaweed concentrate in a very dilute form, no more than a couple of tablespoons in a full watering can. Remember it is not a fertiliser but it does contain lots of trace elements. You can use this solution to water seeds which will absorb all the trace elements.

You can make a spray of seaweed concentrate plus a teaspoon of the trace elements zinc sulphate, iron chelate, magnesium nitrate and boron. Spray it on to the leaves and stems where it will be absorbed by the plant. The liquid will also drip on to the soil where it will improve the soil structure.

Wear gloves when handling lime powders and spraying if it irritates you and remember, of all our natural resources, soil is one of the most important and we must look after it.