Knowing Your Soil

In your organic garden it is very important to have fertile soil to create the best possible growing conditions for healthy, vitamin packed vegetables and great yields. Plants are also far less vulnerable to pest and disease attack when they are growing vigorously, which is particularly important when you're growing organically.

Soil fertility is best when essential nutrients are available to your plants and when the humus levels are at 5% or more.

Humus is the stable decomposed remains of plant tissue. It is a product of composted vegetable matter. The cellulose in humus acts like a sponge and holds moisture in your garden soil, making it available for growing plants, creating better drought tolerance. It has a water-holding capacity of up to five times its own weight.

Humus helps prevent water-soluble nutrients from being leached from the soil from watering or rainfall by binding itself to the nutrients, but at the same time making the nutrients available to the plant roots.

It helps bring about a loose, crumbly structure in heavy clay soils, while allowing free drainage during excessive rain; plus it provides cohesion in sandy soils.

So you see that humus is really the best way to overcome whatever problems you may have with your soil. Humus is also necessary to maintain healthy levels of earthworms, fungi, bacteria and essential soil organisms.

Sandy soils

Sandy soil is made up of large, freely draining particles. Any nutrients present are easily and quickly leached away by watering and/or rainfall.

You need to apply organic matter (compost) to the surface or dig in large amounts of humus to retain water and provide nutrients. All organic matter breaks down over time, so sandy soils will benefit from a large amount of compost, which will need replacing regularly. Always mulch well to reduce evaporation. The less you need to water, the less leaching occurs. Did you know that a 20cm (4 inch) layer of mulch can reduce evaporation by up to 70%?

Some sandy soils can become non-wetting soils, where any amount of irrigation will just run across the surface. If your soil is like this, you will need to add large amounts of organic matter to correct this problem. It will take time for this problem to correct itself, but if you keep adding organic matter, it will eventually behave like normal soil.

Clay Soils

Clay soils are made up of tiny particles. It will hold water well, but the spaces between the soil particles are so small, there's very little room for air, or space for water to escape. Clay soils tend to become boggy in wet weather, and dry out and crack in hot, dry weather. Clay soils often have high amounts of mineral elements, but roots are unable to mine them from the clay. By correcting this problem you'll make the minerals available to your plants.

Gypsum is a well known clay breaker. Dig it into the soil for best results. The clay will become more friable and can then be made more workable by incorporating river sand and organic matter. You may want to build raised beds to increase drainage.

Testing Your Soil

Most soils are somewhere between the two extreme soil conditions above. A very simple, but effective way to test what type of soil you have is to use a glass jar. Add a handful of your soil (dig down about 75mm / 3inches), fill it with water and shake vigorously. Let it stand for a few hours until all the suspended materials have settled. You will see quite distinct layers. Course sand will be the lowest layer, then finer sands, silts, clays and lastly organic matter.

A good garden loam will have approximate equal proportions of clay, sands and silt, with a good percentage of humus or organic matter.

Soil pH

The acidity or alkalinity of your soil is also an important consideration. Most vegetables need a neutral to slightly acidic soil, with a pH of about 6.5. If your soil pH isn't right, then some nutrients will be unavailable to your plants.

You can buy a pH testing kit at your local nursery or hardware store – they are very easy to use and you can re-use them at a later date.

The really great news is that no matter what kind of soil you are starting with, the continued addition of humus and other organic materials will correct nearly ever problem kind of soil. Even your pH levels will balance out over time.