In your organic garden it is very important to have fertile soil to create the best possible growing conditions for healthy, tasty vegetables and great yields. 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 the garden soil, available for growing plants, creating better drought tolerance. It has a water-holding capacity of up to five times its own weight.
It helps prevent water-soluble nutrients from being leached from the soil via watering or rainfall by binding itself to the nutrients, but at the same time making them available to plant roots.
It helps bring about a loose, crumbly structure in heavy clay soils, while allowing free drainage during excessive rain; and 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 essential soil organisms, fungi, bacteria and earthworms.
Sandy soils
Sandy soil has large, freely draining particles. Any nutrients present are leached by watering and/or rainfall.
You need to apply 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. A 20cm (4 inch) layer of mulch can reduce evaporation by up to 70%.
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 copious amounts of organic matter to correct this problem.
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 neither 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 reserves of mineral elements, but roots are unable to mine them from the clay.
Gypsum is a well known clay breaker. Dig it into the soil for good effect. The clay will become friable and can then be made more workable by incorporating river sand and organic matter. You may want to construct raised beds to increase drainage.
Test Your Soil
Most soils are somewhere between the two extreme soil conditions above. A very simple, but effective way to test your soil is to use a glass jar. Add a handful of your soil, 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 – they are very easy to use.
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.
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