There are several major ways of making your soil highly productive and supportive of good plant growth.
Soil without humus is nothing else than finely ground rock. Humus is vital because it contains and maintains the vast population of microorganisms in the soil. These bacteria are the key to fertility, and have a beneficial effect both before and after death. When alive they produce heat and transform complex organic material into forms which will later be available to the roots. When dead they release these dead plant foods together with colloidal gums. It is these gums and plant remains which are humus; the magical material that cements the soil crumbs.
Humus is absolutely essential to a good growing program. For one thing, humus in the soil does not last forever. It must be added on a continuous basis. Long growing seasons and high temperatures increase the bacteria action and the breakdown of humus. Since it is rapidly removed from the soil, adding it once is not sufficient.
Humus does a great deal for the soil. It not only adds life by binding the clay particles together to make the soil loose and friable, but it also adds some nutrients, increases the beneficial bacteria in the soil, and allows organisms like earthworms to live and develop good aeration. You can use many forms of humus, including peat moss, ground bark, rotted leaves and herbaceous plant residue (compost), manures, and green plant material.
Peat moss is a dried bog material found in several parts of the world such as Canada, Ireland and
Germany. This material is in the process of evolution toward becoming coal, but at this stage it has many excellent qualities for building the soil. Since it is acid in nature, it should be used with caution on high pH plants. Do not confuse peat moss with peat. True peat of Ireland is a material which is burned in place of coal and is not suitable for soil building. There is also a black, soil-like material which is bagged and called peat here in the U.S., but peat moss is more suitable for soil building. Peat is the most inactive material; it is clean and easy to handle but it is hardly a humus maker in the true sense of word. It resists breakdown and so crumb-forming gums are not produced.
Ground bark is literally some type of bark, usually pine, which has been ground into a fine material. It is an excellent soil amendment because it lasts much longer than peat moss and is much less expensive. Ground bark has a less acidifying effect on the soil than peat moss and should be used on areas where the plants require a higher pH. Sawdust and barks are slowly broken down by bacteria. This bacteria activity requires nitrogen, and the soil's supply will be robbed if you don't supply nitrogen-rich fertilizer.
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Manure from grain- and grass-eating animals are an excellent sources of humus. These give the same good soil-building characteristics and they are much higher in plant nutrients than the other forms of humus mentioned. but it is important to let manures age before you use them. When they are fresh the large amounts of ammonia which they contain will damage the roots.
Compost is a free and superlative way to add humus continuously to the soil. It consists of plant material like tree leaves, herbaceous stems and leaves, and grass clippings which have been decomposed by bacteria to leave a wonderful residue that is excellent for soil conditioning. These organic materials contain sufficient readily-available nutrients to stimulate active bacteria growth. Heat is produced and soil structure is improved. As a general rule, humus makers of this type are used some time before planting or in an area some distance away from the plant roots. However, the sudden increase in the bacteria population robs nitrogen from the soil. Always add some nitrogen when using raw humus maker.
Green plant material
Green plant material is one of the best continuing methods of adding humus to the soil. These are referred to as green manure or sometimes cover crops, planted for the purpose of plowing or tilling them into the soil to add humus.
One of the difficulties in using humus in the garden is that after plants are growing, it is hard to add humus to the soil on a continuing basis. Flower beds and vegetable gardens which are basically restarted each year are easy; humus may be added at planting time each year. Lawns are more difficult, because humus can be added only as a top dressing which, with some grass types, is not wise. Shrubs and trees are deep-rooted, and in many instances piling humus on top of the roots may be harmful. Therefore, alternative methods of adding organic matter to the soil must be found.
Fortunately, plants produce a large amount of humus themselves. The sloughing-off of roots as they penetrate the soil adds humus. Good nutrient levels will encourage soil bacterias which in themselves are organic matter, and other soil organisms like earthworms develop large amounts of humus. The fertility level of all garden and landscape areas should be kept high to encourage natural humus regeneration in planted areas which are not tilled or replanted each year.
Another way of adding organic material to the soil is through the use of organic fertilizers like dehydrated cow manure, fish oil emulsion, blood meal, cottonseed meal, and chicken manure.