Organic Mulches and Compost – good for your plants and even better for the soil
Applying chemical fertilizer in the garden, supplies the mineral nutrient that the plants need for their growth and development in the cheapest and most convenient way. Organic additives whether dug into the soil like compost, or spread on top of it like mulch, also supply mineral nutrient, but at greater cost, labor and effort. Why then should the organic method be preferred to the chemical one? The reason is that organic matter in sufficient quantities, improves the condition of the soil especially in the long term. Remember that the soil is the habitat in which your garden plants grow, and ultimately, poor soil conditions result in unsatisfactory plant development, irrespective of how much fertilizer is thrown in.
The benefits of high organic percentages in the soil can be summarized as follows:
- The improved supply of oxygen available to the plants’ roots in heavy, clay soils as a result of the crumbly soil structure that develops.
- The improved retention of water and nutrients in light, sandy soils.
- The enrichment of the micro-flora and fauna of the soil. The expanding variety and quantity of micro-organisms actually improves plant nutrition, because while plants absorb nutrients in the form of dissolved mineral salts, nutrient take-up is associated in many ways with the activity of microbes. The association of legumes with Ryzobium bacteria to make nitrogen available to the plants, is but one example.
- The supplying of raw material to larger organisms such as earthworms to establish themselves in the garden. The earthworm is undoubtedly the greatest gardener in the world, which by its activities, aerates the soil, improves its crumbly structure and causes nutrients to be released, thus increasing their availability. It should be noted that earthworm populations in the earth decline and disappear as more chemical fertilizer is used.
- The increasing range and volume of micro-biotic activity creates a healthier ecological balance in the soil. Consequently, pest and disease infestations are reduced to manageable proportions as the populations of pathogenic organisms are controlled.
The importance of organic mulch in hot, dry climates
The benefits of organic mulch materials such as wood chippings have been written about extensively, particularly with regard to weed prevention and water retention in hot weather. Less known perhaps is the role mulch plays in regulating the temperature at the soil’s surface. In hot dry and Mediterranean climates, exposed soil can reach temperatures of 50c in the summer. In these conditions not only do the plants directly suffer, but micro-biotic activity virtually ceases as well, thereby hindering the absorption of nutrients by the plants’ roots.
Furthermore, mulch prevents the excessive drying out of the soil at depths of say 20-50cm, which is common in hot regions as a result of the cracks formed at the soil’s surface. Apart from reducing the loss of moisture through evaporation, the mulch layer, slows down the breakdown of organic matter (humus). Experiments in Israel have shown that a soil well composted in the winter, can contain virtually no humus at the end of the summer, when that soil is unprotected. By way of comparison, in cool climates, humus percentages of 15-20% are quite normal even without the addition of compost.
In conclusion it can be seen that feeding, composting and mulching are horticultural tasks that work together. Compost releases small amounts of nutrient available for the plants to take-up, but it improves the soil in the short term and prevents it from degenerating in the long term. Organic mulch not only provides better conditions in which the plants grow, it also protects the top soil from the effects of sun, wind and rain, and further ensures that the soil will have a larger percentage of the organic matter so crucial to its health and the life it contains.
Article by Jonathan Yaakobi, a professional gardener since 1984. The former head gardener of the Jerusalem Botanical Garden, Mr. Yaakobi now concentrates on building gardens for private home owners and teaches horticulture to students on training courses.