When growing annual vegetables and flowers, it is often difficult to believe that early Spanish settlers were attracted to the Santa Clara Valley because of the fertile soil. Although the soil in most parts of the valley and the Santa Cruz Mountains is excellent for growing a wide range of perennial or woody plants, it may not be as suitable for species with more discriminating taste. Good soil should be well drained, but also have good moisture retention to avoid desiccation. It should also be well aerated for good root penetration and air circulation. Soils with these qualities are usually loose and easily cultivated.

Addition of well composted organic material enhances soil texture so that is more conducive to healthy root development. Organic matter is lighter and coarser than the fine clay particles which most endemic soils are composed of. Without it, soil may be too dense for water and air to circulate freely. Although clay drains slowly, it has minimal water retention. Consequently, soil which has not been amended may be poorly drained if irrigated too generously; but dry out completely if not irrigated enough. When clay soils dry, they may set up like plaster and are difficult to cultivate.

It is important for organic soil amendments to be composted prior to use. If incorporated into the soil too early, nitrogen necessary for decay is not available to roots. Most soil amendments which may be purchased in bales from nurseries or hardware stores have been sufficiently composted. Home composting requires a bit more work, but it is a constructive way of utilizing organic garden waste.

Some of the most popular and most effective soil amendments are by-products of the lumber industry. Redwood compost is likely the most popular soil amendment. It is actually the equivalent of aged sawdust which resulted from processing of redwood lumber. Shredded redwood bark is also available; but it is not normally composted and more commonly used as a top-dressing. Shredded fir bark may be used similarly, but decays faster and may be incorporated into soil sooner. Peat moss is a commonly marketed, but expensive soil amendment. (Peat moss is mined from bogs and not a by product of lumber.) It is useful for fine rooted plants which prefer acid soil. However, it decays very quickly and is not practical for large areas.

Wood chips which may be obtained from tree service establishments are too coarse and too fresh to be used as a soil conditioner. However, they may be useful as a top-dressing to prevent weeds from germinating in areas which are not cultivated. Chips are also a useful mulch around established plants. Eventually, chips decay from the lower layers upward, indirectly amending the soil. Chips of some trees, such as eucalyptus, walnut or camphor, are more effective at controlling weeds, but may be harmful to surrounding plants.

Steer manure is an excellent amendment, but should be used sparingly and watered in to leach out soluble salts. Poultry manure and stable litter may also be useful, but must be aged or composted to avoid burning new plants.

Some garden enthusiasts prefer to plant cover crops which are tilled under to add organic matter to the soil. Cover crops are usually either a fast growing annual grass, such as rye grass, barley, or oats; or leguminous, such as clover, vetch, peas or broad beans. (Species of the family Leguminosae are leguminous and produce fruit known as legumes.) Cover crops are more practical in large gardens in which there is enough area to cycle production. Cover crops may then be grown between productive phases.

Of course, the most practical source of organic soil amendment is compost. Compost which is produced from recycled organic garden waste may be purchased in bulk. However, production of compost in the garden is both very inexpensive and a practical use for ordinary garden and kitchen waste. Next week, I can discuss home composting in more detail.