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Photograph by Shari Kaplan
African Queen: African violets are popular houseplants that thrive on well-drained, rich acidic soil and diffused light.
Proper soil amendments can make the difference
By Tony Tomeo
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 it is more conducive to healthy root development. Organic matter is lighter and coarser than the fine clay particles that most endemic soils are composed of. Without it, soil may be too dense for water and air to circulate freely.
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 before use. If incorporated into the soil too early, nitrogen necessary for decay is not available to roots. Most soil amendments that can be purchased in bales from nurseries or hardware stores have been sufficiently composted. Home composting requires a bit more work, but is a constructive way of using organic garden waste.
Some of the most popular and most effective soil amendments are byproducts of the lumber industry. Redwood compost is likely the most popular soil amendment. It is actually the equivalent of aged sawdust that resulted from processing redwood lumber.
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 is mined from bogs and not a lumber byproduct.) It is useful for fine-rooted plants that prefer acid soil. However, it decays very quickly and is not practical for large areas.
Wood chips that may be obtained from tree service establishments are too coarse and fresh for use as soil conditioners. However, they may be useful as a top-dressing to prevent weeds from germinating in areas that 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 that are tilled under to add organic matter to the soil. Cover crops are usually either a fast-growing annual grass, such as rye, barley or oats; or leguminous crops such as clover, vetch, peas or broad beans. (Species of the family Leguminosae produce the familiar 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 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.
Flower of the Week: African violet
African violets, Saintpaulia ionantha, are one of the most popular houseplants. They require rich, acidic and well-drained soil with regular irrigation. However, one of the most common problems is over-irrigation. They prefer a bit of neglect so that the soil may dry slightly between irrigation. If the soil is too moist, roots rot easily. Stable room temperature between 65 and 75 is optimum.
Although direct sun exposure burns foliage, African violets require at least 12 hours of diffuse light during the day, but may easily be grown with fluorescent light. Fertilizer should be a dilute liquid or African violet (specific) granular. They perform best if slightly crowded in small pots. African violets are easily propagated from either suckers removed from the main stalk or from leaf cuttings.
Horticulturist Tony Tomeo can be contacted at 408.358.2574.
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Willow Glen, California Since 1992
