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The Mexican fan palm, right, is a fast grower that becomes lean and lanky, unlike its close cousin, the California fan palm, at left. The two are sometimes mistakenly used interchangeably.
Photograph by Shari Kaplan
Never call soil 'dirt,' use the proper amendments
By Tony Tomeo
I learned many dirty words in the soil science classes I attended in college. We studied clay, silt, sand, loam and the various amendments used in the horticultural and agricultural industries. The only word that was too offensively dirty to ever use was "dirt." In fact, I still do not know what that word means, only that one should not use it in reference to soil.
Garden enthusiasts in the Santa Clara Valley and the Santa Cruz Mountains do not need to be told of the importance of soil amendments. Although endemic soil is of exceptional quality, it may be too dense in most areas or too sandy in a few areas of the Santa Cruz Mountains. A few other areas may be very rocky.
Organic amendments are very useful for improving drainage and aeration in dense clay or adobe soil, as well as improving moisture retention in sandy or rocky soils. As organic amendments decompose, nutrients leach into the soil, improving fertility. Microorganisms (fungi and bacteria) in the soil proliferate in organic material and convert the most important nutrient, nitrogen, into nitrates that are easily absorbed by roots. (Nitrogen cannot be absorbed directly.)
When selecting organic amendments, the most simple are usually the most suitable. Contrary to what some believe, the more exotic or more expensive is not necessarily better and may be wasteful. For example, peat moss is useful in very well-drained sandy soil or for species that enjoy tannic acid.
However, because peat moss retains so much moisture, it can actually be detrimental to very dense clay soil. Also, peat moss decomposes so rapidly that it should be added more often than other amendments; it is also considerably more expensive.
I prefer to use simple redwood compost in our clay soil because it improves drainage and aeration without retaining too much moisture. It is also very inexpensive and decomposes slowly. We add a small amount to the vegetable garden every year to compensate for decomposition.
Compost from garden waste is actually more appropriate, as a soil amendment, than noncomposted leaf litter and costs about the same. If it is well-composted, it may be incorporated into the soil during planting. Other suitable organic amendments include ground timber byproducts and aged steer or horse manure.
Inorganic amendments, such as perlite and vermiculite, are also useful, but lack nutrients and should only be used for special situations, in conjunction with organic amendments. Although they last longer, they are expensive and only practical for small areas. Gypsum (calcium sulfate) is a chemical amendment that improves drainage and aeration by causing the clay particles to coagulate, rather than bond together in a solid mass.
Potting soil is not intended to be used as a soil amendment and should only be used in containers. Although it contains several components that are used as soil amendments, most types also contain components that are not appropriate, such as peat moss. Potting soil is also very expensive in large quantities.
Tree of the Week: Mexican Fan Palm
Although the California fan palm (Washingtonia filifera) I featured last year is more practical in small gardens, the Mexican fan palm, Washingtonia robusta, is much more common in the Santa Clara Valley, and almost always substituted for the California fan palm. In fact, the excellent collection of California fan palms on the median of Almaden Boulevard in downtown San Jose includes a few Mexican fans that were installed to replace deceased trees.
The Mexican fan palm grows much faster and taller--to about 100 feet. The trunks are lanky relative to their height and usually curve with maturity. . They prefer regular irrigation, but easily naturalize in areas of poor soil without irrigation. Petioles may be completely removed to expose a bare trunk (shaved), or cut close to the trunk (stubble). Beards of old fronds may be left to any length, but larger beards are flammable and may become infested with rodents.
Horticulturist Tony Tomeo may be contacted at 408.358.2574.
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Sunnyvale, California Since 1994
