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Plant Portraits

March 30, 2009

Plant Information

David Deardorff
Lasca Leaves 26:43-45, 1976


It is somehow fitting in this bicentennial year for a plant- portrait article to highlight a species in a distinctive genus of ornamental fan palms named after the “father of our country”. The genus is Washingtonia; it is comprised of just two species: W. filifera, the only palm native to the western United States, and W. robusta.

The name Washingtonia was used by Rafinesque in 1818 for sweet cicely, a genus of herbs in the carrot family. Later on it was used by Wendland for the fan palms and was also once used for the sequoias. According to the International Rules of Botanical Nomenclature, no two genera may have the same name, and the oldest validly published name has priority. Since Rafinesque used the name before anyone else, sweet cicely, not the fan palm, should be named Washingtonia. Nearly a hundred years later, however, Parish prepared a taxonomic monograph of the fan palms (Bot. Gaz. 44: 408-434, 1907.). In this study, he decided that the fan palms should retain the name Washingtonia. He made this decision based on what he considered to be sound nomenclatural grounds and also the fact that by this time the use of the name for the palms was solidly entrenched in the literature and in the nursery trade.

Washingtonia robusta, the Mexican fan palm, is native to northwestern Mexico and may have been introduced to California as early as the eighteenth century by the mission fathers. It has been noted that Prudhomme grew this palm at his home near San Gabriel and apparently obtained his plants from the mission there. The Mexican fan palm was not extensively planted, however, until around 1870. E. J. Baldwin introduced it in his Rancho Santa Anita in the 1890’s. This planting still exists near the Queen Anne Cottage on the grounds of the Los Angeles State and County Arboretum. Several of these magnificent old palms exceed 100 feet in height and one tops them all at 121 feet. This grand old palm at the northeast corner of the Queen Anne Cottage may well be the tallest palm in the continental United States.

Under ideal conditions of good drainage, ample soil moisture, and fertile soil, the Mexican fan palm gains an average of two feet per year in height. At least one record reports a vigorous growth rate of six feet in a single year. It is apparently the ultimate height of the Mexican fan palm which earned it the specific epithet of robusta, since in every other respect it is smaller and more graceful than the relatively massive California fan palm, W. filifera. The smaller leaves, smaller crown, and narrow trunk of the Mexican fan palm result in a graceful habit which is accentuated by the extreme heights it can reach.

The leaves of the Mexican fan palm are palmately divided, the divisions extending about one-third of the distance to the base of the blade. The leaves are as much as four feet long, including the stout spiny petiole, and are persistent for several years. The functional life of the leaf is about one year after which it dies and becomes reflexed, dangling down around the trunk in a skirt or petticoat of thatch. The skirts of old leaves persist for years unless pruned away deliberately or removed by wind or fire. When the dead leaves are deliberately pruned, the leaf bases which remain form a very attractive basket-weave texture for much of the length of the trunk.

The flowers of the Mexican fan palm are small and whitish, borne in large inflorescences which hang down below the leaves. The fruits are small blue-black drupes with a large seed and very little flesh. The seeds germinate readily and small seedling fan palms often spring up abundantly around reproductively mature trees.

The native Americans of the southwest utilized the California fan palm in a variety of ways and, although no specific information seems to be available for the Mexican fan palm in this regard, it may have been used in a similar fashion. The fruits were roasted and eaten or were ground into flour. The trunks were squared off and used as timbers or were split into poles for ramadas and corrals. The leaves provided thatch for roofs and fibers to bind the thatch in place. Thus it may have been for partly utilitarian rather than strictly ornamental purposes that the Mexican fan palm was originally imported by the mission fathers.

Whatever the original reasons for its importation, the Mexican fan palm is highly regarded today as a hardy, adaptable, ornamental palm performing well under a wide variety of climatic and cultural conditions. The plants are hardy to 24 degrees and will withstand drought and poor soil, although growth is faster under better conditions. The most widely planted palm in southern California, the Mexican fan palm is now cultivated in Mediterranean and subtropical regions around the world. It is certainly the most abundant tree in the urban landscape of southern California, dominating the skyline of cities and towns from the coast to the desert. It is a stately street tree and, especially when silhouetted against the setting sun, is quite capable of transforming the most mundane urban landscape into a panorama of genuine beauty. Even more than most trees, however, it achieves its true potential when planted in informal clumps and groves in a park-like setting. The magnificent grove of Mexican fan palms near the Queen Anne Cottage on the Arboretum grounds is an excellent example of their quiet grace.

Dr. Deardorff is a member of the department research staff involved in taxonomic studies.

What a Gardener Should Know About Fertilizers

March 30, 2009

Plant Information

Methods of fertilizer application vary somewhat with soil character, moisture present and kind of crop grown.


by Myron S. Anderson 1
Lasca Leaves 20:14-15, 1970

FERTILIZER IS A TERM that is not easy to define in such a way as to include all the materials sometimes added to soil for the improvement of plant growth. In the general trade, fertilizers for soil improvement fall into three groups, primary, secondary and minor constituents. The primary group includes constituents carrying the chemical elements nitrogen, phosphorus and potassium. Nitrogen is stated on the bag as the element N and is added to promote green plant growth. Phosphorus, stated as the oxide (P205), aids the health of plants, improves growth of roots and to a moderate extent hastens crop maturity. Potassium, also stated as the oxide (K2O), helps the plant to make better use of sunlight and also improves root growth.

The secondary constituents include compounds carrying the chemical elements calcium, magnesium and sulfur. Calcium and sulfur are frequently included as a part of the compounds carrying the primary constituents. Thus some of the nitrogen may be in the form of ammonium sulfate that contains a substantial percentage of sulfur. Furthermore, a chemical compound may also have calcium and sulfur in its composition.

In some areas soils are deficient in one or more minor elements such as iron, boron, copper, zinc, manganese or occasionally a few others. This lack of adequacy of certain elements in the soil may sometimes be detected by characteristic abnormalities in the appearance of plant leaves. Lowered crop yield as measured by both quantity and quality often results. Misshaped apples due to boron deficiency is a well-known example of the latter. These minor elements are so-called because the quantities present and needed are normally very small. Such constituents as compounds of copper and zinc, for instance, are usually stated as a few parts per million in a fertilizer mixture rather than by percentage as is the case with primary constituents.

A GARDENER SHOULD learn to recognize the chemical composition of a mixed fertilizer by the symbols on the bag or box. One of the very commonly used fertilizers of relatively low analysis is designated as 5-10-5. This means that five percent of the weight of the material in the bag is nitrogen. This nitrogen is present as a constituent of one or more chemical compounds in the mixture. The middle number, in this case 10, designates the percentage of the mixture that is phosphorus expressed as the oxide, P205. This is not, however, the chemical form in which the phosphorus actually exists. The third number, 5, represents the potassium of the mixture. The five percent is actually the amount of potassium stated as the oxide.

In a 5-10-5 fertilizer, the total quantity of primary plant nutrients thus adds up to 20 percent. The remaining 80 percent is made up of several items. The plant nutrients are in chemical combination with secondary elements or with other materials of non-fertilizing nature. A high-grade fertilizer material such as ammonium nitrate contains about 40 percent of nitrogen available to plants when placed in the soil. The remainder is a chemical carrier, not plant nutrients. A fertilizer such as 5-10-5 also contains materials known as conditioners. These are added to improve the physical condition of the mixed goods, especially to restrain caking. Inert material of low cast, called filler, is added to adjust the mixture to the total percentage stated on the bag.

Methods of fertilizer application vary somewhat with soil character, moisture present and kind of crop grown. In many places it is well to apply about 10 to 15 pounds of a mixed fertilizer such as 10-10-10 to one thousand square feet of area. This is plowed or spaded in and the soil properly conditioned for planting. When seeds are planted or small plants transplanted a small handful of perhaps 5-10-5 fertilizer per linear yard is placed in a shallow trench about four inches to one side of the plant row at a depth of four inches. When a second crop is grown without preliminary plowing the rate of application of fertilizer may be somewhat less than that used for the first planting.

Fertilizers of different grades are usually carried in garden stores. For best results a gardener frequentiy uses fertilizers of two or more grades. The 5-10-5 material has long been on the market and is widely used for growing many kinds of flowers and vegetables. The 10-6-4 grade is often recommended for use on lawns, while root crops usually respond well to 5-10-10. The 10-10-10 grade serves well to build up garden soil productivity.

CARE SHOULD BE TAKEN to use proper amounts of fertilizer for the area involved. The method of application should be suitable. Commercial fertilizers improperly used may burn plants and cause poor germination of seeds.

Longevity of the usefulness of fertilizers added to soil depends upon the rate and quantity of water added by rainfall or by irrigation, upon the character of the soil, upon fertilizer constituents dominant in the mixture and upon the quantity of fertilizing materials absorbed by growing plants.

In many areas fertilizers may be purchased that are supplied with minor element compounds in adequate yet safe quantities. In the case of tree-crops the appearance of young leaves sometimes give a clue to the likelihood of a deficiency of a certain element. Sometimes a minor element can be better supplied by sprays than in fertilizer applications to the soil. Absorption of a minor element through leaves is often adequate for a current season.

The fertilizer needs vary widely from place to place. A gardener should get as much reliable information as practical regarding the need of various constituents for different crops in the area of his garden. Some branch of a state university is usually in position to inform a gardener as to areas where minor element deficiencies are likely to occur and where other specific deficiencies may be expected. Sometimes this agency is in connection with the agricultural extension service, especially in the office of the county agricultural agent. The minor elements of fertilizers in a local garden supply store may provide some hint as to the likelihood of local deficiencies. One should read the chemical analysis on the fertilizer bag and buy the grade of goods that best suits the local garden situation.

Dr. Anderson is a retired soil scientist with 40 years’ experience, much of it with the U.S. Dept. of Agriculture, as researcher and author.

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