March 30, 2009

Some Outstanding Shade Trees for Southern California

George H. Spalding
Lasca Leaves 21:64-70, 1971

Southern California gardeners are fortunate in having a wide variety of trees available to them. Making a choice in this situation is sometimes difficult. Aside from such horticultural considerations as location, soil, and exposure there is the attitude of the person making the selection, perhaps the most important consideration of all.

None of the trees are perfect, if perfect means being in flower year round and never dropping leaves. Nonetheless, there are a number which, though falling short of this ideal, have, by reason of their adaptability, great value as shade trees. Those discussed in this article are outstanding in this respect.

Podocarpus [now Afrocarpus] gracilior Fern Pine

This beautiful native of Africa is one of the most outstanding shade trees for a wide range of situations. Often sold in nurseries as Podocarpus elatior, it has been grown in Southern California at least for 40-50 years. It is one of the cleanest trees in that leaf drop is no problem as the leaves are so small and needle-like. lt is free of insect pests and disease. In other words, it comes close to being the ideal shade tree for all areas in which it can be grown. Its major drawback, if it can be called one, is that it takes so long to reach its mature growth of 50-70 feet and a width of 20-30 feet.

Seedling-grown plants are quite upright. Cutting grown or grafted plants tend to be rather supple and floppy. They are fine for espaliers because of their tendency to make horizontal growth. They are often used as a substitute for vines along a fence or arbor. Both types make outstanding evergreen hedges, especially when clipped.

As a mature tree it has a billowy outline which is soft and pleasing. The shade is quite dense.

It would be very easy to say that this is one of the best all-around trees in existence. Ideal for street or patio tise and also excellent for container use when young. Very tolerant of a variety of soils, it can be grown over a wide area.

Schinus terebinthifolius Brazilian Pepper

A native of Brazil, Schinus terebinthifolius is another fine, small shade tree for patio or garden. It is one of the best for use as a lawn tree since it thrives on the type of watering program usually given lawns in this area. It heads too low for street use where 14 feet is often required height for the lowest branches.

This species of Schinus is much heavier and more densely foliaged than Schinus molle, the long grown and beautiful California Pepper. The leaves are dark green, somewhat shiny, and evergreen. The inconspicuous flowers are followed by scarlet berries. A certain amount of pruning is necessary to develop an open crown and overcome a tendency to cross branching and heavy growth. The ultimate height will be about 25 feet. One caution should he noted—during the past year or two there has been some evidence of damage and occasionally outright killing of trees by verticillium wilt. The best control is to watch the watering and feed regularly. In spite of this it is one of the best shade trees for this area.

Melia azedarach cv. umbraculifera Texas Umbrella Tree

The Texas Umbrella Tree is practically indispensable for those hot desert areas where very few trees will grow. It is a fast-growing tree which tolerates a wide variety of soil and growing conditions. The foliage is bright green and the leaves are bipinnately compound. In spring the tree is covered with fragrant clusters of small lavender flowers that are followed in the fall by yellow fruits often used for beads. Under garden or lawn conditions it will be a messy tree and will tend to send up suckers because of garden waterings. lt is not good near the coast nor in areas of heavy winds as the brittle branches tend to break. But in the hotter desert areas of southern California where it has been widely planted, the Texas Umbrella Tree is very effective, and those who have enjoyed its shade on a hot summer day in the desert will he ever grateful for it.

Koelreuteria integrifoliola (no common name)

A small, deciduous tree from China which seldom attains a height of more than 30 feet. The large leaves are bipinnate. The leaflets ovate-oblong about 4 inches long. The entire leaf often reaches 14 inches in length. Flowers are small but produced in large terminal panicles in summer when flowering trees are at a premium. The fruit which follows is bladderlike, somewhat resembling inverted Japanese lanterns. They are green at first turning a beautiful salmon pink with age.

This is the smallest of the genus, all of which arc worthwhile ornamental trees. Koelreuteria integrifoliola is well suited to the small city lot and will stand temperatures as low as 20°F, probably lower. In this area it self sows readily and seedlings are easily transplanted. We still do not know the full potential of this tree as it was introduced in the Los Angeles State and County Arboretum in 1958. The oldest tree there is only 19 years old and until its recent removal to a new location, requiring heavy pruning, was rather broad topped and rather attractive. Like the rest of the genus it is free of disease and insect pests.

Magnolia grandiflora Magnolia

Perhaps of the best known of the large evergreen shade trees in Southern California is Magnolia grandiflora. It can become an immense tree, growing to 100 feet in its native southeastern United States. It will probably not reach quite that height here because of the lack of natural rainfall in the quantities needed and because of low atmospheric humidity. Still, we can boast some that are at least 70-80 feet. Most gardeners in this area prefer the smaller growing varieties such as St. Mary. Both the species and its varieties take many years to reach ultimate size.

The large leaves can reach 8 inches in length. They are thick, shiny green above, and usually have a rusty tomentum beneath. The showy white flowers are 6-8 inches in diameter and very fragrant. lt is in bloom through most of the summer and fall.

Magnolia grandiflora is most suitable for parks and large garden areas. The named varieties, such as St. Mary mentioned above, may be suitable for smaller areas. It should be kept in mind that the usual watering practices in this area tend to encourage surface roots and the system suggested for Morus alba can be used with this tree also. However, surface roots can be removed if done before they reach 1 inch in diameter.

Morus alba cv. Mapleleaf

Fruitless Mulberry
Among the fastest growing are the fruitless forms of Morus alba. The family with a new home can have usable shade in three years or less by planting this species or one of the varieties The Mapleleaf variety is particularly fast. Trees can be purchased, bare root, from December to March in sizes from 4 to 12 feet tall or more, which gets you off to a flying start. With proper care a tree 20 feet tall and 20 feet across is possible in three years.

As I mentioned at the outset, no tree is perfect in all respects and this one is no exception. The leaves drop every fall, although in a relatively short period of time. Also, they are very large and easy to rake up. Because the tree grows so rapidly, pruning is a yearly chore, particularly in the formative stage. Branches grow to six feet or more in one year and quickly develop a large top which is sometimes too heavy for the young trunk. So stake well, thin jucidiously and head back long branches during the winter months when the structure of the tree is visible.

DEEP WATERING IS ESSENTIAL. A good method is to sink 3 to 4 foot lengths of pipe (about 4” in diameter) into the ground around the tree at 6-foot intervals and about 6 feet from the trunk. Fill with pea stone or larger and let the water trickle in each section of pipe for several hours. This should be done at varying intervals depending on the type of soil.

Surface watering (except when first planted and until the tree is established) will cause surface rooting and its attendant problems However, this method can be used if the top two inches of soil are cultivated the following day so the soil dries out. This will help to discourage surface roots. If the tile method is used, the tiles will have to be moved outward as the tree grows and additional tiles added as the circumference increases as they should be kept at the drip line. Once the tree is established it is fairly drought tolerant.

If you want a dense shade tree 20 x 20 feet in three years, this is your tree. The kids will enjoy climbing in it too. Let them.

Cinnamomum camphora Camphor Tree

For those with a real love of trees and the space to grow them, the camphor is one of the finest trees that can be grown in the warmer areas of California. This native of China and Japan can reach a height of 50 feet or so, with an equal or greater spread. It is beautiful in all seasons, The new foliage in spring may be pink, red or bronze, depending on the tree. The foliage becomes light-green and the leaves turn shiny as the tree matures. Old trees lose their lowest branches and often have a rather swollen base with large roots protruding above the soil. There is some leaf drop most of the year but the heaviest is in March. This is a detriment to some people, but there is no such thing as a perfectly clean tree. If you have ever seen it on a rainy winter’s day when the trunk and larger branches appear black against the yellow green leaves, you will agree that it is truly one of the real aristocrats among trees. No special care is needed in growing the camphor, but as with any plant, the better the soil and care it receives the greater the reward in growth. While not usually bothered by pests it is subject to verticillium wilt, one of the root rots. When attacked by this rot, twigs, leaves, branches, and sometimes the whole center of the tree will wilt and die. For many years nothing could be done to control this disease. Recently a new systemic fungicide, Benlate (benomil), became available and appears to he of considerable value in controlling verticillium when used as a spray on the foliage. In spite of this, camphors are not difficult to grow.

Jacaranda acutifolia Jacaranda

It almost seems superfluous to discuss this popular and widely planted tree. To newcomers who are not familiar with its beauty some information on its culture may be of value. If a really fine tree is wanted, regular pruning and removal of the water sprouts which occur throughout the tree is necessary It is very tolerant of many types of soils, but of course will not do well in poorly drained or highly compacted soils. The work which may be necessary to develop a well- shaped tree is quickly forgotten when the blooms envelop the tree in a cloud of lavender blue and the ground beneath is carpeted with fallen flowers. This Brazilian native graces the streets and gar- dens of many cities all over the warmer areas of the world. In southern California it has been used for many years as a street tree, for park plantings, and in home grounds. Some consider it a litterbug, but for many more its heavy leaf fall is a small price to pay for the wealth of beauty which often comes twice a year. The heaviest bloom is usually in May or June, but frequently there is a secondary blooming in July or August. The foliage is fine and rather fern-like. It is a round- headed tree which can reach 25-40 feet with 15-30 feet spread, occasionally more. It is slightly tender to frost and infrequently is severely damaged by cold. However it grows rapidly and when lightly frosted recovers quickly.

Cupaniopsis anacardiodes Carrotwood Tree

In this day of small suburban lots, suitable small trees are hard to find. The carrotwood is both suitable and relatively small. A moderate to slow grower, it will eventually reach a height of 30 to 40 feet and a spread of about 20 feet. Multiple trunk specimens will have a considerably wider spread. It somewhat resembles the carob, but is more delicate and airy in appearance and has none of the carob’s faults. The leaves are composed of 6 to 10 leathery leaflets, are evergreen, and provide a dense heavy shade. It is probably one of the cleanest trees available today and is fine for use as patio, lawn or street tree. There has recently been evidence of verticillium wilt in heavy soils where drainage is poor or in lawns where poor watering practices are followed. This can be treated with Benlate as mentioned for camphor. The carrotwood can be grown as a single or multiple-trunked tree and the choice is up to the individual planting it. Either way it is a fine evergreen tree and a fine import from Australia, its native home.

Albizia julibrissin Silk Tree

This is another small tree suitable for use in gardens with limited space. Native over a wide part of Asia from Iran to Japan. this deciduous tree is the mimosa of the eastern United States. It is fast growing and can reach a height of 40 feet with an equal spread. However, it can be kept to a much smaller size by regular pruning. The foliage is pinnately compound and in some respects resembles a coarser jacaranda leaf. A really flat-topped tree, it is especially attractive when viewed from above, as the fluffy pink flowers are held above the foliage. It is usually more attractive when grown in its natural form as a multiple-trunked tree. The foliage is light enough so that grass can usually be grown underneath. Its one fault is heavy litter of fallen leaves and flowers beneath. Another tree particularly useful for the deserts of the southwest, it makes a very fine patio tree because of its light, filtered shade and umbrella form. Flower color will vary from light to deep rose pink when grown from seed. An all-around fine small tree which will grow with a minimum of care.

George Spalding has been on the staff of the Arboretum since its inception in 1948 and over the years has served in a number of capacities. Currently botanical information consultant to the public, he is an advisor to Time- Life Books and other publications.