The Cultural Potential of the Hibiscus to Southern California - The Arboretum
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The Cultural Potential of the Hibiscus to Southern California

In Southern California, inadequate directions on the planting and care of ornamental hibiscus given at point of sale are responsible for the early demise of more plants than the periodic ravages of killing frost.The blame should not be placed entirely on the shoulders of the seller, however, for much of the confusion regarding the culture of this popular garden plant is due to its complicated genetic origin.For ornamental hibiscus, as we grow it today, is in reality a highly polymorphic cross-compatible group of species and complex hybrids and their derivatives. The development of garden hybrids began before recorded horticultural history and is being continued in many parts of the world today.Linnaeus, the father of systematic botany, designated this genetically compatible group as H. rosa-sinensis, or Rose-of-China, and although the earliest known development of hibiscus hybrids seems to have taken place there, none of the species involved in the complex is native to China. Most authorities agree that all forms of rosa-sinensis have evolved from the several known species but admit that there may be some additional lost, or not yet identified, species which have contributed to the early horticultural development of ornamental hibiscus.The species which have been identified as progenitors of our modern hybrids are native to several widely distant parts of the world. They vary greatly in plant vigor, growth habit, flower form, and color, and, therefore in cultural requirements, as do their hybrids. For instance, the Hawaiian whites are strong growers and differ greatly from such species as H. liliiflorus, which is indigenous to the South Indian Ocean islands where it is most often found growing wild as an underwood. Exceptional plant vigor almost always results from a cross between the native Hawaiian white and other species or old forms. This is not the case with hybrids resulting from crosses with H. liliiflorus, which is a weaker grower. For this reason, cultural directions should be more specific taking into consideration the genetic history of the cultivar.In our introduction we stated that inadequate instruction at planting time was responsible for the loss of more plants than frost damage. This statement should rightly be qualified, or rather, should be enlarged upon at this point By frost damage we mean total loss resulting from the freezing of the plant by the extremely low temperatures that periodically occur in many areas of the Los Angeles Basin. This kind of damage is not to be confused with winter losses which are the direct result of faulty selection of planting sites, time of planting, and improper cultural practices, particularly during the late fall and winter.The usual instructions available to the homeowner do not emphasize the fact that in Southern California soils become progressively colder during the winter months and often do not really warm up until June. Modern hybrid hibiscus are particularly susceptible to “cold feet,” particularly when subjected to excess moisture, and are therefore less able to resist sudden drops in temperature or other adverse conditions. In Florida, on the other hand, hibiscus plants will often recover from even severe frost damage because the soils of that state never become very cold despite the catastrophic frosts that sometime occur.In the Los Angeles Basin there are many different thermal areas, some of which are, for all practical purposes, frost free, and others where even the hardiest cultivars will not survive periodic frost damage. Slight differences in elevation, air drainage and other factors affecting temperature often exist quite close together; in some cases they may be found on a single house lot. On my own hillside home in Los Feliz, hibiscus plants have never suffered frost damage in the higher spots, while lower plantings have been lost.It follows that nurserymen should know the approximate temperature conditions in the general area they serve and should advise their customers accordingly. From a practical standpoint such advice could cause some loss of immediate sales, but in the long run would prove profitable. Sydney, Australia, like Los Angeles, has both thermal belts and areas where frosts occur nearly every winter. Some years ago, a Sydney nurseryman decided to specialize in hibiscus. He realized, however, that to be successful he must have customers who themselves were successful with the queen of tropical flowers. He therefore made a survey of the locality which he served, and learned the approximate limits of the thermal belts where optimum conditions for ornamental hibiscus prevailed. He then published this with cultural directions for distribution to prospective customers. His varietal recommendations, too, were based on his findings. The high sales enjoyed by the enterprising nurseryman and the subsequent incidence of hibiscus in Sydney gardens testify to his success.Unfortunately, there are not a large number of varieties of hibiscus propagated for sale in Southern California. Those that are consist mainly of the older hybrids which have been in the trade in this country and Europe for over a hundred years. However, one large producer does make periodic introductions of new varieties on an exclusive basis, usually as patented plants.Reasons for the limited offerings of hibiscus varieties are both cultural and economic. Thirty years ago the list was very much longer, but at that time growers could economically produce grafted hibiscus, just as they do now in most other areas where hibiscus is popular. Today producers say that only cultivars which will root easily from greenwood cuttings and which grow well on their own roots can be economically produced for the retail outlets. Thus most of the highly complex hybrids, such as those in Hawaii, are not considered by local wholesale growers.Limiting the propagation and sale of hibiscus cultivars to proven hybrids does have the advantage of insuring the offering of only such plants as will survive extreme temperatures in most years. But breeding work, such as has been done at the Los Angeles State and County Arboretum in recent years, has resulted in the development of many equally satisfactory hybrids for this area, both in flower quality and plant vigor. Unfortunately, these could not be turned over to individual nurseries on an exclusive basis, and the larger producers say that, as a general rule, they must have this advantage to offset the high cost of advertising and building up stock. Because of these economic factors the results of breeding work have not been fully exploited.Further, there are many suitable cultivars for our area available in Florida and elsewhere which have not been given a commercial trial here. Unless they are given sales-exposure by the nursery trade they will never be known to the public. In Florida, the several annual hibiscus shows held by the various local chapters of the American Hibiscus Society bring out hundreds of new cultivars. There are many Florida nurseries specializing in hibiscus, most of them offering a long list of varieties. Some of these were developed by the writer here, but were not found acceptable by the local nursery trade. The same situation prevails, in a lesser degree, in Australia, where interest in hibiscus has increased tremendously in the past decade. This has been the case particularly in Queensland.As we have pointed out, cultural directions for hibiscus should take into consideration the genetic background of the cultivar. In the following paragraphs, brief general instructions are given for common varieties, with pointers on the specific requirements for some of them.
Well-drained Soils a First Requirement
The average homeowner has little choice of soil types, but he can improve that which is available to him. It is not easy to create better drainage conditions in the heavier soil types. Nevertheless, some effort should be made, particularly in the case of the heavy clays (adobe), because it is difficult to establish hibiscus in such soils. There are inherited reasons for this: most of the species from which modern hybrids were originated are native to areas having soils of volcanic origin, which are naturally well drained. A few specific instructions on this subject will be covered later under the discussion on watering and winter care.
Planting Directions
Full sun is not always available to the homeowner, but hibiscus do equally well in morning sun and afternoon shade, an environment usually found on even the smallest house lot.The planting of hibiscus in lawns and other areas where heavy applications of water are made exposes plants to “wet feet” and therefore a high incidence of winter loss. Perhaps the most attractive home planting is a hedge or border of a single variety, particularly if one of the more vigorous growers is selected and is kept in hand with the pruning shears. The popular White Wings is particularly effective for such use as it is a profuse bloomer over a long season and the foliage as well as the bloom is attractive. It can be pruned shapely at almost any time of the year. It can also be trained as a standard and in this form its growing habit makes it particularly desirable.Unfortunately, there are too few low growers available, the only form that is really suitable for mixed shrub borders. To stand alone, Crown of Bohemia should he selected. Ross Estey is also attractive as a single planting with low growing shrubs of annuals.
Time of Planting
The best months to plant hibiscus depend on the variety and the age and size of the plant. Most growers propagate during the winter and spring, offering plants rooted at that time for sale during the summer and fall. If these plants are planted early enough, that is, not later than September 1, they will become established before the cold weather sets in and are thus able to withstand cold winter soil temperatures. My personal preference is for older plants, setting them out in April or May. Not much growth can he seen the first several weeks, but as the weather warms up the plant gets the benefit of a full growing season before it is exposed to winter temperatures. If late planting is necessary, then the selection of year-old plants in gallons, or older plants in three- or five-gallon containers should be considered. If such plants should appear to be rootbound in the container, a judicious amount of root pruning should be resorted to before planting. Properly done, this will not affect the growth of the plant. In heavier soils it is good practice to put five or six inches of pea gravel in the bottom of the hole before planting, then to fill in with a light soil into which has been incorporated a gallon-can-full of steer manure and a tablespoon of a balanced commercial fertilizer. One readily available mix is that sold as a dichondra food.
Pest Control
Pest control is particularly important during the first year when, it is hoped, the plant will he growing fast. But except for some unusual insects or virus, control can be maintained with a strong spray from the sprinkler. For the record, I was using this method of pest control long before most of the ubiquitous antipesticide partisans were born!
The best time to prune ornamental hibiscus is a frequent subject for debate. But here again the genetic origin of the hybrids must be taken into consideration. First-generation hybrids from almost any interspecific cross, or with a species as one parent, usually show extreme hybrid vigor. This is noted in Agnes Galt and Kona, both of Hawaiian white parentage. Ross Estey is a third-generation hybrid from the same species and it, too, must be kept in hand with the shears. Crown of Bohemia is also a strong grower, but is quite well behaved and seldom becomes “leggy.” The same is true of California Gold. But the common red, called Brilliant, and most other old varieties need attention if they are to keep in shape and flower as they should. Some years ago, before the larger nurseries began to propagate hibiscus from greenwood tips under the mist system, most stock was produced by smaller growers who were not so choosy about the cutting material. lt was the common practice at that time for gardeners hired on a maintenance basis by householders to prune hibiscus under their care in December and January. They then took the prunings with them and either sold them for cutting mate- rial to nurseries, or propagated plants themselves as a backyard venture.Pruning in December and January is an extremely dangerous practice in almost all cases, but particularly so in marginal growing areas. Cutting back sharply, as was usually done by gardeners, is a shock and weakens the plant at a time when it is most susceptible to winter kill. It seems to be the consensus of most experienced and responsible gardeners now to cut back hibiscus a little at a time, thinning out the plant and topping back vagrant growth, then shaping up the plant in early spring after the danger of frost has passed.
In Southern California hibiscus thrive best in a soil with a pH of about 5.5 or 6, but only through experimentation with one’s own soil can this balance be effected.My personal preference for year-round feeding is a commercial mixture of about 4-8-8 with a side dressing of blood meal each month. The high acid fertilizers should be used sparingly as they can cause bud drop. Frequency of application, too, must be guided by experience. The most important point to remember is that hibiscus are good feeders, and both the length of the blooming season and the amount of bloom can be increased by adequate use of plant foods. Most hibiscus in Southern California are undernourished and overwatered.
As a general rule, hibiscus should be given generous applications of water as needed, rather than frequent light sprinkling. Early in the summer, when the soil begins to warm up, individual basins should be worked up around each plant or, in the case of row planting, around several plants. These basins should be filled with a quantity of water sufficient to assure thorough soaking of the roots. In the winter months, however, the basins should be filled in and the soil mounded up around the base of the plants so as to drain the water away during the rainy season. For plantings in heavy soil, a sheet of polyethylene of sufficient size to cover the root zone will help to keep the soil warmer and better drained. In light soils during extended dry seasons in winter, the cover can he removed and the plants watered sparingly. The objective of this winter-care program is to force the plants into a winter resting period.
Container Culture
So far, we have been discussing the planting and care of hibiscus varieties easily available in Southern California. For the venturesome, there exists the possibility of enjoying even the highly complex hybrids such as are grown in Hawaii, Florida, and other more favored areas for hibiscus. This calls for growing the plants in large containers which can be moved into shelter during the winter months if necessary.Almost any variety of ornamental hibiscus will do well in containers, even those as small as 12 inches in diameter. The restriction of the roots does not seem to affect growth or bloom just so long as the plant is adequately fed and watered. The English nurserymen and fanciers grow hibiscus this way out of necessity, and in England one sees huge plants, many years old in 18- to 20-inch tubs.While a small amount of greenhouse or lathhouse space is handy for winter storage, such an arrangement is not necessary. The only requirement is that plants are not exposed to freezing temperatures in storage and, where it is to be a dry storage, a judicious amount of cutting back is done.During the summer the potted or tubbed plants can be placed almost anywhere in the garden or patio. Members of the American Hibiscus Society who live in the colder parts of the South plant in clay containers from which the bottom has been tapped out. In early summer these are planted outdoors in the soil just as they are. Forced along, they usually produce blooms for several weeks before the danger of freezing requires the gardener to remove the container from the soil, cut hack the roots which have grown through the bottom, and place them in winter storage.For those who are interested in growing hibiscus in containers, a membership in the American Hibiscus Society will he extremely helpful. The annual dues, which are five dollars, include a copy of the quarterly, “Seed Pod.” This spritely, well-edited publication carries a wealth uf cultural and other timely material, together with advertisements of nurseries specializing in hibisus who will ship to California. Stock must necessarily come in either as scion wood or bare root. In the former case, if a small area of bench space in a greenhouse is not available for rooting cuttings, it will he necessary to master the simple rules for grafting hibiscus. In some cases the proper conditions can he developed for propagating such material be use of a small rooting outfit heated by a short heating cable, and covered with polyethylene. These can usually be secured through local nurseries or supply houses.Ross H. Gast has been working with ornamental hibiscus for over 35 years. In pursuit of his avocation he has traveled all over the world, notably among the islands of the South Pacific and South Indian Oceans where he rediscovered several species that became the parents of hybrids he developed and introducecd in Florida, Australia and Southern California. A veteran editor and publisher, Mr. Gast has written numerous articles for foreign and American journals, including Lasca Leaves.   

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© 2019 Los Angeles County Arboretum and Botanic Gardens

Phone: 626.821.3222

301 N. Baldwin Ave, Arcadia, CA, 91007