The tropical hibiscus, known for its showy flowers, prefers neither full sun nor shade, but a happy medium.
Sun vs. shade: plants can have very different needs
By Tony Tomeo
When the weather is this warm, it's good to have some shade in the garden. Shade trees or structures make working in and enjoying the garden much more comfortable. Too much shade, however, can be detrimental to many plants that prefer full sun. Fortunately, there are many species well-suited to shady conditions.
Most trees that grow well in shade are "understory" trees. This means that in their natural habitat, they grow under the canopies of taller trees. Some larger species may be understory trees when young, but will also grow in full sun if they eventually get past the taller trees. Although shrubs, perennials and vines, which also grow in part shade, are not classified as understory species, most are accustomed to sharing their natural habitat with other larger plants and trees.
Incidentally, many vines that grow in shade are real social climbers. Ivy, for example, grows at ground level at its juvenile phase as it would in a forest. When it encounters a tree, it clings to the trunk and uses it for support--a horticulturally adolescent phase. When it reaches the top of its host tree, it begins to produce adult growth that supports itself. Adult growth blooms and produces seed. Eventually, the ivy shades out the host tree and may kill it. By the time the tree falls, the ivy has produced more than enough seed to ensure the survival of its species. (Adult growth may appear on ivy planted in full sun, because it thinks it has already reached the top of the forest canopy.)
When gardening in the shade of larger trees, fences or buildings, it is futile to use plant species that require full sun. There is great variety among those that prefer shade. As new landscapes mature and trees grow, some areas become shadier, increasing the necessity of such plants.
Sunset's Western Garden Book includes a list of shade-tolerant plants and is an excellent source of information for research. Remember that the Western Garden Book is not a catalogue, so many species may not be available or well-suited to the Santa Clara Valley (zones 15, 16 or 17). Fortunately, zone preferences are listed with each species.
Among the many other useful lists is one featuring plants tolerant of heat and extreme sun exposure. This may be useful for the other sides of the same fences and buildings that make shade-tolerant plants necessary. It is important to be aware that not all plants on this list are necessarily drought-tolerant; some require regular irrigation. Conversely, not all drought-tolerant plants do well with extreme heat or sun exposure.
Exposures to the south and west are the hottest. Heat and glare (reflected sunlight) are exaggerated by concrete pavement and lighter colored paint on walls and fences. For trees, reflective roofing material is also a concern. From experience in my home, I know that enough of these surfaces can even cause difficulty on an eastern exposure.
More glare is absorbed as plants grow and increase foliar surface area. In some situations, less tolerant species may eventually be added, especially if maturing shade trees are present. With good planning, extreme exposure should be no more of a problem than minimal exposure.
Flower of the Week: tropical hibiscus
The tropical hibiscus, Hibiscus rosa-sinensis, is often grown in part shade and probably just as often in harsh exposure. It actually prefers neither. Although it grows well in part shade, it develops a scrawny structure and blooms are minimal. It enjoys the heat of direct sun exposure or even reflected glare, but foliage will be dense and often burns. Ideally, it can be grown in the warmest part of the garden, but sheltered from the sun during the hottest part of the day. During mild summers, as this one, it may not bloom as profusely as normal. (It also needs frost protection in winter.)
Most garden enthusiasts are familiar with the hibiscus' glossy foliage and distinctive flowers. Available colors range from pale pink to dark red, yellow to orange, including "peach" and white. Flowers are single or double. Some cultivars produce denser growth, while some are more open. Larger types can eventually grow taller than 10 feet.
Tropical hibiscus require good drainage and enjoy regular fertilizing from spring through August. Later fertilization promotes vigorous growth too late in the season, which will be damaged in winter. They also respond well to pruning to remove about a third of total mass prior to active growth in spring.
If space is minimal, hibiscus may be espaliered. It may also be trained into standards (elevated shrubs in which main branches originate at the top of a straight, vertical stem, usually three feet or taller).
Horticulturist Tony Tomeo can be contacted at 408.358.2574.
Saratoga, California Since 1955
