Growing Orchids in Your Garden - Hardcover

Orchids that grow naturally on trees are known as epiphytes. They are not, as people sometimes assume, parasitic. A host tree provides structural support, but suffers no damage from epiphytic orchids.

Epiphytic orchids prefer a position protected from the hot midday sun but exposed to direct early morning and late afternoon sunlight. In the Southern Hemisphere the best positions have a northeast aspect. In the Northern Hemisphere the best aspect is southeast. When the summer sun is directly overhead, the host tree's leaves will shade the orchid. The winter sun, with its weaker light intensity and lower angle, may shine more directly on the orchid to its benefit. In both hemispheres the next best aspect is the east.

In the Southern Hemisphere the northern aspect is good, though the west can sometimes be too hot and dry. The southerly aspect can be too cold and dark, especially if it is in the lee of a building. In the Northern Hemisphere the southern aspect is good. In east coast climates the western aspect can be hot and dry in summer and cold in winter. The northern aspect in the Northern Hemisphere may be too cold and dark, being on the sunless side of the garden. If the only suitable trees or the only suitable areas in your garden have apparently unfavorable aspects, do not despair. You can modify both hot and cold areas by planting trees or shrubs carefully positioned to act as windbreaks or hedges. You can admit more light to dark garden areas by pruning overhanging or shady trees.

Epiphytic orchids have preferences in their host trees, the most important of which is that the tree must have permanent bark. If a tree sheds its bark, then any epiphyte attached to the bark also will be shed. Epiphytic orchids prefer trees with roughened bark, although the degree of roughness does not seem to be terribly important. Roughened bark fulfils two vital functions. First, it retains more water on its surface for longer than smooth bark does. Try spraying water on vertical sheets of sandpaper and shiny cardboard respectively to see the difference. This capacity for holding water longer meets the orchid's need. Second, orchid seed, which is the only source of propagation of orchids in nature, is tiny, dustlike, and wind-borne. It needs to lodge in a position from which it will not be washed easily by rain or blown by wind. The interstices in the bark of a rough-barked tree provide such a position.

Good orchid host trees have open crowns of leaves, which let through filtered sunlight and the rain. Most epiphytic orchids require between 30% and 50% of natural summer sunlight. Too much more light in midsummer might burn epiphytic orchids and dry them out too quickly. Too little light might limit their ability to flower. If you are unsure how much light 30% to 50% represents, check with your local garden center to see the amount of light 70% and 50% shadecloth admits. Open-crowned trees let the air circulate freely around their trunks and branches and hence around the epiphytes growing on them. So, open-crowned trees meet three of the four requirements common to all orchids: light, filtered by the leaves of the open crowned tree; water from the rain which penetrates the open leaf canopy; air from the breezes circulating through the open canopy.

The fourth requirement is food. Epiphytic orchids obtain their food from two principal sources. The first is the decaying leaves, twigs, flowers, and other vegetation that builds up around their stems as they grow on their tree. Some epiphytic orchids even produce special basketlike networks of roots to catch this food source as it falls around them. Added to the decaying vegetable matter are the bodies of dead insects and other animals together with their droppings. While food from this source may be miniscule, it is constantly available. The second source of food for epiphytic orchids is the rain itself. As rain washes through the tree's leaves and down its bark, it leaches small amounts of chemicals and minerals that the tree has brought up from the earth. This sustenance is available to the orchid, albeit in minute amounts, via its root network spreading over the tree's bark. Open-crowned trees that let the rain in are ideal for this reason.

Fortunately, many popular garden trees have the characteristics necessary for epiphytic orchids. Growers in Florida select native trees including southern live oak (Quercus virginiana) which is probably the best host, mahogany (Swietenia mahagonii), buttonwood (Conocarpus erectus), satinleaf (Chrysophyllum oliviforme), and geiger (Cordia sebestena). The Floridian native sabal or cabbage palm (Sabal palmetto) is a popular orchid host as are the queen palm (Syagrus romanzoffiana), the coconut (Cocos nucifera), the dwarf date palm (Phoenix roebelenii), and the silver saw or Everglades palm (Acoelorrhaphe wrightii). The sabal and silver saw retain their leaf bases giving a rough surface into which orchids and other epiphytes can root and to which they are easy to attach. However these leaf bases eventually fall, taking with them any epiphyte that is not securely attached to the palm trunk itself. The dwarf date palm has a wonderfully knobbly stem on which orchids soon take root. The queen palm and the coconut have smoother naked trunks as do Alexandra and Bangalow palms (Archontophoenix alexandrae and A. cunninghamiana) and other suitable palm species. Useful rougher-stemmed palms include the Australian cabbage palm (Livistonia australis) and the Washington palms (Washingtonia filifera and W. robusta).

Gardeners new to the habits of palms should be aware that some palm species are "self-cleaning" — they drop entire dead fronds — while others produce fronds which persist for a time, hanging like a curtain after they die before falling, leaving the frond base attached to the trunk. In either case it is sensible to remove dead and dying fronds before they fall as they can damage epiphytes, especially orchid flower racemes, as they fall. Some species, notably the queen palm (Syagrus romanzoffiana), produce heavy canoe-shaped spathes at the base of each inflorescence. These become quite woody as they age so remove them before they fall as they too can damage epiphytes (and perhaps gardeners who may be working below). Indeed, some palms produce inflorescences heavy with seeds (drupes) which are messy and attract pests to the garden. It makes sense to remove such inflorescences, too, before they can become a nuisance.

Of the Australian genera, Banksia, bottle-brush bush (Callistemon), cypress-pine (Callitris), Australian pine (Casuarina including Allocasuarina), spider flower (Grevillea), paperbark (Melaleuca), and some of the longer-lived wattle (Acacia) species are frequently used with great success to grow orchids in gardens. In Florida, the Australian pine and paperbark are pests, but they do make excellent orchid host trees. Many Australian rainforest species are also suitable including the red cedar (Toona australis), pink euodia (Mellicope eleryana), many lilly pilly (Syzigium) species, hoop pine (Araucaria cunninghamii), and, although not strictly a tree, the tree ferns. Interestingly, epiphytes seldom grow on the quick-growing pioneer rainforest trees. Of the exotics, the African tulip tree (Spathodea campanulata), frangipani (Plumeria), Citrus, Erythrina (especially E. crista-galli), Eugenia, Jacaranda, Liquidambar, and Poinciana are among the best. The lovely yellow-flowered Tabebuia with deep-fissured, corky bark and sparse leaves, is superb while the tropical species par excellence as an orchid host is the calabash...