 Everyone knows that plants grow from seed. Some are more easily grown from seed than others. Fountain grass and Mexican evening primrose grow so easily from seed that they can become invasive. These two examples have not been bred or otherwise improved from the species as they are found in the wild. Seedlings are consequently not much different genetically from the parents and can be perpetuated indefinitely. With irrigation, or in moist areas, nasturtiums may also become invasive, but will eventually revert to a more feral state, because they have been bred to produce varieties that are more appropriate for gardening but lack the genetic stability.
Rhododendrons are not only difficult to grow from seed, but take many years to mature and are usually very different from the parents, which were likely derived from extensive hybridization or mutation. Only those obtained directly from the wild will produce similar seedlings. Rhododendrons are propagated from cuttings because they root so reliably, because cuttings mature more rapidly than seedlings and so that the offspring will be genetically identical to the parent. "Cultivars" are variations of species that require such vegetative propagation, technically known as "cloning," to preserve genetic continuity.
"Varieties," such as the variations of nasturtium, differ from cultivars in that they may be propagated sexually—by seed—to obtain reasonably predictable results. (I don't make up this terminology.) Varieties that are produced as hybrids of very specific parents, such as some tomatoes, revert to a more feral state in fewer generations than those that occur naturally in the wild. For example, yellow violets that grow wild in the Willamette Valley of Oregon will naturally continue to produce yellow-blooming offspring and might be considered a variety of the common violet that otherwise blooms white or "violet."
Simply speaking, cultivars are genetically identical to their single parent, but varieties are essentially genetically indistinguishable from their pair of parents, which may also be indistinguishable, but are technically not genetically identical. I hope this was not too confusing. So, as I said earlier, "Everyone knows that plants grow from seed," but for one reason or another, some are propagated vegetatively.
Houseplant of the Week: Dracaena
Like Boston ferns, coleus and spider plants, dracaenas became very popular during the most recent "green revolution" during the 1970s, but had been popular houseplants for a very long time prior. They are often seen among tropical palms in old photographs of trendy Victorian conservatories. Long before that, they were used both as houseplants and in the landscapes of the Flintstone and Rubble residences in Bedrock.
Dracaena marginata may be grown in gardens of coastal Southern California, but is limited primarily to household culture in the Santa Clara Valley. If grown in the garden, it should be sheltered from frost by a lanai or larger trees. Soil need not be rich, but must be well-drained. The specimen in my office actually grows in light lava rock mixed with moss. Of course, more "inert" media require more regularly applied fertilizer. Dracaena grown in potting soil will not require so much fertilizer, but should be allowed to dry somewhat, so that the upper inch or so of soil is not moist, before irrigation.
Foliage of Dracaena marginata is much narrower than that of other dracaenas, approximately only half an inch wide. Leaves are usually short if sun exposure is sufficient, but may be as long as 18 inches or more. Each leaf has a narrow red margin, hence "marginata." The cultivar "Tricolor" also has a yellow or pale yellow stripe. Mature specimens may be as tall as 10 feet and half as wide but may become somewhat lanky when this large. Lanky stems may be used for air layering, or simply pruned back to promote denser growth. Some garden enthusiasts prefer to root stems that have been pruned out without layering, but mine have always rotted too easily.
Horticulturist Tony Tomeo can be
contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.
|
Contributed photograph