Permanent Plants: Bulbs, Rhizomes, & Tubers

I often receive inquiries from readers about the suitability of using a certain plant, typically exotic or unfamiliar to them, for covering large areas in their yards or gardens.
My advice is always the same: If you are not familiar with a certain plant, or even if you are familiar with it but are planting it in an unfamiliar location, put your horticultural toe in the water before taking the plunge.
In other words, plant a small patch of ground with your chosen annual, ground cover or shrub and see how it grows. If the plant looks good after several weeks, you can then go comfortably forward and complete planting of the area.
Prior to planting, you might even keep the plants in the plastic nursery containers they have been growing in while you evaluate whether they are suitable for the location, in terms of sun exposure, you have picked out for them. Their condition after several weeks will indicate whether they should be removed from their containers and permanently planted where they stand or moved to another location.
Frequently, it seems, the subject of planting on a slope is raised.
Slopes can be a problem because of erosion and excess, wasteful irrigation run-off. I advise against planting anything too exotic on a slope because replanting is such a chore and you want to choose something that will persist for years without very much maintenance or dieback.
The surest plants for slopes are those that spread by bulbs, rhizomes or tubers. Such plants generally are not that needy when it comes to water or fertilizer and can survive all types of extreme weather. In the worst-case scenario, these plants are killed back to the ground by interrupted irrigation or freezing weather. However, owing to their underground storage organs, they will invariably come back to life when irrigation resumes or warm weather returns.
For sunny slopes, daylilies and society garlic are the most reliable selections.
Tuberous daylilies (Hemerocallis hybrids) bloom most famously in yellow and orange, but also are available in red, burgundy, purple, pink, white and many double, striped and other unusual cultivars. There are catalogs and Web sites full of infrequently encountered daylilies that are guaranteed to stimulate your imagination when it comes to planting your slope. The Web site of the American Hemerocallis Society (www.daylilies.org) is a good place to start your acquaintance with these plants.
Society garlic is a rhizomatous stalwart that is on most lists of bullet- proof plants for slopes and other challenging locations. It has pinkish lavender flowers that are in bloom on and off throughout the year. In addition to the common green-leafed type, a green-and-silver-striped cultivar also is available.
Some people refrain from planting society garlic because of its odor, although its scent is only evident when its leaves are crushed or when it is planted in a confined area. On the plus side, in the manner of culinary garlic, society garlic serves as a pest repellent when interplanted with other species in garden beds.
Asparagus densiflorus `Sprengeri,’ commonly referred to as asparagus fern, is a sprawling, billowy plant that is sometimes cursed by gardeners for its staying power. Once it has established itself, it defies deracination.
Yet, on a partially shaded slope where nothing else will grow, this may be the plant you seek. It has a soft look and, due to fleshy, round tubers that grow off of spreading rhizomes, it can live through a drought. Its hardiness extends to the Santa Clarita Valley but it would be a borderline selection further north.
In addition to its lacy foliage, it produces ornamental red berries.
For deeper shade, rhizomatous lilyturf (Liriope species) is the most suitable slope hugger. There are two species seen in the nursery trade, big blue lily turf (Liriope muscari), growing up to 2 feet tall, and creeping lily turf (Liriope spicata).
Both are handsomely dark green, but you also can select from variegated cultivars of each species with either cream-and-green or silver-and-green striped foliage.
The plant has soft fountainesque foliage and almost always blue, but occasionally white, flowers followed by blackish blue berries.
Liriope, probably the most drought tolerant ground cover for shade, encounters two problems, snails and fungus, both brought on by excess water. Foliage that is hopelessly snail-tattered or brown and spotted from fungus disease should be sheared almost to ground level. New foliage will come up green.
Creeping lily turf also has been used as a lawn substitute in light-deprived locations.
Hall’s Japanese honeysuckle (Lonicera japonica `Halliana’), although lacking underground bulbous storage structures, is an outstanding ground cover for slopes.
Capable of withstanding periods of drought, it flourishes with regular watering. It sometimes is considered a weed due to its rampant growth and, once established, benefits every year or two from radical pruning. It is cold hardy and may be planted in the Antelope Valley.
Be careful, though, as snakes have been known to lurk in overgrown honeysuckle plantings.
Tip of the week
Snails are often an over-rated problem. Even where an infestation seems to be out of control, if you spend a few minutes each morning disposing of them by hand, they usually disappear within two to three weeks.
If you choose to spread a snail control chemical and have pets or other critters around, Sluggo is a recommended product since it is non-toxic to dogs, cats and wildlife.
All snail-control chemicals break down when wet so they have to be applied at frequent intervals in well-watered gardens.

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