Fall through winter, into early spring, a pleasant surprise in the ornamental garden is Italian arum, with its bold green leaves above the whiteness of new snow or drab colors of dormant vegetation. Its green vigor may come as a shock if you’ve not grown or seen it before. The large arrow-shaped leaves are startlingly dark green, with pale green veins.
Arum italicum grows to about 8 inches tall in a partially shaded area in my yard. It may grow up to a foot in richer soil. In early summer, a fleshy stalk of small white flowers, partly enclosed by a bract fold, is nearly hidden. It’s closely followed by a spike of green berries, ripening to bright orange in late summer.
The seeds, with their soft exterior, are toxic to humans, and may be topically irritating to bare hands or arms. It may seed itself, or you can gather the berries wearing rubber gloves, mash off the pulpy exterior and plant the revealed black seeds about a half-inch deep in a protected area of your garden. They’ll germinate in late winter. When they’re large enough for you to feel comfortable in transplanting them, do so. Another way to propagate these delightful plants is to divide a clump that’s a few years old, after it flowers.
Arum italicum is often planted with hostas, since hosta foliage fades away about the time of year that the arum is stretching its new leaves. Arum italicum may thrive in full sun, but hostas don’t. This arum thrives in partial shade or sun, so would be ideal with hostas in a partly-shaded bed. You may want to use a border fork or spade to lift the entire clump of arum out of the ground, then divide the plants by hand. Plant at the same depth they formerly grew.
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Hostas, too, may be multiplied by dividing clumps that are more than 3 years old, in the same way as dividing the arum. Slower-growing hostas may need an extra year or two before they’re divided. Slow-growing hostas include the miniatures, those with a lot of white on the leaves, and the tetraploids (that is, those with four basic sets of chromosomes instead of the usual two, one from each parent). Tetraploids are bred to create larger flowers and denser foliage than normal, and are identified on plant tags when plants are purchased.
Hostas tell you when they’re more than ready to be divided, by the death of the center of the clump. You can divide them in spring or summer, but if you do divide them in late summer, do so more than three weeks before the usual average date of hard freeze, and make sure they’re well-watered. Even though hostas are slug candy, a lush bed of hostas is an attractive cool sight in a scorching summer.
Hostas can help hold a slope from erosion, but it’s best to use a variety of plants with different root depths to hold soil on a slope.
I’ve known of newcomers to this area who bought a steeply sloping property, then removed the native sagebrush from the slope. Sagebrush has very deep, strong roots, and those plants can minimize erosion better than most plants. A single sagebrush is an attractive plant, but if you have one in your yard, never give it supplemental water, for it’s accustomed to very low water usage. Too much water kills this plant, and “too much” is very little, I’ve found.
Send garden questions to email@example.com or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.
Plant sale Saturday, April 29
Ada County Master Gardeners are holding a plant sale Saturday, April 29, at the University of Idaho Cooperative Extension office at Marigold and Glenwood. Sale of herbs, houseplants, vegetables, berries and perennials opens at 9 a.m., and continues until noon.