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Q&A with Bob Polomski 18

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Extension Consumer Horticulturist, Clemson University

I've heard that landscaping can conserve energy and lower my utility bills. Can you provide a couple of tips?–V.B., Fort Collins, CO

Answer: The use of shelterbelts of trees to conserve resources dates back to the Dust Bowl years in the Great Plains, when rows of trees were planted to reduce soil erosion. Properly positioned trees, shrubs, and vines can also serve to reduce the fuel needed to heat and cool a home. Depending on which study you consult, savings in heating and cooling costs can reach 25 to 50 percent.

The first step in reducing heating costs is to block the wind. For this, a hedge of vegetation is better than a solid barrier. The optimum amount of reduction in both wind speed and turbulence can be achieved with a 60/40 ratio of solid to opening. This is a barrier open enough that you can see something moving on the other side, but you can't see precisely what it is. Such windbreaks are usually evergreen, but studies of deciduous shelterbelts have shown that they still retain 60 percent of their benefit when leafless. The wind speed is reduced for a distance of 30 times the hedge's height on the leeward (downwind) side of the hedge, and five times the hedge's height on the windward (upwind) side. For example, if the wind is blowing from the west and the hedge is ten feet high, you will gain some benefit 300 feet east of the hedge and 50 feet west of it.

Cooling costs, meanwhile, will be reduced by screening out the sun during the summer. For this purpose, plan to locate deciduous trees on the southern side of a house, where they will provide shade, or plant deciduous vines to cover the south-facing walls. The shade from vine-covered arbors and pergolas will also provide valuable relief.

The area beneath my oak trees looks stark and in need of some kind of planting. Do you have any suggestions?—L.W., Larkspur, CA

Answer: Western oaks can be underplanted, but only with plants that are drought tolerant, since excessive watering can result in tree injury or death.

For the sunny side of your oak trees, consider yarrow (Achillea millefolium) and purple needle grass (Nasella pulchra). Possible shrubs include prostrate coyote bush (Baccharis pilularis ‘Pigeon Point’), Australian fuchsia (Correa ‘Carmine Bells’), hummingbird flower (Zauschneria californica), and island California fuchsia (Z. c. subsp. cana).

For partially shaded northern or eastern exposures, consider Point Reyes bearberry (Arctostaphylos uva-ursi ‘Point Reyes’), maritime ceanothus (Ceanothus maritimus), desert sunflower (Viguiera deltoidea ‘Parishii’), and yerba-de-selva (Whipplea modesta).

Keep these shrubs and groundcovers away from the trunks of your trees. Mulch around the trees to at least four feet from the trunk or up to the drip line, especially on young plants. This will avoid competition for water and nutrients.

I received some living stones from a friend, but no instructions. What care do they need?–K.R., Stateline, NV

Answer: Living stones (Lithops spp.) are curious, slow-growing, long-lived succulent plants that reach a diameter of three-quarters to one-and-a-half inches and resemble stones. The body of the plant is a pair of fused leaves separated by a slit at the top. There are 35 species of Lithops and many subspecies and varieties encompassing an incredible range of colors and patterns. All are native to the deserts of southern Africa. Their peculiar appearance, matching the colors and shapes of the rocks of their surroundings, is thought to protect them from grazing animals. Lithops flower between late summer and winter. The daisylike flower emerges from the slit, and, depending on the cultivar, can be white, yellow, orange, or pink. After flowering, the old leaves die as a new pair of leaves begins to form and develop through winter and early spring.

Lithops species come from deserts with wet summers and dry winters. Accordingly, your living stones should receive bright, direct sunlight in a well-ventilated location where the temperature does not go below 40°F. Plant in a sandy soil mix. Water them from spring, when the new leaves are developed, until early fall. Keep them completely dry during the winter. Remove the old, shriveled leaves in the spring. Lightly fertilize during the summer.

I am confused about the different kinds of potting soils sold for houseplants. How do I choose the best one?–B.S., Wilmot, KS

Answer: There's little unanimity as to what constitutes the best potting mix—every gardener seems to have his or her own favorite. Commercial soilless mixes typically consist of sphagnum peat moss, aged ground pine or fir bark, vermiculite, and perlite. The bark and perlite are added to enhance drainage; vermiculite helps to retain water and nutrients. Lime is also a common ingredient, added to produce a near-neutral pH. Some manufacturers include a starter fertilizer, as well as wetting agents to facilitate moistening and even distribution of water throughout the mix.

The mix can vary to suit specific plants. Orchids require a particularly airy, well-draining mix. Commercial orchid mixtures typically contain chunks of fir bark with some coarse peat, redwood or tree-fern fiber, perlite, and charcoal. For African violets, the African Violet Society of America recommends a mix of equal parts sphagnum peat, vermiculite, and perlite. For cacti and succulents, adding one part builder's sand and half a part additional coarse perlite to two parts premixed soilless mix produces a good potting medium.

For many indoor plants that will remain in containers for years, adding a mineral soil to the soilless mix improves its nutrient-retaining qualities, reducing the need for fertilizer applications. Houseplant expert Tovah Martin uses a homemade formula consisting of equal parts sand, peat moss, perlite or vermiculite, and loam. She adds a cup of bonemeal and 10 tablespoons of ground limestone to each bushel.

Whatever mix you choose, homemade or commercial, it should pass the flow-through test. Fill a six-inch pot with the mix to within an inch of the rim and add water. Hold the pot and watch the flow of water from its bottom. It should look like a shower head, with water flowing uniformly out of each drainage hole. Keep adding water until the potting medium is completely saturated. Water should continue to slowly seep down through a good potting mix. An inferior mix will have standing water. H