A spring shower of queries on stink bugs, shade trees, more

By Joel M. Lerner
Saturday, May 22, 2010; E06

According to the National Oceanic and Atmospheric Administration, April was the warmest on record, going back to 1880. This unusual warmth at the start of the growing season might be one of the reasons readers have a bumper crop of gardening questions.

Q. In a recent column you mention putting down 1 to 2 inches of compost and then a layer of shredded hardwood mulch. When you talk about compost, are you referring to the homemade kind or to the mushroom compost available at nurseries? -- Linda Ferris

A. The compost you want is organic material that still contains nutrients your soil needs. Mushroom compost does not have these natural organisms. Make sure the product you purchase hasn't been treated with wood preservatives or lawn chemicals and has aged for six months to a year, or until it has a fine texture. Use your own compost if it has sufficiently broken down into a dark, friable material. Leafgro is one commercial product that will supply the proper nutrients to your soil.

Q. Are there any trees that can be planted close to a house and deck and will grow quickly and provide shade in summer? -- Ruth Clark

A. Some fast-growing trees that could provide some shade in five to seven years, if the trunks already have a 1- to 2- inch thickness, are heritage river birch, pin oak, black gum, October glory red maple and Zelkova. A shade tree should be planted no closer to your house and deck than about 20 feet, which should be close enough to cast shade. Before planting, track the hours of sun and know where late-day shade is required.

Q. What can I do about stink bugs? I've disposed of dozens of them over winter and spring. -- Teresa Rizzo

A. To control them, learn their life cycle. They are active from spring to fall. Adults can live for several years by hibernating under leaf litter. They can lay their barrel-shaped eggs, up to 100 or more at a time, as many as four times a season on the undersides of leaves. Keep your garden as weed-free as possible, removing low-growing leaves that provide areas for egg laying and hibernation. They have a sharp proboscis that can feel like a pinprick. Use gloves to hand-pick them, or try using a small cordless hand vacuum such as a DustBuster, on low speed, to suck them up.

When startled, they release a smell that is not only repugnant to people but attracts other stink bugs. Dispose of them as gently as possible; dumping them into soapy water should work. They are attracted to the color yellow and to lights. Plant yellow flowers far away from the house to lure them away, and use low-wattage light sources outdoors to discourage them from flying to your property. Yellow pheromone traps, which attract them and monitor the problem, are available at garden centers. Of course, you should place the traps away from your house.

Q. Several years ago you wrote an article about the merits and downfalls of planting evergreens. Our plantings suffered in the recent high winds. Can you please suggest some evergreens to screen an ugly wall that is now very exposed. I need plants that will tolerate semi-shade and are fast growing. -- Fran N.

A. Here are some suggestions: Goshiki osmanthus (O. heterophyllus 'Goshiki'). It can reach 15 feet high and wide after many years in semi-shade, but can be selectively pruned. The creamy yellow variegation on the foliage is attractive in winter. Dragon lady holly has a narrow-growing pyramidal habit that does best with some sun. It grows 6 to 8 feet wide and 12 to 15 feet tall. Chindo viburnum (V. awabuki 'Chindo') is a broadleaf evergreen that has fared well over the past winters. Growing 20 feet high and 15 feet wide, the thick, leathery leaves stay green year-round and offer a tropical appearance in winter. With regular attention, they can be pruned to stay smaller. Goldthread falsecypress (Chamaecyparis pisifera filifera 'Aurea') is relatively shade-tolerant and has a willowy growth habit that stands as a contrast in form and leaf color to other greenery.

Q. My foster hollies sustained heavy damage this winter. Will pruning or topping them encourage fuller growth so they can withstand heavy snows? Are they parthenocarpic? I see lots of bumblebees and other flying insects around them at this time of year. -- John Stark

A. Foster hollies can be parthenocarpic, which refers to the formation of fruit without the need for both male and female plants. They can also produce berries from flowers that have been pollinated. Your hollies will renew as denser, more rigid plants if you prune them. Broken limbs should be removed, and if there is a great disparity in size, your other hollies could be pruned to match the size of those that broke. To shape them, prune the branches you want to remove.

Q. In one of your columns, you listed plants that deer don't eat. I'm not familiar with, nor can I find rohdeas. Can you provide more information? -- Bob Nixon

A. Sacred lily (Rohdea japonica) is a perennial that stays green year-round and which deer do not eat. It forms large red berries in the center of the plant in fall, but they are not readily visible. They are hidden in the center of this evergreen's strap-shaped leaves. This slow-growing perennial will grow in dry or moist soil and prefers shade. It takes several years to colonize an area and is not an overly invasive groundcover in USDA Hardiness Zones 5 to 9.

Q. Is there anything I can do to revive 40-year-old azaleas that are six feet tall and looking thin, tired and anemic? -- David Duberm

A. Azaleas will renew dependably. Prune the oldest, tallest branches at their base. This will encourage new growth from the bottom of the plant. Evaluate after each cut and shape as you prune. Selectively prune healthy stems by heading them back to viable foliage. Try to trim all the shrubs to a fairly even height. Then spread an organic fertilizer for acid-loving plants, such as Holly-tone made by Espoma. Water azaleas during dry spells. This type of cleanout pruning requires patience. Most azaleas can be cut in half or more and still renew quite well.

Thanks for writing and for reading Green Scene.

Joel M. Lerner is president of Environmental Design in Capitol View Park.

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