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Pressure-treated timber Are pressure-treated timbers safe for building raised beds that could be used for vegetable gardening? I am concerned that chemicals could leach into the soil and be taken up by plants growing there.-Address unknown (via the internet)

Manufacturers use several preservatives to treat wood. The two most common types seen in landscape use are creosote, used for railroad ties, and inorganic arsenic compounds. Arsenic compounds are probably the most common wood preservatives and what you're most likely to encounter in landscape timbers. Arsenic preservatives include chromated copper arsenate (CCA), ammoniacal copper quat (ACQ) and ammoniacal copper zinc arsenate (ACZA).

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Although treated wood has come under some suspicion by environmentalists, the Environmental Protection Agency has conducted research on wood preservatives and found no serious risk associated with their use. Further, epidemiological studies of wood-treatment-plant workers found no elevated risk of cancer or any other illness. Extension agents in Texas have even conducted research specifically on creosote- and arsenic-preservative-treated wood in gardens and found no cause for concern. For example, they detected no elevated arsenic levels in the soil, even as close as 1 inch from the treated timbers. Likewise, they found no elevated levels of creosote moving into the soil. The American Wood Preservers Institute (Fairfax, Va.) can provide further information about treated wood. You can call their Treated Wood Hotline at (800) 356-AWPI or look up their web site at www.awpi.org. The web site contains extensive information about safety issues.

Better bunker faces Would Tifdwarf be a good idea for bunker faces to reduce mowing vs. 419 or zoysia?-Alabama

Tifdwarf might save time compared to 419 because it is less aggressive and invasive, but it requires a different type of management, without which it may encounter some problems. Tinker Clift, department chairman of the turfgrass management program at the Texas State Technical College (Waco, Texas), observes that without the close mowing of greens-type maintenance, Tifdwarf can become quite thatchy and may be more prone to disease. "Tifdwarf just isn't made to be unmowed," according to Clift. "At the heights you'd use for bunker faces, that's the same as not mowing it." Conversely, mowing Tifdwarf at lower heights, although more agronomically sound for that cultivar, creates an aesthetic problem because it then will visually clash with the surrounding turf. Therefore, zoysiagrass is probably a better alternative. Though it may require some thatch management, zoysiagrass is less aggressive than most warm-season grasses and slower to invade around greens or other surrounding areas. Plus, notes Clift, many zoysiagrass cultivars match the color and texture of bermudagrasses closely, so they pose less of an aesthetic problem.

Container plants What plants would be good for pots in the winter? We are in the St. Louis area and someone suggested 'Capitata' yews, but they don't seem to survive the winters in a pot.-Missouri

Although people are accustomed to using USDA hardiness zones for evaluating the survival potential of a plant in a given region, it is not a very useful approach for containers. The reason is that root hardiness-a key factor for overwintering container plants-does not consistently correspond to shoot hardiness.

Cliff Ruth, an extension horticulturist with the North Carolina Cooperative Extension Service, is familiar with plant-hardiness issues and notes that plants with similar USDA hardiness ratings often have widely divergent root hardiness. Therefore, according to Ruth, their USDA ratings may be of little use for predicting their success in containers. For example, flowering dogwood, Cornus florida, is hardy to Zone 5, but its roots die in the range of 11 degrees to 21 degreesF, depending on root maturity. Juniperus conferta, with roughly similar shoot hardiness, will not start to lose roots until soil temperatures drop to around 12 degreesF, and larger roots can survive down to about -10 degreesF. Further, as Ruth notes, plant material derived from a warmer region may have less cold tolerance than specimens of the same species with genetic "roots" from a colder region. However, references usually list just the maximum hardiness of the species.

Dessication also is a threat to container plants in winter. Ruth explains that ground temperatures below the top few inches generally do not drop below the 20 degrees to 30 degreesF range, which many plants easily tolerate. However, in containers the soil more closely reflects air temperatures. Therefore, it gets much colder and may freeze completely. Freezing, per se, does not necessarily kill roots, but it does prevent them from taking up water. This makes the shoot system more vulnerable to dessication.

It stands to reason that many evergreen conifers, with their xeric qualities, may tolerate winter water stress better than most broadleaf evergreens. Further, because you're trying to provide winter interest, you need something more eye-catching than a nondescript dormant plant. Again, evergreens come to mind. However, another possibility to consider is using deciduous plants that exhibit some winter interest, such as red-twig dogwood. Deciduous plants are less vulnerable, though not immune, to winter water stress (remember, this is a factor distinct from low-temperature injury). It's easy to forget to keep soil moist in winter, and containers often become quite dry. Be sure to check container soil periodically and, if necessary, add water.

Another practical aspect of this problem is container size and type. Larger containers are less prone to temperature swings than smaller containers. Regardless of the container, remember that larger, more mature roots tolerate much lower temperatures. Thus, older and larger specimens should survive better than younger plants.

The root hardiness of many plant species has not been precisely documented, but a few examples that have been studied and found to be relatively tolerant of low root temperatures are: Taxus media 'Hicksii' (mature roots die at around -4 degrees F); Juniperus horizontalis (roots die at 0 degrees F); and Picea glauca and P. omorika (both species lose roots at -10 degrees F).

Remember that winters vary in temperature, precipitation, snow cover and wind, all of which can affect a plant's survival. Therefore, do not be surprised if a container plant that has made it through a few winters finally succumbs in an especially harsh one. Overwintering plants in outdoor containers in cold climates is not an easy exercise.

A key component of integrated pest management is selecting and using pest-resistant plant varieties. Few pests create as great a need for such a strategy as adult Japanese beetles, which feed on flowers, fruit and foliage of many species. Although it's well known that Japanese beetles show strong preferences for certain plant species, they also seem to prefer particular cultivars. To identify cultivars more resistant to attack, researchers at the University of Kentucky tested 28 cultivars of crabapple, 8 types of linden and 53 rose varieties for their susceptibility to attack by Japanese beetles. The study took place over several years, during which the investigators measured the degree of defoliation by the beetles.

The researchers found significant preferences by the beetles for certain cultivars of linden and crabapple. Although the general level of attack varied considerably from year to year, the relative susceptibility of the cultivars showed more consistency. The four most-resistant crabapple varieties were 'Harvest Gold', 'Jackii', 'Louisa' and 'Jewelberry', all suffering less than 12 percent damage over 3 years. The three most susceptible cultivars were 'Radiant', 'Red Splendor'and 'Dolgo', all receiving greater than 80 percent damage to their foliage over the same period.

'Sterling' and 'Legend' lindens received an average of about 47 and 33 percent damage respectively over 5 years, compared to 'Olympic', 'Greenspire' and Crimean lindens, which all suffered between 80 and 90 percent damage.

Unfortunately, the roses were a different story. Although some differences between cultivars were apparent, all varieties sustained damage at unacceptable levels when beetle flights were heavy. Though the researchers analyzed the level of damage for each bloom color, they found no indication that the beetles preferred particular colors. They devoured most blooms before they ever opened.

The investigators conclude that the availability of resistant cultivars could be important in areas infested with Japanese beetles. Because some cultivars vary in their resistance to Japanese-beetle feeding, they hold potential for selection of varieties less prone to attack. Resistance to Japanese-beetle attack should be one criterion among the many others for which breeders select.

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