Reader  Landscape Plant  Inquiries Answered

By C Rae Hozer, Cumberland County Master Gardener

Plateau Gardening reader Dennis from Fairfield Glade, Tennessee emailed to request a link or web site with instructions on planting various shrubs and plants. Specifically mentioned were nandinas, hollies, grasses and azaleas.

Readers seeking how-to-plant details for green landscape materials should go to the University of Tennessee web page http://GardeningTennessee.edu. Once there, choose the second option on the right hand side, “UT Gardening Publications (free)”. Then select “Landscaping” on the linked page. You’ll find good information on installing trees, shrubs and other landscape plants. If you like, download and print any of the publications using your home pc and printer. It’s a convenient resource and free of charge.

When selecting perennials that should survive winters in this part of the state, get plants suited to United States Department of Agriculture (USDA) Hardiness Zone 6. Pick plants with Zone 6 midway in their cold hardy range. Example: Plants hardy in zones 5—7 should do well in the Upper Cumberlands. Choose shrubs whose mature size fits in the available space. Otherwise, they’ll soon need constant pruning and become a maintenance headache.

Ignore the current warming trend when considering a perennial’s cold hardiness. The problem on the Plateau, particularly at higher elevations like northern Cumberland County as well as near Monterey in Putnam County and along spurs of the Highland Rim to the north and east in Smith County, isn’t how cold it gets. The killing factor is wide temperature swings during late winter and spring. Typically, plants are encouraged to break dormancy and start their spring growth flush too early by extended warm spells in January, February or March. A freeze which hits while plants have succulent new growth is deadly. 

The American Horticulture Society (AHS) in recognition of the impact heat has on an individual plant’s survival or thriving during warm weather, has published an AHS Heat Zone Map. Many plants are now rated for Heat Zone suitability throughout the United States. More information on the effects of heat, high humidity and drought can be found by visiting http://www.ahs.org/publications/heat_zone_map.html. Enter your zip code in the “Heat Zone Finder” to learn your immediate area’s zone. Match plant selections to that local Heat Zone. 

Dennis knew azaleas like an acidic soil. As he has lots of clay on his property, Dennis wondered about adding Canadian peat to lower the soil pH where he will install azaleas. I live nearby and the native soil in my woods tested at a pH of 5.4.  A pH that low is good for blueberries but not lawn grasses or most landscape plants. My soil has a silty-clay texture, too. Sandstone parent material makes the soil here quite acidic. The best advice is—Don’t guess, soil test. Adjust pH according to findings from a reputable soil lab. (Once the site’s soil acidity/alkalinity level matches needs of plants to be grown there, no further adjustments are needed for three or four years.) Experts recommend you not “fluff up” native soil by putting peat or other additives in planting holes for trees or shrubs. Don’t fertilize until a woody transplant has been in place for two years. Do mulch around the plant’s base, but don’t pile mulch against trunks or stems. Leave a 2-inch gap between the trunk and the mulch.

Next week, answers to questions about a sickly red bud and peonies transplanted two years ago. See your plant questions in the newspaper. Email them to mgardenerRae@frontiernet.net.

Plateau Gardening is written by Master Gardeners for those tending home landscapes and gardens in Tennessee’s Upper Cumberland Region. Contact UT Extension Cumberland County, P.O. Box 483, Crossville, TN 38557, (phone 931-484-6743) for quick answers to specific questions, free publications, or to learn about becoming a Master Gardener. Email comments or yard and garden inquiries to Master Gardener Rae, mgardenerrae@frontiernet.net.