Thursday, October 26, 2006
Protecting trees from the frost pocket
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
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Q: Are there any trees that can handle hard freezes and still deliver a respectable showing of color? I live in a valley surrounded by mountains; a frost pocket would probably be an accurate description for the fall and winter months. One of my favorite goals to achieve in the yard around the house is good fall color displays from trees and shrubs. I am not very successful. Almost every fall a hard freeze settles in the valley here and I witness developing fall color on many plants becoming subdued or halted. A closer inspection of the leaves and one can see the plant pigments "browned out" before they had a chance to be enjoyed. I currently have sugar maples, red maples, Japanese maples, witch hazels, fothergilla, ginkgo, bottlebrush buckeye, sweetgum and dogwoods. The yard receives excellent sunshine for at least 8-9 hours daily during most of the growing season where the above-mentioned plants are planted. I make the effort not to over-fertilize or water so that nothing is "over-lush" going into the fall season. I have also tested the planting areas to make sure pH readings are what are recommended for these trees and shrubs. Any advice would be appreciated.
A: My advice starts with ideas to keep your current trees: save rainwater in a huge cistern to supply an overhead irrigation system that is set to come on and cover the trees during nights when freezes are expected; install giant fans to blow the air around, above and through your tree foliage on frosty nights; and/or install heaters through your property to heat up the air around your trees like the heaters that orange growers in Florida used throughout their orange groves when freezes were expected. I won't give details here, since these suggestions are probably expensive and impractical for most of us.
I'll suggest trees that might be able to handle hard freeze and still show fall color, but this is truly a “guessing game.” I'm assuming that you live in the United States Department of Agriculture Hardiness Zone #6, which places you in one hardiness zone with winter temperatures that are colder than what we usually expect here in Roanoke, which is in Zone #7. The hardiness zones have been established to help folks select trees based on coldest winter temperatures normally expected for an area. Hardiness zones with larger numbers have milder winter temperatures, and areas that can expect colder winter temperatures have lower zone numbers. However, this zone system does not address tolerance to the summer stress of heat that is also critical in selecting trees for the landscape.
Trees to try include: (a.) Quaking Aspen, botanic name Populus tremuloides, a fast grower that can reach 40 to 50 feet, but may only live for about half as long as a maple; good yellow fall color; Zone 1 to 6(7); (b.) Downy Serviceberry, also called Juneberry, Shadbush, Servicetree, or Sarvis-tree, botanic name Amelanchier arborea, an attractive small tree that grows to 15 to 25 feet and has yellow apricot-orange to deep red autumn color before leaf-fall in early fall; Zone 4 to 9; (c.) Swamp White Oak, botanic name Quercus bicolor, large tree that can reach 50 to 60 feet height; found in the wild in low lying areas; normal autumn color is yellow; Zone 3 to 8; (d.) Sourwood, also called Sorrel Tree or Lily of the Valley Tree, botanic name Oxydendrum arboreum, a slow grower 25 to 30 feet in height; begins autumn color of yellow, red, and purple in early fall in the Roanoke area; Zone 4 to 9 is possible; (e.) Chinese Pistache, botanic name Pistacia chinensis; I'll plant one of these in my front yard if I can find one; medium-size tree that can reach 30 to 35 feet height; compound leaves made up of small leaflets along a leaf stem; excellent fall color of spectacular orange; or (f.) ‘Cleveland Select' Ornamental Pear, botanic name Pyrus calleryana ‘Cleveland Select'; stronger tree than the devastated ‘Bradford' Pear; medium size, upright-pyramidal tree that grows to 35 feet in height; fall color is reddish purple; supposedly less susceptible to early fall freezes than ‘Bradford' Pear; Zone 5 to 8 or 9.
Q: Every year around this time, I start noticing that my houseplants that spent the summer outside but have been back indoors since early September begin to look bad. I have all the plants in sunny windows. A co-worker told me that I should be fertilizing my houseplants once a month to make up for the shorter days. What do you think?
A: Indoor plants don't make much new growth from fall through spring and will not respond to added nutrients. The big three stressors on most indoor plants at this time are: excessive watering that is not needed because of the low evaporation from cool soil, cool indoor temperatures and reduced sunshine inside.
