Tidewater Gardening - October 2012

Planting Deciduous Trees and Shrubs
K. Marc Teffeau

In last month’s column I briefly mentioned that the fall is a good time to plant deciduous trees and shrubs. Most homeowners think of spring as the best time to plant trees and shrubs in the landscape. One of the reasons for this is the general spring gardening push and the availability of a number of balled and burlaped and container grown woody ornamentals available in the garden centers and nursery lots. However, October and November are generally considered the best time for moving plants in the landscape.
After the drought and heat problems of this past summer, a number of landscape shrubs and trees have died and are in need of replacement. Garden centers and nurseries usually stock a good selection of woody plants at this time of year.
The rains that we got at the end of August and the first week in September went a long way to help reduce the drought conditions that we experienced but we are still in a soil water deficit going into the winter. So you need to make sure, if we do not get adequate rainfall, that you water the newly transplanted trees and shrubs.
A rule of thumb is that you can transplant deciduous trees and shrubs after they become dormant, usually after the first or second hard frost. You can also transplant evergreen trees and shrubs earlier in the fall before they become dormant. The exception to fall transplanting is evergreen seedlings like pines. They do very poorly when transplanted in the fall because they are not able to develop a good root system before the winter sets in.
The same fact applies to digging up and transplanting established evergreens in the landscape in the fall. Wait until early next spring to do this type of transplanting.
As you drive around the area you might notice dead or dying maple trees, especially red and Norway maples. Many of these trees have been showing wilt disease infestation (branch and limb dieback) over the last few years and have finally succumbed to the wilt because of the drought stress this past summer. Verticillium wilt is caused by several species and strains of a common soil fungi Verticillium alboatrum and V. dahliae. This fungus is present in our soils and affects a broad array of woody ornamental trees and shrubs as well as herbaceous ornamentals, field crops and vegetables.
Infected plants may appear yellowed or off-color. Scattered branches may suddenly wilt and die at any time, but most often in July and August. With a severe infection, the entire plant may wilt and die. Sunken cankers and split bark may appear on the trunk.
Many times wilt symptoms are often mistaken for transplanting, winter injury, salt damage or even drought damage. The wilt fungus in the soil invades the fine roots of susceptible plants. Roots wounded by transplanting or construction damage are more easily invaded.
The fungus grows up through the water conducting tissues (xylem). Once the xylem is infected, the fungus can spread upward and outward each year. The plant responds to the presence of the fungus by producing substances which plug the xylem, causing discoloration and wilting. If the tree is under severe drought stress, its entire “plumbing system” will collapse resulting in death of the tree.
A quick way to determine if wilt is a problem is to cut into the bark at the base of wilting branches. The presence of the fungus causes the sapwood to take on brown or green-brown discoloration. This dark streaking is diagnostic of Verticillium wilt.
Laboratory culture of the fungus from the discolored sapwood can provide positive identification of Verticillium wilt. If you are planning to replace the dead or dying maple tree do not replant maples in that area. Choose another tree species. The soil in infested with the wilt fungus and a transplanted maple in that area has a good possibility of picking up the disease.
October is a good time to do maintenance of the trees and shrubs in the landscape. While you can still identify them easily, prune dead and diseased branches from trees and shrubs. Remember, however, that spring flowering shrubs like azaleas, rhododendrons, forsythia and spireas have already set or are forming their flower buds for next spring’s flower display. To prevent reducing next year’s bloom, don’t prune spring flowering shrubs until after they bloom next spring.
Old, fallen leaves may contain disease innoculum for next year’s plant infections. Remove any infected debris from around the plant’s base and dispose of it. We usually recommend mulching newly planted trees and shrubs to reduce weed problems and to conserve moisture. In the fall, however, it is usually a good idea to wait to mulch until after the soil temperatures have reached 32°. Mulches applied too early can do more harm than good.
Mulch is used to keep soil temperatures constant and prevent frost heaving, not to keep it warm. In October the trees and shrubs start to harden for the upcoming cold weather. To encourage this process, remove mulch from around the stems of shrubs and trees. This will also discourage mice and vole damage to the stems during the winter.
Keep your trees healthy by watering deeply, pruning out all wilted and dead branches and fertilize in the fall or late winter with a balanced fertilizer with a N:P:K ratio of 2:1:2. Avoid damaging the roots with salt from sidewalks and roadways during the winter and avoid cultivation around the trees.
Conifers that are exhibiting poor color or weak growth may respond to fertilizer applied between mid-October and mid-March. Light pruning of both needled and broad-leafed evergreens is recommended in the late fall to encourage a strong framework to help the plant overcome any snow damage. Remove any weak or crowded branches.
Remember to water evergreen shrubs thoroughly before the ground freezes, especially if we have a dry fall. Evergreens continue to lose water by transpiring during the winter, but when the ground is frozen, the roots cannot replenish the water lost through the leaves or needles.
Hold a bagworm picking party in October to remove the bags from the trees. This will help reduce the amount of spring hatch from over-wintered eggs in the bags and help to reduce the amount of spraying you may have to do next year.
I have already mentioned in my September column about the need for a good clean-up of the vegetable garden. If the ground in your vegetable garden is dry and workable, and the garden site is not subject to soil erosion, consider doing a fall plowing and letting the ground lay exposed over the winter. Late-fall tilling can help control insects, such as corn borer, corn earworm, cucumber beetle, squash bug, and vine borer, because it exposes over wintering insects to winter conditions. It also makes soil preparation easier in the spring.
Another alternative is to mulch the entire garden in the fall with straw to a depth of 4 to 6 inches. Then in the spring, only pull back the mulch in the areas that you plan to plant. You will need to do this a couple of weeks before planting, however, to give the soil time to warm up.
And don’t forget to add fall color to landscape! Buy your pansies and mums now and set them out in the flower beds to add to the already colorful display of fall leaf foliage. Pansies, when planted in the fall, will become established and survive the winter to bloom again in early spring. You can then remove them when they begin to decline in the early summer heat.
Also consider planting asters. They are colorful in the late summer and throughout the fall. “Flowering” cabbage and kale are also good additions for color. The color in these plants comes from the red, purple and white pigments of the foliage. The colors intensify as the weather gets colder and they usually provide a lasting presence through the end of December.
Happy Gardening!