Thursday, December 13, 2007
Cut back dahlia stems after chilly nights
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
Or send an e-mail. Answers will be given only in this column. Please don't send pictures or samples.
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Q: Do you need a male and a female holly bush in order to get berries? My bush is healthy and was full of red berries several years ago when I planted it. It doesn’t produce any berries now, which are needed at this time of year. Also, I’d like to know when is the correct time of year of dig my new dahlias here in mid Virginia. They had a lot of blooms in late summer and early fall. How do I treat them so they will keep well through the winter?
A: The answer to your holly berry question depends on which variety of holly you are referring to. The most famous evergreen holly that is known for its beautiful red berries is the American Holly species, which does require a male plant within about 200 feet of a female American Holly that will need pollen in order to make a good show of berries.
Some other holly species do not have individual sexes on separate plants. If you’re not sure what kind of holly that you planted, take a stem piece to ask for identification at the nursery where you bought the holly or else to your local extension office that has consumer horticulture staff that might be Extension Master Gardener volunteers.
Dahlias are tuberous-rooted perennials that have tender tubers whose buds will be killed by extremely cold soil. Thus, in mid Virginia and colder areas, all dahlia stems must be cut back to about 2 inches above the soil after chilly fall nights cause the foliage to turn yellow. After a couple of days of drying time, the dahlia tubers should be dug up. Carefully, knock most of the soil off from each tuber and store it in a cardboard box with the name and color of the dahlia written on the box. Store this in a cool but frost-free place until mid spring when the box should be placed outdoors in the daytime sun and sprinkled with water every day or two to stimulate sprouting in order to be ready for planting out after the average date of the last spring frost in your area.
So, if you haven’t had a severe freeze in your area yet, follow the above recommendations immediately. If your area has already experienced frigid weather, your dahlia tubers and buds are likely dead. Follow the procedure for them, but don’t be too hopeful come spring sprouting.
Q: How can I propagate local magnolia trees? I saw colonial door decorations using beautiful magnolia leaves when visiting nearby Williamsburg.
A: There are several species of magnolias, but the species whose large, shiny leaves are used in wreaths and holiday decorations is the stately species commonly called Southern Magnolia. This is fairly easily propagated through seeds and tip cuttings.
To produce new Southern Magnolias from seeds, remove seeds soon after they are ripe in late summer or early fall here in Roanoke. Ripeness is shown as a bright red coloration of seed hulls in their large pod. Then, either sow the seeds outdoors with squirrel protection in the fall so they will experience the natural chilling process of winter that enables them to sprout in the spring when the soil warms up. Or, mimic this natural process by giving the seeds moist-chilling for 4 months in the refrigerator and then sow the seeds indoors as you would in producing any seedlings for the garden.
Magnolia seeds rot easily if they get too wet either in moist-chilling or after they are planted.
Magnolia seedlings grow rapidly and should be transplanted to small individual pots as soon as they have grown several roots.
Some magnolia varieties can be started easily in damp sand from summertime tip cuttings that should include some partially matured wood.
Q: This past fall, some of the leaves of the azaleas planted in the landscape of the previously lived-in house we purchased turned completely yellow. We assumed that this color change was due to the drought, since we saw no pests on the plants. We watered the azaleas a few times during the fall, but now we are worried that the yellow leaves indicated that the azaleas won’t bloom well this coming spring. What should we do?
A: Leaf yellowing in the autumn is a normal occurrence for some azalea varieties. If there were no other symptoms on the azaleas, especially if there aren’t dead, leafless parts, I wouldn’t expect their spring blooming to be poor. There’s not much now that you need to be doing for your azaleas to compensate for the leaf yellowing. The recent windy weather we’ve had in Roanoke reminded me of the helpful job to be done in azalea beds. Regularly look for and remove autumn leaves that have blown onto azaleas, especially those that have accumulated against azalea trunks. With occasional winter precipitation, accumulated leaves will easily become wet and thus will hold potentially harmful dampness against azalea trunk bark.
