More recent landscape questions and answers

Horticulture

Invasive plant control

Since obedient plant or false dragonhead, Physostegia virginianais, is invasive, can I bury chicken wire around the roots when planting, or would this harm it's flowering and maturing capability?

I'm afraid chicken wire will not be enough to contain false dragonhead. The roots of the plant will grow through the wire and soon the crown will follow. Additionally, false dragonhead sets seed and can spread by seeding itself.

If you want to try this plant in a small garden, I would cut the bottom out of a large bucket (perhaps five gallons in volume) to form an open-ended cylinder. Bury this cylinder so that the rim is even with the soil surface and plant the false dragon head inside. You still will need to watch for seedlings but this can be controlled by pulling them if and when they come up.

David H. Trinklein
Department of Horticulture

Light for semi-shade plants

How much sun do a semi-shade plants need? In the front of my house on the north corner the flower bed gets sun from 6 a.m. to maybe noon. I have had no luck in this particular spot for three years. Would full shade vs partial shade flowers work best?

The situation you describe as having sunlight from daybreak to noon would be considered a part sun/part shade location. Most bedding plants are sold with care tags or other point-of-purchase information that indicate the type of exposure that is suitable for the plant in question.

The exposure you described is fairly user friendly to a number of flowering annuals. Therefore you might investigate whether or not there are other factors that limit your success in growing plants in that area. Soil, drainage, fertility, etc. all can cause poor performance even though a species has been selected which is well-suited for the amount of sun present.

David H. Trinklein
Department of Horticulture

Growing prickly pear cactus

I live in Missouri and would like to grow prickly pear cactus in my yard. Where can I find information on how to do this in our climate and soil conditions?

The common name "prickly pear" is given to several members of the genus Opuntia. Opuntia humifusa is a prickly pear that is native to the Midwest and quite hardy in Missouri. As a succulent it prefers a very loose, well-drained soil and is quite easy to grow if provided with those conditions along with a full-sun exposure. Do not water prickly pear excessively. Succulents are much better adapted to handle dry rather than wet conditions. Prickly pear can be propagated simply by removing pads from an existing planting, allowing the cut end to "cure" in the air for several days, and then sticking it into the soil in the garden location you have selected for it.

David H. Trinklein
Department of Horticulture

Heavy frost and covering plants

There is supposed to be a heavy frost tonight. My azaleas have started to bloom and my iris have budded. Many of my perennials are already up. Should my hostas, astilbes, lilies and others be covered?

If you have suitable material available it would be a good idea to cover your plants , especially the azaleas. The frost is more likely to damage their buds than the leaves of the other plants you listed.

David H. Trinklein
Department of Horticulture

Oak gall

I have four 25-year-old pin oak trees that have developed dark brown balls on the limbs. Neighbors tell me it is a fungus that will eventually kill the trees and nothing can be done. Do you have any information regarding this?

Gall It's difficult to say for sure what the growths on your pin oaks are, how to treat them or indicate how damaging they are likely to be, without examining a sample in the MU Plant Diagnostic Clinic. You can see our Web site for sample submission and fees.

One type of growth that can appear to be a hard brown ball surrounding twigs and small branches that we see on pin oak branches submitted to the diagnostic clinic would be insect galls. Control measures for galls are difficult and somewhat dependent on the type of gall present. Not all insect galls require treatment. G7272, Insect and Mite Galls on Missouri Trees has more information.

Simeon Wright
Plant Diagnostic Clinic Coordinator