In the garden
Q
Can you identify this vine for us? It grows from a potato and produces more potatoes on the vine itself during growing season.
It freezes but we harvest the potatoes and store them in a paper bag in the garage and plant them in late spring. Is it available at a nursery in Arkansas or by mail order?
A
The plant in question is commonly called air potato — Dioscorea bulbifera. These plants are members of the yam family and native to Asia and Africa. Air potato is an annual vine in Arkansas because it is not winter hardy. In more southern climes, it can be quite invasive because it does survive the winter. The vines can grow up to 70 feet in length in one growing season. What you are calling potatoes are actually bulbils that form in the axil of the leaf. These bulbils can be the size of a marble or as large as a baseball. They grow along the vines and are found on plants during late summer through fall, and although they look like a potato, they are not edible. I have never seen them sold in Arkansas, but they are a great pass-along plant. I have had samples of the “potatoes” brought into my office for identification when I was working and had them growing without
even being planted. Saving fruit each year to replant is your best bet.
Q
We have a large dogwood which bloomed beautifully in the spring but now has lost many of its leaves. It has received plenty of water, but the large tree that shaded it had to be removed 3 years ago. Any idea what the problem is and how we can correct it?
A
Dogwoods do prefer to be an understory tree getting some protection from hot afternoon sun, but I don’t think sunlight would cause them to drop leaves. Instead it would cause the leaves to sunburn or turn scorched. Shedding leaves is preferable to dead leaves staying attached to the tree, but neither scenario is ideal. Did the foliage have any leaf spots or powdery mildew before they fell? This could indicate a disease. Check the main trunks to see if there are any holes or wounds that could be causing problems. Continue to water the tree and monitor its growth, but I don’t think there is much else you can do at this time unless you see a specific problem.
Q
The small leaves nestled in among my St. Augustine lawn has really taken hold this year [reader sent a photo]. Can you identify it and suggest a weed killer that works and won’t harm the sod? I’d also like to know what is the second plant in the pot with the spade shaped leaves that has nice purple flowers when it blooms?
A
The three-leaved weed is common lespedeza. It is an annual so a pre-emergent herbicide applied in the late winter is best. St. Augustine is very sensitive to herbicides, especially as hot and humid as it is now. The other plant is a common violet, and while it does have a nice purple flower, given a chance in the garden, it can take over — and it is a perennial and much more difficult to control.
Q
I just bought a Hugh Kimberly queen fern. It is gorgeous. The person at the nursery told me that it can take full sun and that I can plant it outside and it will be fine through the winter. I wanted to see what you think about making it through the winter outside.
A
Everyone has different results with their plants, but I don’t think it will do well in full sun, nor will it overwinter outside. Kimberly Queen ferns are much tougher than the Boston ferns that are so common in Arkansas. While it is true they can take more sun than other ferns, I would limit that to morning sun and not full afternoon sun. It is considered winter hardy to zone 9 which is an average low winter temperature of 20-30 degrees. If you want it to come back, I would move it to a protected spot for the winter.
Q
I am enclosing pictures of my hydrangea bush [reader sent a photo]. It starts out every year with beautiful foliage and then these black spots appear starting on the lower branches and soon takes over the whole bush. The plant never blooms. The disease must be in the soil. What can we do?
A
I think you have two problems. Cercospera leaf spot is the culprit of the spots on the foliage. It is rare to find a hydrangea in Arkansas in late August or September that doesn’t have some spots on the foliage somewhere — the fungal disease is that common. The disease is widespread and does start on the older leaves and works its way up to the top of the plant. Usually we don’t recommend spraying because it happens so late in the year. If yours get the problem every year and earlier and earlier, then preventive fungicide sprays could be needed, but they have to be reapplied frequently. I would recommend good sanitation and raking up all the old leaves after they fall. I do not think the disease is the reason your plants are not blooming. It is usually a cosmetic problem, but rarely causes severe problems. Does your hydrangea start growing from old woody growth in the spring or sprout from the ground each year? Big leaf hydrangea set flower buds before they go dormant in the winter and if they get killed back, they will not bloom. If the plant is in deep shade it often will not flower well either. A University of Arkansas Cooperative Extension Service fact sheet with more information can be found at arkansasonline.com/727hydrangea.
Retired after 38 years with the University of Arkansas Cooperative Extension Service, Janet Carson ranks among Arkansas’ best known horticulture experts. Her blog is at arkansasonline.com/planitjanet. Write to her at P.O. Box 2221, Little Rock, AR 72203 or email jcarson@arkansasonline.com