Sedum can be planted in August

Once every month, I feature your questions in this column. I am grateful to readers for their mail and feedback. If you have a garden-related question, please send it to the postal or e-mail address below. I am unable to answer individual questions, so please don’t send a self-addressed stamped envelope. I do my best to answer all questions, either in my Q&A columns, or in other feature columns.

Q: I have six `Autumn Joy’ sedums that were started from slips in 6-inch pots. Should I plant them now or wait until they are dormant ? – E.T., Newport

A: Late August planting for `Autumn Joy’ sedum should be just fine. To ease the potential shock of transplanting the juvenile plants, snip off any flower heads, should they appear. Eliminating flower production will allow the young plants to put all their energy into establishing themselves before a killing frost.

Subsequently, you may find that multiplying your sedum through division in early spring may be a less intensive means of propagation. Simply dig and divide the plants into two or three units in early spring. Replant the divisions. This method of increasing the number of plants allows a full season of growth and a more natural transition to dormancy.

Q: I have had a flowering plant in my yard for a couple of years now. Some call it a hibiscus, others call it rose of Sharon. Either way, it’s a tall plant that blossoms in late summer with large, hibiscus-like flowers. It dies back in the winter and then grows back in the spring from the roots. This year it started out fine, but about a month ago I noticed that some of the stalks were wilting and dying. There is brownish scarring on the first two to three inches of the stalk. Is this from an insect? What can be done about it? – S.T., Hampden

A: Hibiscus syriacus, commonly called – as you mentioned – hibiscus or rose of Sharon, produces gorgeous 3- to 5-inch-wide blooms on 5- to 15-inch stems. Without seeing the damage, it’s difficult to definitively diagnose the plant problem. It is possible that an insect problem is affecting the growth of your shrub. More commonly, however, browning of leaves and stems is the result of a fungal affliction. Stems of hibiscus tend to grow fairly densely. Limited air flow through the shoots of the plant is an open invitation for fungi to infest the potentially moist leaf environment.

Hibiscus is especially vulnerable to fungi: leaf spot, blight, canker and rust. Additionally, it is quite probable that other microorganisms and insects may be working together with fungi to wreak havoc on your shrub. This flowering plant may also have leaves and stems succumb to bacterial leaf spot, aphids, Japanese beetle, scale, nematodes and white fly.

To more accurately diagnose the problem, contact your local Cooperative Extension at (800) 287-1485 to find out how you can send a plant disease specialist a sample.

Q: I have a rhododendron I planted six years ago. It has never had blossoms on it. The leaves are green, and it grows well. Can you tell me what’s wrong with it? – B. E., Dixmont

A: Rhododendrons perform best in partial shade and rich, acidic soil that is moist, yet well drained. Roots of the rhododendron should be protected with a thick layer of mulch. This reduces the evaporation of water from the root zone, thereby reducing the dehydration that comes with even slight winds.

Flower production is affected by many environmental factors, most notably light and soil chmistry. For starters, carefully monitor the sunlight your shrub is receiving. Is it in too deep shade? Perhaps moving it to a site that receives partial sunlight (an area that has morning or afternoon exposure to the sun, for example) would help trigger flowering.

More commonly, a lack of flower production is the result of a less-than-optimal chemical state in the soil. Soil chemistry involves the pH of the soil, the nutrient content of the soil and a complex array of other factors. Commercial synthetic soil amendments that are formulated specifically for rhododendrons may be purchased at garden centers or farm supply stores. This mixture will alter your soil’s pH (the acidity level of the soil) and will provide a perfect balance of nutrients for your shrub.

Alternatively, to more naturally change the chemical profile of the soil, you might want to mix in bone meal and composted manure in spring. The change in fertility may provide the nutrients required to produce blooms in subsequent years.

Reader Connection

The Ellsworth Garden Club would like to invite the public to a garden sale from 10 a.m. to 4 p.m. Saturday, Aug. 26, at Shaw’s supermarket on High Street in Ellsworth. The funds raised from the sale will be used for the upkeep of the Donald Little Memorial Park. Garden-related items will be available – from dried and fresh flower arrangements and wreaths to crafts items, breads, jams, jellies and much more.

Diana George Chapin is the NEWS garden columnist. Send horticulture questions to Gardening Questions, RR1, Box 2120, Montville 04941, or e-mail them to dianagc@ctel.net. Selected questions will be answered in future columns. Include name, address and telephone number.