Although potatoes are common garden crops, here in Maine sweet potatoes are seen much less frequently. With some care, this potato kin can indeed be grown here during our short gardening season.

The flesh of the sweet potato, Ipomoea batatas, is white, yellow or dark orange. The skin may be brown, reddish brown, yellow or purplish red. Some varieties we typically would consider orange-fleshed sweet potatoes are actually yams and belong to an entirely different genus, Dioscorea.

Sweet potatoes are of tropical origin, and although we have to do some altering of our environment to suit their needs, most of our garden soils are quite suited to their culture. These special spuds enjoy acidic soils — pH 5.5 to 6.5 — with lots of organic matter. Heavy, poorly drained soils should be amended with sand or organic matter, or raised beds should be constructed to ensure that the plants will not suffer from restricted root growth.

As with white potatoes, the tuber of the sweet potato may be direct-sown into the garden. But since our growing season is short, a more effective, alternative planting strategy will help ensure that a crop will be harvested by frost.

Slips may be started six to eight weeks before planting. Place sweet potato tubers in a box of moist sand, sawdust or wood shavings. If the box is kept between 70 and 80 degrees Fahrenheit and moistened occasionally, shoots will sprout from the tuber nodes. Roots will proliferate from the parent tuber, as well as from the stems of the young shoots. When shoots are 6 to 8 inches long, snip them — roots included — from the parent tuber and plant them directly in the garden up to their top leaves.

Using the slip method can reduce the chances of having plants develop tuber-borne diseases. Coupled with planting through black plastic mulch, it can hasten crop development.

Since sweet potatoes thrive in poor soils, fertilizing heavily with high-nitrogen fertilizers or fresh manure will only result in lush top growth and poor tuber development.

Although sampling the crop as the young tubers develop in late summer is an inevitabe temptation, the bulk of the crop will be harvested once the tops have been killed back by frost. Dig the tubers as you would white potatoes.

Some gardeners would suggest curing the crop in a warm, well-ventilated area for up to two weeks. This dries the tubers a bit and minimizes the risk of spoilage. Cured tubers can be stored at room temperature.

Your questions

Q: What exactly are essential oils? Please describe. T.O. Orrington

A: Essential oils are plant extracts derived from aromatic plants through distillation. These oils are typically blended with an unscented carrier oil — such as grape seed or jojoba oil — since they can be irritating to the skin if used undiluted.

Essential oils are added to a variety of beauty and body products. And although they have wonderful aromatherapeutic effects, they can be extremely dangerous if misused. Keep them away from children, eyes and those who have sensitive skin.

Some essential oils, including bergamot, lemon verbena and citrus oils, can increase skin’s susceptibility to UV rays and the effects of exposure to sunlight. Some are used to treat a range of medical conditions, but buy them only under the guidance of a qualified herbalist.

Q: I have a rhododendron I’ve been nursing for several years, with poor results. I’m thinking that maybe my soil isn’t acidic enough. Should I have it tested? How do I change the acidity? L.G. Kenduskeag

A: It isn’t the acid in the soil that’s so important to these plants — it’s the availability to the plant of nutrients under the acid conditions. For example, in alkaline — or nonacidic — soils, important nutrients such as iron and magnesium can be “tied up” in a way that plants are unable to absorb them. Under acidic conditions, these nutrients are released and become available for plant uptake.

A healthy plant displays lush, green leaves. A plant with iron or magnesium deficiency displays chlorosis, or yellowing of the leaves.

Special fertilizer formulas are available at nurseries, greenhouses and farm and garden supply stores. Look for formulas or other soil amendments that include sulfur which will acidify the soil. You might want to spend the extra money to test the soil around your rhododendrons. For information on how to contact your local Cooperative Extension for a soil-testing kit, call 1-800-287-0274.

Diana George Chapin is the NEWS garden columnist. Send horticulture questions to Gardening Questions, c/o Maine Weekend, Bangor Daily News, P.O. Box 1329, Bangor 04402-1329. Selected questions will be answered in future columns. Include name, address and telephone number.