Though not as commonly grown as white potatoes, sweet potatoes are easy to grow.

Sweet potatoes are part of the morning glory family.

Like morning glories, they spread and crawl on the ground.

Large heart-shaped leaves and branching stems create a nice ground-cover, choking out weeds.

Sweet potatoes thrive in the summer heat.

They are not usually prone to diseases or pests.

Sometimes, sweet potatoes are referred to as yams, but yams are tubers related to lilies and grasses.

Sweet potatoes are not tubers, they are true roots, called storage roots, that will continue to enlarge as long as the plant continues to grow.

Quality improves with storage.

Sweet potatoes are grown from slips.

Slips are sprouts from the previous year’s crop which can be purchased by mail order or garden centers.

Slips from reputable suppliers will be disease free.

Fresh sweet potatoes or sweet potatoes treated with sprout inhibitors will be harder to sprout.

Plant when the soil has warmed enough (65 degrees), which should be the end of May or the beginning of June.

Sweet potato plants are sensitive to cool soil.

They need loose, well-drained soil. Soil too rich in nitrogen will result in many leaves but few potatoes.

Sweet potatoes in compacted and waterlogged soil will rot.

Add one to two inches of compost to loosen the soil.

When ready to plant, create long ridges eight to 12-inches-high and 12-inches-wide with rows three feet apart.

Plant the slips on top of the ridges, about one foot apart.

Slips should be planted six-inches-deep, with at least two nodes underground and at least two leaves above ground (nodes are where the leaves shoot from the stem).

The deeper the planting, the more nodes in the ground, and the bigger the yield.

Ridges provide depth, better drainage, constant temperature, moisture, and more uniform development of the roots.

Slips do not need to have visible roots when planted.

Water slips every day for the first two weeks.

A mulch of compost, dried leaves, non-treated grass clippings or straw can be placed around the slips to cut down on weeding at the beginning.

Sweet potatoes will cover the soil quickly and shade out most weeds.

Maintain regular watering, one-half-inch per week after the first two weeks, and let them grow until ready to harvest.

Sweet potatoes require 90 to 120 days to mature.

They need to be harvested before the first killing frost.

A hard frost can damage the roots near the surface.

The cold temperature in the soil (below 50 degrees) will result in root rot.

Harvest your sweet potatoes when leaves are beginning to turn yellow before a light frost.

If a light frost burns the leaves, do not wait to remove your potatoes.

If you need to wait to harvest, cut the vines so that the decay does not spread to the roots.

To harvest, be gentle; the tubers will bruise easily and not keep as well if broken or bruised.

You need to cure your sweet potatoes to keep them longer, heal wounds, and improve their quality.

Curing will allow the starch to be converted to sugar.

Don’t wash sweet potatoes before storing; just place them in a single layer in plastic bags to keep humidity high (85-90 percent).

Close the bags tightly, cut some slits for aeration, and place in a sunny part of your house where you can achieve a high temperature (80-85 degrees).

The curing will be done in two weeks.

Properly handled and cured sweet potatoes, stored in a dark location with a temperature of 50-60 degrees, should store well until spring.

“Growing Green” is contributed by Diane Dorn, Lehigh County Extension Office Staff, and Master Gardeners. Information: Lehigh County Extension Office, 610-391-9840; Northampton County Extension Office, 610-813-6613