Not Just For The South
Sweet potatoes have a long history in southern cooking, and maybe because of this many people believe that they can only be grown in the south. Not true. With a little preparation and some patience sweet potatoes will thrive and produce well in any area that has at least 90 frost free days. The key is getting the soil warm enough before planting.
Timing Is Everything
Even in the south, if we plant sweet potatoes in cool soil or if they are exposed to frosty temperatures shortly after planting, the plants will be compromised. This is not the crop to take that sort of chance with (I’ve learned the hard way). Always wait until a couple of weeks after your average last frost date, and even then you should be sure the soil has warmed to at least 65 degrees before planting.
In areas with late frosts and short growing seasons, cover the bed with black plastic for two or three weeks to help it warm up faster. When planting time comes, just cut holes in the plastic and plant right through it: it will help maintain a good hot soil temperature, retain moisture and block weeds.
Preparing The Soil
Sweet potatoes don’t require nutrient rich soil. They do need good drainage, with consistent moisture. The best way to achieve this on both heavy and sandy soils is by adding copious amounts of organic matter. Incorporate a two to three inch layer of manure or compost and about a pound of organic starter fertilizer (like Espoma’s BioTone or E.B. Stone’s Sure Start) per fifty square feet. Shape the bed into a ridge that is 6-10 inches high with a flat top that is about a foot wide. Space the ridges according to the growth habit of your chosen sweet potato variety: bush types may be spaced 4 feet on center, vining types require six feet or more.
Sweet potatoes are grown from slips. Slips are the shoots that grow from the potatoes themselves, similar to the eyes of “Irish” potatoes. The difference is that with sweet potatoes, the slips are removed from the seed potato and planted individually (whereas chunks of “Irish” seed potatoes are planted with multiple eyes that develop into the potato plants). Typically gardeners purchase sweet potato slips, not the seed potatoes. Slips may be purchased “bare root” or as potted plants. Both options work quite well.
When planting, you can vary the crop by adjusting spacing. Tighter spacing tends to produce a bounty of medium sized roots, while wider spacing allows the sweet potatoes to grow to their largest potential. A good average spacing is twelve to sixteen inches in the row, with the rows four to six feet apart.
Sweet potatoes are ready to harvest at 90 – 100 days, but may be left longer if the weather is good. Cool nights will begin to turn the vines yellow, which is a sign that it’s time to harvest. Light frost may not be a problem for the roots, but a hard freeze can do severe damage. I like to get mine out of the ground while it’s still hot if possible, to facilitate the curing process.
For full flavor development and good storage quality, curing sweet potatoes is imperative after harvest. Store the roots in a dark, hot, humid location with good air circulation for two or three weeks. A shed, garage or carport works well while the weather is still summery. When scars have healed over, the sweet potatoes may be moved to long term storage: around 50 degrees with moderate humidity (basement, crawlspace or root cellar). With proper curing and storage, sweet potatoes will store for several months.
Which Variety To Choose
There are dozens of sweet potato varieties to choose from. Their flesh can be white, yellow, orange or purple. They may have a moist or dry texture. Skins may be pink, tan, red, or purple. As mentioned earlier, there are bush types and vining types. Some varieties may take 100 days or more to mature, but the earliest ones need only 90 days. For this reason, it is important to do your homework before ordering. Because of its adaptability and rapid maturity, ‘Beauregard’ is the variety most widely grown commercially and is an easy one for home gardeners to begin with. That was my first and it got me hooked. This year I planted ‘Georgia Jets’, ‘Purple Passion’, ‘Vardaman’,‘Red Japanese’ and ‘Nancy Hall’. All the sweet potato slips were ordered from George’s Plant Farm.