Sweet potatoes belong to the morning glory family and have long, trailing vines that quickly cover the soil surface. There are bush varieties available if you are tight on space. The most common type of sweet potatoes are those with the orange flesh although you can find both yellow and white ones available. Yam and sweet potato are in different plant families though you would not know this based on how often the word yam is used in grocery stores. A true yam grows in the tropics.
North Carolina grows the most sweet potatoes in the United States; and many of these southern varieties do well for us in this region. Beauregard, Jewell, and Centennial are recommended varieties for Northern Illinois. Your harvest window for all of these is between 100-110 days.
You will purchase your sweet potatoes as "slips". Slips are planted at 12-18 inches apart in a bed with at least 8 inches of soil depth. Black plastic can increase soil temperatures, which leads to better yields. In years past, I've used heavy, black plastic for growing sweet potatoes. Yields have been very good. You may find that the sweet potatoes may become the size of smaller footballs by using this plastic. I found that the flavor was still good and that they were not woody. If using a black plastic, know that you may need to water your plants if we enter a period of drought as rainwater will only enter where the plant is planted. Allow 3-4 ft between rows for vines to spread.
In general, sweet potatoes do not have major issues compared to other vegetables. If we have a rainy season, we may see decline in yields and overall development of the sweet potatoes. So good drainage is utmost needed for growing your sweet potatoes. If you've got a heavy clay soil, adding compost before planting your sweet potatoes can put them on the right path. Because of the vining characteristic, weeds are not usually a problem.
In mid-September, you will harvest your sweet potatoes by digging up the sides of the bed, being careful to not cut into the sweet potatoes. Curing will be your next step after harvest. This process is done in fall where the roots are laid out for 2-3 hours than placed in a room around 85 F for 10-14 days then stored.
So start strong with the sweet potatoes and get them in the ground as we enter the month of June!