Garden Variety: Start now to grow your own sweet potatoes
Sweet potatoes are unique in the gardening world in the way they are started and planted. While most vegetable crops are planted from seed or rooted transplants, sweet potatoes are planted from bareroot sprouts called slips.
Starting your own slips is an easy project that is also fun and educational for kids. In Kansas, April is a good time to start slips indoors for planting in the garden in mid-to-late May or early June.
Sweet potato plants need full sun and well-drained soil that is loose enough to allow the potatoes to develop underground during the growing season. Use the time between now and planting season to improve soil drainage by adding compost to the soil, if needed. Commercial growers often use raised rows or beds and incorporate organic matter prior to planting to ensure drainage and workability.
To start slips for planting later this spring, you will need a sweet potato. Decide if you want to grow the slips in water or in sand or soil. If they will be grown in water, select a jar or glass into which the sweet potato will fit. You will also need three to four toothpicks. If the slips will be grown in sand or soil, use a seedling tray (nondraining) and a heat mat.
The benefit of starting the potato in water is being able to see root growth. However, starting the potato in sand or soil produces stronger roots that allow the slip to adjust more easily when transplanted into the garden.
One potato will produce anywhere from 15 to 50 slips, each of which will grow into a plant and produce 1 to 2 pounds of sweet potatoes.
To make your slips, select a potato that is firm and has no evidence of rot or decay anywhere on it. Ideally, use potatoes from your own crop from last year. If this is your first time growing sweet potatoes, look for a local source of potatoes or consider purchasing the slips this year and saving back part of your crop this fall for years to come.
There are a few risks with using sweet potatoes from a store if the grower is unknown. The biggest concern is the potential for movement of microscopic plant disease organisms from other regions where sweet potatoes are grown. Organisms hide in the soil and/or in the crevices on the exterior of the potato. They are not of concern to humans but could be problematic for plants if introduced to your garden. Seed potatoes are checked and/or treated to prevent this sort of pest movement. The other concern is that conventional sweet potatoes sold for consumption might be chemically treated to prevent sprouting.
When you have a sweet potato and a method determined, you are ready to start.
To start sweet potato slips in water, hold the potato vertically and stick toothpicks into it in a horizontal ring. The goal is to have the bottom half of the potato submerged in water in the jar and the top half of the potato held up out of the water. The toothpicks sit on the rim of the jar to hold the potato in place.
To start sweet potato slips in sand or soil, put a layer of sand or soil in the tray, lay the potato horizontally on it and add more of the growing media. Set it so that about half the potato is in the sand or soil and half is exposed. Keep the sand or soil moist, but avoid oversaturation.
Place the jar in a warm place such as a sunny windowsill, or place the seedling tray on the heat mat. Wait patiently; sprouts should appear in a week to a month. Add water as needed for either option.
Sweet potatoes are tropical plants that love Kansas summers. Wait until mid- to late May to plant at the very earliest. They can be planted all the way through the end of June in the Lawrence area, and mid-June is more ideal than mid-May.
When the time comes for planting, break the sprouts from the mother potato, taking care to avoid damaging the tissue or any attached roots. These are the sweet potato slips, and they are ready to plant at this point.
Plant sweet potatoes 1 foot apart in rows or 1 per square foot in blocks. Water as needed to help plants get established. Once the roots take off, the plants should not require supplemental watering. If an extended dry period occurs later in the summer, water the plants deeply and infrequently.
Avoid fertilization or planting in overly fertile soil. When excessive nutrients are available, sweet potato plants often put all their energy into lush top growth instead of potato production.
Vines can put on 6 to 8 feet of growth in the season. They will cover the ground if allowed to spread. Trellis them to save space if desired, but set it up in a way that still allows the vines to shade the soil. Prairie hay or straw can also be used as mulch.
Harvest the potatoes in the fall prior to frost.
— Jennifer Smith works in regulatory horticulture and has worked as a horticulturist for various government entities. She has experience in landscape design and maintenance and as an educator.