Growing Green: Successful potatoes
An early Easter and a late winter have worked together to foil an annual rite of spring. Good Friday has come and gone with no opportunity to get potatoes in the ground. If you haven’t thought about potatoes yet, now is a great time to select varieties and think about planting once the weather cooperates.
Potatoes are grown from seed tubers, not true seed. Purchase disease free tubers from your local nursery, favorite catalogue, or local grocery store (make sure to purchase “seed potatoes”.) Don’t use potatoes you have purchased (to eat) from the grocery store. These are often sprayed with chemicals to prevent sprouting.
Plant seed pieces in early spring as soon as the soil warms. Cut seed pieces at least one day prior to planting to allow the cut surfaces to dry. (Drying allows the pieces to form a wound, which creates a disease protective surface.) Make sure pieces have at least 2 eyes, and are no smaller than about 2 ounces. Larger seed pieces will generally emerge faster than smaller ones. Small potatoes may be planted whole. Plant seed pieces cut side down, 10-12 inches apart and about 3-5 inches deep, in rows 30-36 inches apart. Space pieces closer for smaller tubers and farther apart for fewer but larger tubers. Cover pieces with 4 inches of soil or compost.
Start hilling plants when the main stems are about a foot tall, and once or twice more during the growing season. (At the end of the season, you will have hilled 6-8 inches of soil in total along the plants.) Potatoes will grow on thin side shoots that emerge from the main stem (stolons), and these stolons should be kept covered with soil to avoid exposing the young potatoes to sunlight. Sunlight can turn potatoes green and cause the formation of potentially toxic and bitter-tasting chemicals in the skin and flesh.
Potatoes grow best in well-drained soil with pH 6 to 6.5. Have your soil tested to determine your soil’s pH and whether it should be amended. Water to a depth of 1” (shallow watering is of no value when growing potatoes). Mulch around your plants at a depth of 3-4” to keep the soil cool and moist and prevent weeds. Frequent, shallow cultivation to control weeds is recommended for optimal plant growth and yield.
“New” potatoes can be harvested at 7-8 weeks; fully mature potatoes should be harvested once the leaves have dried. Gently dig the potatoes with a garden fork. If the skins can be rubbed off easily, place your potatoes in a warm, dry, ventilated spot out of direct sunlight for about a week. Then store them in a cool (40-50 degrees) dark location until needed.
There are several pests that may appear during the growing season that can affect your potato production. Colorado potato beetles are a common pest on potatoes. They overwinter in soil and appear in the spring. Regularly check for orange egg masses on the undersides of leaves. Early blight and late blight are fungal diseases that can cause potentially serious problems. Both cause leaf spots and lesions on potato tubers. Verticillium wilt can cause yellowing and wilt in potatoes. Scab is a bacterial disease that causes dark, rough, corky spots on the skin of the potato tubers but does not rot them. For information on how to protect your plants from these pests, visit: www.extension.umn.edu.
Here’s hoping mild weather comes soon, and all your garden plans come true. Until next time, happy gardening!
Robin Trott is a Horticulture Educator with University of Minnesota Extension.