By Jessica Giannotta ©2012
Penn State Master Gardener
If you have never grown potatoes, you might want to try it this year. Potatoes are easy to grow and a fun and rewarding activity for gardeners of all ages and experience levels.
It is important to start with certified seed potatoes. Do not use potatoes sold at grocery stores or ones from last year's garden. Certified seed potatoes are disease- and insect-free, have not been treated with a growth retardant, and are inspected by state authorities. For the best selection, order from specialty growers. See a source list at the end of the column. Potatoes come in many varieties, so have fun picking and choosing.
There are white-skinned, red-skinned, yellow flesh, purple skin with white flesh, fingerling and others. Names you may recognize are 'Yukon Gold' (white-skinned with yellow flesh), 'Purple Majesty' (purple-skinned with white flesh), 'Viking' (red-skinned) and 'Irish Cobbler' (white-skinned). Some varieties are particularly suited for baking or mashing while others are better for boiling or roasting.
Another factor to keep in mind when choosing a potato variety is whether it is an early-, mid- or late-season variety. This refers to how many days potatoes must grow before they reach maturity. This can be anywhere from 75 days for early varieties to 135-160 days for the late-season varieties.
As a general rule, have your seed potatoes in hand 2-3 weeks before the anticipated planting date. At this point, it's time to start the process of chitting, or sprouting.
Place a single layer of seed potatoes in a warm area (60-70 degrees) with exposure to sunlight. Allow them to begin growing sprouts. As they sprout, turn them to ensure that sprouts are green, not white. Ideal sprout size for planting is about 1 inch. Chitting will give you a one- to two-week jump-start on plant emergence.
Approximately 5-7 days before planting, cut the larger potatoes into two to four block-shaped pieces. Each piece should contain at least one sprout with plenty of tissue around it. Smaller, egg-sized potatoes may be left whole. Allow the cut pieces to heal at room temperature. The freshly cut surfaces will develop a protective coating that will prevent decay.
Choose a planting site in full sun with loose, well-drained soil. Compost can be mixed well into the top 6-8 inches of soil to improve drainage and moisture retention. If the potatoes are being planted in an area not previously well fertilized, use a 5-10-10 fertilizer and apply at the rate of 5 to 6 pounds per 100 square feet, or 33 feet of potato row, or use a balanced organic fertilizer according to label directions.
Ideally, soil pH is best kept around 5.5-6.0 to lessen the possibility of scab disease, which can be a problem in alkaline soils. Scab will show up as brown corky tissue on the potato surface. Precautions should be taken with the use of manure and lime because both can render the soil alkaline. Whenever possible, make all lime and manure applications in the fall before planting.
Two weeks before the last frost date, plant seed potatoes 3-4 inches deep, sprout side up, and cover with 2 inches of soil. Seed pieces should be 9-12 inches apart, with 34-36 inches between rows. Water well after planting. If growing potatoes in containers, choose a pot at least 15 inches in diameter and 15 inches deep. Fill your container about one-third of the way with compost or potting soil and plant prepared tubers.
When the plants are 6-8 inches tall, begin hilling. Hilling is the process of mounding soil around the base of the plant. It provides plenty of loose soil for developing tubers and excludes sunlight. Potato tubers exposed to sunlight will turn green and become inedible and toxic to humans. A green potato indicates harmful levels of solanine, a toxin natural to the potato.
If you are growing your potatoes in containers, just add a few more inches of soil to the pot as they grow, making sure the tubers are fully covered. Do this 2-3 weeks after the first hilling and then again in another two weeks. Many people also place straw on top to block light.
Potato plants need an average of 1-1.5 inches of water weekly until just before harvest, and they may need to be watered during dry periods. They produce a lovely flower, as well as a small, round, green fruit. These fruits are not edible. They too contain solanine and are not for human consumption. The fruits do, however, contain the potato plant's true seed.
At about 10-13 weeks after planting, or when they flower, new potatoes are ready to be dug up. New potatoes are the first potatoes that the plant produces and will not be as large as the ones dug at the final harvest. They should be about 1-2 inches in size and are often used for soups, salads and roasting. If you choose to dig up some new potatoes, be sure to leave plenty in the ground to develop further.
Potatoes should be harvested two weeks after the vines have naturally died down. It's best to use a spade or a pitch fork and dig the potatoes from the side of the soil hill, lifting them up from underneath. Do this as carefully as you can, so as not to damage them. It can be a fun activity for kids, like digging for buried treasure.
Allow harvested potatoes to dry for 3-4 days in a warm, shaded, airy spot before storing them. Potatoes exposed to the sun and high temperatures will turn green and may rot. If you are harvesting potatoes at temperatures above 80 degrees, they should be picked up immediately and put in a dark place. Make sure potatoes are thoroughly dry before storing.
Optimum storage conditions for potatoes are 35-40 degrees at moderate humidity. Avoid locations where freezing will occur. Keep potatoes in darkness and check periodically, removing any that are not in optimum condition. Eating potatoes can be just as much fun as growing them!