Potatoes

Of more than 4,000 known varieties of potatoes, only about 100 are commercially marketed and sold in produce markets. While it is impossible for home gardeners to explore all the rest, nurseries and seed catalogs offer dozens of quality possibilities for growing in home gardens.

Potato Basics

• Potatoes are members of the nightshade (Solanaceae) family along with tomatoes, eggplants, and peppers. They exhibit the same blossom structure, but the edible fruits are tubers, swollen fleshy underground stems with white, brown, purple or red skin and white or golden flesh.
• Certified disease-free seed potatoes from nurseries and garden centers are recommended for planting; grocery store potatoes may be diseased or treated with sprout inhibitor.
• Small seed potatoes can be planted whole. It is best to cut large ones into pieces with at least one eye, the origin of growth.
• Leave cut pieces of seed potatoes to dry 1-3 days outdoors or at room temperature. This allows them to form a callus, which decreases rotting after planting.
• For a continuous harvest, plant mid-month March-August. Later plantings may not mature.

Growing Regimen

• Prepare loose soil with ample organic matter to boost fertility and improve drainage. Growth is more difficult in clay soil and can be problematic if manure is added.
• Plant a first crop as early as 3-4 weeks before the last frost if the ground is dry enough and not soggy. Be prepared, however, to cover the first shoots with spun row covers to prevent damage from severe frost.
• Dig a trench 6-8 in. deep and set prepared seed potatoes at the bottom 6-12 in. apart; cover with several inches soil, reserved alongside. As shoots grow, fill in around them to ground level.
• Continue hilling or “dirting” soil around 4-in. tall stems to create a mound after 4-6 weeks with another 3-4 in. of soil or compost. Potatoes will form in the mound rather than deep in the ground. Mounded soil or compost prevents potatoes from too much sun exposure that causes greening, a toxic condition. Green potatoes should not be consumed.

Alternative Methods

• Economize on garden space by growing potatoes in containers. One option is a grow bag, an easy-to-move, porous fabric pot that allows for good aeration and fast drainage.
• Follow the same regimen as planting in the ground—set seed potatoes low in the container in loose soil, such as potting mix, and add more soil as stems grow.
• Increase yield with a similar approach by constructing a growing site with a 3-4 ft. or taller circle of wire fencing filled with loose soil or straw or a combination of both. This method allows you to determine the width and height of the contained area and to plant seed potatoes at more than one level every 10-12 inches, leaving 4-6 in. at the top for filling in as stems elongate.
• Monitor moisture content of soil in containers regularly since it is more exposed to air all around and can dry out quickly. Maintain steady moisture but avoid soggy conditions that promote rot. Daily watering may be needed in summer. Allowing soil to dry completely between waterings may result in rough and knobby skin.

Harvesting

• Watch for blossoms to fade before harvesting small, early potatoes.
• Wait until foliage turns yellow to harvest the entire crop or until foliage dies completely, approximately 90-120 days after planting, especially if you plan to store them for later use.
• Withhold irrigation several days to 1 week prior to harvesting the entire crop.
• Dig vertically into dry soil with a digging fork just outside the planted area to avoid piercing potatoes.
• Brush off excess soil and wash for immediate use. To store, do not wash potatoes until ready to use. Let them rest so they dry completely outdoors or in a warm area, covered to avoid greening, then store in a cool, dark place.
• Do not leave potatoes in the ground for long periods after optimum harvest time to prevent rot.

Avoiding Problems

• Practice crop rotation each year to avoid soil-borne diseases. Do not plant potatoes or other nightshade (Solanaceae) family members in the same bed year after year.
• Look for pests regularly, such as flea beetles and aphids. Use insecticidal soap spray to control aphids and fabric row covers for flea beetles.
• Rely on healthy certified seed potatoes and disease-resistant varieties; maintain even soil moisture to avoid early and late fungal blights.  

Additional Information

• Sonoma County Master Gardener Vegetable Planting Summary
• https://sonomamg.ucanr.edu/Food_Gardening_with_Less_Water/
• http://ipm.ucanr.edu/home-and-landscape/potato/cultural-tips/
• http://ipm.ucanr.edu/home-and-landscape/potato/index.html

February 2022