Why Are My Potato Plants Not Flowering?

A nonflowering potato plant means something is wrong with the plant's growing conditions or care.

Potatoes (Solanum tuberosum) grow well anywhere within USDA plant hardiness zones 2 to 11, where they are typically grown as annuals. They must be started each year from small pieces of tuber called seed potatoes, which take roughly two months to flower.

Potatoes do not need to flower in order to produce their starchy, edible tubers. However, problems with growing conditions and care that can inhibit flowering might also inhibit tuber production and should be fixed whenever possible.

Potatoes belong to the nightshade family, Solanaceae, which also includes common vegetable garden favorites, such as tomato plants (Solanum lycopersicum) and eggplants (Solanum melongena). Potato plants and tomato plants look very similar and produce almost identical flowers, although potato plants typically produce white, pink or purple flowers, while tomato flowers are yellow.

Potato plant flowers typically appear in mid-summer and then fall off, but sometimes the flowers will produce fruit. Potato fruit resembles small green cherry tomatoes, but they are very poisonous due to their high concentration of solanine and should be removed to prevent accidental poisoning.

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Good growing conditions are vital for growing potatoes at home. Learning what constitutes good conditions will help you troubleshoot problems, such as a lack of flowering in your potato plants.

• Low light is a potential cause of a lack of flowering in potato plants. Potato plants need at least six hours of full sun each day to flower and form tubers. A shaded bed will not provide the right growing conditions for flowering or for potato tubers to form.
• Potatoes grow best in loose, fertile soil with a pH between 5.8 and 6.5, which is slightly acidic. The right soil conditions help with nutrient uptake. Poor soil conditions can create nutrient deficiencies and stress the plant, which can inhibit flowering and tuber production.
• Amend the soil at the planting site with a 3-inch-thick layer of compost or aged manure worked into the top 12 inches of soil, which will enrich the bed while also giving the soil the light, loose texture that potatoes need to form tubers.
• Slow soil drainage can also impact the overall health of a potato plant, leading to poor blooming. If the soil doesn't drain quickly after wet weather or heavy watering, the soil likely has sluggish drainage, and you should avoid planting your potato plants there.
• Soil temperature is another factor in when and how well a potato plant blooms. Cold soil at planting time can delay or even prevent blooming. For the best results, wait to plant potatoes until soil temperatures stay above 55°F during the day and 45° at night, which will help ensure that the plant blooms on time.

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Providing your potato plants with the right care throughout the growing season will help encourage blooming as well as a good potato crop.

Water Needs

Potatoes need plenty of water during the growing season to form flowers, leaves and tubers. Provide 1 inch of water each week from planting time until the end of their growing season, when the plants start to turn yellow and die back.

Fertilizer Requirements

Potato plants are vigorous growers that require plenty of nutrients during the growing season. Amended soil will help provide a good base for your potatoes, but fertilizing twice during the growing season will also help the plants bloom and produce tubers.

Feed with 10-0-10 fertilizer at a rate of 7 1/2 pounds per 100 feet of row length. Make the first application at planting time and the second application in midsummer.

Frost Protection

Potatoes that are planted early in the season need a little bit of protection from late spring frost to ensure good blooming and healthy, strong growth. Late frost can also damage new growth on potato plants, which can set back their tuber production.

Cover your plants with a fabric row cover, straw or warming fleece if a frost is forecasted. Remove the cover as soon as possible after temperatures warm up.

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When you choose to harvest potatoes depends on what type of potatoes you want to eat.

New potatoes are the earliest crop that a potato plant will produce. They are thin-skinned and delicate with a mild flavor. New potatoes are harvested when a potato plant is blooming, and a lack of blooming can make you miss out on this delicacy.

Mature potatoes are harvested at the end of the growing season at the main harvest time. Most home gardeners wait until the plant dies back, which is when the tubers of most potato varieties are the largest.

• Carefully lift the potatoes from the soil using a steel-tined potato fork, taking up as much soil as possible.
• Remove the potatoes from the soil and set them in a cool, dry place to cure for just long enough for their skin to dry out.
• Throw away any potatoes with hints of green on the skin, because they will have a high concentration of solanine, the same poisonous compound found in the potato fruit.