Cucumbers are among the most popular garden vegetables, and growing them can be rewarding and delicious. Cucumbers thrive in Iowa’s warm summer and quickly produce a bounty of fresh, homegrown cucumbers perfect for salads, sandwiches and pickling. While relatively easy to grow, cucumbers can have some potential pitfalls. Horticulturists with Iowa State University Extension and Outreach answer questions to help solve some of the problems you may encounter when growing cucumbers.
My cucumber plants are blooming heavily but aren’t producing many fruit. Why?
Cucumbers and other vine crops are monoecious. Monoecious plants have separate male and female flowers on the same plant. Male and female flowers are similar in appearance. However, the female flowers have small, immature fruits at their base. Pollen is transferred from the male to the female flowers by bees and other pollinators. When properly pollinated and fertilized, the female flowers develop into fruit.
The first flowers to appear on cucumbers and other vine crops are predominantly male. As a result, fruit production is poor when the vines begin to flower. The cucumber vines should start producing a good crop within a few weeks as the number of female flowers increases.
Poor weather and the use of insecticides can also affect fruit set on cucumbers. Cold, rainy weather during bloom reduces bee activity. Fewer bees visiting the garden results in poor pollination and poor fruit set. Apply insecticides in the garden only when necessary to avoid harming bees and other pollinators.
Why are some of my cucumbers bitter?
The compound cucurbitacin produces the bitterness in cucumbers. Cucurbitacin is generally found in the leaves, stems and roots of cucumber plants. The cucurbitacins spread from the vegetative parts of the plant into the cucumber fruit when plants are under stress. Hot, dry weather is usually responsible for bitterness in cucumbers in Iowa.
Cucurbitacins tend to be concentrated in the stem end of the cucumber and just under the skin. To eliminate most of the bitterness, cut off the stem end of the fruit and peel the remaining portion of the cucumber. To avoid the problem, plant bitter-free cucumber cultivars, such as ‘Sweet Slice’ and ‘Sweet Success.’ Watering cucumber plants once a week during hot, dry weather may also be helpful.
Why are some of my cucumbers misshapen?
Poorly shaped fruit are usually the result of poor pollination. Poor pollination may be due to cool, wet weather and improperly applied insecticides that limit bee activity. When insecticides are necessary, select an insecticide with low toxicity to bees and apply it early in the morning or late in the evening to reduce the risk to bees.
Will cucumbers cross-pollinate with other vine crops?
While closely related, cucumbers will not cross-pollinate with squashes, pumpkins, muskmelons or watermelons as they are different species. Cucumber varieties can cross with one another. However, the quality of this year’s crop is not affected. An exception is the cross-pollination of parthenocarpic cucumber varieties with standard varieties. Parthenocarpic varieties develop fruit without pollination. As a result, the non-fertilized fruit do not contain seeds. Parthenocarpic varieties must be isolated from standard varieties to prevent cross-pollination and seed development.
How do I control cucumber beetles?
Striped and spotted cucumber beetles are common pests of cucumber and other vine crops in the Midwest. Both beetles are yellow-green and between 3/16 and 1/4 inches long. The striped cucumber beetle has three black stripes that run the length of its body. The spotted cucumber beetle, also known as the southern corn rootworm, has 12 black spots on its back. Both can be damaging, but the striped cucumber beetle is more problematic because of its ability to transmit the disease bacterial wilt.
Early in the season, feeding by larvae can stunt and even kill seedlings and small transplants. Adult beetles feed primarily on leaves but will feed on stems and cause cosmetic damage to fruits if populations become too high. Once cucumber plants have established and begin to mature, they can survive high levels of defoliation. However, striped cucumber beetles can still be very damaging to plants due to the transmission of bacterial wilt through feeding.
Covering young cucumber plants with row cover or frost fabric can protect them from cucumber beetles but remember to remove it when plants start to flower to allow for pollination. Keep an eye on your plants and act quickly if beetles cause damage. Scout also for bacterial wilt and remove any affected plants immediately. Planting a trap crop, like Hubbard squash, nearby, can lure beetles away. Once populations build up, treat the trap crop with pesticide to reduce beetle numbers without spraying your cucumbers. Use pesticides cautiously, as they can harm beneficial pollinators. Insecticide options include neem, pyrethrins, permethrin, bifenthrin and carbaryl. Always apply only when necessary and according to label directions.
