causes of flowers but no fruit on cucumbers

Are you frustrated by cucumber plants that produce flowers, but no fruit? If so, you’re probably wondering why it happens, and what you can do about it. So, why do cucumbers flower but produce no fruit? A cucumber plant will flower but produce no fruit if there is a lack of either male or female flowers on the plant. A lack of fruit will also occur due to poor pollination. Growing conditions, such as temperature, weather, and nitrogen levels, can affect pollination and flower production. Sometimes, it just takes patience to get fruit from your cucumber plants. However, there are times when you can take steps to help your cucumber plants with their fruit production. In this article, we’ll talk about why a cucumber produces flowers but no fruit and what you can do about it. Let’s begin. Why Do Cucumbers Flower but No Fruit? There are several possible reasons that your cucumber plant will produce flowers, but no fruit. Some of the causes are: Lack of female flowers (since the male flowers come first)Lack of male flowers (in gynoecious cucumber varieties)Lack of pollination (not enough bees)Temperature and weather (too cold, too hot, or too rainy)Nitrogen Levels in Soil (too much nitrogen can reduce flowering) A lack of female flowers (shown here) is a common cause of lack of fruit set on cucumber plants. A lack of female flowers is the most common reason, and often is not a cause for concern. Lack of Female Flowers It is important to remember that most cucumber plants are monoecious. This means that the male and female flowers are found on the same plant. According to UC Davis: male cucumber flowers are found on shorter stems, and grow in clusters of 3 to 5. They produce pollen, but no fruit. The stem behind a male flower is thinner.female cucumber flowers are found on longer stems, and come in single flowers rather than clusters. They cannot produce pollen, but they have a small fruit behind the flower. This makes the stem behind a female flower look thick and swollen. You can see pictures of both male and female cucumber plants on the South Dakota State University Extension website. On monoecious cucumber plants, male and female flowers are produced in about equal numbers. However, the catch is that they are not produced in equal numbers at the same time. According to the New Mexico State University: “The time between the first development of male flowers and the female flowers depends on plant variety and environmental conditions. Your problem may just be that the female blossoms have not formed yet.”https://aces.nmsu.edu/ces/yard/2008/072608.html On cucumber plants, male flowers appear earlier than female flowers. Early in the growing season, the plants put their energy into producing male flowers first. Without female flowers, cucumber plants cannot produce fruit. Female flowers come later in the season, after males have already blossomed. This ensures that there is enough pollen present for the female flowers when they arrive later in the season. In fact, according to the Old Farmer’s Almanac: “They often begin producing male flowers several weeks before the females appear.”https://www.almanac.com/fact/why-wont-my-cucumber-plants-produce-fruitsr Male flowers only stay on the plant for about a day, and then they fall off. Needless to say, this can be discouraging for both new and experienced gardeners alike! However, it is not a cause for concern, at least not right away. Some of the earliest male flowers on a cucumber plant will fall off before any female flowers appear. How To Increase Female Flowers In Cucumbers Cucumber plants should start producing a crop of fruit once the female flowers start to appear. However, if you planted too late, high temperatures could cause some of the female flowers to abort. Cooler temperatures encourage female flowers to form sooner and stay on the plant. However, cooler temperatures may discourage formation of male flowers early in the season. High temperatures discourage female flowers from forming on cucumber plants. According to the Iowa State University Extension: “In the case of cucumbers, squash, and pumpkins, cool temperatures promote development of female or perfect flowers at a node closer to the base of plant, and the ratio of male to female flowers is reduced. Generally high temperatures promote male flowers, and delay female flower development.”https://hortnews.extension.iastate.edu/2016/07-29/cucurbits.htm So, if you want more female flowers to appear sooner, keep your plants cool! Plant them outside, not in the greenhouse. If necessary, give them a little shade during the hottest part of the day to protect them from the sun’s heat. You can learn more about sunlight for cucumber plants in my article here. One other option to increase female flowers in cucumber plants is to cultivate mostly gynoecious varieties in your garden. This will give you more female flowers, but it may cause another problem: lack of male cucumber flowers. Let's talk about that problem next. Lack Of Male Flowers On the other hand, a lack of male flowers on a cucumber plant can also be a problem. Although this is less common than a lack of female flowers, it can still happen. A lack of male flowers is most likely to happen with gynoecious cucumber varieties. A gynoecious variety is one that produces mostly (or all) female flowers and very few (or no) male flowers. The good thing about gynoecious cucumber plants is that they produce more female flowers. This gives them the potential to produce a lot more fruit in a season. A gynoecious cucumber plant produces few or no male flowers. The downside is that gynoecious cucumber plants need a nearby plant with male flowers on it to produce fruit. How to Increase Male Flowers in Cucumbers One solution is to plant your garden with mostly gynoecious cucumber plants. Then, plant a small number of seeds from a different cucumber variety that is monoecious. This will ensure that there are enough male flowers (from the monoecious plants) to provide plenty of pollen. It will also give you lots of fruit (from the gynoecious plants). Also remember that higher temperatures encourage male flowers to form. Lack of Pollination Even if you have plenty of male and female flowers on your cucumber plant, there could still be a delay in setting fruit. Without proper pollination, you could have lots of flowers with no fruit set. According to the New Mexico State University: “If you see the female flowers on your cucumber plants, but they are not "setting" fruit, then the problem may be that you do not have pollinators.”https://aces.nmsu.edu/ces/yard/2008/072608.html Often, bees are the ones to carry pollen from male flowers to female flowers to pollinate cucumber plants. Bees often do the work of carrying pollen from male flowers to female flowers on cucumber plants. However, you may have a lack of bees in your yard due to use of pesticides (by you, a neighbor, or a nearby business). Do Cucumbers Self Pollinate? Unlike tomatoes, cucumbers are not self-pollinating. Something needs to carry pollen from the male flower to the female flower to start fruit production. In most cases, bees and other pollinators fill this role. However, you can do it yourself if the need arises! How to Hand Pollinate Cucumber Flowers There are several ways to hand pollinate cucumber flowers. You can use: a soft-bristled brush (such as a paintbrush or toothbrush)a cotton swabthe male flower itself (break it off and touch the stamens inside the male flower to the inside of the female flower. Don’t feel bad about doing this – the male flowers will fall off anyway, and besides, they cannot produce fruit!) A toothbrush is one way to hand pollinate cucumber flowers. It doesn't need to be an electric toothbrush. The idea is to get the pollen from the inside of the male flower to the inside of the female flower. To do this, there are some things to keep in mind. According to UC Davis, you should only use freshly opened male flowers, and you should hand pollinate early in the day. Look for the newest male flowers that have appeared on your plants. This will increase your chances of success with hand pollination. According to the New Mexico State University: “Each morning collect pollen from the stamens in the center of the male flowers and then transfer that pollen to the stigma in the center of the female flowers. Use a small, soft bristled paint brush to do this. If you are successful, you should see small cucumbers forming within a few days.”https://aces.nmsu.edu/ces/yard/2008/072608.html The time to fruit maturity will vary, depending on the type of cucumber. According to the Michigan State University Extension: small pickling cucumbers (1 inch diameter or less) take 4 to 5 days to maturelarge pickling cucumbers (2 inch diameter) take 8 to 10 days to matureslicing cucumbers take 15 to 18 days to mature Pickling cucumbers are smaller and take less time to mature than slicing cucumbers. You can learn more about when cucumber plants produce fruit in my article here. Just remember that temperature plays a big role in pollination, and whether you will need to do it yourself. If temperatures are too cool, bees won’t come out to work. If temperatures are too hot, female flowers may abort, preventing pollination. Temperature and Weather As mentioned earlier, temperature matters when it comes to flower formation for cucumber plants. Cold temperatures can damage cucumber plants. Frost will spell the end for cucumbers, and temperatures below 50 degrees Fahrenheit (10 degrees Celsius) will cause slow growth or damage to plants. Frost will spell the end for cucumber plants, and cold (under 50 degrees Fahrenheit) will damage them. When it is hot, a cucumber plant tends to produce more male flowers. At cooler temperatures, a cucumber plant produces more female flowers. The variety of cucumber also affects how the plant responds to different temperatures. The variety also matters in terms of when a cucumber should be planted, how long it will take to form flowers, and how long the fruit takes to mature. Vining varieties produce more fruit and take up more space. Bush varieties produce fruit a little bit earlier in the season than vining varieties. Both types can benefit from support, such as a trellis. You can learn how high cucumbers will climb (plus how to support them) in my article here. Weather also plays a role in flower formation. For example, rainy weather may stop bees from doing their work. This will result in fewer pollinated flowers and less fruit. Nitrogen Levels in Soil Cucumbers are heavy feeders, especially when it comes to nitrogen. However, it is possible to have too much of a good thing. Excessive amounts of nitrogen can burn plants, especially when applied all at once. However, too much nitrogen can have another effect on cucumber plants: delayed production of flowers. According to the Iowa State University Extension: “High nitrogen fertilization can also delay production of female flowers. Heavy nitrogen application will often lead to vines remaining vegetative for longer periods of time, producing female flowers only later in the season.”https://hortnews.extension.iastate.edu/2016/07-29/cucurbits.htm In other words, too much nitrogen causes green growth at the expense of flowers and fruit. Too much nitrogen can also worsen the problem of a lack of female flowers on cucumber plants. Excessive nitrogen is often caused by heavy application of high-nitrogen manure or concentrated fertilizers with a high nitrogen content. You can burn plants with too much manure. High levels of nitrogen can also delay female flower formation on cucumber plants. Conclusion Now you know why your cucumber plant is producing flowers but no fruit. You also know what you can do about it. Just remember that sometimes, patience is all it takes! You might also want to read my article on why cucumber plants wilt after transplant. I hope you found this article helpful. If so, please share it with someone who can use the information. If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here. Enjoy! ~Jonathon