Too Many Male Flowers On Squash And Cucumber

Squash, cucumber and pumpkin belong to the cucurbit family and most garden varieties produce both male and female flowers. Since only female flowers produce fruit, gardeners get concerned when they see too many male flowers and like any other gardening problem they invent lots of ways to fix the problem. Unfortunately most of these so-called fixes don’t actually work.

What causes too many male flowers on cucumbers, pumpkins and squash, and what can be done about it?

Male vs Female Flowers

You can easily tell the difference between male and female flowers. The female flower has a small fruit-shaped structure right behind the flower even before the flower opens. Males lack this structure.

It is normal for young plants to start producing only male flowers and as the plant matures it produces both male and female flowers but even a half grown plant still has more males than females. Older plants produce more and more females relative to males and some cultivars even stop making male flowers. This is all normal behavior.

The ratio of male to female flowers is controlled by generics, age of the plant and the environment.

Note that this post deals with the sex of flowers and not pollination problems.

How Do You Get More Female Flowers?

The internet is full of advice for increasing the number of female flowers including the following.

• Cut male flowers off
• Water more
• Cut the tip off vines
• Fertilize more
• Fertilize less

There are also some interesting explanations for the higher number of males:

• The plant is too happy and does not need to make seed, so you have to stress the plant more.
• Male flowers are produced first so they can test the environment to see if the plant should make female flowers.
• Males are made first to bring pollinators to the area.

Now let’s have a look at the science and see which of these work.

Start With A Healthy Plant

An unhealthy plant will respond to stresses in unexpected ways but it usually results in more male flowers than normal.

The problem for the gardener who has such a plant is to figure out what caused it to be un-healthy and fix the problem. It could be poor watering, a nutrient deficiency or poor drainage.

For the rest of this discussion I am going to assume the plant is growing well.

Are There Too Many Male Flowers?

It is normal for cucurbits to have more male flowers than female flowers. I think most gardeners have the correct ratio but they just want more female flowers so they can get more fruit.  The plant is growing normally and there really is no problem to fix.

Time To Flower

It is important to understand that the sex of a flower is determined very early in its development – long before most gardeners even see a bud developing. This is one reason gardeners have difficultly understand the cause that determines flower sex. They equate the events of the last couple of days to the flower in front of them, instead of the events that took place a couple of weeks ago.

The sex of a cucumber flower is determined about 15 days before the flower opens.

Effect Of Temperature On Cucurbit Flowers

Cool temperatures promote the development of female flowers. In cool weather some summer squash may even make female flowers before any males are produced.

High temperature promotes male flowers and delays the formation of female flowers. An early hot spell could mean no females for quite some time. “For instance, in pumpkins, temperatures of 90F (32C) day/70F (21C) night lead to abortion of female flower buds“.

Extreme heat in the middle of summer can result in a low number of fruits just as the season gets going.

The optimum temperatures for pumpkin squash, cucumber and muskmelon is 65F-75F (18C – 24C) and for watermelon it’s 75F-85F (24C – 29C).

Effect Of Light On Cucurbit Flowers

High light levels promote females and shady conditions reduces the number of female flowers.

Photoperiod also has an effect with long days favoring male flowers. Gardeners who live farther from the equator will see more males.

Effect Of Nutrient Levels On Flowering

High nitrogen levels can delay the production of female flowers. A study looking at pumpkins found that either high or low amounts of nitrogen delayed the production of the first male and female flower.

Cutting Off Male Flowers

Cutting off male flowers is a common suggestion. The claim is that by removing them, the plant wastes less energy to produce them and then has more energy to produce female flowers. That sounds convincing, but is it true?

The first problem we have is that people generally remove male flowers once they are open or at least well along the development process, so the saving of plant energy is limited.

The second problem is that even if the plant has more energy, it might just make more male flowers.

But there is a more critical problem with this line of thinking. When gherkin cucumbers were tested it was found that it takes a negligible amount of energy to make male flowers. A plant produces just as much growth and fruit with or without the removal of male flowers (assuming pollen is available).

None of the reliable sources of information for growing cucurbits that I looked at, recommended the removal of male flowers. You can be sure greenhouses would do this if it resulted in higher yields.

What About The Other Claims?

Watering or fertilizing more won’t help a plant that is grown properly. In fact extra fertilizer may increase the nitrogen level and curb the production of females. Drought conditions do favor males, so watering would help in such an extreme situation, but that is usually not the case in gardens.

A few people recommend cutting off the tip of the vine in order to stress the plant into making female flowers. The thought here is that a stressed plant tries to make seed as a means of survival. Even if cutting the tip stresses the plant, stresses generally favor the production of male flowers which is the opposite of the claimed effect.

What about the claim that “male flowers are produced first to test the environment”? How exactly do flowers “test” the environment? What conditions are they looking for?

The idea that male flowers bring pollinators to the area is very common. The male flowers probably do that since they have pollen and nectar. What I don’t understand is why the pollinators hang around for several days until female flowers show up? If the male flower really did a good job of attracting pollinators, would it not be better for the plant to produce them at the same time as female flowers? Do the male flowers somehow condition the pollinators to visit the plant each morning?

An interesting fact about nectar. In winter squash, nectar is produced from dawn of the day the flower opens until noon, at which point any unused nectar is reabsorbed by the plant. Female flowers on most cucurbits need to be pollinated in the morning to be successful.

What we do know is that both types of flowers attract the stripped cucumber beetle which is not great for the plant. We also know that leaf damage by the beetle increases flower fragrance production but only in the male flowers. So, producing more male flowers results in attracting more cucumber beetles. How is that beneficial to the plant? This is all very complex and there have been few studies that looked the attraction of both herbivores and pollinators by cucurbit flowers and yet gardeners think they know why a plant produces male flowers first.

Why do cucurbits make male flowers first? It has been suggested that in a wild population of plants where seed germination is variable and you find plants of various ages, producing male flowers first increases the chance of pollination in the first female flowers in the group because there are always males blooming. I did not find a study to support this idea. If you find one, let me know in the comments.

What Can You Do To Reduce The Number of Male Flowers?

The first thing to understand is that it is normal to have more males than females. Secondly, too many males is not the problem. What you really want is more female flowers.

A gardener has no way to know if there are too many males. The number produced is based on the species, cultivar and environment and there is no simple formula to give you the correct number for your patch of plants.

What can you do to try and reduce the relative number of males?

• Grow the plants in full sun. High light levels promote females.
• Select cultivars that produce a higher ratio of females in your environment.
• Don’t add excessive amounts of nitrogen.
• Start plants indoors to get a head start on the season. Larger plants produce more females.
• Have Patience.

Other Cucumber Myths

You will find more cucumber myths in these posts.

Pruning Cucumbers – Will It Produce a Higher Yield?

Are Burpless Cucumbers Really Burpless?

Should cucumbers, squash, muskmelons and watermelons be grown near each other?

Myths About Growing Cucumbers