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Why are my cucumbers falling off, or becoming deformed?

It’s time for a short course in cucumber pollination. On Internet gardening groups and mailing lists, this question keeps coming up, over and over: “Why are my cucumbers falling off, or becoming deformed?”

To answer the question, we have to go back to some basics, because many new gardeners don’t understand them.

Male (lower) and female (upper) cucumber blossoms

Male (lower) and female (upper) cucumber blossoms

First off, cucumbers have separate male and female flowers. They are produced on the same plant – and the plants are basically self-fertile, although there is evidence that pollination is improved when there is cross pollination between separate plants.

Pollen must be transferred from the male blossoms to the female blossoms. It’s amazing to me that many people assume that this heavy, sticky pollen will just jump from one to another all by itself.  Believe me, it does not jump – it would take a gale wind to move pollen from the male – and that kind of wind would destroy the plant.

Bombus impatiens (bumblebee) on a cucumber blossom

Bombus impatiens (bumblebee) on a cucumber blossom

Some plants are wind pollinated – corn, grasses, pecan and hickory trees, ragweed – but these make light, fluffy pollen grains that are produced by the billions.

Bees are the workhorse pollinators for cukes - basically honey bees and bumble bees; with occasional minor help from other bee species. Some will also say some beetles, ants, and other insects can tranfer pollen – but these are negligible.

A brawny and fuzzy bee is the best possible pollinator. They are totally equipped with branched hairs and strong electrostatic charges to carry pollen. A bee pushes its way through the flower structures and picks up large quantities of pollen on its body.

Honey bee on a female cucumber blossom

Honey bee on a female cucumber blossom

Now a bumble bee has been shown by studies, to transfer about three times as much pollen per flower visit than a honey bee. But honey bees make up in numbers what they cannot do in comparison to bumble bees. A typical bumble bee colony is about 100 workers, while a honey bee colony may have 20,000 to 30,000 workers.

Many gardeners assume that when a bee goes to a flower, that it is instantly pollinated. While this can be true for a fruit with a single seed (like a peach), it is not true of multi-seeded fruits like cucumbers. Many grains of pollen have to be delivered – and this takes numerous visits by bees.

If no or very little pollen is delvered, the fruit simply aborts. There may well be spoilage, starting from the blossom end. This is due to an opportunistic fungus, but no fungicide will fix poor pollination.

Cucumber aborting due to very poor pollination

This cucumber is aborting due to very poor pollination

Well suppose then, that a few more grains get delivered to the flower – and some seeds get fertilized by those pollen grains.

Extremely poorly pollinated cukes are badly deformed and very slow to grow

Extremely poorly pollinated cukes are badly deformed and very slow to grow

The fruit may grow, instead of abort, but it will be slow growing and can be highly deformed.

A poorly pollinated cucumber sliced to show seeds

Note that there are no seeds on the deeply curved part in the center, and few seeds on the top end. The development of the flesh of the fruit is governed by the fertilized seeds

The only portion of the cuke that developed was the portion where the seeds were – which is on the outer curve of the cucumber. On the inner curve there are NO seeds, so the flesh didn’t develop in this area at all. Also note that on the top end, there were very few seeds that formed, so the top end is also undersized.

Compare pickle cucumber pollination

The upper pickle cucumber is well pollinated; the lower has missing seeds on the right side

When a full complement of pollen is delivered and evenly distributed across the stickly stigma of the female flower, the finished cucumber will look like the top one. It will grow rapidly, and be crisp and good flavord.

If some pollen is missing – and some seeds do not get fertilized the deformation of the fruit in the area of the missing seeds will show up in the shape of the fruit, as in the lower example in the photo above. The fruit forms a “neck” on the right side, due to missing fertilized seeds.

Cucumbers need to grow fast to be of good quality. Lack of water, excessive heat or cold, fertility, or plant disease can slow down growth. This makes the flesh tougher and dryer – and it can be bitter as well.

Anything that slows growth can cause bitterness – and this includes inadequate pollination. A poorly pollinated cucumber of the same size as a well pollinated one will usually be a day or two older. It will be tougher, and is more apt to be bitter.

Comparison of slicer cucumber pollination

The upper slicer cucumber is poorly pollinated; the lower has good pollination

Another problem with poor pollination is that the deformed area is the first place that spoilage will occur, if the grower tries to store, or send to market his or her cukes.

All in all, we see that good bee populations are critical to obtaining the perfect cuke.

A perfectly pollinated pickle cucumber

A perfectly pollinated pickle cucumber

Now, it is possible to hand pollinate cukes – yes, we can do the bee’s job, and we’ll talk about that in future articles. But, if you have more than a few plants that you are trying to hand pollinate, you’ll quickly come to appreciate the tremendous service the bees do for us!

2 Responses to “Why are my cucumbers falling off, or becoming deformed?”

  1. August 3rd, 2011 at 11:18 am

    Rachel says:

    Found you through the Pollinator Digest. Thank you for a very interesting article on cucumbers and pollination. The photos are great, I never knew why some cukes were misshapen and others weren’t.

  2. August 5th, 2011 at 5:31 am

    How large can a cucumber harvest be(e)? | Ordinary Bob says:

    [...] few days later, our first cucumber was ready to eat. The sam day, my honey came across this article, which explains cucumber pollination, and shows pictures of what cucumbers look like if they aren’t pollinated enough. Few people [...]

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