My courgettes are dying… They are turning yellow and rotting… why and how do I fix it?

Experienced gardeners often ask me: “My courgettes are breaking down. What are the reasons ? »

And when it comes to less experienced gardeners, who do not understand what is going on, the question is put differently: “The tops of the fruits begin to turn yellow and then rot. Why ? »

Regardless of the wording, this is a question that often comes back to me.

And rightly so, spontaneous abortion of zucchini is a common and even normal phenomenon at the beginning of cultivation…

But it is clear that this is no longer the case when the problem persists.

We can see here and there that the only real cause of zucchini abortion (because it is) is poor pollination…

But even if it is indeed very often the reason, it is not the only one.

But that’s what we’re going to see now.

Why do zucchini abort?

Courgettes are sometimes broken down due to defects…

The first fruits often have a deficiency of mineral elements.

Very often the plant is not yet developed enough to properly nourish the fruits that appear (the weak root system will not pump far).

Or, and this is also very common, the soil is still fresh at the time of the first flowering, the mineral elements of the soil are not released correctly…

This shortage is then temporary.

But let’s see this concretely with the first zucchini plant, which was planted in my greenhouse this spring:

aborted zucchini
The first zucchini has broken off on this young plant… still bees come into my greenhouse…
First zucchini broken off but not the second
A second courgette has developed well on the same plant
2 well-developed courgettes
And a third zucchini is now very beautiful

Everything is fine here…

Despite an aborted first fruit, everything quickly returned to normal.

The soil is rich in organic matter.

There is no real deficiency in the soil, just a defect in the release of nutrients at the start of cultivation, probably due to the lack of heat in the soil (very cool and rainy month of May, etc.).

I could also rule out the lack of pollination from the start, since the bees were already active in the greenhouse (open every day), while the tomatoes were already well formed.

But that’s not necessarily the case with you…

Perhaps a second or even third zucchini has broken off as well (or will break down if your zucchini plants are less advanced).

You could then deduce that there was a real soil shortage (we’ll see how to deal with this later).

Or a lack of pollination….

Zucchini also breaks down due to lack of pollination

Zucchini is a monoecious plant (the same plant bears both male and female flowers) with unisexual flowers (there are several male flowers and female flowers, unlike hermaphroditic flowers).

Here’s how to distinguish female flowers from male flowers on a zucchini plant (this distinction does not apply to all varieties):

female flower

Zucchini female flower.  Will she have an abortion?
Female flower – The corolla contains several stigmas that form the pistil
Female Zucchini Flower - Visible Embryo
On a female flower, the embryo of the fruit is visible at the base of the flower

male flower

Male zucchini flower - 1 stamen
On a male flower, the corolla contains a single stamen
Male Zucchini Flower - No Embryo
There is no fruit embryo at the base of a male flower

It is the female flowers that will produce zucchini.

But for the fruit to develop properly, the female flower must be pollinated.

And for that, the male flowers are also essential: bees or other pollinators will indeed collect pollen from these male flowers, both on the plant and on another plant, and then deposit it on the female flowers.

Only in this way can the female flower be fertilized and bear beautiful fruits.

We then understand that there can be 2 causes for a pollination defect:

  • no male flowers nearby (on the plant itself or on another plant nearby)
  • no pollinators – this can be the case for a closed greenhouse, for very early cultivation (the bees are not yet active) or due to a very polluted environment or with little nature…

In the first situation, you have no choice but to wait for male flowers to appear on your zucchini plants (or other plants for that matter…).

In the second situation, you can act… We’ll see how later.

If it’s the first zucchini on a young plant, spontaneous abortion is very common… let nature take its course.

However, you can remove this first zucchini once it starts to rot to prevent it from pumping out more nutrients.

On the other hand, if your first 3 or 4 zucchini break down, there is likely a real problem, either from deficiency or from pollination.

You can then act quickly:

In case of shortage

At the start of the season, there is usually no shortage, strictly speaking, but a blockage of the mineral elements.

As we have seen before, this blockage is related to a too cool soil.

If you’ve mulched, spread the mulch out temporarily to let the soil warm up… It should settle pretty quickly.

But if the problem persists, the cause should be looked elsewhere.

  • or your soil is really deficient: then bring compost to the base of the plant or water it with a preparation based on comfrey – But above all you will have to fertilize your soil appropriately in the future (I cannot go into details here steps natural fertilization… but keep in mind that this is a central axis of Mon Potager au Naturel)
  • either there is a pollination problem…

With bad pollination

Here we assume that male flowers are present, directly on the plant or nearby (knowing that a zucchini plant can be pollinated from another plant – even from another vegetable species) belonging to the Cucurbitaceae* family – on several hundred meters away!).

As we have seen, the lack of pollination is then due to a lack of pollinators.

If you grow in a greenhouse and if you never open the greenhouse, pollinating insects will of course not be able to get in. Open the greenhouse wide…

Zucchini should no longer be broken down.

Otherwise, you just play the role of pollinator in the greenhouse or outdoors!

*In the absence of male flowers on your zucchini plants, you can even take pollen from a plant of another plant of the Cucurbitaceae family… the fruit obtained will indeed be a zucchini!

On the other hand, if you want to save the seeds for sowing the following year, you will fail, because then there has been a cross (see this article on pumpkin seed reproduction).