Zucchini that has been pollinated

My zucchinis aren’t growing and rotting at the ends

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Do you have a problem with your zucchinis (or squash or pumpkin or cucumbers) being stunted and not progressing past the size of your thumb?

Perhaps they are getting to a certain size and then they just start rotting. Or they grow a bit funny looking (big on one end, short on the other)

There are a couple of reasons that this can occur…

Not pollinated

The first, the most common response to this is the fruit may not have been pollinated. This will be extremely common in areas that lack bees, but also if you only have one plant and your male vs female flower ratio is off (which can be caused by old seed).

Butternut pumpkin female flower that hasn't been pollinated
Butternut pumpkin female flower that hasn’t been pollinated

The plant should produce a sway of male flowers before the female flowers as a way of bringing the bees to the yard, but often some hybrid varieties will just go nuts with both flowers.

Butternut pumpkin female flower
Butternut pumpkin female flower – see the tiny fruit

Each plant has a male and female flower, you can tell the difference as the female flower will have what looks like a tiny fruit at the end of the flower. The male flower is just a flower.

QLD blue pumpkin male flower
Butternut pumpkin male flower

You can take matters into your own hands by doing the job of the bees and moving some of the male pollen onto the female flower (a paintbrush, cotton tip or just your fingers will do the trick). Or better yet, make sure you plant heaps of plants around that will bring in the bees.

As the fruit is growing, you can tell if it hasn’t been pollinated as the flower on the end of the fruit will shrivel and look brown. A pollinated fruit will look plump and have a bit of colour to it.

Zucchini that has been pollinated
Zucchini that has been pollinated – see the plump flower

Blossom End Rot

Another reason for the rotting of the end of your fruit and not growing is Blossom End Rot, it’s common to see this in tomatoes, but it does affect the squash family as well.

Blossom End Rot isn’t a disease, it’s due to the plant’s inability to get calcium, which can be caused by a few things:

  • Lack of calcium in the soil in general (restore it by adding Dolomite Lime or crushed eggshells). It is very rare for your soil to be calcium deficient and is likely to be more to do with the below reasons.
  • Soil PH is either too high or too low (do a PH test to check)
  • Disturbed roots of the plant
  • Watering inconsistency (the most likely cause especially if you’ve had a lot of rain)

Flower or fruit damage

On the odd occasion the flower becomes damaged before it opens so the pollen is no longer viable. I’ve noticed this particularly on super hot summer days (the flower basically cooks) or from bug damage – aphids, 28 spot ladybugs or other insects that get into the flower before it’s fully formed.

But probably one of the most common issues we have here is fruit fly, they seem to just give up once stung and turn to mush. We find the yellow ones seem to attract the fruit fly like nothing else. The best way to avoid this is to net them, and you need to do this at a very early stage as they tend to sting them as soon as the female flower has formed. Then of course you will need to hand pollinate to ensure the fruit has set, so it’s a lot more work.

Here in the subtropics we always avoid zucchini over summer with our unpredictable rainfall, intense heat and sway of bugs that make them not worth the space they take up. Instead we get a crop in early Spring and again in early Autumn.

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