Why are your zucchini rotting and not growing

Why are your Zucchini rotting

Do you have a problem with your zucchini (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 to rot. Or they grow a bit funny looking (big on one end, short on the other). Here are some common reasons why.

Lack of pollination

The first, the most common response to this is the zucchini 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 or environmental factors).

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 occurs due to the plants inability to get calcium. This can be caused by a few things:

  • Watering inconsistency (the most likely cause especially if you've had a lot of rain)
  • Soil PH is either too high or too low (do a PH test to check)
  • Disturbed roots of the plant
  • 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 but this is the answer that most people will resort to in garden groups.

Flower or fruit damage

On the odd occasion the flower becomes damaged before it opens so the pollen is no longer viable. We've noticed this particularly on super hot summer days (the flower basically cooks) or from bug damage.

Bug Damage

Bugs that can damage flowers include aphids, 28 spot ladybugs, pumpkin beetles or other insects that get into the flower before it's fully formed.

Cucumber fruit fly

Probably one of the most common issues we have here is fruit fly. Specifically the cucumber fruit fly which looks a lot like the QLD 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 using exclusion nets. This needs to occur at a very early stage, as they tend to sting fruit as soon as the female flower has formed. Unfortunately this will require hand pollination as excluding the bad bugs will also exclude the pollinators.

Here in the subtropics we 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.

Need help troubleshooting your specific veggie garden issues? Come on over and join us inside Dirt Lovers.

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