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I've tried growing courgettes (zucchini) for the first time this year and the plants have been delightfully easy to grow. (For reference, I'm in NE England, UK, btw.) However, many of the fruits rarely get thicker than my index finger before starting to rot from their tip. What am I doing wrong?

Should I be putting straw or something else dry underneath them to stop them touching the soil?

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up vote 10 down vote accepted

This could be Blossom End Rot (BER) to which most of the cucurbit family are susceptible. It is caused by a calcium deficiency - see my answer here.

However, given that some of your courgettes are growing normally, and those that are rotting are very small, I think the problem is almost certainly caused by inadequate pollination:

No fruit, or fruit rotting when very small: This is a physiological problem, caused by the growing conditions, not a pest or disease. It is a problem when the weather in early summer is cool and this causes inadequate pollination. Remedy: This is usually a temporary problem, and once the weather starts to improve, so will pollination. You can try to hand-pollinate plants yourself by removing a male flower (male flowers don’t have a swelling at their base) and brushing the central parts against the centre of a female flower (female flowers have a swelling at the base – this is the beginning of the fruit). But this is a bit of a hassle, and normally the plant will correct this problem itself.

Courgettes /RHS Gardening

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Thanks - intermittent watering (mentioned in the linked answer) definitely sounds like a plausible reason for it; I'm a really inattentive gardener. :) I'll also have a go at manual pollination, as the veg plants are in a bed a good distance from the flowers in my garden and I was already a bit concerned that they weren't getting enough attention from bees and the like. – Mal Ross Jul 22 '11 at 12:10
@Mal Ross: You're welcome. There are times when I'm not a very attentive gardener, myself ;) I'm planning to try my hand at asparagus next year - I'm pretty sure I'll have some teething troubles, and I'm relying on this site for advice. Good luck with the courgettes. – Mancuniensis Jul 22 '11 at 18:39

It does, indeed, sound like blossom end rot, but from what I've read, it's actually rarely the case that the soil being calcium deficient is the cause of the problem. Calcium may be implicated in blossom end rot (but that doesn't mean the soil is deficient).

Here's a link where Carolyn Male (a well-known tomato expert) tells us all about blossom end rot and how most people don't need to add extra calcium to their soil.

Anyway, from my own experience, I gave plants loads of basalt rockdust (which is high in calcium). I even gave them things like calcium nitrate and eggshells. It was a pretty bad problem with several plants, this year, notwithstanding the calcium they had. If anything, I'm convinced that too much calcium can cause blossom end rot, but I could be wrong.

Really, though, the weather seemed to correlate rather strongly with blossom end rot, this year. It was very, very hot, and dry. When it cooled, the plants didn't have as many problems.

I've read on a forum that one person likes to use straw to prevent it (by burying it a few inches below the soil where the plant is). Straw/hay is actually high in nutrients (such as nitrogen) and it may do similar things for your soil as manure. I hear it can encourage good microbes (especially alfalfa hay). It can also act as ground cover. Anyway, that was only one person, but it really sounded like it worked, and it perked my interest enough to tell you about it.

Considering the fruits are small when they're rotting, that reminds me of a Yellow Straightneck squash with the problem I have this year. The squash appears to have a fungal infection at the roots, actually. I don't know if that's related to the problem, but possibly. It doesn't have enough light, though. A lack of light may be your problem.

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