Marrows, Courgettes and Cucumbers are sometimes slow to set fruit, especially if there are not many bees about, so I thought it might be useful to give a bit of advice about hand-pollination, which can improve the chances of getting a good crop.
OK, first off, learn to recognise the difference between male and female flowers. The upright Marrow flower in this photo is a female. You can see that it has an embryonic fruitlet behind the yellow petals. Unless the flower is fertilised by pollen from the male flower, this will not develop. [Ignore the developing Marrow fruit in the bottom left of the picture. This is the result of a previous successful union!]
This one is a (rather "past it") male. It has a long slender stem, without the embryonic fruitlet.
Here's a pair of prospective parents, looking vigorous and ready to "make babies". The fact that both types of flower are ready at the same time is of course an important factor.
I think you will agree that any self-respecting bee would find such an impressive array hard to ignore - and of course the normal method of flower-pollination involves a foraging bee's visit to a female flower shortly after one to a male flower, with pollen being transferred on the hairs on the bee's body.
Right, now let's look at the "bits"... These are the relevant bits of a female flower.
And this is the relevant bit of a male flower.
Now, the "act" itself. (Those of a fastidious nature, please look away now...)
What you do is pick the lucky male flower, (this is a one-off opportunity for him, you understand), strip off the yellow petals, exposing the central stamen, and then gently insert the male flower into the female, brushing the female parts with the male parts to enable pollen to be transfererred. Do it sensitively, with all due respect, of course!
If you prefer, you can achieve the same thing by using a soft paintbrush to take pollen from one to the other (but they may not enjoy it so much...).
Assuming successful pollination, the little fruitlet will begin to grow within a couple of days. This is what it may look like 10 days later. Although it appears bigger in my photo, this Marrow is only about 10cm long. Compare it with that grey pipe, the diameter of which is 2.5cm.
You'll notice that I have placed a piece of tile underneath the fruit. This keeps it out of contact with the damp soil, which could cause it to rot.
Last year I only got two marrows off my Bush Baby plant. I'm hoping to do better this year, which is why I have carried out the procedure described above.