Your zucchini is not broken.
Its first flowers are male and fall without fruit. Tell the two apart, and hand pollinate in one sunny morning.
Zucchini, pumpkin and cucumber carry separate male and female flowers on the same plant. The first flush is usually male, so early flowers fall without fruit and that is normal. If a female opens and the little fruit behind it yellows and drops, poor pollination is the usual reason. Pick a male early in the morning, strip the petals and touch its pollen to the centre of the female, or carry it across with a soft brush. Plant a few flowers nearby and the bees usually take the job back.
The plant is enormous, the flowers are the size of your hand, and there is not one zucchini. Then a tiny one appears, sits for a few days, yellows at the tip and drops. Watching a little fruit you were counting on go soft and drop is a genuine let-down, and it can look like disease. More often it is timing or pollination: no female flowers yet, or a female flower that nobody visited.
Once you can tell the two flowers apart, hand pollination takes only a few minutes on a sunny morning, whenever both a male and a female are open.
Two kinds of flower on one plant
Look behind the petals. A female flower sits on a miniature zucchini, a swelling the size of your little finger that is already fruit-shaped. A male flower sits on a plain, thin, straight stem with nothing behind it. Inside, the male carries a pollen-covered spike and the female a small, lobed centre waiting for that pollen.
Check in the morning, when the flowers are open. By afternoon on a warm day they have closed and the difference is harder to see.
Why the first flowers fall
Young plants usually open a run of male flowers first, often for a week or more, before the first female shows up. Those early males open, close and fall without fruit, and gardeners read it as failure. It is the plant building size before it commits to a crop. Nothing needs doing. The females arrive when the plant is ready.
Why a small fruit yellows and drops
That little zucchini behind a female flower is only a fruit if the flower is pollinated. Miss the pollen and the plant abandons it: the tip yellows, the fruit softens and it falls within days. The usual reason is a shortage of bees, which is common in new suburbs, on wet mornings and early in the season when the mornings are still cool. In the hottest weather the plant itself often tips the balance, setting plenty of males and few females, and very hot days can spoil the pollen even when bees are about.
Blossom end rot is a different problem and worth telling apart. It is a calcium shortage inside the fruit, usually brought on by irregular watering rather than by a lack of calcium in the soil, and it shows as a dark, sunken, leathery patch at the blossom end, the end away from the stem. Even, steady watering is the best guard against it, though it will not repair a fruit already marked, and root problems and other stresses can play a part too. A clean yellowing from the tip on a fruit that never got going usually points to poor pollination instead.
Hand pollination, in a morning
It takes a few minutes and one open male flower.
- Go out early, while both kinds of flower are open.
- Pick a male flower and peel its petals back or off, leaving the pollen-covered spike.
- Touch the spike gently onto the centre of an open female, turning it so the pollen coats the lobes. A soft paintbrush or cotton bud works if you would rather not pick.
- One male will cover several females.
- Repeat on the following mornings while new females keep opening.
Use a male from the same plant, or another plant of the same kind. Zucchini, cucumber, pumpkin and melon do not pollinate one another, so match like with like.
That is all. A pollinated fruit swells quickly and is usually picking size within about a week in warm weather.
Bring the bees, so you can stop
Hand pollination is a rescue, not a routine. A few flowers within a metre or two of the patch usually bring enough bees to take the job back: marigolds, nasturtiums, borage, alyssum, and a coriander plant left to flower does the same. Water at the base rather than over the flowers in the morning, and keep any spray, including the organic ones, away from open flowers, since bee poisonings from garden and crop chemicals do happen in Australia.
The same rules for pumpkin, cucumber and watermelon
Pumpkin is pollinated the same way, though it takes longer to mature. Cucumber and watermelon follow the same pattern, though some cucumber varieties set fruit without pollination and the open-pollinated types most home gardeners grow still want a visitor. Rockmelon and honeydew are a little different: instead of separate male and female flowers, they carry male flowers alongside flowers that have both parts. Those fruit-bearing flowers still sit on a small swelling, so the swelling behind the petals is still the thing to look for, and they still rely on insects to move the pollen. Arrangements vary between varieties. If a small fruit yellows and drops, the answer is the same brush.
A note for every zone
The flowers work the same way in Brisbane, Sydney, Melbourne, Adelaide, Perth, Canberra and Hobart. What changes is the pressure on them. Brisbane's heat brings the season on early, so the morning window matters from the first flowers. Perth's and Adelaide's dry heat can push a plant into all-male mode; taking the edge off the worst afternoons with a square of shade cloth may help, and steady water and a change in the weather usually do the rest. Hobart's and Canberra's cool spring mornings mean fewer bees early, so hand-pollinate while the first females are opening and let the bees take over as it warms and they arrive.
Grow it: seeds for this lesson
Zucchini Black Beautythe standard dark green, quick and generous once the females start.See the seeds
Zucchini Grey Lebanesepale, tender and the one for the Middle Eastern kitchen.See the seeds
Zucchini Ronde de Niceround fruit for stuffing, easiest to spot a female on.See the seeds
Pumpkin Butternutthe same flowers on a longer season, sown once the soil is warm and frost has passed.See the seeds
Cucumber Lemonround and yellow, and the cousin that follows the same rules.See the seeds
Learn the two flowers and the plant stops being a mystery. A lot of zucchini plants that seem to "never fruit" are simply waiting on a pollinator, and a minute with a brush on a sunny morning is usually all it takes. For the pumpkin side of the family, including curing for storage, our pumpkin growing guide picks up where this leaves off, and the What to Sow Now page has the month's sowing list for your postcode.
Frequently asked questions
Can I eat the male flowers?
Yes. Male flowers are the ones stuffed and fried, and picking a few does the plant no harm. Leave two or three open each morning for pollination.
Why has my plant made only male flowers for weeks?
It is still building. Young plants and stressed plants both favour males. A week or two of males is common, and some plants run longer. Keep it watered and growing steadily and the females follow, usually once the plant has a good spread of leaves.
What time of day do the flowers open?
Early morning. They close again in or by the early afternoon, sooner when it is hot, and each flower opens for a single day, so pollination, by hand or by bee, is a breakfast job.
Does a cotton bud work as well as a picked flower?
Yes, as long as you can see pollen on it after touching the male. A small soft paintbrush is easier to load.
Is a soft, yellow baby zucchini blossom end rot?
Most often it is an unpollinated fruit, but blossom end rot can show on small fruit too. The clue is the mark: a clean yellowing from the tip points to poor pollination, while a dark, sunken patch at the blossom end, the end away from the stem, points to blossom end rot, which even, steady watering helps prevent.
Will more fertiliser make more fruit?
Not if the problem is pollination. The plant does need feeding to crop well, but extra fertiliser cannot make up for flowers that were never pollinated.
