Cucurbits flowering heavily but not setting fruit, causes of poor female flower and fruit set.
7 Answers
Many cucurbits open a lot of male flowers first and only later produce female flowers (the ones with a tiny fruit behind the petals), so early heavy male flowering alone is normal. Poor fruit set usually comes from too few female flowers, weak pollination, very high temperature, excess nitrogen pushing vine growth, or lack of pollinating bees. Reduce heavy nitrogen, keep soil evenly moist, and protect or encourage bees rather than spraying during flowering hours. Hand pollination in the early morning by touching male pollen to the female flower can set fruit when bees are scarce. If you use parthenocarpic polyhouse hybrids, keep bees out, as those set fruit without pollination. Confirm variety behaviour and nutrient balance with your KVK.
In my Jaipur garden the lauki gave only male flowers for weeks and I panicked, but female flowers came once the vine matured. Cutting back the heavy urea I had given helped the females set.
Hand pollination early morning saved my cucumber set when bees were few. I just touched a male flower onto the female ones around 7 am and got far better fruit.
A point that helped: I kept the soil evenly moist and protected the bees instead of spraying during flowering hours. The female flowers then set fruit much better on my lauki.
I learnt to look behind the petals for the tiny fruit, that is the female flower. Once I knew what to count I realised my plants were fine, they just opened a run of males first before the females started.
In the peak heat my cucumber dropped a lot of set even after pollination. Some light shade and watering in the cooler hours eased it, the very hot midday spell was clearly hurting the young fruit.
A point for anyone on polyhouse hybrids: if they are the parthenocarpic type they set without pollination, so keep bees out. I mixed that up once and the few bees that got in gave me curved misshapen fruit.