Gardeners sometimes have problems with growing pumpkins, particularly setting fruit. The obvious answer is no pollinators (i.e. bees, bumblebees, squash bees etc.). With no pollinators the transfer of pollen from the male flower to the female flower doesn’t happen. If that is the case, you will need to hand-pollinate the flowers next year. Just so you know, the female has a little round ball at the base of the flower. The male flower does not.
But I had a nagging feeling there might be more to pumpkin story than the no cross-pollination explanation. I starting digging into the possible causes of low/no pumpkins fruit set, and I discovered there many other factors that affect fruit set in pumpkins!
Besides no pollinator activity — which happens if you spray insecticides — weather and/or soil conditions also affect pumpkin fruit set. In fact, weather and soil conditions may play a bigger role in growing pumpkins than many gardeners realize.
- Pumpkin plants needs plenty of sunshine to produce flowers! You need at least six or more hours of direct sun to grow pumpkins. Shady conditions equal no pumpkins.
- Hot temperatures aborts flower buds (especially female flowers). Day temperatures in the high 90s or even night temperatures in the high 70s for several consecutive days, nixes your chances of pumpkins. No pumpkins.
- Hot and dry weather may reduce pollinator activity, which translates into fewer pumpkins for the gardener. Less pumpkins.
- If you don’t water, drought can lead to a higher than normal male/female flower ratio. Result? Fewer pumpkins per plant.
- Don’t crowd in too many plants into one bed; you will end up shading some plants. Less pumpkins.
- Adding higher-than-recommended nitrogen fertilizer, which leads to excessive green growth, delays/reduces flowering and fruit set. Results range from no pumpkins to a less-than-normal pumpkins.
- If you don’t water during a drought, the dry parched soil causes a higher than normal male/female flower ratio. Fewer pumpkins per plant.
- Too much moisture in the soil for long periods – if you water too much — can shut down the pumpkin plants’ roots, debilitate the plants and cause flower and fruit abortion. No pumpkins.
Now that you know what affects pumpkin fruit set, you can also grow any of the other members of the Cucurbitaceae family (i.e. melons, cucumbers, zucchinis, watermelons, squash etc.). Information is a marvelous thing! Yay! Growing pumpkins.
Penn State Cooperative Extension. Alex Surcică. Pumpkin pollinators.
Purdue University. Liz Maynard. 2003 Does pumpkin planting date affect yield?
YouTube. Hand pollinating pumpkins