When Do Pumpkins Start to Form?

A vegetable patch with bright-orange pumpkins in September and October attracts attention, especially as Halloween approaches. To create that pumpkin crop, a gardener sowed seeds 85 to 100 days earlier in the year, usually in late spring to early summer. Pumpkin plants grow as annuals and are not tolerant of shade or frosts. As long as the soil is warmer than 60 degrees, sunlight plentiful and soil evenly moist, pumpkin vines grow robustly and develop fruits after flowering.

Once sowed, a pumpkin seed germinates in about seven days. The first 10 days after the seedling emerges from the soil, it is developing a larger root system and creating its first leaves. From 10 to 40 days in age, pumpkin plants rapidly elongate their vining stems and accumulate more leaves. Anytime from 40 to 60 days old, the pumpkin plants begin producing flowers. By age 70 days, the plants bear their first swelling, immature, green fruits. The fruits enlarge and eventually turn orange anytime from 80 to 120 days, depending on cultivar.

The most important stage in growing pumpkins is flower production. About six weeks after planting, the plant bears its first large, golden yellow flowers on the ground-hugging stems under the leaves. Blossoms are either male or female, based on sex organs present. Only female flowers become pumpkin fruits. Look at the flower's base to determine its gender. Female pumpkin flowers have a swollen, ball-shaped ovary at the base. Male flower stems are thin and slender. The first flowers that occur on the pumpkin plant are male. About a week later, both male and female blossoms occur.

Pollen transferred from male blossoms to female blossoms is needed for the fruit to develop. Bees are the pollinators. Pumpkin plants do not produce many flowers, so bees aren't frequent visitors. Up to 15 separate visits to a female flower by bees carrying pumpkin pollen leads to sufficient pollination, according to the Ontario Ministry of Agriculture, Food and Rural Affairs. Once pollinated, the female flower withers, but the ovary at the base begins swelling. Male flowers drop off after staying open for only one day.

Water from the root and carbohydrates from the many large leaves cause the ovary to swell and become a small pumpkin fruit. Both the fruit's rind and seeds are growing. Two to seven weeks of pumpkin fruit develop after pollination. Small pumpkins, those that naturally mature up to 5 lbs., mature the fastest. The massive pumpkins as big as 50 lbs. or more take more time to reach such impressive size.