Field Study and Observations on the Impact of Flowers on Pumpkin Pollination and Fruit Set … including 2023 data and updates.
Pumpkins (Cucurbitaceae, specifically c. pepo, c. maxima, and c. moschata) are a monoecious plant that requires transfer of pollen from male to female flowers for pollination and successful fruit set and yield. Due to a myriad of factors, the pollinators that pollinate this crop are in decline. The most common way of increasing pollinators on a farm is to bring in honeybee hives. However, this is not always feasible and often requires additional maintenance and clear contractual agreements between the farm and beekeeper. Due to the popularity of cut flowers, such as sunflowers, zinnias, etc. and their usage as a form of farm revenue, the question was posed: Can a cut flower or flower field located near a pumpkin field provide increased pollinator diversity? Related to this central question are also the questions of what species of pollinators are represented? And, does the increase in pollinator activity directly impact fruit set and yield?
Method
To test these questions, research was conducted each summer between the years 2019-2023 in a one-acre pumpkin field. The field’s location was in an urban area and the soil composition was sand-loam with a pH of 6.8. In 2019, the flowers were located next to/ intercropped with the pumpkins. In 2020, the flowers were located 200 feet away from the pumpkin rows. Then, in 2021, the flowers were located 300 feet away from the pumpkin field. In 2022, the flowers were located 400 feet away from the pumpkin field. 2023 returned to the method of locating the cut flowers in rows directly next to and intercropped with the pumpkins.
In early August of each year, on August 5th, a 100 foot row of “Gladiator” pumpkins was examined for the ratio of male to female flowers and also the amount of pollinator diversity. Out of 100 pollinators observed while walking the row, the species of the pollinator was recorded. Two weeks later, on August 16th or thereabout, the amount of initial fruit set was determined on each pumpkin plant. After harvest in late September through mid-October, this number was compared to the actual yield as well as the cultivar yield approximates to determine the effect of the pollinators on yield, if any. The average set to yield ratio was measured out of 100 “Gladiator” pumpkin plants to determine an approximate for the entire crop.
Data
For growing season 2019, the flowers were located in rows directly next to the pumpkin field, and a row of zinnias (cultivar “State Fair”) and other assorted, deer-resistant summer annuals were also intercropped in the center of the field.
| Flower cultivars | Zinnias, tithonia, ageratum, vinca, and melampodium. |
| Male blossoms per 100 plants | 7 |
| Female blossoms per 100 plants | 3 |
| Out of 100 pollinators… | 90% were Bumblebee, Bombus spp. 5% were European honeybee, Apis mellifera 3% were Swallowtail butterfly species, Eastern Tiger (Papilio glaucus) and Eastern Black or Parsley (Papilio polyxenes) 2% were Squash bee (Eucerini) |
| Average fruit set per 100 plants | 5 |
| Average yield per 100 plants | 4 |
During the 2020 growing season, the same mixture of flowers were located 200 feet from the pumpkin rows and field.
| Flower cultivars | Zinnias, Tithonia, ageratum, vinca, and melampodium. |
| Male blossoms per 100 plants | 6.8 |
| Female blossoms per 100 plants | 2.5 |
| Out of 100 pollinators | 97% were Bumblebee 2% were European honeybee 1% were Squash bee |
| Average fruit set per 100 plants | 4 |
| Average yield per 100 plants | 3 |
In 2021, the flowers were located 300 feet away from the pumpkin field.
| Flower cultivars | Zinnias, Tithonia, ageratum, vinca, and melampodium. |
| Male blossoms per 100 plants | 6.5 |
| Female blossoms per 100 plants | 2.8 |
| Out of 100 pollinators | 98% were Bumblebee 1% were European honeybee 1% were Squash bee |
| Average fruit set per 100 plants | 4 |
| Average yield per 100 plants | 3 |
During the 2022 growing season, the flowers were located 400 feet away from the pumpkin field.
| Flower cultivars | Zinnias, Tithonia, ageratum, vinca, and melampodium. |
| Male blossoms per 100 plants | 6 |
| Female blossoms per 100 plants | 2 |
| Out of 100 pollinators | 98% were Bumblebee 1% were European honeybee 1% were Squash bee |
| Average fruit set per 100 plants | 3 |
| Average yield per 100 plants | 2 |
Then in 2023, the flowers were again positioned directly next to the pumpkin field. Although yield has yet to be determined, the set is comparable or even increased from what it was in 2019.
| Flower cultivars | Zinnias, Tithonia, ageratum, vinca, and melampodium. |
| Male blossoms per 100 plants | 8 |
| Female blossoms per 100 plants | 4 |
| Out of 100 pollinators | 90% were Bumblebee 5% were European honeybee 2% were Squash bee 2% were Swallowtail (Both Eastern Tiger and Eastern Black) 1% were Monarch butterfly (Danaus plexippus) |
| Average fruit set per 100 plants | 6 |
| Average yield per 100 plants | 5 |
These findings and observations suggest that planting flowers directly next to or even intercropping flowers in a pumpkin does increase the diversity of pollinators present. However, many factors influence pumpkin fruit yield from growing and weather conditions, to insect and mammal pests, and plant pathogens, specifically powdery and downy mildew. Thus, concluding that increased pollinator diversity directly influences fruit set and yield would not be advised. That said, more pollinators do increase the likelihood of fruit set and ultimately fruit yield. Future research is needed to determine if flower species have any bearing on these findings, such as the impact of planting both cultivated and native pollinator plants and just native plants near pumpkin fields. Future research into the total amount of pollinators present throughout the growing season in these various field and flower field rotations would also be suggested to better gauge pollinator traveling distances and estimate seasonal averages. These findings do suggest that the planting of cut flowers is a viable alternative to beehives in certain agricultural settings, and would enable the farm to also earn revenue from the flowers, thereby increasing their bottom line.
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