Cinderella rode to the ball in a coach that her fairy godmother crafted from a pumpkin in the garden. A fairy tale, yes, but growers of giant pumpkins (Cucurbita maxima) are able to routinely grow pumpkins the size of a small car, if not the size of Cinderella’s horse-drawn coach! In fact, the world’s record for the heaviest pumpkin ever grown was recorded last year in Italy and weighed in at 2,702 pounds, which is heavier than some compact cars!
If you are looking for a fun gardening activity for your children or grandchildren, growing giant pumpkins could be just the thing to keep the kids engaged in the garden all season long, as the process can be fascinating for children and adults alike. Even if you have already planted pumpkins in the garden, here are some tips that will help you maximize the size of the fruit in your garden this season.
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Genetics key to size
The key to growing super-sized pumpkins is genetics. To grow truly giant pumpkins worthy of Circleville Pumpkin Show acclaim, one should plant an Atlantic Giant variety of pumpkins. Seeds of this variety of pumpkin are widely available online and I have also seen them available at local garden centers this spring.
Modern monster pumpkin genetics go back to a farmer in Nova Scotia, Canada, who spent 30 years breeding giant pumpkins. Every world champion pumpkin has come from the offspring of seeds grown by that farmer.
Many other pumpkin varieties can also yield large pumpkins in excess of 100 pounds, which may not break any world records, but should be large enough to break the record in your neighborhood!
Plenty of sun, water and space required
Growing large pumpkins requires a full sun location, one that receives no shade at any time during the day. A large growing space is also key to producing large pumpkins, so allow a minimum of 500 square feet per plant for vine growth. Growers who produce record-breaking-size pumpkins allow up to 1,200 square feet per plant!
Large amounts of water are required to grow large pumpkins, so be prepared to water frequently, keeping the soil moist at all times, but not soggy. A trickle irrigation system or a soaker hose is helpful to keep the soil moist but avoid the use of overhead sprinklers, as wet foliage increases the incidence of diseases such as powdery mildew, leaf spot and leaf blights.
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Cultural requirements for large pumpkins
While many growers of monster-sized pumpkins utilize hand pollination to increase the number of seeds that develop and the likelihood of bigger fruit, natural pollination by bees and other pollinators will work well for most gardeners. To maximize fruit size, it is best to initially allow only four to six pumpkins to develop per plant after pollination when the fruit begins to grow.
Once pumpkins grow to the size of a volleyball, it is best to remove all but one pumpkin per plant. The more you reduce the competition for nutrients and space, the greater your success rate will be for growing a large pumpkin.
Large pumpkin vines require 1 pound of nitrogen, 1.5 pounds of phosphorous, and 3 pounds of potassium per 500 square feet of growing space. This amount of fertilizer should be supplied through several applications made at planting and after pollination and fruit set.
The site where you plant should be used only once every three years to reduce the incidence of insect and disease pressure. Striped cucumber beetles can transmit bacterial wilt and aphids can vector viruses, so be aware of these early- and late-season pests. Prepare to manage them if they arrive in significant numbers. Once a bacterial or viral infection has occurred, there is no way to stop it. Other insects such as squash bug and squash vine borer can quickly damage pumpkin vines, so always examine plants and be prepared to employ cultural and chemical insect control methods when needed.
Provide extra TLC for larger fruit
Because of the size and fast growth of large pumpkins, training vines and root pruning is important. This will prevent stem breakage and splitting. While the pumpkin is basketball-size, curve the vine 80 to 90 degrees away from the fruit. About 3 feet out from the fruit, curve the vine back in the general direction it was headed. Clip roots 3 feet out on the vine. This will allow the vine to easily move upward as the pumpkin grows.
To reduce the potential for damage from soil-dwelling insects and decay of the skin of large pumpkins, you can place a thick piece of cardboard or piece of plywood under the pumpkin so that the skin does not rest directly on the soil.
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As the fruit gains size, shade it with shade cloth, burlap or an old bed sheet to prevent scalding and reduce overheating. Providing shade will allow the skin to remain more flexible and the fruit will be less likely to split. Harvest your pumpkin at the end of the season just before the first frost. Some larger pumpkins won’t color to the bright orange of a jack-o’-lantern type of pumpkin, but will appear pale yellow to orange-red when it is ready for harvest.
For more tips on growing large pumpkins in the home garden as well as tips for growing regular size pumpkins and squashes go to: go.osu.edu/growingpumpkinsandsquash.
Mike Hogan is an associate professor at Ohio State University and an educator at the OSU Extension.