Plant Lovers’ Almanac: How to grow a giant pumpkin

This time of year pumpkin festivals abound throughout the country and often the highlight of the festivals is “the biggest pumpkin” contest.

Few other vegetables can grow to the size of some cultivars of pumpkins and squash (last year the world record was set by a 2,624.6 pound pumpkin). But how in the world do you grow something of this size, particularly in a backyard garden? It can be done but will take special attention, time and a whole lot of space.

There are four main species of pumpkins and squash. Giant pumpkins fall into Cucurbita maxima species. ‘Dill’s Atlantic Giant,’ ‘Big Max’ and ‘Big Moon’ are some of the cultivars available to backyard gardeners. While they are referred to as giant pumpkins, some of the commercially available varieties are actually squash.

What is considered a “giant pumpkin?” Usually any pumpkin/squash weighing over 150 pounds is considered to be a giant. Giant pumpkins take about 120 days from planting to maturity.

Enthusiasts may not grow varieties that are available in garden centers, but may use seed from varieties that have been developed through careful breeding and informal field trial selections. Seed from lines proven to produce award winners have been known to cost hundreds of dollars per seed.

The growing area for the pumpkins should be prepared the fall before planting by adding and incorporating organic matter. The plants prefer a soil pH of 6.5-6.8 and full sun.

Giant pumpkins are warm-season annuals and will not tolerate frost. Backyard gardeners can start seedlings indoors to be transplanted when the conditions are favorable, but do not let the plant become root-bound, and be sure to “harden” them off to the outdoor environment before planting.

Each plant will need about 2,500 square feet for the best growth. Adequate and consistent watering will be necessary (at least 1 inch per week.) The addition of fertilizer before planting should be based on a soil test. After fruit set, a water-soluble fertilizer high in phosphorus should be applied on a weekly basis.

Pumpkins, like most cucurbits, have separate male and female flowers on the plant. The male flowers open first in order to attract bees to pollinate female flowers. After the female flowers are successfully pollinated, the plant will start to set fruit. Farmers of giant pumpkins will only allow one fruit per vine to ensure that all of the plant’s energy will go into that one fruit.

Experienced giant pumpkin farmers will also perform other tasks such as root pruning. Root pruning is done because the plant will send out roots at the nodes which anchor the plant and can cause the fruit to break off.

Giant pumpkins sometimes are not the color that one usually expects. Because they are so big, they are not covered by leaves and are exposed to sunlight. Sunlight can cause the rinds to harden and crack, so growers often cover the fruit to protect it, but this also causes the rind to be a lighter color, even white.

Backyard growers will usually wait until there are a couple of fruits on the vine, select the fastest-growing, most robust fruit and remove the rest. The vine should then be repositioned to be 80 to 90 degrees perpendicular to the pumpkin, and if it seems like the vine is going to kink, move the pumpkin back several inches.

Pests like cucumber beetle and diseases like powdery mildew will have to be managed in order to keep the plant healthy from the time the seedlings are transplanted in the field until harvest.

Giant pumpkins will not have the traditional round shape due to their size, and often growers will carefully turn the pumpkin until they can’t do it anymore. Giant pumpkins can grow up to several pounds per day. Often growers will place cardboard, straw or even a pallet to keep the pumpkin off the ground and avoid rot. Harvest when the rind is hard, the vine is drying back and the pumpkin has developed a solid color.

While requiring more work and time than regular pumpkins, growing giant pumpkins can be a lot of fun and who knows, you could grow the next record-breaker.

Jacqueline Kowalski is the Summit County Agriculture and Natural Resources Extension Educator for the Ohio State University. For questions on local foods, food production, or other garden-related questions, contact her at kowalski.124@osu.edu or 330-928-4769 ext. 2456. Call the Extension Master Gardener Volunteer Hotline from 9 a.m. to noon Tuesdays at 330-928-4769, option 3 or extension 2481 or 2482.