Cinderella rode to the ball in a coach that her fairy godmother crafted from a pumpkin in the patch. A fairy tale, yes, but growers of giant squash, Cucurbita maxima, are growing pumpkins that are approaching the size of small cars.
The giant prizewinners trace their roots back to Howard Dill’s Atlantic Giant, (Cucurbita pepo ‘Dill’s Atlantic Giant PVP’). Mr. Dill spent the better part of 30 years growing and breeding these pumpkins from the Mammoth pumpkin varieties (Langevin, 1993).
Growers across the country and around the globe continually strive to grow larger and larger pumpkins. If you think you would like to try your hand at it, the following is a beginner's guide that will help you grow a potential prizewinner.
If you are a first-time grower, it doesn’t really matter where you get your seeds if you are planting Atlantic Giant. Numerous catalogs and garden centers carry seeds, and most are capable of growing pumpkins in excess of 400 pounds.
But to grow pumpkins in excess of half a ton, it all begins with superior genetics. Growers trade and sell seeds from their giant fruits. These can be found at numerous websites or from growers in your area. When you are looking at seeds online, you will see information regarding the genealogy of the parent pumpkins it came from, such as:
1050 Liggett 16
1016 Reeb X 1901 Larsen
Let’s interpret this:
1050—This is the weight in pounds of the pumpkin this seed was taken from.
Liggett—This is the surname of the person who grew the pumpkin.
16—is the year that it was grown (2016).
1016 Reeb—the female plant that was planted to begin with.
1901 Larsen—the male plant that was used to pollinate the female.
Site Selection and Planting
Growing space in the garden is important. Each plant should be allowed approximately 1,000 square feet. This area may sound quite large, but it is essential for vine growth. Pumpkins prefer long hours of sunlight, so select your garden site accordingly. Avoid shaded areas and select an area with good surface drainage. Proximity to a water source is important, also, as these pumpkins will require large amounts of water to reach maximum size.
Preparation of the site should start the fall before with incorporation of organic matter such as composted manures or leaf litter. The addition of organic matter (manure, compost) to the garden is important to establish good soil tilth. Some growers will plant a fall cover crop such as oats, annual rye, or clover to add organic matter to the soils.
Fertilizer and Lime
A soil test is recommended in the fall to address issues related to pH, and whether soil amendments such as lime and other macronutrients need applied prior to spring planting. Always apply lime and fertilizers based on soil test recommendations. Providing adequate nutrients throughout the growing season will insure healthy, vigorous vines, not to mention larger pumpkins.
In the spring, granular fertilizers should be applied as a broadcast application over the soil surface and incorporated into the soil 4 to 6 inches deep a few days ahead of setting out your transplants. Giant pumpkin vines require approximately 2 pounds nitrogen (N), 3 pounds phosphorous (P2O2) and 6 pounds potash (K2O) per 1,000 square feet of growing space.
A foliar feeding or fertigation program should be started after pollination and fruit set have occurred. There are several foliar fertilizers available. Follow label directions and continue application throughout the growing season.
Planting and Space Requirements
Growing giant pumpkins requires an early start. Seeds should be sown individually and started indoors in 12-inch peat pots about the end of April. A well-balanced potting medium is recommended. Plants are ready for transplanting when the first true leaf is fully expanded. This is usually 10 to 14 days after seeding. Transplants can be protected from late spring frost using a floating row cover, cold frame, or small greenhouse.
Pumpkins are shallow rooted, so water slowly with at least 1 inch of water per week if rainfall is not adequate. More water may be required during hot, windy summer days. Water during morning or early afternoon hours so foliage dries by evening. This helps prevent the spread of leaf diseases. Trickle irrigation is best, but soaker hoses also work well. Overhead sprinklers are effective; however, wet foliage increases the chance of disease, especially angular leaf spot, bacterial leaf blight, and powdery mildew.
If planting is done in a well-prepared bed, weeds will seldom be a problem and can be controlled by hand weeding or hoeing. Continue to remove weeds until the vines cover the ground. At this time, the dense foliage will shade out most weeds.
Plastic mulches are very effective for controlling weeds. Plastic mulches also warm the soil and can maintain good soil moisture levels. The plastic can be installed when the soil is in good planting condition, any time from a few days to two to three weeks before planting. If you do not use plastic, pumpkins will benefit from organic mulches applied in the summer after the soil has warmed.
When summer mulching materials are used, such as straw, additional nitrogen is recommended. Mix 1 tablespoon of ammonium sulfate, calcium nitrate, or nitrate of soda per one bushel of mulch. Apply once or twice during the early growing season. A complete fertilizer that is high in nitrogen may be substituted for any of the above. Apply the fertilizer when the mulch is moist.
Herbicides are also available for weed control. However, only a trained and licensed applicator should apply these materials.
Windbreaks are necessary to protect young plants from being "wind whipped" prior to becoming fully rooted. Windbreaks should be positioned on plants most susceptible to southwest winds until late June when side-runners are 3 to 4 feet long. The use of a snow fence and burlap can make an excellent windbreak. Covering the vines at each node with soil will help anchor vines down and promote secondary root development.
Insects and Diseases
The site where you plant should only be used once every three years to reduce the incidence of insect and disease pressure. Without following a regular pest scouting and management program for insects and diseases, your success rate for producing a giant pumpkin will be significantly reduced. An insect and disease control program must be initiated at transplanting.
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. There are other pests like squash bug and squash vine borer that growers also need to monitor for throughout the season and be prepared to manage if necessary.
Powdery mildew is the disease every grower will see every year; the fungal colonies resemble powdered sugar sprinkled on both sides of the leaf. Bacterial diseases like angular leaf spot and bacterial leaf spot are favored by wet weather. Soil-borne diseases like Fusarium, Phytophthora, and Plectosporium are also favored by wet weather and unfortunately are not easily controlled using fungicides. When using fungicides, remember to rotate the Mode of Action (MOA) or Fungicide Resistance Action Committee (FRAC) number to reduce disease resistance.
For general pesticide recommendations to control insects and diseases, check with your local Extension educator for current rates and products. You may also refer to the Midwest Vegetable Production Guide for Commercial Growers (Bulletin 948) available at extensionpubs.osu.edu or Homeowner's Guide to Fungicides (University of Kentucky Fact Sheet PPFS-GEN-07). Licensed pesticide applicators will have more options regarding insecticides and fungicides available to them.
Although hand pollination is the preferred method to fruit setting, natural pollination by honey bees, squash bees, and bumble bees will work well. Hand pollination allows for a more controlled genetic cross. On main vine pollinations, most fruit are grown around 15 feet down the main vine from the root stump. Initially, it is recommended to allow only four to six pumpkins per plant. Once pumpkins reach volleyball size, trim back to one pumpkin. The more you reduce the competition for nutrients, the greater your success rate will be for achieving a giant size pumpkin.
Because of the size and fast growth of these 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. Pumpkins long in shape tend to push the vine forward, resulting in a kink. If this happens, slide the pumpkin back about 4 to 5 inches—this is usually necessary when the pumpkin is about 300 pounds. Pumpkins round in shape are difficult to rotate without damaging the stem.
To protect the pumpkin from direct sunlight, construct a shade out of burlap or other lightweight material. A plain white bedsheet draped over the pumpkin with the stem exposed will also suffice. This will prevent premature hardening of the outer skin and will allow the pumpkin to reach its full genetic potential in terms of physical size.
Harvesting and Moving Your Pumpkin
The day will finally come that you will want to harvest and move your pumpkin either to a weigh-in or to be displayed. Pumpkins on the smaller end of the weight scale (under 400 pounds) can be moved with a heavy-duty tarp and the help of some friends.
Giant pumpkins approaching 700 pounds will need a different type of technique to move and transport them. There are several types of lifting frames and straps that can be constructed to use with skid loaders and tractor mounted front-end loaders.
Smaller pumpkins can be transported in the bed of a pickup truck. Wider pumpkins will require a trailer with straps to securely move and transport your prize pumpkin to the weigh-in or other destinations.
Homeowner's Guide to Fungicides, University of Kentucky Fact Sheet PPFS-GEN-07. Available at plantpathology.ca.uky.edu/files/ppfs-gen-07.pdf.
Langevin, Don. (1993). How-To-Grow World Class Giant Pumpkins. Norton, MA: Annedawn Publishing.
Midwest Vegetable Production Guide for Commercial Growers. (2019) Ohio State University Bulletin 948. Lafayette, IN: Purdue University. Available at extensionpubs.osu.edu.
Original author: David Mangione, Pickaway County, Ohio State University Extension. (Originally published in 1994.)