Growing Giant Pumpkins

A variety of large pumpkin cultivars are available to gardeners. However, if you are looking to grow the largest pumpkin possible, there is only one to consider — Dill’s Atlantic Giant, a variety bred by Howard Dill of Nova Scotia. Dill, who held the record for heaviest pumpkin four years in a row back in the late 1970s and early 1980s, bred his variety from two other giant pumpkin varieties: the Mammoth Chile and the Goderich Giant, a variety descended from Warnock’s seed. Confusingly, there is also a variety called Atlantic Giant, but it typically doesn’t grow as large as the Dill’s variety.

Many garden seed companies carry Dill’s Atlantic Giant, and their seeds will do for backyard enthusiasts. However, for those seriously thinking of entering pumpkin weigh-offs, competition-quality seed — derived from past winners — is available from certain specialty seed companies. An Internet search for “giant pumpkin seeds” will lead you to several sources of seed; and giant pumpkin seed swapping groups can also be found online. In many cases, the parentage of different seeds can be traced back several generations to award-winning pumpkins.

Garden location

Your pumpkin patch will need to receive full sun to grow the largest pumpkins. You will need at least a 20-by-30-foot plot for each plant, larger if you don’t intend to prune the vines. (I once had vines that grew almost 100 feet.) And if you’re serious about growing pumpkins competitively, you may have to move. Every world record pumpkin has been grown within the “golden zone” — between the 40th and 50th parallel. In addition, most have been grown in the eastern United States or Canada, perhaps because the most well-established pumpkin weigh-offs are held there.       

The soil

Pumpkins require soil with good drainage. They do best in slightly sandy loam with a pH around 6.5. Soil analysis from gardens of past winners indicate that soil with 6 to 12 percent organic matter, 65 to 80 percent calcium, 12 to 15 percent magnesium, and 4 to 8 percent potassium is ideal. You don’t need to get that technical to simply grow a garden giant, however. If you start with “good garden soil,” stir in a moderate amount of compost or composted manure. Add enough compost to make the soil rich and fertile, but not so much as to interfere with drainage. This amount will depend on the current state of your garden soil. Above a certain level, the size of pumpkins does not correlate with the amount of compost you add, so you don’t need to overdo it.

If you know your garden is deficient in nitrogen, phosphorus or potassium, add the appropriate fertilizer to remedy this, but don’t overdo it. Once the nutritional needs of the plants have been met, adding more fertilizer — especially nitrogen-rich fertilizer — will spur vine growth, but it does not correlate to growing larger fruit. Too much nitrogen will actually lower the probability of a female flower setting fruit. A popular saying in giant pumpkin circles is, “You’re not growing salad. You’re growing fruit.” (In everyday terminology, pumpkins are vegetables. Botanically, however, they are a fruit — and giant pumpkin growers typically refer to the pumpkin as fruit.)  

Seed starting

Competitive growers start their seeds indoors to get a jump on the growing season. Growers in the “golden zone” generally start two to three weeks before their expected transplant date, which is the average last frost date for their region. A competitive grower will always attempt to sprout many more seeds than will actually get transplanted into the garden.

The seeds are placed in sterile potting mix and set on heating mats so that the soil temperature is around 90 degrees Fahrenheit. The potting mix should be kept moist, but hot and wet conditions can lead to fungal growth and the sudden wilting of seedlings. Some growers will treat the potting mix with fungicide to prevent this; others will simply try to keep the potting mix moist, but not constantly wet.

The plants are transplanted into the pumpkin patch when the first true leaf appears. Sometimes, growers will build a “mini greenhouse” — a cloche or hotbox —over the young plants until the weather warms a bit. They are removed when the interior temperatures climb to over 80 degrees Fahrenheit during the day.

Even if you’re taking a more casual approach, sprouting the plants on a heat mat is a good idea — giant pumpkins do not sprout well at lower temperatures. If you wait until your average last frost date to plant your pumpkins, you can then transplant them into the garden as soon as they emerge.

Growth

Pumpkins are vining plants that sprawl on the ground. They grow a long primary vine, as well as multiple secondary and tertiary vines. Most giant pumpkin growers train the primary vine to grow in a straight line. Secondary vines are trained to grow perpendicular from the main vine. Tertiary vines are pruned. Because older secondary vines are longer, the fully grown plant resembles a wedge or Christmas tree when viewed from above. Training the vines makes the patch more tidy and ensures that the leaves from one vine aren’t shading the leaves on another.

Vines can be trained by staking them to the ground or, better yet, by burying them. Burying the vine additionally limits the ability of squash vine borers — one of the most common insect pests — to lay their eggs on the plant.

Pumpkins root at every node — wherever a leaf stalk emerges or a secondary vine sprouts from the main vine, the plant will send down roots. Since all the vines become rooted to the ground, the plant is stabilized in moderate winds. Because of their large leaf size, however, giant pumpkins are vulnerable to high winds. Some growers construct barriers around individual plants for wind protection.

Left to grow, the main vine of a pumpkin can easily exceed 100 feet. And, the oldest secondary vines can get almost as long. In practice, growers clip the growing tips of vines when they reach the edge of their allotted space. Not too many years ago, growers thought that the biggest plants would yield the biggest pumpkins. These days, though, growers are learning that they can grow giants with a well-tended plant in a smaller space.  

Fertilizers

Pumpkins are large plants, grown with the intention of producing giant fruit. Many people have the idea that this is done by adding lots of fertilizer to the pumpkin patch. However, modern growers fertilize their plants to the point that they produce healthy foliage, but don’t overdo it. If the plants are fed too much nitrogen, their leaves turn blue-green and none of the flowers will set fruit.

Two of the most popular fertilizers are seaweed extract — or kelp extract — and fish hydrolysate. Compost tea and solutions with humic acid in them are also frequently used. These can be applied as foliar feedings or applied to the soil. And remember, the pumpkin has roots running all along its vines, so you can side dress along every vine at every node.

The amount of fertilizer that is applied depends on the fertility of the soil and the health of the plant. Many competitive growers favor frequent feedings with diluted solutions over adding large amounts of fertilizer in a single application. The idea is to give the plant just enough nutrients as it needs them. When the plants begin flowering, growers typically keep nitrogen additions to a minimum.

Setting fruit

In approximately eight weeks, when the main vine reaches 10 to 15 feet, the plant will begin to flower. The first few flowers will be male. Later, female flowers will be interspersed among the male flowers. It is easy to distinguish between male and female flowers because the female flower has a small, unfertilized pumpkin at its base. Initially you should attempt to hand pollinate every female flower. The idea is to set as much fruit as possible, then cull down to the fastest growing pumpkins when they are roughly the size of a volleyball.

You can hand pollinate by taking a small paintbrush and brushing the pollen off of the stamens of a male flower and onto the stigma of a female flower. Pumpkin pollen is a yellow powder, so it is easy to see how much your paintbrush has picked up. For the highest probability of success, it is best to pollinate early in the morning, right after the flowers open. That way, the store of pollen in the male flower won’t be depleted by insects. In addition, female flowers are more likely to set fruit if they are pollinated at cooler temperatures.

In the past, competitive growers would grow long vines, then cull down to a single pumpkin along the main vine. These days, growers will set fruit on both the main and secondary vines, and cull down to the fastest growing fruits. They will retain multiple fruits as long as they are at least 10 feet apart.

Growing fruit

Once you’ve culled down to your final pumpkins, it’s time to grow a monster. Hopefully, each pumpkin has at least 10 feet of vine with healthy leaves surrounding it in both directions. Photosynthesis in the leaves nearest the fruit is what will drive its growth.

Most growers gently turn the fruit so it is lying on its side, and the stem and main vine form a 90-degree angle. This is done by moving the fruit slightly over several days. Move the pumpkin only until you feel some tension on the stem. Some growers will place a platform under the fruit so that it is not lying in the soil; others don’t bother. For maximum growth, the fruit should be shaded. The most common way to do this is to erect a small tent directly over the fruit. Be careful, however, to shade as few of the nearby leaves as possible.

As the pumpkin grows, gently lift the vine it is attached to, carefully pulling up the roots on the adjacent nodes of the vine. Make sure that, as the fruit grows, the vine is not pulling the stem down.

One of the biggest problems with growing giant pumpkins is blossom end rot. The blossom end of the fruit can suddenly turn black, and then the fruit will progressively rot toward the vine. Blossom end rot usually appears when the soil has been allowed to go almost dry and then there is a heavy rain. Keeping the plant evenly watered will almost always prevent blossom end rot. Having sufficient calcium in your soil will also lower the probability of blossom end rot, as does good drainage.

Another inevitable problem is collapse. Sometimes the pumpkin will grow so large that it forms a crease, called a Dill ring, around the fruit. This is a weak point in the fruit, and if it grows large and fast enough, the pumpkin can collapse. In order to be eligible at a pumpkin weigh-off, the fruit must be intact. There really is no way to prevent this. If you’re swinging for the fences, sometimes you’re going to strike out.

Birth of a champion

In reasonably fertile garden soil, in a pumpkin patch that gets full sun, a Dill’s Atlantic Giant pumpkin can be left to sprawl and yield a set of very large fruits — 50 to 100 pounds. With increasing effort by the gardener — preparing the site with compost, training vines, controlling weeds, even watering, culling down to only the fastest growing fruits, and frequent feedings with seaweed extract and fish hydrolysate — you can grow progressively larger pumpkins. Many casual growers yield 300 to 400 pounds of pumpkins in their gardens with a moderate amount of effort. To grow competitive-sized pumpkins, you will need an optimal garden space (in the “golden zone”), seed from a championship lineage, a lot of hard work, and a healthy dose of good luck.  

Top Tips for Growing Giant Pumpkins

• Grow in well-drained soil (pH 6.5), amended with compost.

• Pumpkins should receive full sun and have plenty of room to grow (at least 20-by-30 feet).

• Start seeds indoors and transplant into garden as soon as danger of frost is gone.

• Leave 10 feet between fruits.

• Pollinate every female flower; cull down to fastest growing fruits when they reach the size of a volleyball.

• Water evenly and provide frequent feedings of diluted fertilizer solutions (seaweed extract, fish hydrolysate, humic acid, and compost tea). Don’t over-fertilize.

• Shade the growing fruit with a tent.

What Do You Do With Them?

• If you plan to grow giant pumpkins, prepare for people to ask you why. What do you do with them? The flesh of giant pumpkins isn’t good for eating, so it’s not as if you could bake hundreds of pies from your fruit. So what can you do with them?

• If you’re a casual grower, your answer may be to simply admire them. It takes a lot of work to grow a gigantic pumpkin. If some people can enjoy planting flowers to look at, why can’t a pumpkin grower enjoy a large cucurbit sitting in her garden?

• If you have kids, you can have them scratch their name lightly in the outside of the pumpkin, and watch their signature get larger as the fruit grows. You can also carve them for Halloween — some giant pumpkins have been carved into very elaborate works of art.

• One of the most fanciful things to do is scoop out the inside of the pumpkin and enter a giant pumpkin regatta. Several of these events occur around the country every fall.

• If you grow a real monster, of course, you’ll want to find the nearest state fair or farm festival that holds a pumpkin weigh-off. The prize money at these events keeps going up, and growers of winning pumpkins can literally make thousands of dollars selling the seeds from a single champion.

• Or, maybe you’ll find a way to combine your gardening obsession with another of your hobbies. I did. I live in Texas, and my garden gets shaded for a decent part of the day, but I still like attempting to grow giant pumpkins. I know I’ll never grow a world record orange squash, but they get big enough that I can combine them with another favorite hobby of mine — brewing beer. I hollowed out a couple pumpkins and fermented some beer inside them.

Chris Colby is an avid gardener who lives in Bastrop, Texas, with his wife and their cats. His academic background is in biology (a Ph.D. from Boston University), but his main interest is in brewing beer. He is the editor of Beer and Wine Journal, a website for home brewers and home winemakers.