Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Did you know that most of those giant pumpkins you see at competitions are grown by ordinary gardeners in their backyards? You can grow these monsters too. All you need is lots of sun, good soil, some fertilizer and the right seeds.
How to Choose the Right Seed for Giant Pumpkins
The first and most important step in growing giant pumpkins is choosing the right seeds. The normal bright orange pumpkins that you see offered for sale will never grow to a gargantuan size. Prize-winning pumpkins are all varieties of Atlantic Giant (Cucurbita maxima) which feature a paler orange skin. You can purchase Atlantic Giant seeds from most vegetable seed companies or you can purchase seed directly from past winners who have developed their own varieties of Atlantic Giant.
How to Prepare Your Soil to Grow Giant Pumpkins
You should begin preparing your garden in the fall. Choose a spot that gets full sun, at least 6 to 8 hours daily. Have a soil test done to find out the pH (acidity) and nutrient needs of your soil and make the appropriate amendments. You are aiming for a pH between 6.5 and 6.8. Use lime to raise the pH or sulphur to lower it as necessary.
Compost is a good amendment for your soil. It improves the soil texture as well as adding nutrients. You want a loamy soil that is well-drained so that your plants and fruit don’t rot. You can also add well-rotted manure. Don’t use fresh manure. It will burn the tender roots of your plants in the spring. Cow and horse manure is recommended. Avoid chicken manure.
How to Start Giant Pumpkin Seeds Indoors
You should start your seeds indoors 4 weeks before your last frost date. Use a peat pot so that you can plant them directly into your garden and not disturb the roots of your vines. Fill the pots with potting soil and plant the seeds point down. Pumpkins need heat to germinate. Use a heat mat under your pots to warm the soil.
Plant the Seedling Vines in Mounds
Plant your seedling vines out in your garden after all danger of frost. Vines should be planted in mounds to ensure proper drainage. Plant only one vine per mound and space the mounds 20 feet apart. Continue mounding the soil over your vines to encourage secondary root growth. You want as many roots as possible to support the large vines and fruit. Protect your tender vines from wind and cold by surrounding them with a barrier or fence for a few weeks.
Never water from above your vines. The water will splash soil on to the leaves resulting in powdery mildew which will kill the vines. You should always water close to the roots at the rate of 1 inch per week, more during dry periods. Drip irrigation is best. Pumpkins are 90% water. Don't let them dry out.
In addition to regular watering, you should fertilize your vines weekly using a water soluble fertilizer that is high in phosphorous (15-30-15) to encourage root growth. Once your vines have produced fruit, switch to a balanced formula (20-20-20).
Be very careful when you are weeding around your vines. Pumpkin vines have very shallow roots which don’t like to be disturbed. Keep in mind that the roots extend about 4’ out from each vine. Always cut the weeds at the surface of the soil rather than pulling them up. Mulch is an excellent solution. It keeps down the weeds and prevents evaporation of moisture from the soil.
Pollinate Your Flowers
When the vines flower, you can hand pollinate or leave it up to the bees and other pollinating insects. Pollinate using male flowers from the same vine (self-pollination) or male flowers from a different vine or variety (cross pollination). To hand pollinate, choose a male flower (straight stem, no bulge) and strip the petals away to expose the stamen and pollen. Apply the pollen by gently rubbing the stamen on the stigma of a female flower. Female flowers are easily identified by the tiny pumpkin that is growing behind the flower. You can also hand pollinate using an artist’s brush.
Measure Your Pumpkins
Pollination of the female flowers should result in multiple pumpkins per vine. To grow the largest pumpkins, you should have only one pumpkin per vine so that the plant can concentrate its energy growing that pumpkin. To determine which pumpkin you want to grow out, you should begin weekly measurements of the length and width of the pumpkins on each vine. Choose the one that is growing the fastest and remove the others from the vine.
Pruning and Moving Your Vines
To encourage your vines to put all of their energy into growing the pumpkin and not more vine, you will need to prune your vines. Prune the main vine 10’ beyond the pumpkin. Prune side vines 8’ from the main vine. Completely eliminate any tertiary vines. You should be “training” the side vines perpendicular to the main vine to allow room for the pumpkin to grow.
As your pumpkin grows larger, the stem and vine will become strained. Either or both could become cracked and even break. To prevent this, as the pumpkin develops, you should gradually roll the vine until the stem is perpendicular to the vine. Then as the pumpkin matures, the stem will try to lift the vine which will have become rooted in the soil. Remove these roots to a distance of about 4’ on either side of the stem so that the vine can lift easily without straining or breaking.
Shade Your Pumpkins
The sun, which your vines need to grow, can dry out your pumpkin causing cracks. Shading your fruit will prevent this. You can build a frame around each pumpkin and cover the frame with material or you can just throw a sheet over each one.
How to Harvest Giant Pumpkins
When the weather turns cold, it’s time to harvest your behemoths. Recruit some friends to help you with this. Cut the stem and then gently roll the pumpkin onto a tarp. Use the corners of the tarp as “handles” to move your pumpkin.
Growing huge pumpkins is not difficult. Choose the right seed, provide the right conditions and then enter your pumpkin in a local competition. Who knows? You could win!
Questions & Answers
Question: How long does it take for a pumpkin to start growing?
Answer: That depends on where you live and what kind of pumpkins you are growing. In my NJ zone 6 gardens, I direct sow my culinary pumpkin seeds at the end of May and see pumpkins start to develop mid-July.
© 2013 Caren White
Caren White (author) on November 07, 2013:
Hi Flourish! Yes, watering technique is critical for a lot of plants. Thanks for reading and commenting.
FlourishAnyway from USA on November 07, 2013:
These are great instructions for the dreamers among us. That watering thing always trips me up. Simple but true!
RTalloni on November 06, 2013:
Very interesting to learn about growing giant pumpkins, and enticing! Thanks for a good look at getting the job done.
Caren White (author) on November 06, 2013:
Me too! Thanks for reading, Rebecca.
Rebecca Mealey from Northeastern Georgia, USA on November 06, 2013:
I would love to grow giant pumpkins someday. Thanks for these instructions .