University of Maryland Extension

Giant Pumpkins

giant pumpkins growing in field

Pumpkin is a summer-growing annual of the genus Curcurbita and the family Curcurbitaceae, which also includes gourds. Growing giant pumpkins is a lot of fun and can win you the ooohs and ahhhs of neighbors and prize money at county and state fairs!

Planting

Check seed catalogs and garden centers for cultivars known to produce large fruit- such as ‘Atlantic Giant’, ‘Big Max’, or ‘Big Moon’. It will take 4 months to get these pumpkin varieties to produce pumpkins in the 100+ pound range.

Select a full-sun, level part of your garden with soil that is high in organic matter. Then incorporate compost and 2 lbs. of 10-10-10 fertilizer (or the equivalent) in a 100 sq. ft area. Mound up soil in the middle of this area and plant 3-5 pumpkin seeds about ½ in. deep when the soil has warmed and there is no danger of frost (mid-May in the Baltimore area). The seeds will germinate in 7-10 days. When the plants have their second set of leaves keep the strongest plant and cut the others at ground level with scissors. (Pulling them out could disturb the root system of your prize-winning pumpkin plant.)

close up female squash flower
Female squash flowers

male and female squash flower
Male flower on left; female on right

Special note about pumpkin sex

Like other members of the squash family, pumpkins produce separate male and female flowers. Male flowers usually appear first. This is a normal growth habit and varies with cultivars. For a flower to develop into a fruit, pollen must be carried by insects from male flowers, on the same plant or on different plants, to the female flower (the one with the tiny pumpkin below the flower). Poor fruit-set is common during rainy weather when bees are inactive. Avoid using pesticides during the bloom period because bees are easily poisoned.

Cultivation

Select one fruit – Monitor the growth of the baby pumpkin fruits on your plant. When they are 6-8 inches in diameter you should keep the largest and fastest growing fruit and remove the others. Remove all new blossoms that appear. Place a piece of cardboard under your giant pumpkin to prevent soil rots. You may want to try rolling the pumpkin very gently into a new position each week to keep it from becoming lopsided.
Prune vines – After selecting your one fruit, pinch back the ends of your vines to direct the plant’s energy into the fruit. Some gardeners gently lift and move the vines to run in one direction to make access easier. Trim main vines and lateral vines as needed again later in the season.
Fertilizing – Fertilize plants with a water-soluble fertilizer every week according to label directions. Apply the liquid fertilizer to the soil around the base of the plant. The fertilizer should supply nitrogen, phosphorous, and potassium. Alternatively, you can apply ½ cup of 10-10-10 fertilizer (or the equivalent) around the base of your plant every 2 weeks. Over-fertilization can cause excessive vine growth and split your pumpkins.
Watering – Water deeply and regularly at the base of each plant, especially during hot, dry weather and once the fruits start to form. Time your watering so leaves have time to dry before dusk. This will help reduce disease problems.
Weeding – Remove all young weed seedlings by hand or with a hoe and use a mulch around plants to keep weed seeds from germinating.

Common Problems

Harvesting

Generally, pumpkins are harvested in late September or early October. They should be fully colored and the rind should be hard. Use a sharp knife or pruning shears to cut them from the vines, leaving 3 to 4 inches of stem attached to each fruit. Try to avoid cutting or bruising the fruit. Store your giant pumpkin on a pallet so that air can circulate underneath, and keep it in a protected and shaded location.

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Author: Jon Traunfeld, Extension Specialist, Vegetables & Fruits; May, 2010

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