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Pumpkin: Sow and Grow Guide

Pumpkin: Sow and Grow Guide


Pumpkins are winter squash, grown and harvested like any other winter squash. An extremely versatile vegetable, many varieties are delicious in both savory dishes (e.g., soups, casseroles, roasts) and sweet dishes (e.g., pies, muffins, breads). Some varieties are especially suited for baking use, as the flesh is dense and smooth. Other varieties are more suited for decorative purposes because the flesh tends to be stringy and/or watery. If you were wondering how to grow pumpkins from seed, you've come to the right place!

GENERAL SOWING

When to Sow Outside: RECOMMENDED. 2 to 4 weeks after your average last frost date, and when soil temperature is 70°โ€’90°F.

pumpkin flower

When to Start Inside: Not recommended except in very short growing seasons, 2 to 4 weeks before your average last frost date. Sow in biodegradable pots that can be planted directly in the ground. Transplant after your average last frost date, when weather is warm and settled.

How many do I plant?: Usually, space is a bigger factor for pumpkins than the amount of harvest, since pumpkins can take up a fair amount of room in the garden. Keep in mind the larger the fruit, the fewer a vine tends to produce, so for a large pumpkin you may just get one or two per plant.

INDOOR SOWING

If you have a shorter growing season, you may consider starting your pumpkin seeds indoors. Use a lightweight seed starting mix/media (sterile, and lighter than potting mix), and sow seeds 1" deep. Sow 2-3 seeds per pot, thinning to the strongest plant once leaves appear (clip extra plants at the soil level using scissors). The strongest plant may not be the tallest; look for thick, strong stems and deep color. By thinning early, you minimize the negative impact of crowding, like stretching for light. Read about more indoor sowing tips.

Containers

Containers should be clean, sanitized, and have drainage holes. If you choose to sow in cell packs, you may need to up-pot seedlings once into larger containers before transplanting outside

Transplanting

Harden off seedlings after 2 ½ to 3 weeks. Hardening off is the 7 to 10 day process of introducing pampered seedlings to the intense outdoor sun and temperature swings. Read more about hardening off. Transplant into an area of full sun (6 or more hours a day), when soil temperature is at least 60°F. If you don't have a soil thermometer, this is often about 2 weeks after your last frost, but double-check the weather forecast. Transplant on a cloudy day or in the evening to reduce stress. Remove the bottom of the biodegradable pot when transplanting into the planting hole. This allows roots to escape easily while the remainder of the pot breaks down. Consult the seed packet for appropriate spacing.

OUTDOOR SOWING

How to Sow

Winter squash is commonly grown in mounds (see packet for mound spacing). Raised mounds warm the soil more quickly in spring, and drain well. Small to medium-sized pumpkins can be grown on a trellis to save space, and increase airflow, which helps prevent fungal disease. If you choose to grow on a trellis, plants may be spaced more closely (half spacing). Larger fruits (over 4 lbs.) should be supported with a makeshift sling made of material like old t-shirts, pantyhose, or other soft materials. Keep in mind the vine length and mature fruit size if you choose to use a trellis. Extra-large, competition-sized pumpkins should be grown in mounds. Black weed barrier fabric or plastic sheeting can be employed to warm the soil, keep down weeds, and retain moisture. Lay a sheet of the barrier fabric or black plastic sheeting over the soil in your planting area. Cut 4"-6" diameter holes in it, and sow the seeds within the cut holes. The best way to irrigate when using this fabric or sheeting is with a soaker hose or drip irrigation underneath. Remove the fabric or sheeting at the end of the growing season.

Thinning

When the seedling has several leaves, thin to 1โ€’2 plants, or just to 1 for extra-large pumpkins.

Water

Keep evenly moist; pumpkins need lots of water, especially for extra-large ones. Avoid overhead watering, as pumpkin plants are very susceptible to powdery mildew.

Fertilization

Pumpkins are heavy feeders and can benefit from an initial application of slow-release, balanced fertilizer (equal parts nitrogen, phosphorus, and potassium) at sowing time, and a light application of a water-soluble fertilizer, regularly thereafter. Begin with a balanced fertilizer, and change to a low-nitrogen fertilizer once flowers form.

Weeding

Keep plants well weeded. Weeds compete with crops for light, nutrients, and water, and can harbor insects and diseases.

Special care

To form a flat bottom on your pumpkin, gently set it upright if it emerges growing on its side. Keep pumpkin patch well-weeded. If you are trying to grow an extra-large pumpkin, allow only one fruit per plant. As the vines grow, pick off any new pumpkins that start to form.

POLLINATION

Pumpkins are monoecious (having both pollen-producing flowers, and flowers that are able to produce fruit only when pollinated). Pollen-producing flowers appear earlier in the season, in theory, to attract bees to the area. Sowing pollinator-attracting plants near pumpkins can assist in proper pollination, resulting in a bigger harvest and well-shaped fruit. Floating row covers are highly recommended for pumpkin plants during the early days of their lives to protect the young plants from squash vine borer and cucumber beetles. Hand-pick and destroy any squash bugs or cucumber beetles. Remove covers when plants begin flowering. Another method to avoid vine borers is to cover the base of the stems near the ground with mulch, foil, or fabric material, as the base of the stem is where insect eggs are laid. Pumpkin plants are also susceptible to fungal disease, so make sure plants have ample space for air circulation.

HARVESTING

Fruit

Harvest pumpkins before the first fall frost, and when foliage has begun to dry out. Cut stem with a knife, leaving 2"-4" of stem on the pumpkin. Do not hold the pumpkin by the stem; if stem attachment gets broken, or any part of the pumpkin bruises, the pumpkin may rot. Brush off any dirt or leaves.

pumpkin pie

Blossoms

Look for pollen-producing flowers that have long stems and harvest just before use (fruit-producing flowers have a very small, developing squash at the base of the flower and shorter stems).

Curing

Cure at 80°-85°F and 80โ€’85% humidity or a warm, sunny spot with good air circulation for 1 to 2 weeks before eating or storage. Do not allow harvested fruit to get wet.

Storage

Brush off any dirt, clean and sanitize the outside rind, and store pumpkins in a cool, humid area, ideally 50°โ€’55°F with 70โ€’80% humidity and good air circulation. Store in a single layer (not stacked), keep off the basement floor (which can be too cold), and away from apples (which shorten storage times).

COMMON PESTS AND DISEASES

Row covers at transplant or sowing can go a long way in pest prevention. You will not need to remove row covers until flowers appear, allowing plants to get a good, healthy head start. Scout unprotected plants for pests and disease weekly to catch any symptoms early. Attract native parasitic flies and wasps with small-flowered pollen and nectar plants like dill, cilantro, or alyssum.

pumpkin garden

Squash Vine Borers

Squash vine borer moths hatch out of their overwintering cocoons in the soil. These red bodied, wasp-like moths lay reddish-brown eggs around the stem close to the soil line. Deter moths by covering the base of the stems near the ground with soil, mulch, foil, or fabric material. The first sign of squash borers are eggs laid on the stem near the soil line, next to a pin-head sized hole, and sawdust-looking frass near the hole the borer made entering the stem; then part or all of the plant wilts. You can inject the stem with Bacillus thuringiensis (Bt) to kill the larvae or use a sanitized knife to cut above the entry hole, remove the larvae, and bury the damaged stem in hopes it will create new roots and recover. Because the caterpillars overwinter and rise again in the same fields, removing and destroying (not composting) infected plants is paramount in preventing ongoing borer infestations.

Squash bugs

Squash Bugs attack all squash including pumpkins. Both adults and nymphs suck plant juices, causing damage to the plant, which can result in a reduced harvest. Squash bugs' shiny bronze-colored eggs are most often found on the underside of the leaves, as a group of 10–20, in evenly spaced patterns. Squishing eggs is the most efficient way to eliminate infestation. Eggs hatch in about a week, making regular scouting and squishing necessary. Nymphs are pale green when young, becoming darker as they mature. Adults are fast crawling, brownish black, flat-backed bugs. Protect young plants with floating row covers (remove covers prior to flowering to allow pollination, or hand-pollinate flowers.) Handpick all stages of squash bugs from the plant base and undersides of leaves and squish or put in a bucket of soapy water. Place boards on the ground around plants, and destroy adults found underneath every morning by scraping them into a pail of soapy water. Neem (an extract of the Indian Azadirachtaindica tree) has an odor that deters gray or brown adult squash bugs and if they eat it, it will disrupt their ability to reproduce (don't expect immediate knock-down). Insecticide soap and horticultural oil is effective with contact to young nymphs (adults are very difficult to kill) and will need to be reapplied to survivors or subsequent hatches. Kaolin clay products work to coat the leaf surface with a layer of clay creating a physical barrier for eating and egg-laying. Kaolin clay washes off with rain and will need to be reapplied. Also, sowing successions monthly, using row cover allows you to trap bugs and destroy infested plants and start fresh.

Cucumber Beetles

Cucumber beetles look like ladybugs but are yellow with black dots or yellow with black stripes. Both beetles spread disease like bacterial wilt and should be controlled as soon as possible. Kaolin clay products create a layer of clay that makes feeding on the plants difficult for the cucumber beetles. Spinosad is a soilborne bacterium that is the active ingredient in other organic cucumber beetle controls. Straw mulch makes beetle movement more difficult and creates habitat for wolf spiders, which prey on cucumber beetles. Intercropping broccoli, nasturtium, or radish with squash has been shown to reduce damage from cucumber beetles.

Powdery Mildew

Powdery Mildew, one of the more common fungal diseases in the garden, will first appear as powdery white or gray spots which rapidly spread to cover leaves, tender stem tissues and flower buds. Infected leaves often shrivel and dry, which exposes fruit to sunburn, and may cause small fruit size and poor texture. Powdery mildew thrives in humid conditions, especially with cool nights. Healthy plants are less susceptible to infection by powdery mildew fungi, so keep plants properly fertilized and watered, and thin plants to improve air circulation around leaves and stems. Avoid overhead watering of foliage, and water early in the day so any wet leaves will be quickly dried by the sun. Thorough fall clean-up of plant debris will remove overwintering sites for fungi. Do not compost infected plant material. Organic controls include copper, sulfur, compost tea, horticultural oil plus baking soda, milk, and neem-based products. Try a spray of compost tea or baking soda plus horticultural oil, spraying plants thoroughly and frequently every 7 to 10 days to prevent the spread of the disease. Compost Tea, long used as a fertilizer, may also help fight fungal diseases. Begin with a burlap or cheesecloth bag containing 1 gallon of well-aged, manure-based compost. Place in a 5-gallon bucket of water, stir well, and steep it in a warm place for 3 days. Then remove the bag, put the liquid in a sprayer or watering can, and spray or sprinkle the entire plant. Oil Spray combined with baking soda has been found to prevent powdery mildew, also. Mix 1 tbsp. of baking soda and 2 tsp. of horticultural oil in 1 gallon of water, and spray plant thoroughly once a week. Be sure to follow the application directions on the oil label; if the plant you are treating is not listed on the label, test the spray on a few leaves first, waiting 48 hours to make sure there is no spotting or discoloration. Some studies have shown that milk can be as effective as commercial fungicides, suggesting that a 10% solution is effective if used several times a week or 20–50% was needed if used weekly. Dilute milk to the desired percent in water, and add a couple drops of natural soap to help the spray stick to leaves, rather than rolling off.



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