Butternut Squash
Growing Guide
Butternut squash (Cucurbita moschata) is one of several annual winter squash plants. Squashes are native to North and Central America and were grown by Native Americans prior to the arrival of Europeans.
In the mid-1940s Charles Leggert crossed some pumpkin and gooseneck squash varieties to give us the modern butternut squash. It got its name from its buttery flesh and nutty flavor.
It is green as it grows and when ripe it will turn to a light tan color and the stem will begin to shrivel up. It is grown during the summer and is classed as a winter squash due to their winter storage qualities. Acorn squash and spaghetti squash are also popular winter squash varieties grown by gardeners.
Starting from Seed
Butternut squash has a long growing season and in the northern growing zones it is helpful to start them from seed and give them a head start.
Follow the seed packet instructions. In general, they can be started indoors 6 to 8-weeks before your last expected frost date.
Sow the seeds 1/4-inch deep in a sterile seed starting mix in cell packs or pots. Lightly cover with the seed starting mix and keep moist.
Bottom watering is the easiest way to keep moist without disturbing the newly sown seeds. The seeds should germinate in 2 to 3-weeks. They can be transplanted into individual pots after the true leaves appear.
To harden off your plants put them outdoors when the temperature is in the 40s to the 50s. Put them in an area out of the direct sun and is sheltered from the wind for a few hours. Keep them watered and increase the time outdoors each day and allow them to get some direct sun. After about a week they can be left outdoors, but bring them indoors if frost threatens.
A cold frame is very useful in hardening off plants, making sure to open it up during the day or they could get burned from the heat of the hot sun. It can be closed at night if frost threatens and can protect your plants from animal damage. Hardening off prepares the plant for the outdoor environment and reduces transplant shock.
For more guidance our seed starting page will be helpful.
Soil Preparation
Plant in full sun in a nice loose well-drained garden soil. As soon as the soil is frost-free and can be worked, till the soil by digging down 8 to 12-inches turning the soil over with a garden fork, removing any large rocks. The small pebbles remaining will do no harm and actually benefit the soil by adding some micronutrients to the soil. They will do best in a slightly acid soil with a pH range of 5.5 to 6.8.
Planting Butternut Squash
Plant the butternut squash seeds in full sun directly in the garden after all danger of frost. They will grow best when the soil temperature is 60-degrees or higher. Most varieties need 75 to 100-days to mature.
If you do not have much space, you can choose a bush variety. There are several compact varieties that can be grown in containers.
To lessen the chance of getting vine borers, plant later in the season. Waiting a few weeks after the last frost date to plant or using a light row cover can be very helpful.
They can be planted in rows or hills.
When planting in rows, sow the seeds 1/4-inch deep, 6 to 12-inches apart, in rows 6 to 8-feet apart. After the seeds germinate and are a few inches tall thin them to one plant every 2 to 3-feet by sniping off the extra plants.
When planting in hills dig up an area about 3-feet across adding good rich garden soil leaving a slight mound about a foot high. Each hill can be 4 to 6-feet apart depending on the size of the variety you are growing.
Sow 4 to 6-seeds per hill and when the plants are a few inches tall thin them to 2 to 3 per hill by sniping off the extra plants.
Each vine can grow 10 to 12-feet long with each one producing 4 to 5 butternut squash. You need to figure that each vine will need about 9-square feet without overshadowing your other vegetables.
A rough guide is that you could have 3 to 4-plants in a 4 by 8-foot raised bed. On each end of the bed, you would place your seeds or started transplants and they will have room to grow towards each other.
Another option to save some space is to let them grow on a trellis.
Watering and Care
When the plants are a few inches tall add a nice loose mulch of shredded leaves or pine straw to shade the roots.
This will keep the weeds out, the soil cooler and help retain moisture. Keep the mulch a couple of inches away from the stem. Weeding and cultivating can damage the shallow roots. During dry spells give some water each week.
If needed you can feed with an organic fertilizer such as Espoma Garden-tone.
Harvesting Butternut Squash
Depending on the variety, it will take 85 to 90-days for it to reach maturity.
They are ripe and ready for harvest when the color turns to a nice light tan color and all green is gone and the stem starts to shrivel up.
For proper storage the stem needs to remain on. Leave an inch of stem on and cut it with a sharp knife or a branch lopper. Do not move it by holding the stem since it may break off and it will not store very well. The squash skin has a natural protective wax which should not be washed off. Lightly brush off any excess soil before carefully placing them in storage.
Storing winter squash is a time-honored tradition of having fresh produce during the cold winter months. You can expect butternut squash to keep for 2-months or longer, but proper storage is important. For proper storage a temperature of 45 to 55-degrees F in a well ventilated cool dark location is ideal. High humidity can cause rot, so they should be stored on a shelf in a single layer on newspaper or cardboard. Periodically turn and inspect for spoilage as you remove any for eating. You can expect butternut squash to keep longer than acorn squash.
Diseases
Downy mildew and powdery mildew are common in some areas. Choosing resistant varieties and maintaining good air circulation around the plant are the best ways to avoid any problems. Remove any diseased leaves and put in the trash, not in the compost pile.
An organic product such as Bonide copper fungicide can be applied to the leaves as a preventative following the product label instructions.
Pests
Butternut squash vines have a hard stem which makes it difficult for the borer to get into the stem.
There are several squash vine borers that can cause problems. Examine your vines often near where it comes out of the ground. Look for a small entry hole and what looks like sawdust. To save the plant you need to remove the 1-inch-long caterpillar.
To do this make a lengthwise slit near the entry hole and spread the sides of the slit to reveal the caterpillar, which is usually found several inches above that point.
Use tweezers to carefully remove it, doing as little damage to the vine as possible. Now pile some soil over the slit to encourage the growth of new roots there. Cover with mulch and water when needed.
Cucumber beetles and squash bugs are common pest problems. Sticky traps and hand picking are used by many gardeners as well as some organic sprays. Examine your squash plants often, especially on the bottom of the leaves where the adults hide and lay their eggs.
Duct tape is a very effective way to remove the adults and eggs. Take a piece about 8 or 9-inches long and attach the ends together to form a loop with the sticky side out. Put one hand through the loop and with the other lift up a leaf looking for any eggs or adults. If you find any adults stick them to the tape and do the same for the eggs.
For serious problems an organic product such as Bonide Captain Jack's containing spinosad can be used. Spinosad is a natural insecticide made by a soil bacterium and is effective at killing squash vine borers, but only when they just hatch. It will not be effective once the borer is in the plant.
Planting your squash in a new location each year will help lessen the occurrence of diseases and pests.
Popular Varieties
Standard varieties have long vines and 3 to 5-pound fruit: Metro, Waldo, Waltham.
Compact varieties have shorter vines and 1 to 3-pound fruit: Autumn Glow, Butterbaby, Butterbush, Butterscotch, Honeynut, Pilgrim.
Sources: Burpee, Gurney’s, Johnny’s Selected Seeds.
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