The 6 Butternut Squash Growing Stages: A Complete Guide

There are several stages of growth for butternut squash plants and each one has its own set of unique challenges and benefits.

Butternut Squash

Butternut Squash grows in 6 stages:

  • Seed Preparation
  • Seed SowinG
  • Seedling
  • Fruit Development
  • Maturation
  • Harvesting.

Let’s go over these different stages and how you can get the most out of your butternut squash harvest.

Stage 1: Seed Preparation

butternut squash seeds

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Seeding depth: 1/4″ (6mm)

Soil temperature requirements: 70°F (21.1°C), optimum 85°F (29.4°C)

Preferred pH range: 6.0 to 7.0

Butternut squash is a member of the deadly nightshade family, which also includes tomatoes and potatoes, so gardeners with sensitive skin should take great care in handling this plant. 

The leaves and stems contain solanine, a fungicidal toxin that acts as an immune system stimulant in small doses but causes nausea, cramps, and diarrhea when ingested in large quantities. 

In fact, carnivorous plants such as the Venus flytrap evolved from nightshades, and they still produce toxins that ward off insects.

The mature seeds look like this:

butternut squash

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They are completely black, with a hard shell, and should not be eaten by humans or animals. Butternut squash is a member of the Cucurbita genus, which includes pumpkins and other squashes. 

The genus name “Cucurbita” comes from the Latin word for gourd (“Cucurbita”) combined with the -“tus” suffix for possession (so it means something like “one gourd”). 

In case you’re wondering about the nomenclature of these plants, keep in mind that there is no one set system for naming them; like everything else, they develop through a complex interplay of evolution and folk taxonomies. 

Stage 2: Seed Sowing

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Seed spacing: 4″ (10cm) between plants

Row spacing: 3′ (0.9m) between rows If you’re growing butternut squash as an annual vegetable, the best way to preserve your seed is to save some for planting next year. 

You’ll need both male and female flowers to produce fruit–the first blooms will be unisexual male blossoms that appear before the females do, so remove all but one flower from each plant. 

The females will grow in clusters of three or more small fruits beneath the leaves; these are ready to pick when they feel hard and heavy in your hand. These are immature green fruits, with the flower still attached to the stem.

 After picking them, allow the fruits to ripen inside for several days in a warm, dry location that is well-ventilated but protected from insects and rodents. The color of ripe butternut squash is deep orange or reddish-orange.

Never eat any plant with even a hint of green on it. When they’re ready, store your seeds in an envelope in a cool place until planting season next year.

Stage 3: Seedling 

Germination temperature: 75°F (23.9°C), optimum 85°F (29.4°C)

Seed viability: 6 years Butternut squash seedlings are remarkably resilient. They can survive at fairly low soil temperatures for a few weeks, but these conditions will delay germination. For best results, use warm soil to hasten the seed’s journey into the light.

Seedling growth rate: 1″ (2.5cm) per week Harvest them when they are about 8″ (20cm) tall and their stems are strong enough to support their own weight without drooping or breaking. Handle them with care.

Green plants have particularly fragile roots. If you plan on saving seeds from your crop, it’s important not only to keep butternut squash plants well-watered but also to save water by mulching around the plants with straw. 

Waterlogging will kill the developing fruits by taking all the oxygen out of the soil, so allow at least three weeks between waterings; butternut squash roots are extremely capacious and can recover their buoyancy very quickly.

Stage 4: Fruit Development 

The flowers will develop into small fruits that eventually mature into this:

These are unripe green butternut squashes, with the flower still attached. Harvest them when they’re about four inches (10cm) in diameter by cutting the stem with a sharp knife or pruning shears. 

Continue picking winter squash as soon as they reach a good eating size to encourage further fruit development on the vine.  

Always handle them carefully. You don’t want to damage those delicate stems or you’ll end up with a lot of lost fruit. When picked, each squash should feel solid and heavy in your hand. 

Stage 5: Fruit Maturation 

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These are mature green butternut squashes, with the flower still attached. Harvest them when they’re about four inches (10cm) in diameter by cutting the stem with a sharp knife or pruning shears. 

Continue picking winter squash as soon as they reach a good eating size to encourage further fruit development on the vine.  Always handle them carefully! You don’t want to damage those delicate stems or you’ll end up with a lot of lost fruit. 

When picked, each squash should feel solid and heavy in your hand. If left on the plant too long, these squashes will change color from dark green to a yellow-olive green. If this happens, harvest them immediately because the fruit will have begun to rot. 

In addition, you should break off any flowers still attached to the stem of a mature butternut squash plant; this will help increase the concentration of starch in its root system and ensure that all available energy goes into increasing your yield.

If your summer days are less than hot and humid, then these tips can help:

  • Plant fast-maturing varieties.
  • Ensure soil remains moist throughout the growth period 
  • Provide a thick mulch around plants

Stage 6: Harvesting 

The seed-bearing vines from which you harvested immature fruits may be removed from your garden after frost arrives since they no longer produce edible butternut squash. In addition, wait until the vines have completely died back to the ground before you search for seeds. 

In fact, if it’s your first time-saving butternut squash seeds, then you should probably allow a second season of growth by pruning the vines into a compost pile. 

This will ensure that sufficient time has elapsed between plantings and give late-developing flowers a chance to mature their fruit and produce viable seeds.

In nature, butternut squash seeds begin germinating in autumn; but don’t expect them to do so unless they’ve been subjected to at least 70 days of frost.

In addition, always harvest your own seed from at least 20 plants since cross-pollination can occur between different varieties. 

In order to dry these seeds, spread them out on newspaper in a cool spot for at least three weeks. After that time, store them in an airtight container until next year’s planting time.

Cultivation of Butternut Squash is relatively easy

The only challenge is its pollination since it has both male and female flowers on the same vine. The flowers must be carefully hand-pollinated by transferring pollen from the stamen (male flower part) to the pistil (female flower part). 

It’s a technique that takes a little time to master but once you’ve done it a few times, your vines will start to produce fruit in no time.

Butternut Squash Trial, University of Maine, Highmoor Farm, 2014
VarietyLbs./PlotNo. FruitFruit SizeComments
Atlas7097.8Large, fat fruit with long necks, ribbing
Ultra HP6497.1Large, with very long necks, variable size
Avalon64164.0High yield, uniform, blocky
Victory51153.4Good yield, variable size, and shape
XRB4757A50133.8Good yield, nice shape, uniform
Butternut 174446172.7Good yield, variable shape, late maturity
Butternut 40146172.7Good yield, dumbbell shape, fasciation
Waltham40113.6Heavy fruit, variable size, few culls
Butterfly39123.2Uniform size and shape, variable maturity
Butternut 90038123.2Uniform length, variable shape, high cull rate
JWS 6823 PMR36152.4Fair yield, small, variable
Metro PMR33142.3Low yield, small fruit, uniform, late
Chieftain33132.5Low yield, small fruit, uniform
RXB4756A32103.2Low yield, long, thick necks, late
LSD 0.05215Units must differ by this much to be different

Growing Butternut Squash

Butternut Squash grows best where summers are long and hot, which means that cooler regions with shorter growing seasons may require doubling up on plantings. 

This is to ensure a continuous supply of Butternut Squash during autumn and winter. In general, Butternut Squash seeds should be planted when the soil temperature is at least 60 degrees F (16 degrees C).

Helpful Hints:

  • Plant in full sun – choose rich, well-drained soil with plenty of organic matter mixed in – space seeds or seedlings 18 inches apart. 

As they begin to grow, remove any flower heads so that sugars will be available for developing fruit instead of making seeds – water regularly but don’t over-water. 

When vines touch the ground, cover them with mulch or straw to keep roots cool and moist – provide support for vines as they get larger – harvest when the skin is hard and the Butternut Squash feels heavy for its size.

  • The fruit can also be stored in a dry, well-ventilated area such as a garage or root cellar where temperatures range from 35 to 45 degrees F (2 to 7 degrees C).

How To Grow Butternut Squash

1). Plant your seeds deeply. The deeper you plant them, the longer they will take to germinate and grow into squash vines. If you bury your seed up to its first set of true leaves, it should be fine if there is no frost in late fall. 

If you have a long winter with lots of snow cover, you can wait until early spring to start harvesting your butternuts. Otherwise, start harvesting as soon as possible so that they don’t become too large or tough over the course of winter storage.

2). Trellis the vines so that their leaves won’t rot and their blossoms will pollinate. I made a trellis for mine using wooden poles and some twine, but you can use anything that is sturdy enough to support the weight of the vines.

3). Don’t get frustrated when your squash plants wilt during the heat of summer. It’s normal! Keep them watered and they’ll bounce back quickly.

4). Water regularly, especially in hot weather or if there is no rain predicted for several days.

5). If you leave an uncut Butternut on your plant long enough, it will turn into a Jack-o’-lantern. 

6). To save seeds, leave your best-looking fruit on the vine until it’s really ripe (but watch it closely so that bugs don’t eat into it). 

Cut open and take out the seed/pulp. Put a paper bag over it and let it dry for a week or so. Then, shake the seeds out and store them in an envelope or jar to plant next year.

7). If your vines die back suddenly one fall, you might have borers. They’re white things about 1 inch long that fly around at night and look like moths. 

8). If your Butternuts don’t grow because the soil is too wet or too dry, you can still eat them as summer squash. They’ll taste much better if picked when they’re young.

9). Enjoy planting and eating this delicious and long-bearing plant

Conclusion

You can tell whether your seeds are sufficiently mature by the fact that they turn brown and begin to rattle inside their shell once you shake them. 

If you’re saving seeds from several varieties of butternut squash, then label each type using an indelible marker before storing it away for winter; you don’t want to be sorting through all your stored seeds next year when you could be outside planting.