Butternut Squash Growing Stages

Squash plants are often considered some of the easiest vegetables to grow in the home garden. You don’t need years of experience under your belt to secure a good harvest! While there are countless squash species, varieties, and cultivars to choose from, butternut squash (Cucurbita moschata) is by far one of the most popular.

Butternut squash is a winter squash with a distinctly buttery, nutty flavor. (Can you guess where the name came from?) The medium-sized fruit can be turned into soups, purees, or just cubed and seasoned for good eating.

In this article, I explore the basic butternut squash growing stages and what each means for the development of this hardy plant. 

Conditions for Growing Butternut Squash

Butternut squash’s needs are very similar to the growing stages of their winter squash cousins. Though butternut squash likely originated in Central and/or South America, it grows well in USDA Zones 2 to 11. It’s an annual, so you don’t need to worry about overwintering (though you do need to pay attention to your growing season’s length).

As with most squash plants, space is a big concern when growing butternut squash. Each plant needs an average of 10 to 15 feet to sprawl out as it grows.

Worried you don’t have the garden space to spare for a good squash crop? There are a few ‘bush’ varieties — compact plants that require far less room. ‘Burpee’s Butterbush’ is one such variety that is very highly recommended.

Squash plants are traditionally grown in soil mounds. The benefits are twofold: The mounded soil warms up more quickly in the spring and allows excess moisture to drain away from the root system. Raised beds or large containers work in a similar manner.

However, you choose to plant your butternut squash, make sure it receives at least 6 hours of direct sunlight per day. It’s normal for the leaves to wilt in the afternoon sun, especially if you live in a particularly hot climate. Installing a temporary shade cloth can help protect the foliage.

Last but not least, butternut squash is a hungry, hungry crop. The site should be prepped before the growing season with aged manure or compost. Plant to side-dress plants with your choice of balanced fertilizer several times throughout the season.

Butternut Squash Growth Rate

As annuals, squash plants have a lot of growing to do in just a few short months. Vining varieties can grow up to 15 feet long or tall by the end of the year. Bush varieties usually only grow about 3 to 4 feet tall and wide.

The vines of particularly vigorous varieties of butternut squash can grow almost 12 inches per week during the growing season. Bush-type varieties are much more reserved in their growth rates, growing just a few inches on average each week.

Growth Stages of Butternut Squash

Butternut squash takes an average of 100 to 120 days to go from seed to harvest. Just the time it takes for the fruit to mature after pollination can be up to 55 days alone! 

Different varieties have different estimated maturity times. For example, the variety ‘Victory Early’ requires just 85 to 90 to mature. The aforementioned ‘Burpee’s Butterbush’ is another fast grower, maturing in just 75 to 85 days.

Despite the name, winter squash is susceptible to frost damage. It’s important to align the plant’s life cycle with your local weather, or else you may lose your hard-earned harvest to a harsh drop in temperature. 

These so-called short-season butternut squash plants are ideal for cooler climates where the number of frost-free days is often limited. Season length isn’t much of an issue for gardeners in warmer regions, though impatience may still push you to grow some short-season varieties.

Regardless of the growth rate or habit of your chosen butternut squash, all plants follow the same basic growth cycle:

1. Seed Germination

The seeds of butternut squash are practically indistinguishable from those of pumpkin and other types of winter squash. The large size and high germination success rate make butternut squash seeds very easy to work with.

According to Cornell University, winter squash seeds (including butternut squash) take about 5 to 10 days to germinate in ideal growing conditions.

Butternut squash seeds germinate prefer soil temperatures at or above 70°F — 95°F is ideal. The soil temperature must be above 60°F or the seeds will rot before sprouting. 

Some gardeners achieve these soil temperatures early in the spring. However, many must start their butternut squash seeds indoors, or else there won’t be enough frost-free days for the fruit to mature before winter.

Once germination begins, the butternut squash seed produces its very first root called the radicle. This root anchors the seed into the soil and will eventually develop into the plant’s mature root system.

The seed’s first vegetative growth — a stem topped by two embryonic leaves called cotyledons — then emerges from the same spot. Unlike the radicle, the cotyledons can sense the direction of the soil’s surface and grow accordingly.

2. Seedling

We typically think of the moment the cotyledons breach the soil’s surface as the start of the seedling stage. 

Cotyledons are simple, rounded leaves that provide energy while the seedling grows. A seedling’s cotyledons rarely look like the plant’s adult foliage, so different seeds are tricky to tell apart at this stage of growth. 

Seedling

About 7 to 10 days following germination, the butternut squash will develop its first ‘true’ leaves. These leaves will resemble the adult foliage, just smaller. It’s perfectly normal for the cotyledons to die off once the true leaves take over.

3. Vegetative Growth

As the butternut squash plant grows larger, it will develop one or two main vines. These vines tend to sprawl out in opposing directions unless trained otherwise. Secondary and tertiary vines will grow from the main ones — similar to the way a tree branches out.

In addition to large, rough leaves, winter squash vines also have small tendrils. The tendrils are essential if the plant wants to climb, as they wrap around structures securing the vine.

Many gardeners opt to cut back their squash vines once they reach a certain size and begin setting fruit. This strategy can help keep larger varieties under control, especially in a small garden. Do not cut back the main stems, only smaller, tertiary growth. 

4. Flowering

Your butternut squash will likely start flowering anywhere from 45 to 60 days after planting. 

Squash plants are monoecious, so they have separate male and female flowers. The very first flowers to appear are usually male, and won’t produce any fruit. Once the female flowers begin blooming, however, pollination can occur.

5. Pollination

Before a butternut squash vine can actually start producing squash, both a male and female flower need to be open at the same time. (This could be two flowers on a single plant or two flowers on separate plants in your garden.)

Common pollinators of winter squash include classics like bees, butterflies, and other flying insects. You can also hand-pollinate the female flowers by rubbing the pollen of a fresh male flower onto the stigma.

The easiest way to tell a male flower from a female one is to look at the base where the petals meet. Female flowers have small bumps that look a lot like tiny, undeveloped squash. These bumps contain the ovules and will — if pollinated — eventually turn into mature fruit.

Butternut Pollination

6. Fruit Development

It takes about 7 days for butternut squash fruit to start forming once a female flower is successfully pollinated. Don’t get excited just yet! The fruit should ideally stay on the vine for 50 to 55 days before harvesting.

Fruit Development

During this stage, the squash fruit will get slightly larger each and every day. It will soon start to take on the distinctive pear-like shape of a mature butternut squash and you’ll eventually notice the rind begin to fade to a soft yellow.

When to Harvest Butternut Squash

Harvest time for butternut squash starts around September, depending on the climate and the variety being grown. The harvest can then go all the way up to the area’s first frost date.

Check whether or not your butternut squash is ready to harvest by examining the rind texture and color. According to Iowa State University, ripe squash should have tough skin that can’t easily be punctured by a fingernail. It should also be an even shade of tan or light yellow.

It’s very important to harvest your butternut squash before your garden experiences a hard frost. Even if the full 55 days haven’t yet passed, it’s better to harvest a little early to prevent damage caused by freezing temperatures at night.

If you have enjoyed this article, here’s a link to Soybean Growth Stages that you may also find interesting.

FAQ Butternut Squash Plant Stages

How many butternut squash grow on a vine?

Butternut squash production can vary greatly, from just one squash per plant to as many as 15! Most varieties produce an average of 3 to 6 squash per plant, though even this number can vary based on growing conditions.

Do butternut squash vines need to climb?

Though butternut squash has a vining growth habit, the plant prefers to scramble along the ground versus climbing a trellis or similar structure. You can, however, train the vines to climb if desired. Just keep in mind that the fruit can be quite heavy and will likely need extra support.

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Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.