The Squash Growing Stages From Seed to Harvest

Squash are a productive addition to home gardens, offering a diverse range of shapes and flavors. These plants are categorized into two main groups: summer and winter squash. While both are warm-season crops, their primary distinction lies in harvesting. Summer varieties are picked when immature with soft skins, while winter types are harvested mature with hard rinds for storage.

Seed Germination and Seedling Stage

A squash plant begins with a seed. For successful germination, soil temperature is a primary factor, with an optimal range between 70°F and 95°F (21°C and 35°C). Plant seeds a half-inch to one inch deep in fertile, well-drained soil. Sprouts should emerge within six to fourteen days.

Shortly after emerging, the seedling displays its first leaves, known as cotyledons. These initial leaves are simple and rounded, providing the plant with stored food from the seed. Soon after, the plant develops its “true leaves,” which have the characteristic shape of the mature plant’s foliage. Once seedlings have one or two true leaves, they should be thinned to the most vigorous plant to prevent competition.

Consistent moisture is important as seedlings establish their root systems. The soil should be kept moist but not waterlogged to avoid root rot. Providing seedlings with plenty of direct sunlight is also necessary for strong growth and to prevent them from becoming weak and leggy.

Vegetative Growth Stage

After the seedling stage, the plant enters the vegetative growth stage, a period of rapid development of its leaves and stems. During this phase, the plant builds the framework that will support flowering and fruit production. The growth habit of the squash variety also becomes apparent, a consideration for garden space planning.

Squash plants have two main growth structures: bush or vining. Bush varieties, including most zucchini and other summer squashes, grow in a compact form, occupying an area of about three to four feet. Their stems are shorter, and the foliage grows in a dense pattern from a central point. Vining types, common among winter squashes like butternut and pumpkins, produce long, sprawling vines that can travel many feet.

Vining varieties require significantly more space and can take over a garden bed. To manage their growth and save space, many gardeners grow them vertically on sturdy trellises. This practice contains the plant and improves air circulation around the leaves, which helps reduce fungal diseases like powdery mildew. All squash plants require full sun to fuel this expansive growth.

Flowering and Pollination Stage

After the vegetative stage, the squash plant enters its reproductive phase, marked by bright yellow blossoms. Each plant produces separate male and female flowers, a condition known as monoecious. Distinguishing between these two flower types is necessary for a successful harvest, as only female flowers can develop into fruit.

Identifying the flowers is straightforward. Male flowers appear first, are more numerous, and are situated on long, slender stems with a pollen-covered stamen inside. Female flowers have shorter stems and are distinguished by a small, swollen ovary at their base, which looks like a miniature squash. Inside the female blossom is the stigma, the part of the flower that receives pollen.

For the ovary of a female flower to develop into a squash, pollen must be transferred from a male stamen to the female stigma. This process, known as pollination, is carried out by bees and other insects attracted to the flowers. Pollinators carry pollen on their bodies as they move from male to female blossoms, facilitating fertilization.

Hand-Pollinating for a Better Harvest

Sometimes, natural pollination is insufficient due to a lack of bee activity from weather or a low pollinator population. Gardeners may notice female flowers withering and falling off the vine without producing fruit. The process can be done by hand to ensure fruit set.

To hand-pollinate, identify open male and female flowers in the morning when they are most receptive. One method is to pick a male flower and peel away its petals to expose the pollen-laden stamen. Gently dab the pollen from the stamen directly onto the stigma in the center of a female flower. Alternatively, a small paintbrush or cotton swab can be used to collect pollen from the male stamen and transfer it to the female stigma.

Fruit Development Stage

Successful pollination initiates fruit development. Once a female flower is pollinated, its petals wilt and fall away, while the ovary at its base begins to swell. This confirms fertilization has occurred and a squash is forming. If pollination was unsuccessful, the small fruit will turn yellow, shrivel, and drop from the plant.

The growth rate of developing squash can be fast, particularly for summer varieties like zucchini. This rapid expansion places a high energy demand on the plant, requiring a consistent supply of water and nutrients. Inconsistent watering during this phase can lead to stress and issues like blossom-end rot.

Harvesting Stage

The final stage is the harvest, which requires different approaches for summer and winter varieties. The timing and techniques for picking are distinct for each type, designed to maximize either immediate flavor or long-term storage. Proper harvesting ensures you enjoy the fruit at its peak quality.

Harvesting Summer Squash

Summer squash, including zucchini, yellow squash, and patty pan varieties, are harvested when immature. At this stage, their skin is tender and glossy, and their seeds are small and soft. Pick most elongated varieties when they are about six to eight inches long. If left on the vine too long, they become large and watery with tough skin and seeds.

Frequent harvesting is important for summer squash, as picking the fruits regularly encourages the plant to produce more. Use a knife or pruning shears to cut the squash from the plant, leaving about an inch of stem attached. This clean cut is better for the plant than twisting or pulling, which can damage the vine.

Harvesting Winter Squash

Winter squash varieties like butternut, acorn, and spaghetti squash must be harvested when fully mature. This ensures they have developed the hard rind and high sugar content needed for long-term storage. Indicators of ripeness include a deep, uniform color and a rind firm enough to resist being punctured by a fingernail.

Another sign of maturity is a dry, withered stem connecting the fruit to the vine. When harvesting, leave one to two inches of this stem attached to the squash. This “handle” helps slow moisture loss and protect the fruit from rot during storage. After harvesting, many winter squash varieties benefit from curing by being kept in a warm, dry location for a week or two to harden the skin.