Zucchini & Summer Squash


Summer squash, which includes zucchini, pattypan squash, crookneck squash and more, are among the most prolific growers in a garden.  They tend to grow quickly and can give you several fruits per plant.  The plants themselves can get large and may need to be managed closely to prevent them from vining in an undesired direction, but a well-maintained plant will be among the most productive in your garden.  


Summer squash plants are a hot crop, so only plant them once all risk of frost has passed and the nighttime temperatures are safely above 12oC – usually three weeks after the last frost date in your region.  They can be direct-seeded into your garden or started indoors and transplanted once it’s warm enough.  When starting them indoors, start them no earlier than three weeks before the last frost date, or they may get too large for a seedling pot.  Transplant them carefully as it’s important not to disturb the roots.  As a result, it’s often easiest to direct-seed them into your garden since they grow quickly.    

Summer squash is a full sun plant, so select the sunniest and hottest place in your garden and give them plenty of space to vine out.  As squash is a heavy-feeding crop, add plenty of compost to the soil before planting.  Be sure to cultivate the ground, as squash plants like well-draining soil.  Plant the seeds approximately ¾” deep and spaced 18-24” apart.  


Summer squash plants are heavy-feeders that need consistent watering, particularly when fruiting, and occasional fertilizer top-ups.  Focus initial fertilization on nitrogen and phosphorus and later fertilization on phosphorus, potassium, calcium, and magnesium.  Provide additional water on really hot days when the plant’s leaves droop.  Unless the plant is actively fruiting, decrease watering levels once you start to see morning dew (usually late July onward) as the plants will be susceptible to powdery mildew at that time. 

Top-dress the squash plants with compost at least once midway through their growth cycle.  This provides a new flush of nutrients to these heavy-feeders as they continue to grow.  In addition, add calcium and magnesium to help prevent blossom-end rot, firm up the fruits, and encourage new growth.     

Summer squash plants need insect pollinators to produce fruit.  Plant some native wildflowers near the squash plants to attract pollinators.  If no pollinators exist, use a cotton swab or a small paintbrush to gently dab all flowers every 2-3 days to ensure adequate pollination – otherwise, the small, unpollinated squash fruits will shrivel up.

Pests and Diseases

All squash plants are susceptible to pests at all stages of their lives.

In the early stages, they are susceptible to cucumber beetles, squash bugs, and aphids.  These sap-suckers can weaken plants and occasionally act as vectors for a mosaic virus.  

In mid-summer (typically mid-June through mid-July), squash vine borers are a common pest.  These moths lay their eggs at the base of squash plants.  When the eggs hatch, the larvae crawl into the squash vines to eat and can often kill the plants.  Use a fine-mesh row cover or insecticidal soap such as diluted castile soap to prevent most pests.  If you don’t use row cover, you can still protect the plants from vine borers by wrapping the bottom 6” of the vine (plus 2” beneath the soil) with tin foil to prevent any vine borer eggs. 

In their late stages, squash plants have broad leaves that are susceptible to powdery mildew.  Always irrigate the soil and never spray the leaves.  If the plants get powdery mildew due to rainfall or morning humidity, spray the leaves with a baking soda solution to delay the spread. 


Closely monitor the fruits of summer squash as they mature.  Zucchini can grow quickly and become too large within a few days.  Size is key when determining when to harvest – the larger the size, the more diluted the flavour.  The ideal size becomes a matter of preference.  For zucchini, the ideal size is usually 8” in length.  Also, aim to leave a small amount of the stem on all squashes when harvesting them.  Harvesting often will encourage the growth of additional fruits.  

Harvested summer squash should be stored in a cool area (or in a refrigerator – away from the coldest areas at the back) for up to 2 weeks.

© Homestead Toronto / Derek Barber