Pumpkins & Winter Squash


Pumpkins and winter squash can be great plants to grow in your garden as they can be incredibly productive, you can store the harvest for months, and the plants themselves tend to hold up well against most pests and weeds, with some exceptions.


Squash plants are distinctly hot crops.  They should only be planted outdoors once the soil temperature has warmed and once the nighttime lows are safely above 12oC – this is usually three weeks after the last frost date.  While you can start squash indoors three weeks before the last frost date, you must be VERY careful not to disturb the roots when you transplant them outdoors.  As such, it’s usually easiest to direct-seed them into your garden since they grow quickly.    

Squash is a full sun plant, so select the sunniest and hottest place in your garden and give them lots of space to vine out.  As squash is a heavy-feeding crop, add plenty of compost to the soil before planting.  The seeds should be planted approximately ¾” deep and spaced 18-24” apart for smaller varieties such as acorn or delicata and 36” apart for larger varieties such as pumpkins.  


Squash plants are heavy-feeders that will need consistent watering at first and occasional fertilizer top-ups.  The initial fertilizers should focus on nitrogen and phosphorus, while the later fertilizers should have lots of phosphorus, potassium, calcium and magnesium.  Provide additional water on really hot days when the plant’s leaves droop.  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.     

Squash plants also need insect pollinators to produce fruit.  Place 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

Squash plants are most susceptible to pests in their early and late stages.  They are generally hardy in their middle stage of life and can withstand most infestations.

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.  Squash vine borers are also a common pest in early summer.  These moths lay their eggs at the base of squash plants.  When the eggs hatch, the larvae crawl into the squash vines and often kill the plants.  Use a fine-mesh row cover to prevent pests and insecticidal soap to remove pests from the squash plants.  If you don’t use a 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.  In addition, if the plants get powdery mildew because of rainfall or morning humidity, spray the leaves with a baking soda solution to delay the spread. 


The key to harvesting winter squash is to let them ripen.  The squash will become sweeter, and the flavours will enhance as it ripens.  There are three successive tests to determine when squash is fully ripe:

Once harvested, winter squash should be cured in a dry, sunny spot for 1-2 weeks and then stored in a cool, dark location after that.  Wipe winter squash with a diluted bleach solution to prevent mold from forming on the skins.

© Homestead Toronto / Derek Barber