Squash

Start from seed: September-December

Optimum soil temperature for germination: 21-32°C

Plant seedlings: October-January

Plant spacing: 50-100 cm

Days to maturity: 50-110 days

Introduction

Squash (Cucurbita spp.) belongs to the Cucurbitaceae family along with pumpkins, zucchini, melons, and cucumbers. The term “squash” encompasses a diverse range of varieties, with two main categories: summer squash e.g. zucchini, pattypan squash, tromboncino that are harvested while immature with tender skin; and winter squash e.g. butternut, crookneck, Hubbard that are harvested when fully mature with hard rinds for storage.

It is useful to know which varieties belong to each species because varieties of the same species will cross pollinate.

Cucubita pepo incudes zucchini, pattypan squash, acorn squash, Delicata and spaghetti squash

Cucurbita moschata incudes butternut and crookneck squash

Cucurbita maxima includes larger pumpkins such as Hubbard, Jarrahdale, Ironbark

Squash originated in the Americas, with evidence of cultivation dating back over 8,000 years in Mexico and Central America. Indigenous peoples grew various squash species for their nutritional value, versatility, and storage capabilities. Today, squash is grown worldwide and prized for its culinary versatility and nutritional benefits.

Squash plants possess large, lobed leaves with both male and female flowers on the same plant. The male flowers appear first, followed by female flowers that have a small, round, swollen ovary at their base. Summer squash varieties like zucchini and patty pan have a bushy growth habit, while many winter squash varieties produce sprawling vines.

Site and soil

Squash thrives in full sun, requiring at least 6 hours of direct sunlight daily for optimal growth and fruit development. In Canberra’s climate, choose a sheltered position protected from strong winds and frost.

Squash prefers rich, well-drained soil with high organic matter content. Before planting, prepare the soil by incorporating plenty of compost and aged manure. Form small mounds or hills about 15-20 cm high and 50-100 cm apart to improve drainage and help the soil warm more quickly in spring.

The ideal soil pH for squash is between 6.0 and 6.8. If your soil is too acidic (below pH 6.0), add lime or dolomite to raise the pH. If it’s too alkaline (above pH 7.0), sulfur can be added to lower it.

If growing in containers, choose large pots at least 40-50 cm wide and deep with good drainage. Use a high-quality potting mix enriched with compost. Note that bush varieties of summer squash are better suited to container growing than vining winter squash types.

For details on preparing the soil and pots, including the use of lime, dolomite, gypsum and fertilisers please refer to the COGS guide to garden bed preparation.

Planting Seeds and Seedlings

In Canberra, squash should be sown after the danger of frost has passed and soil temperatures have warmed to at least 21°C. This is typically from early October to December. The optimum soil temperature for germination is between 21-35°C.

For direct sowing, create small mounds spaced 50-100 cm apart (depending on the variety) and plant 3-4 seeds per mound at a depth of approximately 2-3 cm. Water gently but thoroughly after planting. Once seedlings emerge and develop their first true leaves, thin to the strongest 1-2 plants per mound.

To get a head start on the growing season, seeds can be started indoors in individual pots, not cell trays, 3-4 weeks before the last expected frost. If available, biodegradable pots minimize root disturbance during transplanting, as squash seedlings don’t like their roots being disturbed. Otherwise, regular pots can be used successfully. Plant seedlings outdoors once all danger of frost has passed and seedlings have 2-3 true leaves.

For those purchasing seedlings, look for healthy plants with strong stems and no signs of disease or pest damage. Plant at the same level as they were growing in their containers, being careful not to disturb the roots.

After planting, water thoroughly with a seaweed solution to reduce transplant shock and stimulate root development. Apply a layer of organic mulch such as straw or sugar cane mulch around plants (but not touching the stems) to conserve moisture, suppress weeds, and keep developing fruits clean.

Cultivation

Squash plants need consistent watering, especially during flowering and fruit development. Water at the base of plants rather than overhead to reduce the risk of fungal diseases. In Canberra’s hot summer weather, frequent watering may be necessary.

If not used at planting time, apply a balanced organic fertilizer when plants begin to flower and set fruit. Foliar applications of seaweed extract or a combination of seaweed, compost tea and worm juice every 2-3 weeks can help provide trace elements and strengthen plants against pests and diseases.

For winter squash, consider providing a trellis or support structure for the vines if space is limited. However, if growing squash on a trellis, the developing fruits may need support with slings made from old stockings or fabric. 

Summer squash plants generally have a bushier habit but can still spread 60-90 cm. Winter squash vines can spread 1.5-3 meters or more, so plan accordingly.

Hand pollination may be necessary if there are insufficient pollinators or during periods of extreme heat or rain that limit bee activity. To hand pollinate, transfer pollen from a male flower (with a straight stem) to a female flower (with a small, round swelling at its base) using a small paintbrush or by removing the male flower and touching its centre to the centre of the female flower.

Harvesting

Summer squash varieties like zucchini, patty pan and crookneck, should be harvested when young and tender, usually when they’re 10-15 cm in size. Harvest frequently, every second day, to encourage continued production. Summer squash is typically ready to harvest 50-60 days from planting.

Winter squash varieties like butternut, Hubbard, Ironbark, and spaghetti squash should be left on the vine until the rind is hard and cannot be pierced with a fingernail. The stem should be dry and corky, and the fruit should have reached full size and colour for its variety. This is usually 70-120 days after planting, depending on the variety. Some like to wait until after the first frost to harvest winter squash, however, this is not necessary. The main sign is that the leaves have died off and stopped pumping photosynthate into the fruit, at which point the stem will be hard and corky.

For both types, use a sharp knife or pruning shears to cut the fruit from the vine, leaving a short stem attached. 

Handle winter squash carefully to avoid bruising, which can lead to decay during storage. Never pull or twist fruits off as this can damage the fruit leaving a passage for fungi to enter and rot the fruit from the inside. Make sure fruit are clean and dry prior after harvest, Curing involves storing them in a warm place for a few weeks during which time some of the starches are broken down into sugars sweetening the fruit and the skin hardens. Thereafter they can be stored in a cool, dark place.

Summer squash should be used within a week of harvesting. Properly cured winter squash can be stored for several months in a cool (10-15°C), dry place with good air circulation.

Problems

There are numerous pests and diseases that can affect squash. The best approach is to have a reliable Australian reference book to identify problems. Garden Pests, Disease and Good Bugs by Denis Crawford is recommended.

A general strategy to follow with any problem is to observe the plant carefully before taking action. Identify the problem then carefully consider the course of action. For example, with pest insects, you often can see a predator nearby. If you watch and wait the predator may deal with the problem for you. Beneficial predatory insects which feed on pest insects can be purchased from suppliers such as Bugs for Bugs. If the problem needs further action the above recommended book has suggestions. 

Practicing good garden hygiene, crop rotation, and maintaining plant vigour by providing adequate nutrients are key strategies for prevention.

Several pests and diseases can affect squash in Canberra’s climate:

Wilting leaves during the day. It is common for the leaves to wilt during the day. As long as they perk up again in the evening it is not a problem. If not, you need to give them more water.

Powdery mildew is one of the most common diseases affecting squash, appearing as a white powdery coating on leaves. It thrives in warm, dry conditions and spreads rapidly. To prevent it, ensure good air circulation around plants by proper spacing. A spray made of 1 tablespoon baking soda mixed with 2 teaspoons of horticultural oil in 4 liters of water can help control mild infections. Alternatively, a milk spray (1 part milk to 9 parts water) or seaweed solution applied weekly can be effective.

Downy mildew appears as yellow spots on leaf surfaces with grey fuzzy growth underneath. Unlike powdery mildew, it favours cool, humid conditions. Improve air circulation and avoid overhead watering to help prevent it.

Aphids These small sap-sucking insects can transmit celery mosaic virus. They often cluster on the undersides of leaves, causing distortion and stunting. Small populations can be controlled by washing them off with a strong stream of water or using insecticidal soap. Alternatively, neem oil or pyrethrin can be used. Beneficial predators like ladybugs and lacewings should be encouraged and can be purchased for release on the crop. Look for aphid mummies which are evidence that the aphid has been parasitised. Eggs can also be parasitised and will appear bronze in colour. Generally speaking, plants that are high in soluble nitrogen (nitrates and ammonia) are prone to attack by sap sucking insects. Ideally avoid using soluble nitrogen fertilisers and ensure plants have adequate trace elements. This can be achieved by using foliar sprays.

Cucumber beetles are small yellow and black striped or spotted beetles that can damage leaves and spread bacterial wilt. Row covers can protect young plants until they start flowering.

Fruit rot can occur when fruits are in contact with damp soil. Use mulch or place a tile or board under developing fruits to keep them dry.

Not enough fruit. Apparently hot weather favours the production of male flowers at the expense of female flowers whereas cooler weather favours female flowers. Therefore in hot weather, if there are less female flowers there will be less fruit. It is quite normal for one vine to only produce 2-3 fruits especially if they are large.

To reduce pest and disease problems, practice crop rotation by not growing squash or related crops (cucumbers, melons, pumpkins) in the same location for at least 2-3 years. Remove and dispose of any diseased plant material at the end of the season, and maintain good garden hygiene.

Recommended Varieties

Winter and summer squash varieties perform well in Canberra’s climate. For zucchini and summer squash suggestions see the Guide for Growing Zucchini.

There are many varieties of winter squash to choose from. Some suggestions are: Waltham butternut, Australian Butter, Triamble, Ironbark, Potimaron, Futsu, Jap, Jarrahdale and Spaghetti squash (features pale yellow, oblong fruits with stringy flesh that resembles spaghetti when cooked. Excellent storage life).

Look for varieties with powdery mildew resistance (sometimes labelled as “PMR”) for best results in Canberra’s conditions. Local nurseries, farmers markets, and local seed suppliers can provide varieties that are well-adapted to the region.

References

1. Bubel, Nancy. The New Seed-Starters Handbook. Rodale Books, 2018.
2. Crawford D. Garden Pests, Disease and Good Bugs. Australia: ABC Books; 2015.
3. Dove, Helena. Botany of the Kitchen Garden, Kew Publishing, Royal Botanic Gardens Kew, UK, 2023. 
4. Fanton, Michel and Jude. The Seed Savers Handbook. The Seed Savers Network, Australia, 1993.
5. Gardenate. Growing Squash (Crookneck, Pattypan, Summer squash) in Australia – temperate climate [Internet]. 2024 [cited 2025 May 6]. Available from: https://www.gardenate.com/plant/Squash
6. The Seed Collection. How to Grow Summer Squash Seeds [Internet]. 2024 [cited 2025 May 6]. Available from: https://www.theseedcollection.com.au/growguide/summer-squash-seeds
7. Yates Australia. How to Grow Squash [Internet]. 2024 [cited 2025 May 6]. Available from: https://www.yates.com.au/how-to-grow/squash/