How to Grow Pumpkin

Botanical Name: Cucurbita sp.

Plant Type: Tender Annual

A few generations ago, the typical Australian diet consisted of meat and three vegetables, and one of those vegetables was the pumpkin. In the past when many Australians still lived on the land, the pumpkin was ubiquitous in the garden plot, being easily grown and highly productive. Once harvested, it was capable of being stored for many months without refrigeration, making it the perfect staple veg throughout the cooler months. It is these very characteristics that have made the pumpkin, and its cousins the squash and zucchini, important staples in the diet of many nations. Another closely related group known as gourds have been used by indigenous peoples as kitchen receptacles and as ornamental decorations.

Pumpkins need a long warm season, deep organic soils, and plenty of water while they grow. They also need lots of space for their spreading vines, although they can be trained up a trellis and grown vertically in gardens with limited space.

Varieties

Part of an enormous group of edibles, the Cucubitaceae, which includes zucchini, cucumber, squash, and melons, they all share the common characteristic of growing on a prostrate vine. However, if we are referring to Pumpkins, as we know them, there are three main species grown in our gardens: Cucurbita maxima, C. moschata and C. pepo.

Cucurbita maxima includes some of the largest pumpkins available, but they are mainly grown for their hard skin and excellent storage.  Popular Australian examples include ‘Queensland Blue’, ‘Ironbark’ and ‘Jarrahdale’.

Cucurbita moschata is a tropical pumpkin that grows in all climates and is the most tolerant of humidity. This group includes the ever-popular ‘Butternut’ and the Japanese ‘Futsu’.

Cucurbita pepo is a diverse group including the world’s largest pumpkin (‘Dill’s Atlantic Giant’) and some of the smallest, including ‘Kakai’ and ‘Jack Be Little’. This group also includes the decorative gourds and summer squash.

Knowing the species is really only important if you plan on saving seed, as you should only grow one of each species to avoid cross-pollination.

Cultivation

Pumpkins are a good place for a beginner to gain their experience in growing cucurbits, because they are less fussy about their environment than, say, watermelons or rock melons. While pumpkins can be grown in a flat bed, we suggest a mounded bed to improve drainage during the critical establishment phase. Sow three seeds per cluster to ensure adequate germination, to give each other support and as a backup for any losses.

To restrict their spread, pumpkins can be trained to a trellis. Simply allow the vine to develop and when it reaches at least 1m, tie to a trellis. As fruit develops, create a cradle using stockings to allow the stocking to support the fruit, rather than the vine.

Sun: Full Sun           

Pollination: Insect Pollinated

Soil: Pumpkins perform best in deep, moderately rich organic soil, preferably enriched with well-decomposed animal manure and compost. They tolerate a wide soil pH, from as low as 5.5, though the optimum is up around 6.8.

Growing from seed

Sow: Direct or in punnets

Ease of Germination: Easy

Germination Temperature: 15-32°C

Germination Time: 7-10 days

Spacing: 1m

Harvest: 100-130 days

Yield: 3-30kg+ per plant

Pumpkin seeds will germinate in soil temperatures as low as 15°C, but seed should be sown when temperatures are over 20°C and up to 32°C. Within this temperature range, seed will take up to two weeks to germinate at the lower temperatures and only a few days at the warmer end of the scale. The time of year when the soil temperatures are suitable for pumpkin seed germination will, of course, vary according to climate and, for the novice, the best approach is to monitor the temperature with a soil thermometer and talk to local gardeners. From our experience, if the soil is warm enough to transplant tomatoes, then it is probably adequate for sowing pumpkins. Above all, though, the seed cannot be sown if there is any risk of frost, even if soil temperatures are high enough.

Maintenance and Additional Care

Applications of a liquid seaweed/fish emulsion is ideal for pumpkins on a monthly cycle, with the addition of other trace elements such as potash and rock dust every 2-3 months.

Companion Planting

Good companions: Corn, Marjoram and Radish.

Bad companions: Potato.

Pests and Diseases

Pumpkins fall victim to several fungal infections. ‘Dampening Off’ while young, which is when the seeds are sown too deeply, they grow and then suddenly die from a band just above the soil surface. The most common fungal diseases when they mature is powdery mildew and downy mildew.

Downy mildew typically produces light-gold angular spots (which in the later stages are covered by a fine white powder that turns brown) on the leaves and purple spots on the undersides. Warm, humid weather, particularly extended periods of summer rain, favour outbreaks of downy mildew. Powdery mildew is readily identified by the presence of fuzzy white patches on top of the leaves, eventually spreading to kill whole leaves. Outbreaks are encouraged by warm days followed by nights of heavy dew. Rain generally inhibits outbreak of powdery mildew.

In our experience, these two diseases tend to be a problem only in the latter part of the season, and being largely environmental, are difficult to control.

Blossom end rot can also occur and, like tomatoes, is caused by calcium deficiencies in the soil, waterlogging of the soil, or irregular watering.

Pumpkins are generally not attractive to most pests, that is until your fruit sets and then you need to watch out for rats.

Container Gardening

While pumpkins are long trailing plants, they can be grown in pots if the roots are given enough space and you have room for their long vine. A larger pot will hold the trellis if you wish to grow pumpkins in a small space.

Always use a premium potting mix for vegetables and water regularly.

Harvesting

Harvesting of the fruit can occur at any stage with baby squash being particularly sweet and a delicacy that should be experienced by all gardeners. If large pumpkins are desired, then the correct strategy is to let a minimum number of fruits set and remove all other newly formed fruit as they develop, so as to direct all of the plant’s resources into the growth of the older fruit. This is, in fact, the approach used by gardeners to produce those gigantic-sized pumpkins we sometimes see in the media.

While you may not grow a world beater, you will obtain larger pumpkins by removing the excess fruit, plus the benefits of baby squash on the dining room table early in the season. Mature pumpkins can generally be identified by the stem turning particularly woody and brittle. Various varieties undergo colour changes as they approach maturity so that, for example, grey or blue pumpkins go through yellow and orange before taking on their final colour.

When harvesting fruit, it is advisable to use a pair of secateurs rather than breaking the stems. Should the stem slip from the fruit, then the resulting wound provides access for bacteria and fungi to the flesh of the fruit, which greatly reduces its storage life.

For pumpkins intended for storage, the best method of harvesting is to cut the stem 3 cm to 5 cm from the fruit. It is most important in selecting fruit for storage that there are no splits, fissures or holes produced by rodent attack, because these blemishes are the source of future infections that will cause the pumpkin to deteriorate prematurely.

Seed saving

Seed longevity: 4-6 years

Isolation Distance: 400m

How to Save Seed: Pumpkins seeds are large and readily saved. Harvest pumpkins when mature, as you would to eat the flesh. Wait at least 4 weeks for the seed to fully ripen and remove from the pumpkin. The flesh can be cooked, while the seed should be rinsed and washed to remove the pulp. Viable seed will sink, and this should then be placed on paper towel to dry before being stored in an envelope before being placed in a dark, dark environment. 

Tips and Tricks for Success

• in cooler areas with short seasons, one approach is to sow the seed indoors in punnets and grow the seedlings until the risk of frost has passed. With this approach the seedlings can be transplanted with a head start and take full benefit of a limited growing season. It is important to note that pumpkin seedlings can be a little touchy and will suffer shock if carelessly handled, so some care has to be taken with this approach. It is our recommendation that, in general, pumpkin seeds should be direct sown if possible.
• always to sow more than is required in case of losses. It is far easier to thin out plants than to sow some extra seed and put up with a later harvest. This is particularly important in cooler climates.