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Growing oilseed pumpkins

Organic Agriculture Centre of Canada

Oilseed pumpkins (Cucurbita pepo pepo Styriaca) have hulless seeds containing 40-50% oil. The crop can produce 0.5-1.4 tonnes/hectare of seeds, which are high in essential fatty acids and Vitamin E. They can be used whole or processed into oil, which contains higher levels of antioxidants than extra virgin olive oil, or oil from walnuts, hemp or sunflowers.

Researchers for the Organic Science Cluster of the Organic Agriculture Centre of Canada are studying the organic cultivation of oilseed pumpkins -- the best varieties, weed management and fertility requirements.

Varieties
Styrian pumpkins are large plants with vines 2.5-3 m long. The fruit weigh an average of 6 kg. The flesh is coarse and stringy, suitable for animal feed. Seed breeders have developed bush varieties with smaller fruit, earlier maturation and more uniform ripening times.

Soil conditions
Pumpkins are heavy feeders. In a crop rotation, they are best grown after a green manure or an application of compost. In general, it is thought seed production is enhanced by high levels of phosphorus and boron, but reduced by high levels of nitrogen.

Planting
Growers should wait until the soil is warm (e.g., above 15°C) and the threat of frost has passed before planting. The naked seeds are vulnerable to rotting in cool soil due to the lack of a hull on the seeds. Packing after planting will improve germination rates. However, transplanted seedlings grow faster, and produce larger fruit and more seeds than direct-seeded plants.

A spacing of 1-1.5 plants/m2 is ideal. Plants can be 1.5-2 m apart in a row with the widest possible spacing between rows. When plants are too dense, the number of fruit per plant is reduced.

To reduce wind damage to the large-leafed plants, growers can provide wind breaks or plant in sheltered locations. Floating row covers can provide additional warmth and protect seedlings from pests. The covers should be removed before flowering.

Weed control
Focus on early weed control. With the stale seedbed approach, the soil is prepared as soon as it can be worked. The ground is cultivated once weeds appear but before they become established. This process can be repeated, with more shallow cultivation, until planting time.

Another method is to sow a cover crop (e.g., a cereal with a legume) in the fall or spring before planting. Incorporate the cover crop at least a month before, or flail just before, planting pumpkins. Another option is to transplant seedlings into black plastic mulch.

Once the crop is established but before the vines run, the crop can be cultivated, and a straw mulch applied or living mulch planted.

Care during growing season
Pollination by insects is required for seed production. The more visits by pollinators (up to 16 visits), the greater the fruit set, fruit size and weight, and number of seeds. To increase pollination rates, growers can bring in 5+ hives/ha of bumblebees. Bumblebees are preferred over honeybees because they remain active in cool and damp weather.

Pumpkins and related cucurbits should not be planted in the same location more than once every 4-5 years. Crop rotation and providing habitat for beneficial organisms helps prevent many pest and disease problems. However, to avoid the zucchini yellow mosaic virus, it is critical to have clean seed and reduce infestations of pests (e.g., aphids and striped cucumber beetles which spread the virus). Aphids and striped cucumber beetles are deterred by floating row covers, neem oil and reflective mulches (e.g. aluminum-coated or silver plastic). The beetles can also be controlled by Surround, a kaolin clay product, floating row covers, vacuuming and using other cucurbits as trap crops.

To reduce problems with powdery mildew and other fungal diseases, provide adequate air circulation, avoid overwatering, spray milk on plants and/or treat plants with Serenade (Bacillus subtilis).

Harvesting
Harvest the pumpkins when the leaves are yellow and the fruit has turned orange, or before a hard frost. Remove seeds at harvest or after the pumpkins have matured during storage. Fully mature fruit have seeds with greater oil content than those from immature fruit.

The crops can be stored for several months at 10-13°C at a relative humidity of 50-70%. Dry the seeds until their moisture content drops to 8-10%.


This article was written by Janet Wallace on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the Organic Federation of Canada and industry partners. For more information: oacc@dal.ca or 902-893-7256.


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Posted October 2011

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