Varieties
Japanese pumpkins are slightly smaller and flatter than Jarrahdale, with a drier, sweeter flesh and a mottled yellow and green skin that is easier to peel. They do not store as well as Jarrahdale pumpkin and have slightly lower yields. Average fruit weight is 3 to 4kg.
Butternuts have smooth, beige skin. They are sweeter than Jarrahdale with a nutty flavour and are easier to peel. Fruit size varies from 0.5 to 2kg.
Jarrahdale has a tough, green-grey skin and has a diameter of about 25 to 30cm. Fruits average 4 to 8kg, with 5 to 6kg preferred at the markets.
Golden nugget, sweet dumpling and minikin are small-fruited (6 to 12cm diameter) bush types that set their fruit around the central stem. They have good flavour, but a short storage life and moderate yields.
Sowing
Seeds need a minimum soil temperature of 16oC to germinate after 7 to 12 days. The best air temperature for germination is 21 to 35oC.
A total of 1.5 to 3.0kg of fresh seed will be needed per hectare. Two to three seeds may be planted 2 to 4cm deep at each site for open-pollinated varieties, and one to two seeds per site for hybrid varieties. If there is sufficient labour, seedlings are thinned to one per site after germination. A precision seeder may be used to obtain the correct seed spacing.
In the south-west, plant from October to December. Many growers use a cup-type planter to sow seed with a band of fertiliser.
In Perth, pumpkins may also be transplanted in cell-packs from mid-August so that plants are ready for harvest before Christmas. Normal plantings are direct-sown from late August to early January.
In Carnarvon, sowing is from mid-January to early September. In Kununurra, seeds are sown from late March to August.
Large-fruited pumpkins are planted in rows 1.8 to 3.0m apart, with 1.0 to 3.0m between plants within the rows. Butternuts are planted at 1.5 to 2.5m between rows, with small-fruited pumpkins planted at 1.5m between rows. Both butternuts and small-fruited pumpkins are planted at 0.6 to 1.0m within the rows.
Fertilising
Pumpkins do not require much fertiliser as the roots are efficient in absorbing available soil nutrients.
On loam and heavy soils, apply a nitrogen, phosphorus, potassium (NPK) based fertiliser to supply 35kg/ha (banded) to 84kg/ha (broadcast) phosphorus. Apply one or two dressings of 46 to 57.5kg/ha nitrogen and 50kg/ha potassium at three and six weeks after planting.
In Carnarvon, apply sufficient phosphorus-based fertiliser to supply 21kg/ha phosphorus before planting and two dressings of nitrogen-based fertiliser to supply 32kg/ha nitrogen at three and six weeks after planting.
On the sandy soils of the Swan Coastal Plain, apply phosphorus-based fertiliser to supply up to 87kg/ha phosphorus before planting. Apply nitrogen and potassium weekly from a week after planting to two weeks before harvest, building to a peak at early fruit setting stage and declining towards harvest. Apply to a maximum total of 299kg/ha nitrogen and 300kg/ha of potassium per crop. Also, apply 5kg/ha magnesium five weeks after planting.
Trace elements are generally not needed if they have been applied in the last two years. Heavy soils need only copper, zinc and molybdenum. Trace elements are usually not needed in the Carnarvon region. On the Swan Coastal Plain, apply a general trace element mix to vegetables every 12 months. This would include manganese sulphate (25kg/ha), copper sulphate, ferrous sulphate, zinc sulphate and borax (each applied at 18kg/ha) and sodium molybdate (2kg/ha).
Sodium molybdate at 1kg/L may be needed as a foliar spray three weeks after planting, especially on acidic soils. Plants with molybdenum deficiency are stunted with pale leaves, and scorching on the margins of the leaves.
Most fertiliser can be applied through the irrigation system if required. If irrigation water contains some nitrogen and potassium, reduce fertiliser rates.
Soil analysis before planting can give information on the nutrient status of the soil. Leaf analysis of the youngest mature leaf a few weeks after planting will provide a guide to whether the fertiliser program needs to be modified.
Irrigation
Pumpkins have a deep root system but need large amounts of water when they are growing vigorously. Irrigation is needed on all soils when rainfall is insufficient. Water stress will substantially reduce fruit set and yield.
A full canopy crop will need to be irrigated to 100% of evaporation replacement on sandy soils. Water can be applied by sprinkler, drip system or furrow. Furrow irrigation is the main system in Kununurra. Trickle irrigation requires the least water, especially when combined with polythene mulch.
Tensiometers can be used to measure soil moisture levels and provide a guide on when to water.
Pumpkins have medium tolerance to saline water. Yields decrease as the electrical conductivity (salinity) increases above 130mS/m.
Allow the soils to dry out as the vines mature to allow the fruit to ripen with less risk of rots.