When planning your planting calendar, think about pumpkins. They are always a good option with consistent market demand and a long storage life depending on the variety you choose.
Like fellow members of the cucurbit family, these plants are sensitive to temperature with germination minima at between 12°C and 16°C. At 25°C seed takes only two days to germinate while at 12°C it takes about 12 days.
Root system development takes place between 16°C and 20°C and vegetative growth occurs between 16°C to 18°C and 25°C to 30°C.
Flower formation is affected by very high temperatures and long days. At 35°C the number of male flowers on the vine can be very high and the number of female flowers can be very low. Vegetative growth will be strong.
When days are short and temperatures are down to less than 18°C the number of male flowers can be low and female flowers high. Growth can be slow with small leaves and short internodes.
Sandy loam to loam soils with good drainage are suitable for this crop which can tolerate some degree of soil acidity. However at a pH of below 5.5 apply agricultural lime at the recommended rate. Fertiliser must be applied according to soil test results but if these are not available apply a fertiliser like 2:3:4 at 100g/m2 (1 000kg/ha), as a 40cm wide band worked lightly into the soil before planting.
Top dress three weeks after plant emergence with 120 – 150kg/ha of LAN applied 10cm from the stem of the plant and water it in well. Compost at 4 hand scoops per m2 to supplement the fertiliser and reapply a top dressing five weeks later, again watering it in well.
A stand of pumpkins should be between 2 500 to 3 500 plants per hectare at a planting distance of 1m in the row and 3m to 5m between rows. The ideal planting depth is 3cm to 5cm. Some growers plant with rows 2.5 m apart and plants 0.5 – 0.6m apart.
Pumpkins like a deep, fine seed bed with loosened soil. Incorporate compost or fertiliser thoroughly into the soil 4 – 6 weeks before planting. At planting cover the seed with dry soil. The seed should not be covered with wet soil which may form a crust, so cover it with dry soil. Add compost around the young plants after germination.
The crop needs a lot of water in the growing period but do not over-irrigate. Check the soil moisture regularly during plant growth and make sure the plants are not subjected to water stress.
Irrigate early in the day, rather than late, to stave off a common fungus of pumpkins called powdery mildew which can eventually kill the plant. Never apply water directly to the leaves.
Once the fruit starts to go orange, reduce the water. A week to 10 days before harvest stop irrigation altogether to get longer storage out of the pumpkin. It is important to not get water on the leaves, and water in the morning instead of late in the evening, to help stave off fungal diseases.
When your pumpkin fruit starts to turn orange, gradually decrease the amount of water. Your pumpkins will store longer if you cut off water 7 – 10 days before you harvest.
Weeds are unwelcome competition and the cultivated area should be regularly weeded. Rotate with any of the leafy crops of with legumes to keep diseases down.
Separate male and female flowers occur on the one vine but only female flowers produce fruit. For pollination to take place there must be male and female flowers and bees to move pollen from the male to the female flowers.
Male flowers appear lower down on the plant nodes while the female, developing later, will be on the upper nodes. Female flowers have a distinct bulge just below the bloom, which is the ovary- later to develop into the fruit.
A ratio of 1 female to 7-10 male flowers is considered adequate.
The female flowers open for one day only, early in the day and close by mid afternoon. They are receptive to pollination early in the morning when the bees are at their most active. For good pollination the flowers need a minimum of 12 bee visits. Introduce bee hives if there are not enough bees and keep irrigation and spraying to time when bees are not active. (late afternoons and wet or windy weather).
References: Agricultural Research Council; Production Guidelines for Summer Vegetables.