Farmer's Weekly (South Africa)
Get that spacing right!
When growing pumpkins, spacing is far more important than many farmers realise. Indeed, it is often claimed that a higher plant population produces a higher yield. But the opposite is often true.
When I produced vegetables commercially many years ago, 25t/ha was considered a good Boer pumpkin yield. An average weight of 6kg resulted in a yield of about 4 000 pumpkins/ha.
To achieve this, it was recommended that the seed be planted at a rate of between 2kg/ha and 3kg/ha. But this meant planting several seeds to get one pumpkin. This didn’t make sense, especially as each plant could bear more than one fruit.
I then started to experiment with planting density and soon discovered that the number of seeds planted was less important than the inter-row distance.
In cooler conditions and on shorter days, the fruit will set closer to the crown
Anyone who has grown pumpkins will have noticed that, at some stage, a second fruit on the vine starts turning yellow. This often occurs when there is a full canopy of leaves. At the time I was working on these pumpkins, it was speculated that the yellowing was due to bees being unable to find the flowers in the thick foliage.
However, I observed bees flying in under the canopy and found all the pollen stripped from the stamens on the male flowers. So this was not the cause.
Boer pumpkins produce female flowers some distance from the crown, and then produce more relatively close together. At least that’s what happened when I introduced wider interrow spacing. I also noticed that the second fruit on the vine would not develop when the rows were closer together.
Safety feature
It turns out this is a safety feature stored in the plants’ genes. When the vines grow on open ground with full sunlight (provided soil fertility, moisture and climate are also optimal), the plant continues to produce additional fruit.
Soon there is not enough leaf area to feed these fruit up to seed maturity. Thus, through natural selection, plants that set more fruit in an overcrowded environment do not have offspring and hence die out, forming the basis of this genetic safety mechanism. The problem nowadays is that each variety has a different spacing requirement for maximum yield.
Very compact growers will often only set one fruit near the crown. When this fruit develops, the plant lacks enough leaves to produce another fruit. In this case, rows can be spaced closer together.
With intermediate growth types it becomes more complicated, so it’s best to obtain guidance from the seed company. Doing your own trials is also advisable.
In cooler conditions and on shorter days, the fruit will also set closer to the crown. So you might also have to adjust the spacing according to the time of year.
• Bill Kerr is a vegetable specialist and a breeder of a range of vegetables. Email him at farmersweekly@caxton.co.za. Subject line: Vegetable production.