Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
There are a number of pollinizer systems that have been successful for seedless watermelons. The original research with seedless production showed that for standard size seedless watermelons a 1:3 ratio of pollenizers to seedless maximized yields and field space. A 1:2 ratio did not increase yield. A 1:4 ratio gave similar results often to a 1:3 ratio. However, if there were any pollinizer losses, the reduction in pollen production had a much greater yield effect. For example a 20% pollinizer loss in a 1:3 ratio results in a final ratio of about 1:3.8; in contrast, a 20% pollinizer loss in a 1:4 ratio results in a final ratio of 1:5 which can be pollen limiting.
Pollenizers can be planted in several configurations (Figure 1):
- In separate rows in between seedless rows
- Every fourth plant in the seedless row at even spacings
- Evenly spaced seedless plants with the pollinizer placed between every third and fourth seedless plant.
Research has shown that this third in-row pollinizer planting method has the highest yield potential per area planted.
Figure 1. Pollenizer configurations for seedless watermelon plantings. S represents seedless plant placement in the row and P represents pollenizer plants.
One issue with in-row pollenizer planting is the need to have a separate pollinizer planting operation at the same time the seedless is being planted. This has led to problems with mixing up pollenizers and seedless plants by planting crews. One way that this can be avoided is by spraying a white particle film clay product on the pollenizers to “color code” them so that crews can tell them apart from the seedless. Research at UD has shown that this coating has no effect on pollinizer performance as new leaves that are produced are normal green in color.
Another way that this issue has been addressed is by a unique program being offered by one seed company. In this program, the trays come preplanted with every third plant double planted with a seedless and a pollinizer plant. The planting crew then pulls plants in order from the tray and the correct ratio (1:3) of pollinizer to seedless is planted without needing a separate planting operation. This eliminates the need for separate planting trays of pollenizers to keep track of and also reduces by ¼ the amount of trays to be carried in the field.
With seedless spacing, research has shown that with standard seedless types (36-60 count seedless), a 3 foot spacing between plants give the best yield and economy (plants used). Closer spacing did not improve yield while wider spacing (4 ft. between plants or greater) reduced yield.