Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Often it is necessary to evaluate seedless watermelon fields to estimate potential yield or remaining yield. While simple in theory it is often difficult in practice, due to the fact that watermelon fruits are sometimes hidden under the foliage or vines. With that in mind, the following are guidelines on how to get a yield estimate from a watermelon field.
- Flag out plants in a row representing 1/200 of an acre. The table below gives the number plants to flag out (seedless only, no pollenizers).
| Between Row Spacing (ft) | In Row Spacing(ft) | Number of Plants to Sample |
| 6 | 2.5 | 15 |
| 6 | 3 | 12 |
| 6 | 3.5 | 10 |
| 6 | 4 | 9 |
| 6.5 | 2.5 | 13 |
| 6.5 | 3 | 11 |
| 6.5 | 3.5 | 10 |
| 6.5 | 4 | 8 |
| 7 | 2.5 | 12 |
| 7 | 3 | 10 |
| 7 | 3.5 | 9 |
| 7 | 4 | 8 |
| 7.5 | 2.5 | 12 |
| 7.5 | 3 | 10 |
| 7.5 | 3.5 | 8 |
| 7.5 | 4 | 7 |
| 8 | 2.5 | 11 |
| 8 | 3 | 9 |
| 8 | 3.5 | 8 |
| 8 | 4 | 7 |
- Count the number of harvestable watermelons from those plants. This requires that you trace watermelons to the plant. As an alternative you can count the number of watermelons found on the plastic bed and in one row middle next to the bed where the plants have been flagged out.
- Weigh 10 watermelons and get an average weight per watermelon.
- Multiply the average weight per watermelon x the number of watermelons plants flagged x 200 to get estimated yield per acre. Note: this is planted area and not field area – drive rows must be subtracted to get yield per whole field acre.
- Repeat this process at for each 4 acres planted (for a 40 acre field do 10 sample areas) and then average all weights to get the estimated yield. Include one edge row for each 3 to 4 middle rows sampled.