Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
The population research with once-over harvest of pickling cucumbers done in Delaware and other states with gynoecious hybrids has shown that between 55,000 and 65,000 plants per acre optimizes yield and quality with the least seed cost under good growing conditions (good irrigation, optimal nitrogen) in 28-30 inch rows with most varieties.
In studies with in-row and between row spacing of pickles, 15 inch rows with 4 inches between plants showed the highest yields and grade-outs. However, this narrow row planting has to be balanced against the costs of setting up planters with extra rows, narrow row cultivators (and narrow tired tractors), sidedressing equipment, and extra seed cost.
I was recently asked about the potential to switch from 30 inch rows to 20 inch rows. The high target should be 3 plants per foot (78,000 seeds per acre, 4 inch spacing) looking at the few studies done with this row spacing. Some work in Michigan showed that there was no difference in yields at narrow row spacing between 4 and 5 inch spacing between plants.
My research in 2010 showed that for most varieties (22 varieties tested), there will be 2-3 harvestable fruits per plant. Higher densities produced closer to 2, lower densities closer to 3 for the once over harvest.
The exception is with parthenocarpic types. These are types that set fruit without the need for pollination. They can produce up to 6 harvestable pickles per plant (most commonly 4-5) for once-over harvest. Small plot work with experimental parthenocarpic cultivars has shown similar or higher yields than standard types at 40% of the population in 30 inch rows (27,000 plants per acre). New releases of parthenocarpic pickle varieties adapted to Delmarva conditions will be available in the near future with high yields and acceptable length to diameter ratios. These should be considered for trial plantings. In a 20 inch system, planting parthenocarpic types at 8 inches between plants (40,000 seeds per acre) may have potential for even greater yields.