Volume 11 Issue 4
Effect of Planting Density on Growth and Yield of ‘Sweet Sunrise’ Strawberry– 2022
By Brenda Madrid (Graduate Research Assistant) and Lisa DeVetter (Associate Professor)
Objective
The focus of this study was to identify if June-bearing strawberry, ‘Sweet Sunrise’, could be:
- Grown in a mulched system using polyethylene (PE) mulch for improved weed management and promotion of crop growth.
- If plant density could be increased to promote yield per unit area.
Methods
The study was conducted at Washington State University’s Northwestern Washington Research & Extension Center (NWREC) in Mount Vernon, WA. Bareroot ‘Sweet Sunrise’ strawberry plants were established on 8-inch-high raised beds in staggered double rows using PE mulch in May 2020. Treatments followed within-row spacing at two planting densities: a) standard plant spacing of 12 inches apart within a row and rows spaced 10 inches apart and (“Standard”), b) an increased planting density of 6 inches apart within a row and rows spaced 10 inches apart (“Modified”). The experimental design was a randomized complete block with four replications per treatment.
To evaluate the impact of the treatments on growth and yield, the crown diameter of 10 plants within the middle of each plot were measured using a digital caliper in August 2020 and 2021. Strawberry plant harvest was conducted on June 6, June 14, and June 21, 2021. Total fruit weight was measured per plot after each harvest. After harvest, 5 representative, marketable fruits per plot were selected for fruit quality analysis including ˚Brix, pH, and titratable acidity (TA). At the end of the harvest season strawberry plants were harvested for biomass determination. Three plants per plot were collected and separated by crown, roots, leaves and petioles. Samples were dried in an oven at a temperature of 65 C˚ (149˚ F) for 3 days and weighted thereafter to obtain plant biomass.
Results:
Table 1: Average crown diameter of ‘Sweet Sunrise’ strawberry. Ten plants were measured within the middle of each plot for each planting density. ± denotes standard error.
| Treatment | Average crown diameter (mm) |
| Standard – 12 inchz | 39.7 ± 1.1 b |
| Modified – 6 inch | 45.0 ± 1.1 a |
| P-value | 0.0061 |
z Means followed by the same letter within a column are not significantly different at P<0.05.
Table 2: Total yield and fruit quality of ‘Sweet Sunrise’ harvested on June 6, June 14, and June 21, 2021. ˚Brix, pH, and titratable acidity (TA) was taken using 5 representative marketable fruits per plot on each harvest date and averaged. ± denotes standard error. Each plot measured approximately 25 ft in length.
| Treatment | Titratable acidity (%) | pH | Total soluble solids (◦Brix) | Total yield (g) |
| Standard – 12 inchz | 5.67 ± 0.2 | 3.81 ± 1.1 | 9.36 ± 2.7 | 7871.12 ±1446.73 |
| Modified – 6 inch | 5.54 ± 0.3 | 3.81 ± 1.1 | 9.36 ± 2.7 | 7016.03 ± 1403.45 |
| P-value | 0.72 | 0.91 | 1.0 | 0.68 |
Table 3: Plant biomass of strawberry plants separated by average crown, roots, petiole and leaves. Weight was averaged across four plots for each plant density treatment. Three plants were harvested per plot in August 2021. ± denotes standard error.
| Treatment | Roots (g) | Crown (g) | Petiole + leaves (g) |
| Standard – 12 inch | 34.70 ± 3.6 | 29.92 ± 3.0 | 103.97 ± 18.7 |
| Modified – 6 inch | 31.00 ± 2.1 | 26.35 ± 1.5 | 77.98 ± 8.8 |
| P-value | 0.38 | 0.29 | 0.22 |
Conclusions
The findings from this study suggest:
- ‘Sweet Sunrise’ can be grown using a plasticulture system for reduced weed pressure.
- Average strawberry crown diameter was greater for plants established in the modified (6 inch) spacing (Table 1).
- Total fruit yield was not affected by the plant density treatments during the first harvest year (Table 2). Although yield was numerically greater for the standard (12 inch) density, it was not statistically significant.
- ˚Brix, pH, and TA was the same between the two planting densities (Table 2).
- Strawberry plant biomass was not impacted by planting density (Table 3). Although biomass was numerically higher at the standard (12 inch) spacing, it was not statistically significant.
- Given the lack of yield and fruit quality differences, data from this report suggests to continue with the standard (12 inch) plant density relative to the modified (6 inch) plant density as there were no statistically significant gains in yield that would cover the increased cost for plant material at the higher density.
Thank you for collaboration in this research! Please feel free to email or call Lisa if you have any questions (email: lisa.devetter@wsu.edu ; cell phone: 515-480-0383).