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Pump it up! Timing of Calcium Uptake in Raspberry Fruits

Volume 12 Issue 1

Alexandre Dias da Silva1, Dave Bryla2, and Lisa DeVetter1

1Washington State University Mount Vernon Northwestern Washington Research and Extension Center, 16650 State Route 536, Mount Vernon, WA 98273

2U.S. Department of Agriculture, Agricultural Research Service, Horticultural Crops Production and Genetic Improvement Research Unit, 3420 NW Orchard Avenue, Corvallis, OR 97330

Rationale of Work

Calcium (Ca) is an essential macronutrient associated with fruit quality. Many growers apply Ca to promote plant health and fruit quality, but there are no studies reporting the best stage for Ca fertilizer application in raspberry. This study aimed to understand timing of Ca accumulation across raspberry genotypes to better inform fertilizer strategies.


Determine the timing and peak uptake periods of Ca across raspberry fruit development stages and genotypes. The genotypes included in this study were ‘Meeker’, ‘WakeTMField’, and ‘WakeTMHaven’.


In 2022, seven developmental stages of flowers and fruits were collected from ‘Meeker’, ‘WakeTMField’, and ‘WakeTMHaven’ following a scale developed by Kozhar and Peever (2018) (Fig. 1). The sampling location consisted of a single field located in Whatcom County, WA. Soil type within the sampled location was classified as a Kickerville silt loam. The field was managed conventionally, and no foliar fertilizers were applied within the sampled area. Sampling was carried out on both sides of three permanent transects (i.e., transect = row) per genotype with transects starting 50 ft from the edge of the field. All samples were collected between May to August of 2022 and each sampling event included all available and predominant stages of development. Leaves and soils were also sampled from each transect on Aug. 5, 2022 (data not reported). Flower and fruit samples were analyzed for Ca and other nutrients by the Bryla lab.

Fig. 1. Developmental stages of flowers and fruits: S1 – closed green buds; S2 – half open flowers; S3 – open flowers; S4 – half developed (“immature green”); S5 – green fruit (“mature green”); S6 – immature fruit (“white fruit”); and S7 – mature fruit (“red fruit”). Source: Kozhar and Peever (2018), Phytopathology.

Preliminary Findings

  • The peak period of Ca uptake across all genotypes was between S4-S6 (i.e., “immature green” and “white fruit” stages; Fig. 2).
  • Beyond the S4-S6 stages, minimal-to-no uptake of Ca was observed in the fruit or receptacle tissues.
  • Fruit and receptacle uptake of Ca appeared greatest in ‘Meeker’ through S6, but ‘WakeTMHaven’ retained more Ca in fruits at S7 (i.e., “mature red” fruit stage) than ‘Meeker’ or ‘WakeTMField’.
  • Calcium content declined between S6 and S7 likely due to Ca retained in the receptacles, which were not included in mature fruit at the final sampling stage.


Fig. 2. Calcium content (mg/berry) in A) ‘Meeker’ B)’WakeTMField’ and C) ‘WakeTMHaven’ raspberry fruits sampled May-Aug. 2022 in northwest Washington.

Conclusions and Next Step

  • Fruit uptake of Ca in fertilizers is likely optimized when applied and available during peak periods of uptake between S4-S6 (e., “immature green” and “white fruit” stages). Applying foliar Ca fertilizers outside of these periods is unlikely to lead to Ca accumulation in fruits. Soil applications of Ca fertilizers should be timed so Ca availability in the root zone coincides with peak periods of uptake.
  • ‘Meeker’ may have a higher demand for Ca between S4-S6 than ‘WakeTMField’ and ‘WakeTMHaven’.
  • A replicated field trial is planned for 2023 to validate our results and measure the effects of Ca fertilizer treatments on yield and fruit quality.
  • Additional next steps include analyzing other nutrients in the fruit (e.g., Mg, K, etc.) and using microscopy to understand how fruit surface characteristics influence fruit uptake of Ca.



Funding for this research was provided by the Washington Red Raspberry Commission (WRRC). Student support was provided through a scholarship granted by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES) – Finance Code 001. We also thank Brian Maupin,​ Kayla Brouwer, ​Emma Rogers, ​Adriana Barsan, and Dakota McFadden​, Mike Kraft, and Riley Spears for project assistance.