‘Mini Blues’ highbush blueberry after renovation. 2 Dec 2021.
(A) ‘Mini Blues’ highbush blueberry, conventional highbush pruning (“HB”), removing larger canes and thinning laterals and whips (5 Feb 2021). (B) speed pruned treatment (“Speed”), removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane (20 Feb 2023). (C) “Thinned” treatment: renovated in 2021–22 by cutting all canes to 30 cm above the ground, thinned in 2022–23 by removing all but the best 10 to 12 canes (20 Feb 2023). (D) “Unthinned” treatment, renovated in 2021–22 by cutting all canes to 30 cm above the ground, low growth removed (20 Feb 2023).
Yield response of ‘Mini Blues’ highbush blueberry to four pruning treatments: HB = conventional highbush pruning, removing larger canes and thinning laterals and whips; Speed = annually removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane; Thinned = renovated in 2021–22 and then thinned to the best 10 to 12 canes in 2022–23; and Unthinned = renovated in 2021–22 and no cane thinning in 2022–23. The solid arrow indicates time of renovation and the dashed arrow indicates time of cane thinning. Error bars represent standard error.
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‘Mini Blues’ highbush blueberry (Vaccinium sp.) was released in 2016 as a high-quality, machine-harvestable cultivar for processed markets. A planting was established in Oct 2015 in western Oregon and an initial study, published in 2022, included the following pruning treatments, which began in Winter 2017–18: 1) conventional highbush pruning (HB); 2) removing one or two of the oldest canes per bush (Speed); 3) leaving plants to grow from 2017–21 (Unpruned); and 4) hedging after fruit harvest in 2018 (Hedge) and then unpruned afterward. Hedge plants were considered identical to Unpruned at the end of the initial study. In Winter 2021–22, this study began when Unpruned and Hedge treatment plants were renovated by cutting all canes back to a height of ∼30 cm and thinning to the strongest 8 to 10 canes per plant. In Winter 2022–23, half of the renovated plants were thinned (“cane thinning”), leaving 10 to 12 strong canes, and the other half were left unthinned. Pruning time, yield, berry weight, and total soluble solids (TSS) were measured from 2022 to 2024 to determine how quickly plants recovered from renovation and what the economic considerations are for this practice given the loss of yield in 2022 after renovation. Cane thinning in Winter 2022–23 reduced yield compared with all other treatments in 2023, but all treatments had similar yield by the third season after renovation (2024). Berry weight and TSS were similar among treatments, except Speed had smaller berries in 2023. Cane thinning required 331 h/ha compared with 44 h/ha for Unthinned (removing low growth) and 376 h/ha for HB in 2022–23. The highest post-renovation economic returns, as well as cumulative returns (2018–24) came from Speed pruning, followed by unpruned with renovation and no cane thinning. Cane thinning reduced yield for 1 year, cost more for labor, and showed no significant benefit in the 2 years since it was performed. ‘Mini Blues’ continues to perform well with reduced labor practices and does not need to be pruned using conventional techniques.
The current North American market for small-fruited (<1 g), processed blueberry is mainly fulfilled by lowbush blueberry clones (Vaccinium angustifolium Ait.) and ‘Rubel’, a selection made from a wild northern highbush blueberry (V. corymbosum L.) population in the early 1990s (North American Blueberry Association, unpublished). ‘Mini Blues’ (Vaccinium hybrid: 75% V. corymbosum L. and 25% V. darrowii Camp) was released as a viable alternative to lowbush and other existing small-fruited highbush cultivars for the specialty processed market and was described as a vigorous, high-yielding, machine-harvestable cultivar, producing very small fruit (0.9 g) with high total soluble solids (TSS) and excellent aromatic flavor and processed quality, exceeding that of ‘Rubel’ (Finn 2017; Finn et al. 2016). However, the growth habit of ‘Mini Blues’ is vigorous, with the plants producing many thin fruiting laterals, making it difficult and time-consuming to prune by conventional methods used for northern highbush blueberry (Lukas et al. 2025).
Pruning northern highbush blueberry plants annually each winter is important to stimulate vigorous renewal of growth and improve airflow and light penetration within the plant canopy, which helps maintain consistent yield, good fruit quality including berry size, and a condensed fruiting season. Pruning method or severity of pruning has a significant impact on pruning time and costs on a commercial scale, as well as on fruit yield and quality (Mainland 1989, 1993; Siefker and Hancock 1987; Strik et al. 2003; Yáñez et al. 2009). In a small-fruited cultivar like ‘Mini Blues’, there is likely more tolerance for a reasonable reduction in berry size with alternative pruning methods, considering the specialty market is targeting small fruit. A previous study (Strik et al. 2022, 2023) assessed whether ‘Mini Blues’ could be pruned using different techniques, including summer hedging, “speed pruning” (annually removing one or two of the oldest canes per bush), or not pruning at all (“unpruned”), and comparing these techniques to conventional northern highbush pruning (“HB”). That study showed that summer hedging was unsuccessful because there was not enough time for shoot regrowth and flower bud development, even when hedging occurred immediately after harvest. However, annual speed pruning reduced pruning labor costs by 85% and maintained yield and berry weight similar to HB, and when plants were unpruned, berry size was slightly smaller, yield was slightly lower in most years, and pruning costs were slightly lower than speed pruning. After the sixth growing season in 2021, effects of not pruning were observable and indicated that plants needed to be renovated (Strik et al. 2022, 2023).
Renovation, also known as rejuvenation pruning, can be used when bushes become overgrown or have too much old, unproductive wood that has become weak (Gough 1997; Lukas et al. 2025). Because this is a technique usually reserved for weak, unkept, and potentially diseased plantings, there is relatively little research on the topic. However, Stafne and Smith (2021) found that pruning plants to 50 cm above ground level resulted in faster yield recovery compared with pruning to ground level in rabbiteye (Vaccinium virgatum) blueberry. Szwonek and Laszlovszky-Zmarlicka (2009) found that highbush blueberry returned to full production 2 years after renovation. In aronia (Aronia mitschurinii), a multistemmed fruiting shrub native to North America, renovation resulted in increased shoot growth and similar yield to unpruned bushes by the third year after pruning, with no effect on TSS (Lentz et al. 2023). Additionally, shoot thinning after aronia renovation increased individual fruit weight but decreased yield compared with unthinned plants in the year they were thinned but had similar yield in year 2 after thinning.
The objectives of this study were to determine the yield response of ‘Mini Blues’ after renovation, with or without cane thinning, and to determine the economic tradeoffs of reduced pruning labor compared with yield loss the recovery period after renovation.
The study site was within a 0.1-ha block established in Oct 2015 at the Oregon State University North Willamette Research and Extension Center (NWREC; lat. 45°16′47″N, long. 122°45′23″W). Weather data for this site are available from an AgriMet weather station (US Department of the Interior 2016). The soil is mapped as a Willamette silt loam (a fine-silty, mixed, superactive mesic Pachic Ultic Argixeroll). Details on planting establishment and management according to standard commercial practices are described by Strik et al. (2022). Composite samples of plant tissue (most recent, fully expanded leaves in late July to early August) and soil (in autumn) were collected each season and used to determine fertilizer needs for the following season (Hart et al. 2006; Strik and Davis 2023). Plant spacing was 0.9 m in the row and 3.0 m between rows (3588 plants/ha), with five plants per plot and 2.7 m between plots to allow for clearing of fruit between treatments when machine harvesting. Treatment plots were arranged in a completely randomized design with five replicates.
Plants were pruned to remove flower buds for the first two growing seasons (2016 and 2017), then pruning treatments for the initial trial (2018–21) commenced, consisting of 1) conventional highbush pruning, removing larger canes and thinning laterals and whips (HB); 2) removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane (Speed; Strik et al. 2003); 3) leaving plants to grow for several years before doing a hard renovation prune when necessary (Unpruned); and 4) using a mechanical hedger immediately after fruit harvest to remove the top and sides of the bush (Hedge). Treatments were repeated annually except for hedging, which was unsuccessful due to insufficient regrowth and flower bud development after hedging (Strik et al. 2022). Plants in the unpruned and hedge treatments did not require pruning until the end of the initial study period (Winter 2021–22) and were considered identical treatments based on measured variables and canopy architecture. At that time, the present study began, keeping HB and Speed treatments in place, and renovating the unpruned and hedge treatments by cutting all the canes and whips back to a height of ∼0.3 m from the base of the crown or soil level; the remaining wood was then thinned to the best eight to 10 canes per plant, depending on plant vigor, with a goal of leaving the remaining canes in a vase shape (Lukas et al. 2025; Fig. 1). In Winter 2022–23, half of the renovated plants were left unpruned (Unthinned) and half were thinned to the best 10 to 12 canes/plant (Thinned). Thus, the treatments in the present study include HB, Speed, Thinned, and Unthinned (Fig. 2A–D). The goal was to determine any potential advantage in plant architecture or longevity of renovation response; therefore, thinning was not repeated in subsequent years. In Winter 2023–24, HB plots were speed pruned to improve bush architecture uniformity across the planting. Low growth, which would interfere with machine harvest, was removed from all treatments.
Citation: HortTechnology 35, 6; 10.21273/HORTTECH05745-25
Citation: HortTechnology 35, 6; 10.21273/HORTTECH05745-25
Fruit were harvested every 7 to 14 d, starting in mid-July, using a self-propelled, over-the-row machine harvester (Littau Harvester, Stayton, OR, USA, in 2022 and Oxbo International, Roosendaal, the Netherlands, in 2023 and 2024). Ground speed during harvest was maintained at ∼0.5 to 1.0 km·h−1; rotary heads were typically adjusted to 250 to 300 rpm for the first harvest and increased to 400 to 750 rpm for later harvests depending on picking number per season, harvester type, and shriveling due to heat in some seasons.
Harvested fruit were weighed from each plot and divided by the number of plants per plot to calculate yield per plant for each pick. A random subsample of 25 berries was taken from the harvested fruit from each plot on every harvest date to determine average berry weight; a weighted seasonal average mass was then calculated. Berries in the subsample were then homogenized by hand in a zippered plastic bag and measured for TSS (%) using a temperature-compensating digital refractometer (Atago, Bellevue, WA, USA).
The time required to prune each plot was recorded in 2021–22 and 2022–23 to determine costs related to renovation and thinning practices. For these economic calculations, time was estimated for 2023–24 based on the average time required for speed pruning the prior two seasons (HB and Speed) and the time required to remove low growth only (Thinned and Unthinned). Labor was valued at $19.25/h for general pruning labor, which included worker’s compensation, unemployment insurance, and other labor overhead expenses (Delbridge et al. 2024). Labor requirements for pruning presented here are based on pruning by one to two researchers experienced in blueberry pruning but may be faster or more efficient with a commercial pruning crew. The value of fruit was estimated at $1.68/kg based on the average processed price for Oregon blueberries from 2021–2023 (US Department of Agriculture, National Agricultural Statistics Service 2024).
Statistical analyses were performed using PROC MIXED in SAS version 9.4 (SAS Institute, Cary, NC, USA), and means were separated at the 5% level using Tukey’s honestly significant difference test. PROC UNIVARIATE was used to ensure a normal distribution of data before analysis, and log transformations were applied as necessary. Effects of year were not analyzed because changes during the study period were expected.
There was no yield in 2022 for plots that were renovated in the preceding winter (Thinned and Unthinned treatments) and yield was very low for the remaining plants (0.6 and 1.4 kg/plant for HB and Speed, respectively) compared with prior years due to severe bird pressure, despite use of bird scare devices (Table 1 and Fig. 3). In 2023, there was no difference between pruned plants and renovated plants that were Unthinned, whereas Thinned plants had significantly lower yield (Table 1). This full yield recovery after 2 years in Unthinned has been shown for other blueberry cultivars, indicating the ability to rapidly recover from a severe prune (Stafne and Smith 2021; Szwonek and Laszlovszky-Zmarlicka, 2009). In 2024, there was no difference between treatments in yield per plant, and average yield (15 tons/ha) was similar to the highest yield in the prior study (Strik et al. 2022).
Citation: HortTechnology 35, 6; 10.21273/HORTTECH05745-25
In 2023, berry weights were similar among all treatments (averaged 0.70 g/berry) except Speed pruned, which was lower (0.56 g/berry) while in 2024 there was no difference in berry weight (Table 1). Berries were smaller than normal in 2024, likely due to an early heat event that stunted berry development for this cultivar. Other research in blueberry has shown variation in species and cultivar sensitivity to heat (Lobos and Hancock 2015), and that evaporative cooling during the growing season can increase berry weight in sensitive cultivars (Yang et al. 2020). However, the poor response to heat, which has been evidenced by small or shriveled berries despite adequate irrigation and soil moisture, is somewhat surprising for this cultivar, given that it has 25% V. Darrowii in its background (Finn et al. 2016), which has been found to have greater thermal stress adaptation ability than V. Corymbosum (Callwood et al. 2021). Strik et al. (2003) found that berry size was reduced when bushes were not pruned after one season in ‘Bluecrop’, whereas speed pruning took two seasons to reduce berry weight in ‘Bluecrop’ and ‘Berkeley’ highbush blueberry. Similarly, ‘Brigitta’ highbush blueberry had larger berries after a larger percentage of the canopy was pruned in the previous winter (Retamales et al. 2023). In contrast, average berry weight for ‘Mini Blues’ over 4 years was not significantly different with speed pruning compared with standard pruning but not pruning at all reduced berry weight (Strik et al. 2022). In southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid), summer pruning rarely affected berry weight the following season (Kovaleski et al. 2015).
As in the prior study (Strik et al. 2022), TSS was unaffected by pruning treatments in any year (averaging 17.2% over all treatments and years), and average TSS was high compared with typical northern highbush cultivars which often range from 12% to 15% (Strik et al. 2017; Yang et al. 2009) but normal for ‘Mini Blues’ (Table 1; Finn 2017). Cane thinning and HB pruning resulted in a higher proportion of fruit harvested on the first pick in 2023 (averaged 41% compared with an average of 29% for Unthinned and Speed pruned plants). Speed pruned had the highest proportion on the third pick (Table 1). In 2024, there were fewer differences in proportion harvested on each pick. This is likely because the two growing seasons since cane thinning was performed allowed plants to regrow and reduce variability, demonstrated by all treatments having the same yield in 2024 (Fig. 3). In ‘Bluecrop’, conventional pruning advanced harvest by 3 to 5 d compared with unpruned plants, but this may have been related to higher yield for unpruned plants (Strik et al. 2003), whereas HB had the highest yield in 2023 but a similar proportion of fruit on the first pick as Thinned (with the lowest yield) in the present study.
As reported by Strik et al. (2022), renovation required about triple the time compared with Speed pruning, but less than half the time required to prune HB plots. In 2022–23, HB pruning and Thinned plots required statistically similar amounts of time (376 and 330 h·ha−1, respectively), whereas Unthinned and Speed plots took 84% less time on average (45 and 69 h·ha−1, respectively). In comparison, typical pruning labor for mature (≥6 years old) commonly grown northern highbush blueberry cultivars is estimated at 250 h·ha−1 (Seavert et al. 2025). When the costs of pruning are considered alongside potential returns from fruit sales, the highest cumulative economic returns (2022–24) came from Speed (US$56,084), followed by HB pruning ($52,640), which were not renovated (Table 2). Over the first 2 years of harvest since renovation, Thinning resulted in approximately half the cumulative returns ($23,215) compared with Unthinned ($46,053) due to higher labor inputs and lower yield. However, these plants could likely fruit for at least 3 more years before requiring intensive pruning or renovation again, so these economic considerations would continue to change. Strik et al. (2023) showed enough differences in the ripening period between treatments that an additional harvest may be necessary for unpruned or speed pruned plants, but the small cost of an additional harvest did not outweigh the labor savings in pruning. On the basis of the present study, the Thinned treatment could likely be harvested fewer times (Table 1), but harvest costs are low relative to pruning costs. There could be additional economic incentive for renovation because fewer fungicide and insecticide applications are needed in the nonfruiting year after renovation, but those expenses were not included in these calculations.
After calculating returns compared with pruning costs for the first seven harvest seasons (2018–24), Speed pruning resulted in 24% higher returns than the next treatment, which was Unpruned, renovated, then Unthinned (data not shown). However, that treatment was very similar to HB. Unpruned, renovated, then Thinned had the lowest returns (42% lower than Speed and 19% lower than HB).
Speed pruning is likely the most sustainable long-term production practice for ‘Mini Blues’, given the cultivar’s small fruit size and dense canopy, which is time-consuming to prune using standard methods. However, leaving plants unpruned for several years and renovating as canopy density and diminishing berry size requires is a viable alternative. Cane thinning the year after renovation is likely unnecessary, although further years of study would help determine the longer-term impact of that practice. These low-input methods are increasingly important for an industry with ongoing concerns about the cost and availability of skilled labor while maintaining high-quality fruit and economic profitability.
‘Mini Blues’ highbush blueberry after renovation. 2 Dec 2021.
(A) ‘Mini Blues’ highbush blueberry, conventional highbush pruning (“HB”), removing larger canes and thinning laterals and whips (5 Feb 2021). (B) speed pruned treatment (“Speed”), removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane (20 Feb 2023). (C) “Thinned” treatment: renovated in 2021–22 by cutting all canes to 30 cm above the ground, thinned in 2022–23 by removing all but the best 10 to 12 canes (20 Feb 2023). (D) “Unthinned” treatment, renovated in 2021–22 by cutting all canes to 30 cm above the ground, low growth removed (20 Feb 2023).
Yield response of ‘Mini Blues’ highbush blueberry to four pruning treatments: HB = conventional highbush pruning, removing larger canes and thinning laterals and whips; Speed = annually removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane; Thinned = renovated in 2021–22 and then thinned to the best 10 to 12 canes in 2022–23; and Unthinned = renovated in 2021–22 and no cane thinning in 2022–23. The solid arrow indicates time of renovation and the dashed arrow indicates time of cane thinning. Error bars represent standard error.
Contributor Notes
We appreciate funding support provided by the Oregon Blueberry Commission.
S.B.L. is the corresponding author. E-mail: scott.lukas@oregonstate.edu.
‘Mini Blues’ highbush blueberry after renovation. 2 Dec 2021.
(A) ‘Mini Blues’ highbush blueberry, conventional highbush pruning (“HB”), removing larger canes and thinning laterals and whips (5 Feb 2021). (B) speed pruned treatment (“Speed”), removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane (20 Feb 2023). (C) “Thinned” treatment: renovated in 2021–22 by cutting all canes to 30 cm above the ground, thinned in 2022–23 by removing all but the best 10 to 12 canes (20 Feb 2023). (D) “Unthinned” treatment, renovated in 2021–22 by cutting all canes to 30 cm above the ground, low growth removed (20 Feb 2023).
Yield response of ‘Mini Blues’ highbush blueberry to four pruning treatments: HB = conventional highbush pruning, removing larger canes and thinning laterals and whips; Speed = annually removing one or two of the oldest canes from the base of the plant or pruning back to a more vigorous section of the cane; Thinned = renovated in 2021–22 and then thinned to the best 10 to 12 canes in 2022–23; and Unthinned = renovated in 2021–22 and no cane thinning in 2022–23. The solid arrow indicates time of renovation and the dashed arrow indicates time of cane thinning. Error bars represent standard error.
