Producing blueberry trees for sustainable blueberry production

Progress report for OW23-377

Project Type: Professional + Producer
Funds awarded in 2023: $65,857.00
Projected End Date: 12/31/2024
Grant Recipients: North Willamette Res & Ext Center; Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Dr. Wei Yang
North Willamette Res & Ext Center
Dr. Yongjian Chang
North American Plants LLC
Sam Doane
J. Frank Schmidt & Son Co.
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Project Information


The current commercial blueberry production systems in the northwest require high cultural inputs and extensive harvesting labor to sustain profitability. Growers are increasingly dependent on machine harvesters to meet market demand. However, the natural blueberry plant architecture, particularly the large plant base created by multiple canes, causes up to 15-30% yield loss during mechanical harvesting. A monopodial blueberry tree can eliminate this yield loss and improve harvesting efficiency, thus significantly reducing the cost of harvesting labor. A blueberry tree can be produced by grafting blueberry cultivars onto a monopodial rootstock (Vaccinum arboreum L.). After more than ten years of research at the North Willamette Research and Extension Center of the Oregon State University, this rootstock has been developed. Because the new blueberry rootstock is difficulty to propagated by cuttings, we are requesting funding to work with the Oregon nursery industry to develop and improve the clonal propagation methods, rooting and growing protocols, and grafting techniques to produce blueberry trees. Our research is focusing on the expansion of tissue-cultured stage II plantlets, increased rooting percentage, and optimal nutritional needs for growing and grafting the new blueberry rootstock. The outcome of this research will give nursery growers confidence to grow this new and highly beneficial rootstock, therefore producing blueberry trees for commercial blueberry growers. We will disseminate the information on how to produce blueberry trees to  nursery growers through workshops, meetings, publications and online videos. Our project will position Oregon nursery producers as global leaders in a new blueberry tree production market.

Project Objectives:
  1. Improving the efficiency of producing stage II tissue culture Vaccinium arboreum plantlets (Producer one).
  2. Enhance the rooting percentage of Vaccinium arboreum plantlets (Producer two).
  3. Growing blueberry rootstock (V. arboreum) plants (Principle investigator and producer three).
  4. Grafting blueberry cultivars onto the blueberry rootstock to produce blueberry trees (Principle investigator and producer three).
  5. Disseminate information to nursery growers on how to grow the V. arboreum rootstock and use grafting to produce blueberry trees (Principle investigator).

The proposed project lasts 21 months. Major research activities are illustrated in the following Gantt chart. The milestone for each research objective is reflected by the end of data collection and statistical analyses described in the research plan section.

Gantt chart – Research activities to accomplish stated objectives 1-5.

Gatt chart project timeline


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  • Jonathan Jasinski - Producer


Materials and methods:

Research facilities and major instrumentation and equipment

Microplant Nurseries and North American Plants, LLC are commercial tissue culture labs. They are well equipped to conduct research and develop experiments for new plant materials.

North Willamette Research and Extension Center (NWREC) has plant growing facilities certified as an operational nursery. The NWREC has a climate-controlled greenhouse, several hoop houses, container growing pads, various moisture and EC sensors, LI-COR from the nursery program, and general computer and software for statistical analysis. 

Plant materials: Unrooted tissue-cultured plantlets of V. arboreum rootstock will be produced by Microplant Nurseries Inc. The V. arboreum rootstock in 1” plug liners will be received from North American Plants, LLC (NAP) in July 2023.

Growing conditions and substrate: The NWREC’s greenhouse can regulate temperature, humidity, light, and provide bottom heat. Outdoor growing facilities include standard landscape fabric covered pads with micro-spray irrigation. The fertigation and overhead micro-spray irrigation systems are available for water and nutrient management. We will grow the rootstocks in 1 gal size containers using either a commercial blueberry growing mix from LEGRO (LEGRO of USA, Thousand Oaks, CA) or our own mix of peat, coir, and perlite based on costs and availability.

Nutrient solutions: We will use fertigation to deliver various nutrient treatments to the 1 gal size containers. The nutrient solution will be based on published studies of growing tissue culture blueberry plants in pots (Yang et al., 1997) except varying nitrogen amount as the main treatment. The nutrient recipe consists of (in mM) 0.3 P, 1.0 K, 1.0 Mg, 0.5 Ca, 2.8 S, and (in uM) 89.5 Fe (as EDDHA), 34.2 B, 10.0 Mn, 1.0 Zn, 0.01 Cu, and 0.02 Mo.

Treatments: We will assign the treatments as a 3x2 factorial experiment with three nitrogen concentrations (low, medium, and high at 1 mM, 2.5 mM, and 5 mM respectively) and two pH levels (normal and high at 4.5 and 6.2 respectively). The source of nitrogen will be ammonium sulfate. Fertilizer treatments will be delivered weekly to containers via drip irrigation and controlled by a Dosatron pump. Based on commercial practices of substrate blueberry production, we will monitor the electric conductivity (EC) in the effluent and maintain it at 0.8 ds/m.


Experiment 1. Investigate the effect of in vitro medium pH on shootlet production.

Location: Microplant Nurseries

In our previous collaboration with Microplant Nurseries in winter 2019, a tissue culture protocol for the V. arboreum rootstock using axillary buds was established. The young developing buds from dormant excised shoots from a V. arboreum plant selected and evaluated at the NWREC were forced by using a Floralife solution in the greenhouse. Woody plant medium (WPM) was used with various plant growth hormone combinations (no details due to proprietary information) for axillary bud proliferation in vitro. Based on a recent in vitro propagation study of V. arboreum (Li et al., 2021), the pH of tissue culture medium affected the rate of shoot proliferation. In our experiment, we will adjust the pH of WPM to five levels: 4.5, 5, 5.5, 6.0, and 6.5. Ten tissue culture glass jars for each pH level will be prepared. The light and growing conditions will be the same for all tissue culture jars placed on the same culture bench. After two months of growth, the number and the length of shootlets in each jar will be recorded. Based on previous experience, there shall be around 30-60 shootlets in each tissue culture jar. Data for shootlet number and average length will be analyzed as an one-factor (pH treatment) ANOVA by SAS statistical software (Gary, NC USA).


Experiment 2 Effect of IBA dipping on rooting percentage of V. arboreum rootstock.

Location: North American Plants LLC

All the micro-propagated shootlets from experiment 1 (We anticipate to have at least 400 1.5”-2” tall shootlets) will be rooted under a climate controlled hoop house. The shootlets from Microplant will be grown in 1” liners filled with peat and perlite prepared in house at the NAP. They will be evenly divided into two groups. One group of shootlets will be treated with 1 g L−1 indole-3-butyric acid (IBA) by dipping the cutting into the IBA solution, while the other group will remain as an experiment control. Both shootlet groups will be placed under a misting system which delivers irrigation and nutrients, and controls relative humidity in the hoop house. After two to three month of growth under the hoop house, we anticipate rooting will take place. Once the fine white roots fills the 1” liners, they will be checked for the success of rooting by cutting the liners open perpendicularly. Shootlets with and without the white fine roots will be recorded. Then they will be moved to a semi-outdoor greenhouse to acclimate and grow in size. Regular irrigation and nutrition will be maintained for rooted 1” liners until they reach 6” tall, a stage III size ready for the container experiment below. The percentage of rooting will be calculated and analyzed by a one-factor (IBA treatment) ANOVA by SAS statistical software (Gary, NC USA).


Experiment 3. Determine the optimum nutritional needs of V. arboreum rootstock.

Location: NWREC or J. Frank Schmidt and Son, Co (No guarantee due to seasonal space limitation for commercial operation)

A total of 180 1” liners of the blueberry rootstock supplied from NAP will be potted up into 1 gal size containers in September 2023 and placed in the NWREC greenhouse. For each nitrogen and pH combination, 36 plants will be grouped as one replication with 5 replications arranged in a randomized block design. The container moisture and EC will be monitor by using a TEROS 12 sensor (Meter Group, Pullman, WA) twice weekly. The amount of water supplied for irrigation will be based on a water balance method to supplement daily plant evapotranspiration plus moisture loss from the container. When the outside temperature reaches 60 F during the daytime, the containers will be moved to the outdoor growing area and continue to be fertilized in their original assignment in the new location. In late September 2024, the containers will be moved back into the greenhouse for continued growth during the winter time. We will quantify the growth differences with deconstructive harvest data that will be collected three times (10 plants each time) over the entire course of the growing cycle. Non-destructive leaf chlorophyll and leaf gas exchange will be collected monthly with a LI-COR photosynthesis meter. The level of net leaf photosynthesis (Pnet) will indicate the effect of nitrogen rate on plant growth. Based on previous experience with V. arboreum seedlings, the V. arboreum rootstock plants shall reach a graftable stem diameter (>0.8 cm at 14” height) in 10-14 month. At that time, The data collected will include monthly plant height, initial and final stem diameter at 14” height, plant root and shoot dry weight, chlorophyll readings and Pnet, which will be analyzed with SAS (Gary, NC USA) PROC GLM as a 3x2 factorial in a randomized block design. Treatment means will be compared for statistical differences by Fisher’s LSD. The RSREG procedure will be used to fit quadratic response surface of fertilizer nitrogen rate changes over time so the best treatment to grow the rootstock will be identified at each pH level.


Experiment 4. Determine the percentage of graft take of two blueberry cultivars.

Location: NWREC greenhouse

We will select 120 V. arboreum rootstock plants from Experiment 3 for grafting in November 2024. Side grafting technique will be used with a grafting height at 14”. Dormant scion wood of blueberry cultivars Draper and Legacy will be obtained from the NWREC research plot at grafting time. The choice of these two cultivars will allow comparison of grafting take rate between northern highbush blueberries and blueberries with southern highbush traits. The whip cut of the scion wood of 4”-6” long will be inserted into the ‘lip’ of the cut rootstock between two nodes so that the cambium layers match up well. For each dormant scion wood, at least three vegetative buds will be visible after the grafting union is wrapped with grafting tape. All grafted plants will be kept in containers from Experiment 3 to allow continued rootstock growth in the greenhouse at the NWREC. Regular irrigation and fertilization will be maintained based on our previous experience of growing potted blueberries in a greenhouse setting. Data taken will include the percentage of grafting success for each cultivar, indicated by the new growth coming out the dormant scion wood. When the longest new shoot from the scion wood reaches more than 4 inches in length, we will consider the graft has successfully taken. The percentage of successful grafts will be calculated and analyzed by a one-factor (Blueberry cultivar) ANOVA by SAS statistical software.  

Research results and discussion:

Working with Producer One (Microplant Nurseries Inc.), we successfully achieved Objective One by producing over 1500 stage II tissue-cultured (TC) Vaccinium arboreum plants at the Microplant facility from dormant shoots of field-grown V. arboreum plants. Microplant modified the experimental procedure by utilizing woody plant media at a pH level of 5.75, which represents the median of proposed pH levels, simplifying the laborious laboratory work. The results were impressive, with each tissue culture jar yielding 30-50 shootlets. Building on this initial success, we are now planning to produce another potential V. arboreum rootstock using the established TC methods in April 2024.

In spring 2023, after delivering more than 1500 TC V. arboreum shootlets to Producer Two (North American Plants - NAP), the shootlets were cultivated in 1” liners filled with peat and coco fiber at the NAP facility. All shootlets underwent treatment with indole-3-butyric acid (IBA) by immersion in the IBA solution. These shootlets were then placed under a misting system, which provided irrigation, nutrients, and controlled relative humidity in the hoop house. After two to three months of growth in the hoop house, rooting began to occur. NAP allocated dedicated greenhouse bench space for the rooting experiment using the proposed experimental method. After two to three months of rooting, the rooted shootlets were transported to the North Willamette Research Extension Center, where the Agricultural Technical Advisor (W. Yang)and his research assistant evaluated the rooting percentage of TC shootlets. The average rooting rate exceeded 73%, with some shootlets failing to root and subsequently dying. NAP expressed satisfaction with the rooting results, confirming the successful completion of Objective Two.

For Objective three, Producer three (J. Frank Schmidt and Son, Co. - JFSS) received rooted plantlets from NAP in late June 2023. These rooted plantlets were grown in 4 inch pots with a commercial maple growing substrate. After more than three months’ growth in the high humidity growing house, the tallest plants reached more than 14 inch in height. The growth rate was impressive under the JFSS growing facility. These plants were moved to the section of the greenhouse without bottom heat to undergo overwintering and through the spring. The aim for the 2024 growing season is to enhance their caliper size in readiness for grafting. At the NWREC, In July 2023, a total of 180 V. arboreum plants were transplanted into 1-gallon size containers and placed on nursery fabric beds in the NWREC cravo. These plants were cared for based on the protocols outlined in Experiment 3. However, due to the late potting time, the growth of these plants were unsatisfactory. To address this issue, we plan to adjust our fertilizer programs in 2024 and aim to complete the growth measurements for these plants as proposed.

Participation Summary
3 Producers participating in research

Research Outcomes

Recommendations for sustainable agricultural production and future research:

The successful tissue culture from Producer 1, acceptable rate of rooting of Vaccinium arboreum from Producer 2, and excellent growth of V. arboreum plants in the nursery facility of Producer 3, provided valuable knowledge to scale up the new blueberry rootstock production for grafting and producing blueberry trees in the final phase of this project. Once the final phase of the project is completed in fall 2024, we will produce production guides for the production of blueberry trees for the sustainable blueberry production systems. Further research activities will be recommended. 

1 Grant received that built upon this project

Education and Outreach

7 Consultations
1 On-farm demonstrations
2 Tours
7 Webinars / talks / presentations
5 Workshop field days

Participation Summary:

213 Farmers participated
50 Ag professionals participated
Education and outreach methods and analyses:

In 2023, three blueberry educational workshops were conducted at the NWREC including machine harvesting, blueberry nutrition, and blueberry pruning workshops. In these workshops, we introduced the concept of blueberry canopy management and ways to reduce ground loss of fruits, including the potential of using rootstocks plants for producing grafted blueberries. During the Oregon blueberry field day, Yang showed blueberry grower and nurseryman of the nutrition experiment. Yang also gave a presentation on the funded project to a group of nursery professionals touring the NWREC. Yang participated in the WSARE’s BPASS and gave a presentation about the funded project. A summary of the activities is listed in Table 1 and a timeline is listed in Table 2.

Table1. Summary of educational activities



Number of attendees


May 26, 2023

2023 OSU Blueberry machine harvest  Workshop


Growers, harvester companies

July 26, 2023

OSU Blueberry field day


Growers, nurserymen

October 19, 2023

2023 Blueberry nutrition workshop



December 15, 2023

2023 Blueberry pruning workshop- field demonstration teaching


Growers, pruning company

December 15, 2023

2023 Blueberry pruning workshop-classroom teaching


Growers, pruning company


Table 2. Timeline of completion of the educational activities achieved so far. 







a. Stakeholder workshops




b. Stakeholder training workshops




c. Conferences




Obj#2-Stakeholder field days




Obj#3-Popular publications

Pending *



Obj#4-Educational video




Obj#5-Extension and peer-reviewed publications





* OSU Intellectual Property (IP) Office required the Agricultural Technical Advisor (Dr. Yang) to complete the patent application of the experimental rootstock used in this project. As a result, some publication activities were delayed due to concerns of Public Disclosure which may lead to the loss of patent rights. This issue has largely been resolved as OSU’s IP office is preparing to fill the patent application in April 2024. we anticipate being able to proceed with all remaining education and outreach activities as planned.

Education and outreach results:

The workshops we conducted were a combination of classroom teaching and in field hands-on demonstrations. We surveyed the attendees after some educational events (Nutrition and pruning workshops) and have the following findings. For our pruning workshop, there were estimated 25% participants of professional Spanish-speaking farm worker. The findings on knowledge gains and possible adoptions indicated effectiveness of our workshops (Table 3). 

Table 3. Measurements of knowledge gains and probability of adoption recommended practices


Knowledge gains z

Likelihood of adoption recommended practices y

Pruning (Classroom)



Pruning (Field demo)






Z Likert scale rating of 1 = poor, 6= excellent; y Likert scale rating of 1 = least likely, 3= most likely.

60 Farmers intend/plan to change their practice(s)

Education and Outreach Outcomes

Recommendations for education and outreach:

It is still early in the project to make recommendations for education and outreach. However, pruning practices regarding using the grafted blueberries will be a needed educational goal in 2024. Other possible outreach activities will be inviting nursery growers to learn grafting practices when the blueberry trees are produced. Learning nutritional needs of blueberry plants are also important topics to ensure the success of growing healthy grafted blueberry plants. 

30 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
Key changes:
  • There were two key areas which increased the knowledge of farmers: one is the understanding of blueberry pruning practices in canopy management which including the use of blueberry trees; the other is the understanding of blueberry nutrition which is critical to cultivating grafted plants.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.