Over the past two decades, the Oregon State University Extension Service and the Oregon Agricultural Experiment Station have focused research on fertilizer practices for blueberries, raspberries, blackberries, strawberries and kiwiberries. The work addresses key grower questions around timing, rates and methods of application.
Nitrogen is the primary nutrient used in berry production. Its application timing and rate have major impacts on plant growth, fruit quality and environmental outcomes.
This research has helped berry growers across the Pacific Northwest reduce input costs, improve yields and apply fertilizers more efficiently.
The late Bernadine Strik, then professor of horticulture and Extension berry crops specialist at the North Willamette Research and Extension Center, led foundational research in this area. Her work tracked nitrogen uptake in berry crops based on how much and when fertilizer was applied. Strik found that nutrient needs differ among berry types. These discoveries led to crop-specific recommendations.
In June-bearing strawberry, applying fertilizer in spring reduced fruit quality and didn’t increase yield. As a result, growers are now advised to fertilize only after harvest.
In raspberry and blackberry, fertilizer applied in early spring is essential for primocane growth. Missing this timing can reduce plant vigor and yield.
In blueberry, fertilizer isn’t absorbed until bloom. OSU Extension updated recommendations to delay application until that time.
Higher nitrogen rates often did not improve yield. They also increased costs and the risk of nitrogen leaching.
Strik’s research supported the use of moderate nitrogen rates. Split applications or fertigation through drip irrigation helped increase yield and improve fruit quality.
These methods saved growers up to $300 per acre. OSU Extension published updated nutrient management guides for both commercial growers and home gardeners across the Pacific Northwest.
Strik, Amanda Davis, senior faculty research assistant, and Scott Lukas, leader of OSU’s Northwest Berry Production and Management Program, also studied nutrient concentrations across growing seasons and cultivars. They focused on blueberry, blackberry and kiwiberry.
Their research also addressed soil pH management for blueberry production in Eastern Oregon. They identified optimal leaf tissue sampling times and revised nutrient sufficiency ranges.
These updates help growers better evaluate plant nutrient status. They also improve the precision and effectiveness of fertilizer programs.
In 2006, increased interest in organic berry production led to more research. Organic growers needed guidance on whether alternative fertilizers and methods could be used effectively.
The team studied fertilizer sources and application methods in certified organic blueberries and blackberries. They found that blackberry plants tolerated different fertilizer types, but blueberry plants were more sensitive.
Some organic products, when fertigated, saved growers money on labor and application. Lower nitrogen rates were also successful, saving organic blueberry growers up to $900 per acre.
Organic fertilizers often contain potassium in addition to nitrogen. Common products like fish solubles and compost added potassium even when it wasn’t needed.
Long-term overuse of potassium led to reduced yields. This was especially true in mature blueberry plantings.
When potassium-containing products such as soy-protein–based fertilizers and compost were discontinued, yields improved by up to 50% after two years. This emphasized the importance of balanced nutrient management.
Lukas and Davis continue to focus on sustainable practices for berry growers. They share their research through presentations, Extension publications and peer-reviewed articles regionally, nationally and internationally.
This research has helped berry growers across the Pacific Northwest reduce input costs, improve yields and apply fertilizers more efficiently through crop-specific, science-based recommendations. By promoting sustainable nutrient management, it supports long-term farm profitability while protecting soil and water quality.
