Get It Growing: Ask a Master Gardener — What to use for growing blueberries
Published 1:30 am Wednesday, May 6, 2026
Q: We would like to grow blueberries and have been told that they need acidic soil that is high in organic matter. Online sources recommend use of sawdust, wood chips, bark, or peat moss to increase organic matter in soil when growing blueberries. Are any of the following also acceptable: sawdust from building projects, ash from wood fires, sphagnum moss collected from local forests, or coir?
A: Just a quick reminder: pH is a measure of acidity, ranging from 0 to 14. A pH of 7 is neutral. Values below 7 are acidic and values above 7 are alkaline. The lower the number below 7, the more acidic. The higher the number above 7, the more alkaline.
Blueberries are acid-loving plants that need a soil pH of 4.5 to 5.5 to thrive. They also are sensitive to high levels of phosphorus and salt in the soil, which can cause micronutrient deficiencies and root damage.
Because blueberries have superficial roots that dry out quickly, the plants grow best in soil with a high water-holding capacity.
Incorporating organic matter increases the water-holding capacity of all soils. So, what kinds of organic matter are best for blueberries?
Wood products
Sawdust, wood chips, and bark from trees that grow naturally on the Olympic Peninsula (e.g., Douglas fir, pine, and most hardwoods) are acidic (pH range: 4.0 and 5.5). They also have a low phosphorus and salt content and are a good way to increase soil organic matter for blueberries.
Some sources warn against use of fresh cedar products because cedar trees produce natural pesticides that act against insect pests and pathogens. There is no documented evidence, however, that these chemicals influence the growth of other plants.
Can you use sawdust or wood chips from a building project? It depends on the product. It is safe to use untreated, natural wood from both conifers (e.g., pine, Douglas fir, hemlock) and deciduous trees (e.g., maple, oak, and birch).
Do not use sawdust from composite wood or wood that is pressure-treated, painted, or stained. These woods can contain toxic chemicals (e.g., arsenic, chromium, and heavy metals) that can be taken up by plants, especially in acidic soils.
Do not use wood ash — the powdery residue left after burning wood — on soils intended for blueberry plants. Although used to increase soil potassium, calcium, and magnesium, wood ash does not increase soil organic matter content and is highly alkaline (pH above 9).
Peat moss and sphagnum moss
Peat moss is a fine-textured and highly acidic organic material (range: pH 3 to 4.5). It is formed through the breakdown of sphagnum moss and other organic materials that have accumulated in boggy areas over thousands of years. Peat moss becomes acidic through the release of organic acids during decomposition in a low-oxygen, waterlogged environment.
Peat moss is an excellent source of organic matter for soils that grow blueberries. It is not used as commonly as wood products because it is expensive and considered a non-renewable resource.
Sphagnum moss harvested from the forest floor is a large component of peat moss. Sphagnum moss, however, is still living or has only recently died. It has not gone through the low-oxygen decomposition process like peat moss and has a neutral pH. It is not an appropriate amendment for soils used for blueberries.
Coir
Coir is a natural, biodegradable fiber produced from the outer husk of coconuts. It is used in gardens and plant containers to improve soil aeration and enhance water retention. As opposed to peat, it is considered a sustainable byproduct and is increasingly being used as a soil additive.
Coir, however, tends to have a neutral pH (range: 5.8 to 6.9) and high salt content. It is not an appropriate soil amendment for sites where blueberries are to be planted.
Applying organic matter
Once you have selected an acceptable organic material, spread two to four inches of the material over the entire area to be planted.
If you only amend the soil in the planting hole, the bush’s roots will not grow into the surrounding native soil and, over time, it will become rootbound.
Incorporate the organic material into the soil by digging or tilling to ensure uniformity of the soil.
Microorganisms will break down organic matter and consume nitrogen in the process. To aid in the decomposition process and provide sufficient nitrogen for your blueberry plants, apply about three ounces of nitrogen per 100 square feet of soil.
For more information about blueberry planting and growth requirements, see Oregon State University’s “Growing Blueberries in the Home Garden” available for free at https://extension.oregonstate.edu/catalog/ec-1304-growing-blueberries-your-home-garden.
Join Jeanette Stehr-Green for “All About Houseplants: Selection, Care, and Propagation” on Thursday, May 7, from 6 p.m. to 8 pm, at the Vern Burton Community Center, 308 E. Fourth St. in Port Angeles. This lecture is free to the public.
Woodcock Walkabouts return on Thursday, May 7, at 10 a.m. A Master Gardener will lead a tour of the garden. The topic for May is “Intro to New Gardens.” Expect a one-hour tour. Wear appropriate shoes as this is a working garden and may be wet and muddy. The Woodcock Demonstration Garden is located at 2711 Woodcock Road, Sequim.
In Port Angeles, Master Gardeners will provide tours of the Fifth Street Community Garden and answer Plant Clinic questions on Saturday, May 9, from 10 a.m. to 11:30 am. The Fifth Street Community Garden is located at 328 E. Fifth Street, Port Angeles.
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Upcoming gardening events
Join Jeanette Stehr-Green for “All About Houseplants: Selection, Care, and Propagation” on Thursday, May 7, from 6 p.m. to 8 pm, at the Vern Burton Community Center, 308 E. Fourth St. in Port Angeles. This lecture is free to the public.
Woodcock Walkabouts return on Thursday, May 7, at 10 a.m. A Master Gardener will lead a tour of the garden. The topic for May is “Intro to New Gardens.” Expect a one-hour tour. Wear appropriate shoes as this is a working garden and may be wet and muddy. The Woodcock Demonstration Garden is located at 2711 Woodcock Road, Sequim.
In Port Angeles, Master Gardeners will provide tours of the Fifth Street Community Garden and answer Plant Clinic questions on Saturday, May 9, from 10 a.m. to 11:30 a.m. The Fifth Street Community Garden is located at 328 E. Fifth Street, Port Angeles.
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Jeanette Stehr-Green is a WSU-approved Clallam County Master Gardener. She is a berry-enthusiast and is sharing her berry knowledge and experience in the 2026 Homegrown Berries Series. For more information and to register, go to https://www.signupgenius.com/go/berryseries#/
