Blueberries often grow better in mineral soil when mulched, although many successful plantings have no mulch. Mulching to a depth of 5 to 6 inches on the soil surface of mature plantings keeps the soil cool, helps conserve soil moisture, adds organic matter to the soil, improves soil structure, and aids in preventing annual weeds from becoming established. Mulch is less effective against perennial weeds.
Blueberry roots tend to grow in the soil, and the mulch. Thus, as the mulch decomposes, many of the roots will be exposed. Mulch should, therefore, be maintained by adding 2 to 3 inches every 2 to 3 years in a 3 to 4 foot band under the plant.
Do not allow sawdust to pile around the crown of the plant, as this encourages rodents. Sawdust is commonly used as a mulch for blueberries. As a general rule, sawdust decomposes at the rate of about 1 inch per year in the Pacific Northwest.
Sawdust usually has little effect on soil pH. However, fresh sawdust can tie up a lot of nitrogen. When mulches are used, an additional 50 to 100 percent N may be necessary for the first few years to compensate for increased microbial activity (see Nutrition). It is best to use partially-decomposed sawdust. Stockpile sawdust at least 1 year prior to spreading, if possible.
Other organic materials (e.g. pine needles) may sometimes be used as a mulch. However, straw and deciduous leaves are not recommended as they tend to pack, thus not allowing adequate water penetration. Straw also decomposes quickly.
Black plastic has been used effectively as a mulch in some countries. However, drip irrigation tubes must be placed underneath the plastic, fertilizer application is difficult, and plastic usually deteriorates after 2 to 3 years.
Weed matting, consisting of a woven polypropylene fabric, is used successfully as a mulching material in Michigan and Australia. Water passes through the mat. Edges must be covered with soil to keep the weed mat in place.
This fact sheet is adapted from Oregon State University Extension Publication PNW215, Highbush Blueberry Production. The authors of Highbush Blueberry Production are – Oregon State University: Bernadine Strik, Glenn Fisher, John Hart, Russ Ingham, Diane Kaufman, Ross Penhallegon, Jay Pscheidt and Ray William; Washington State University: Charles Brun, M. Ahmedullah, Art Antonelli, Leonard Askham, Peter Bristow, Dyvon Havens, Bill Scheer, and Carl Shanks; University of Idaho: Dan Barney. PNW215, Highbush Blueberry Production can be purchased from the Department of Extension & Experiment Station Communications, Oregon State University. How to Order