Blueberry mulch

Asked April 5, 2015, 11:37 PM EDT

I just planted 6 blueberry plants. I was told to mulch with Douglas fir sawdust or shavings. Do you know a Portland source?

Multnomah County Oregon blueberries horticulture soil and fertility issues

1 Response

Sawdust and wood shavings are often recommended for mulching blueberries. In Portland these mulches are available at a variety of general purpose plant nurseries, the garden centers of “big box” stores, wood-working shops, lumber mills and landscaping companies that sell garden soil, rock, compost and so forth. A web search should reveal options close to where you live.

A caution: make sure the mulch is what your blueberry plants need. Blueberries like a soil pH of 5.5 – 6.5. Know your soil’s pH level. Then identify options for adjusting the pH to the blueberries’ advantage.

Oregon State University Extension publication EC1304 Growing Blueberries in Your Home Garden describes a variety of ways to get the desired soil pH level.

The answer to a previous question about mulching blueberries contains useful information and is repeated here.

You will note that we generally recommend Douglas fir sawdust as a mulch because it's usually readily available and it has a pH of about 4.5 (good for blueberries). However, there are other products that might be more readily available for home gardeners. For example, bark mulch is a good choice (also has a low pH). The reason we use a mulch is that blueberries like high organic matter soils, the mulch helps control annual weeds, and helps conserve soil moisture making irrigation management easier. We have studied various mulches and have some other specific comments/recommendations as a result. Homegardeners often like to use yard debris compost as a mulch/fertilizer. However, this material has a high pH (7 to 8). While a little bit can be added as a mulch, it's best to avoid using a lot of this type of product when mulching blueberries. Also, avoid manures or horse bedding for the same reason. Managing soil pH should be your first concern. While peat moss is acid, it is very expensive and when it dries out its hard for water to get through it (hard crust layer). For these reasons, I wouldn't recommend peat as a mulch. The second consideration should be how will the mulch affect weed growth/management? Sawdust works pretty well as seeds don't germinate readily in sawdust. Compost holds moisture better and is nutrient rich so weeds germinate readily in compost. Finally, we've looked at using porous landscape fabric (see picture below where compost mulch is in foreground, sawdust in middle and weed mat further down the row). Weed mat or landscape fabric controls weeds well, but you would need to have a drip irrigation line under the weed mat or the plants may not get watered well enough. It's also best to put some organic matter under the weed mat, like bark or sawdust -- no more than 2" deep. It's easier to manage a weed mat mulch when the weed mat is zippered with pins holding it in place (see picture); this way you can open the weed mat to add any needed fertilizer. Finally, if you are adding an organic mulch like sawdust, do not put on more than 3 inches at once so plant roots don't suffer. You will need to renew the sawdust mulch every few years to maintain the 3 inch depth.

-Dr. Bernadine Strik, Extension Berry Crops Professor, Oregon State University