These blueberries are being grown with weedmat to control weeds.

Compost Not a Good Mulch for Blueberries

By Juanita Popenoe, Commercial Fruit Extension Agent

Blueberries like growing in soil with high organic matter and a low pH. Growers in Florida typically use pine-bark incorporated into the planting bed and as mulch to provide these characteristics to our sandy soils. However, the cost of pine bark makes alternatives attractive. Municipal compost or on-farm compost are two much cheaper options. Oregon blueberry growers also have this dilemma, and Oregon researchers decided to check these products out.

Experiment

Although the study was also a comparison of various highbush blueberry cultivars, I will only present the information on mulches. Researchers compared a preplant amendment of compost plus sawdust with a surface mulch of compost topped with sawdust to weed mat with no preplant amendments but with a sawdust mulch on top. Fresh Douglas Fir sawdust was used. The weed mat was black, woven polyethylene groundcover.

Results

There was no effect of amendment-mulch treatment on percent fruit set, and little effect on berry weight except in some cultivars. Three out of the ten cultivars had larger fruit when produced with weed mat than with compost/sawdust. Fruit harvested from plants on weed mat were firmer and most cultivars had greater yield with weed mat. The use of farm compost as a preplant amendment and as part of the mulching program increased soil pH from 4.9 to 6.9 which was likely the cause of reduced growth and yield in some cultivars.

The full article can be found at: Northern Highbush Blueberry Cultivars Differed in Yield and Fruit Quality in Two Organic Production Systems from Planting to Maturity. HortScience 52(6):844-851. 2017. By B.C. Strik, A.J. Vance, and C.E. Finn.

Photo credit: Oregon State University blog

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