Successful blueberry bushes (Vaccinium spp.) rely on acidic and well-draining soil, coupled with rich organic matter. With the blueberry's natural tendency to grow shallow, fine root systems, water is another key ingredient for high fruit yields. To conserve soil moisture and add nutrients at the same time, you can spread grass clippings around your blueberries as a mulch. However, there are both benefits and drawbacks to this inexpensive mulch.
With a maximum height of 8 feet in preferred U.S. Department of Agriculture plant hardiness zones 3 through 7, dried clippings can be applied to blueberry bushes in the same manner as other organic mulches. In general, spread up to 4 inches of dried clippings under the bush, although 2 inches is an average depth. Because they are dried, the grass does not decompose into a water and air barrier -- it retains some air pockets within the layer for rainfall penetration. Take a good look at your dried clippings before you spread them out, however. If the grass had gone to seed, you are potentially adding weed seeds to your blueberry garden.
In contrast to dried grass, blueberry bushes can only use fresh grass clippings as mulch if the clippings are properly applied. Spread a thin layer of fresh grass under your blueberry bush. To reduce the chances of forming a natural barrier to water and air, make sure this layer is only about 1/4 inch deep. Because the clippings are continually decomposing, repeat this thin layering once a week. As a result, you add natural nutrients into your soil while preventing widespread drought from water evaporation. It is imperative, however, that you know where your grass clippings came from -- any residual herbicides on the grass may damage your blueberry plant.
Fresh Clipping Drawbacks
As fresh grass clippings decompose, they generate heat. If you spread a thick, fresh clipping layer under your blueberries, the roots are easily damaged from this heating process. As a simple solution, allow your fresh grass clippings to dry out before adding them to your garden. Once dried, the decomposition heat abates and allows you to spread the mulch thickly for root protection. Drying your grass clippings also prevents nitrogen from leaching from the soil. Critical for chlorophyll production and photosynthesis, nitrogen becomes scarce as fresh grass decomposes. By using dried grass, your soil's nitrogen supply remains steady.
Juicy blueberries need a lot of water throughout their growing season for a high fruit yield. Properly applied grass clippings insulate the plant's shallow roots from heat and cold exposure for maximum root uptake of nutrients and moisture. In addition, the added organic matter from the decomposing grass clippings provides an extra nutrient boost for the fruiting bush. Weeds looking for a fertile soil environment cannot proliferate under the grass clippings, which prevents stress to your blueberry plant, especially during the fruit development period.
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