Q. Dear Peter, 1. the local Starbucks store saves coffee grounds for gardeners like us. I know that Blueberries and Roses like acidic soil. What other fruits, vegetables and flowers thrive in soil made acidic with coffee grounds? 2. One of our Rhodies died due to a disease of some sort. Is it a bad idea to plant another Rhodie in the same spot? If not, is there some thing that we can treat the soil with there before planting another Rhodie? Is there a period that we need to wait before safely replanting another Rhodie there? Bill and Sue Spencer – Fox Island, WA
A. Coffee grounds are a great addition to the garden as a side dressing for plants or even into the compost pile providing nutrients (roughly 2 percent nitrogen and potash and a small amount of phosphorus) and humus. There is research that indicates a dressing of coffee grounds around the base of plants can reduce slug damage. Although coffee grounds will contribute to soil acidity, one teaspoon of lime or wood ash is all that is needed to neutralize each five pounds of grounds. Most conifers prefer acidic soil as do rhododendrons, azaleas, heathers, beech and oak trees. For veggies good candidates would be potatoes (helps reduce scab), sweet potatoes, radishes, parsley and peppers to name a few. Most plants have a range of soil pH that they will grow successfully in. So it is a good practice to monitor you soil pH each year and make adjustments as needed to keep the soil in the optimal range for the plants you are growing. The coffee grounds will not immediately impact the soil pH since much of the acidity results from the decomposition of the grounds by certain acidifying bacteria. If your rhododendron died from a soil borne disease it would not be prudent to plant rhododendron or azaleas in this spot again. It is important to determine the cause of the disease (the County Extension may be able to help) since some soil borne diseases may also prevent you from growing other species of plants that are also susceptible to the disease. Many soil borne diseases can remain dormant for years determining the disease and planting a resistant species is very important.