Do you have any suggestions for improving the soil in a raised bed vegetable garden?


Two years ago I made a small raised bed garden approximately 10×6 ft. I regret that I filled it with several cube feet of Pro-mix soil. Last year not much grew, not even Zucchini! Do you have any suggestions for me to improve the soil?


Abi Griffith, Horticulture Community Education Assistant

Sorry to hear about your last season! For raised beds, we recommend 75% loam (the mineral component of soil) with no more than 25% organic matter (finished compost) mixed together well, rather than a potting soil. This provides most plants with the nutrients and soil structure they need to be healthy. ProMix is ok for seed starting and potted plants but doesn’t seem ideal for a longer term garden bed. Guessing since it has been in there for two years, you may have room to just add new material? There are no standard guidelines for loam or compost, so it’s worth looking at the material first and asking questions of the seller.  Ideally, you’ll be looking for a soil with moderate drainage. Some loam is sold pre-mixed with organic material, such as compost. You may want to ask the seller about the origin of the compost, too.

Information about additional factors to consider when purchasing soil are listed in UMaine Extension Bulletin #2283, Tips for Purchasing Soil for Gardens and Landscape Projects.

Also, our fact sheet, Gardening in Small Spaces, has some more information on raised bed gardens.