raised bed soil

Asked January 14, 2018, 8:47 PM EST

my research recommends 1/3 vermiculite , 1/3 peet moss, and 1/3 compost. where do i get good quality compost? I heard the leaf compost at College Park or other places is OK but does not have all one needs. Can I get some of that and some horse manure? I have 4 - 4' X 4' 8" deep beds to fill.

Montgomery County Maryland

1 Response

Here are some thoughts.
Purchasing soilless mix is not recommended unless you have one or two small raised beds. In that case you can use a 50:50 mix of Pro Mix (bale) and compost or leaf gro.

Test the existing soil where the raised bed will be located even if you plan to add purchased topsoil. Pay for a basic soil test from a certified soil lab (more accurate and complete and usually less costly than diy testers. The pH level should be in the 6.2-6.8 range.) Test your soil for lead. Soil test page with link to list of certified soil testing labs. http://extension.umd.edu/hgic/soils/soil-testing

Types of organic matter include composted yard waste (home-made, purchased from your landfill, Leafgro). Mushroom compost is a good garden compost. Well-rotted farm manure added and turned under in the fall is good but can introduce weed seeds. You can increase soil organic matter levels with buried kitchen scraps, cover crops, and yearly additions of compost. Here is information on beginning your own home composting.hgic.umd.edu/content/documents/HG35BackyardComposting10_2010final_000.pdf

If you want to use the existing soil:
If the soil is in good shape (not compacted, drains well) add 4 inches of compost and mix it with the top 4-inches of existing soil using a tiller, spade, or garden fork. You can also help loosen soils with high clay content by pushing in your garden fork and rocking it back and forth. Move the fork 6-8 inches and repeat across the entire bed.

If you want to make the bed deeper:
Try to locate a business that produces and sells a compost/topsoil mixture (often 70% topsoil; 30% compost). There are mulch/topsoil suppliers that sell this. If you purchase topsoil with no added compost you should plan on adding at least 2-inches of compost.
Topsoil sales are not regulated. Determine quality of purchased topsoil before it’s delivered. Determine quality of purchased topsoil before it’s delivered. Watch out for soils that are white, gray, or black, smell bad or don’t look or feel like topsoil. Ask the company for soil test reports and information on the origin and quality of the topsoil.
See our website on Preparing the Soil http://extension.umd.edu/hgic/plants/prepare-your-soil