soil for a raised bed garden
I have constructed a raised bed that will need approximately 8 cubic yards of soil. What materials and ratios are recommended? I visited Pioneer Sand and they suggested a planters mix of 70% top soil, 20% biocomp compost, and 10% dairy compost. Is this reasonable? Any other suggestions?
Larimer County Colorado
The key to raised-bed soil is that is must be well-drained and doesn't compact easily. I am not familiar with the Pioneer mix, but it sounds like it contains some good organic matter. Make sure the dairy compost (manure) is well composted as it could increase salt levels. Having organic matter (peat moss, compost, composted manures) will greatly improve drainage and soil health. It will also provide some nutrients (not a lot) to the soil. Some references recommend 1 part organic matter to 1 part perlite to 2 parts soil (50% soil, 25% perlite, and 25% compost). Your 2-1 ratio of soil:compost is close to this recommendation.
You could also consult with other companies in the area that sell soil mixes and see what their "recipes" include. There isn't a perfect soil mix. As you begin gardening, you'll also do some amendments throughout the years. Be careful of over-amending. A soil test now (up front) and every 2 to 3 years would be helpful so you can keep track of your organic matter content, salt levels, and nutrition. A soil test can be done at Colorado State University for $31: http://www.soiltestinglab.colostate.edu/