Compost Use in Filling Raised Vegetable Beds
I am the communications coordinator for Emmet County Recycling/Waste Disposal/Composting. We make compost from local yard waste and a relatively small proportion of food scraps from restaurants and households.
I would like to share a recommendation for use of our compost in a mix for filling raised vegetable beds. I saw one answer that said 70% topsoil, 30% compost, but that was from Maryland, so I thought I’d better check in for a cooler climate.
Also, some of our customers are using 100% our compost to fill their raised beds. Should we actively discourage this? In at least one case, we heard they were very pleased with the results after two years (see pic of girl with carrot raised in such a bed, attached).
We have a variety of soils up here: straight sand, nice top soil over sand, nice top soil over clay…
Thanks for considering our question. I love your service!Kate Melby
Emmet County Michigan
Hello and thank you for using MSU Extension's eXtension with your compost question. The definitive answer is it depends. A typical healthy soil has at least 5% organic matter incorporated into it. A compost mix with 30% would be considered a loam soil.
Any good blend of up to 30% would be acceptable soil blend presuming it is being used to incorporate into already poor soils where this ratio will be reduced once incorporated. If your compost is manure based, not more than a ratio of 1:8 is recommended.
Planting in pure compost is fine. Note with the popularity and success of “layered” or “lasagna” gardening technique. Over time compost continues to decompose and mineralize on its own. This is the reason why many areas of poor soils need continued inputs of organic materials to maintain optimum growing conditions, i.e. topdressing lawns. This also does not always replace the need for adding fertilizer. I always recommend regular soil tests to determine if additional inputs are needed.
The most important role of compost besides adding organic matter to the soil is its role in inoculating organisms back into the soil. Thus helping to maintain a balanced soil ecosystem that plants need to remain healthy.