How often have you been advised to add more organic matter to your garden beds? We all know compost is a magic elixir, but can you over do it? Most of us can barely make enough to keep up with our needs, so maybe this question is moot, but I was curious, none the less.
I’ve read that you shouldn’t start seeds in pure compost. I’ve never gotten a definitive answer as to why, but most experts are in agreement with a general “No”. However I know a couple of gardeners who swear by it and the tomato plants that have volunteered in my compost heap look healthier than the ones that have been putting on a valiant show in my garden.
But back to my original question, can there be too much compost?
Short answer, yes. However the real problem is that compost can be so variable. As with top soil, there are no regulations governing what can be called compost. It all depends on what goes into it and how well decomposed it is.
Let’s Assume Your Compost is Perfect
Even the best of compost is not recommended for permanent plantings, like lawns, trees and shrubs. The organic material eventually decays and compacts the original soil in the process. So you’re left with a concave lawn that does not drain well.
However when used in moderate amounts in beds that are reworked or replanted every year, there are clear benefits. Good soil should contain about 5% organic matter by weight or 10% by volume.1 And while compost is not high in nutrients, those it has are slowly released into the soil.
But the real beauty of compost is that it improves the ecosystem in the soil, attracting the microbes and other beneficial organisms that do the true magic of releasing nutrients in a form that plants can access.
While it may seem logical to think more nutrients lead to healthier plants, there actually is too much of a good thing. An excess of nutrients can lead to problems with your plants, but very often this excess is simply washed away into the ground water and eventually into nearby bodies of water. If we all do that, it can lead to a domino effect of problems, since our water sources effect every part of the natural world.
Top dressing with compost or working a couple of inches into the planting bed is fine. The best thing to do is to have your soil tested, so you know what it actually needs. I’m generally too busy, or lazy, to do that in the spring. Instead, I try and let the plants tell me if they’re happy. I guess not being able to make enough compost to meet my needs makes me a lucky gardener. Who’d have thought?