How to buy good bulk and bagged compost
Compost has gained a lot of attention and attracted a number of new products to the market. How can you make sure that what you're buying is really compost or, even better, a high-quality compost? Here are some best practices.
Good compost has lab results and is certified
Many of compost’s benefits are microscopic, so regular testing is the only way to give full feedback to the composter and transparency to the buyer. When looking at a lab report, here are a few things to look for:
The report should be signed and from a lab that at least sounds reputable
Compost needs to pass tests for pathogens (either fecal matter or salmonella) and metals so that it is safe to use
Look at stability, maturity, organic matter, and (potentially) nutrient content to see if the compost will be good for your garden
Seed germination and vigor results demonstrate if the compost will help your plants thrive. This is arguably one, if not the most important, thing in a report since it shows if the compost works.
The U.S. Composting Council (USCC) has two programs to help people find better bulk and bagged compost. First, if a compost maker regularly tests their finished compost, they can join the USCC's Seal of Testing Assurance Program (STA). Second, if the compost meets certain criteria, the U.S. Composting Council endorses the compost as part of their Consumer Use Program. Our Grow Good Compost is certified in both programs. Look for this compost certification and these endorsements when buying bulk or bagged compost:
Checking compost without a lab report
If a lab report from the past three or four months isn't available, you may be able to observe some red flags with the compost.
When made incorrectly, compost can harm soil quality and plant growth,
potentially leading to costly plant replacements and longer-term poor soil quality.
Compost should be a dark brown or black color, even inside of any small twigs. If the inside of a twig is still white or green-ish, or the material looks like a mulch (the size of the individual pieces are mulch-like), the compost may not be processed long enough. As a result, using this unfinished compost could tie up nutrients instead of adding them.
Good compost should small natural and earthy. Avoid compost that smells like ammonia, has any foul odors, or that doesn't have any small -- all signs of a bad compost.
Compost should feel smooth and have some small clumps that break apart easily. Avoid compost that feel slimy or grainy since these can be signs of non-organic material or inadequate processing.
All compost should undergo a Process to Further Reduce Pathogens to kill pathogens and weed seeds.
High-end composting systems can make compost in 45 days. If made without the help of state-of-the-art technology, compost typically takes four to nine months. Because it's a biological process, there are no short-cuts.
Compost can contain a variety of feedstocks--yard debris, food scraps, manure, and human waste, for example--as well as "nutritional" additives. These inputs aren't always readily disclosed, so ask about specific ingredients and make sure you are comfortable with them.