"Why is our compost not very uniform, not very black, and still contains large sawdust particles? We mostly use wood pellet bedding."
STALL BEDDING: It is good that you are using wood pellet bedding because you generally get less wood products in the compost mix. It has a finer texture, a higher surface area, and will ultimately break down faster than shavings. That being said, wood breaks down slowly, even under optimized composting conditions. In my opinion, an ideal mix consists of 80% manure and 20% stall bedding. That can be difficult to achieve if you are composting all of the manure waste. Do your best to minimize the stall bedding in the mix.
COLOR: The color of the compost is a function of the feedstocks going into the process. Horse manure and a wood-based stall bedding material will yield a brown (not black) finished compost. You can deepen the color of your compost by adding grass clippings to the mix. Most compost that we see in the market place is derived from green waste which yields a dark brown to black product. However, compost quality is not a function of color.
QUALITY: There are many ways to determine the quality of your compost:
- Lab testing (e.g. Wallace Labs in El Segundo, CA);
- Simple growth trials with a 50:50 mix of your compost with potting soil in your tomatoes, peas, and beans;
- Placing a 2-cup sample in a sealed Ziploc bag for ~2 weeks to check for weed seeds; and
- Smelling it (it should smell like rich topsoil).
APPEARANCE: Horse manure compost is typically "lumpy and chunky" when removed from the compost bin. The lumps are where you will find a majority of the beneficial micro-organisms and nutrients. They will break down over time as the compost continues to cure. Many of our clients spread their compost on pastures and mow or harrow over the top to break up the lumps and incorporate the compost into the root zone.
As the woody fraction continues to break down, it releases organic acids that help reduce compaction of overly dense soil. This also helps with infiltration of and retention of rainwater, and increases draught resistance. The woody fraction will initially capture some of the available nitrogen from the soil but, over time, it acts like a nitrogen bank account releasing the stable, plant-available form of the nitrogen (nitrate-nitrogen) back into the soil.
MOISTURE CONTENT: At the 21-30 day mark, it is a good idea to dig a hole into the core of the pile to check the moisture content. I use a posthole digger to accomplish this. If the core is dry, remove the compost from the bin and rewet it as you transfer it back into the curing pile. In arid climates (e.g. AZ and NM), it is recommended to "flip" the compost once from one bin to another and rewet it as you do so.