A prospective client gave me the opportunity to help him make sense of the various quotes he received today for lawn installation and bed preparation. He’s a smart consumer, and not the source of the title quote, “Isn’t it all just dirt?” But I’ve definitely heard the question before, even from others in the trade. So, here are some excerpts from my reply to him:
Loam (sometimes pronounced “loom” in MA) technically refers to soil composition, not necessarily soil quality. it should have approximately equal parts of sand, silt and clay, but may or may not have a high organic content. “Loam” in the trade refers to any harvested soil (usually dug up from housing lots or fields prior to development). As sold, it is typically low in organic matter, though it may be screened to remove large rocks & debris. More organically-rich topsoil is harvested & sold separately, at a higher price. Compost is made of decomposed plant material, and is high in organic matter, microbial life, and nutrients.
So, what’s the big deal about compost? Many weeds thrive in nutrient-poor, compacted soil, while turfgrass and many other cultivated plants like rich soil with pores to hold air and water. Addition of compost makes lawns more favorable to grass and other desirable plants than to weeds. In fact, we’ve seen weed reduction in lawns over time primarily due to regular addition of organic matter. When compost is added as a topdressing instead of tilled in, it becomes incorporated into the top few inches of soil over time through the activity of worms and beneficial insects (assuming that you don’t use pesticides that kill the bugs you want with the bugs you don’t want).
What about peat moss as a soil conditioner? Because we’re accredited in organic landcare by NOFA, we voluntarily adhere to their standards, which frown on peat. It’s a harvested, non-renewable (short-term, anyway) resource. It also acidifies the soil, requiring application of lime to counterbalance it’s effects (vs. compost, which has a nearly-neutral pH). Conventional contractors use peat moss because it is very light, therefore cheap to install. It also holds a heck of a lot of water, making it less likely that the seeds will dry out before germination if someone forgets to set up a timer on the sprinkler. However, at the rate it’s usually applied, it adds a negligible amount of organic matter to the soil.