I want to enhance the soil in my back yard to plant perennials. What proportion of compost, manure and peat should I add to the existing soil?
Tompkins County New York
Thank you for contacting us about a soil mix for perennials. I'll assume you already have beds in which to plant. If you are just now converting lawn to beds, there would be some differences.
Both compost and manures serve the same function. That is, they add organic matter to the soil which improves water retention, tilth, and plant nutrition. Compost is generally made from plant materials or kitchen waste. Manure is made from animal waste. Both must be decomposed to the point where it is no longer "hot" as soil microbes break it down. Bagged products are usually ready-to-use. If you buy fresh materials in bulk, make sure they have ample time to decompose before using them. This can take 3 months to a year, depending on composting methods.
"Good" garden soil is usually composed of 3 to 5% organic matter, but most residential soils have less unless they have been amended. There is no reason to add both compost and manure, however, I suggest alternating applications in order to optimize the nutrient and microbe diversity.
The organic materials should not be tilled into the soil unless you plan to wait for 3 to 6 months before planting. Since they are only partially decomposed, the action of microbes can cause a short-term deficiency of nitrogen in the soil. If you plan to plant soon, do not till in the organic materials. Instead, apply up to 1-inch of compost or decomposed manure across the surface of the soil after planting. We also strongly recommend topping this off with about 3-inches of organic mulch. The mulch will prevent erosion, maintain soil moisture, and add additional organic matter to the soil as it gradually breaks down over time.
If your soil is especially poor, sandy, or clay-ey, you may want to do more than one application of organic material each year. Generally, spring and fall are good times to add compost and manure. Fall applications will be utilized by plants the following spring. Spring applications will be used later in the season. Using too much does not provide any greater benefit to your plants, and excess nutrients will eventually leach out into rivers and waterways.
You also mentioned using peat moss in the garden beds. We no longer recommend the use of peat because of the environmental degradation caused by its production. Peat has been used in the past as a soil conditioner but it does not provide any plant nutrition. It is essentially what is left long after plant material was totally decomposed and sequestered for ions. Compost and manure will have the same conditioning effect and feed the soil as well.
Peat has also been used to acidify soils; however, it has only a temporary effect on the soil pH since soils will always revert back to the pH created by the source rock minerals. Before attempting to modify soil pH (either higher or lower), you should have your soil tested by a qualified laboratory. This link may help you: