Standard Topsoil & Hydroseed Installation Practice
Topsoil is often a loosely used term. When we refer to topsoil in the industry, we mean blended and screened materials that are combined together to formulate topsoil that is within the municipally-specified topsoil mix.
"Muni spec" topsoil is:
Peat moss (organics)
These elements are all in appropriate portions to compose the specified topsoil.
Here in Anchorage, we are fortunate enough to have a large enough supply of peat moss to use it as the base of our topsoil product.
Peat moss is decomposed organic matter that has a PH that is preferably about 7.5. The loam and sand are added to provide drainage and the ability to become somewhat firm, but allow roots to freely spread as deep as needed to gather as much nutrients from the soil as possible.
We have several grades of topsoil based on the end need and use. With deeper planting beds for trees and shrubs, we can commonly curb cost by using a larger opening on the screen we use for sifting stones and sticks from the process. We use a 1" screen for "class B" topsoil. We use a smaller 1/2" screen when screening, for example, a lawn that will be walked on and mowed and such, as you would not want too big stones or sticks in your lawn. In bedding it's not an issue, as there is more than likely a topping of weed fabric and stone or bark mulch over the soil.
Another process becoming very common is the blending of compost into our topsoil blends. We make our compost from wood chips from the tree felling part of our operation and lawn and leaf debris from our grounds maintenance division. We roll the piles periodically to infiltrate air into the composting material. We also use red wiggler worms to aid in the composting process. When the final product is screened, we are left with a finely graded, nutrient rich, PH-balanced compost that is excellent when added into our topsoil blend.
More about our topsoil process
Topsoil will be installed at a depth of 3-4” after compaction. The soil will be sacrificed to receive hydroseeding with maximum result. The seed application rate will be approx 7 LBS per 1000sf. This is nearly 3x the recommended minimum application rate. Starter fertilizer will be added to the hydroseed slurry.
We use a combination of wood cellulose fiber mulch and virgin wood fiber mulch. The combination of mulches is a great water retention agent and aids significantly in erosion control on 3:1 slopes or less.