Why Did My Hydroseed Turn to a Black Crust?

Soil Testing and Preparation

• A soil test is a must prior to seeding a lawn. This will tell you the pH of the soil so you can amend it if necessary. The average soil pH for grasses is neutral or 6.5 to 7.0 but it does vary by grass variety. Improper soil pH can affect seedlings ability to intake water and nutrients. Acidic soils can burn the roots of tender new seedlings. It can also adversely affect germination. Soils for grasses require 2 to 3 percent organic matter in the topsoil. This means you should top dress the soil with topsoil or compost before hydroseeding.

  Improper soil preparation can leave you with a seed bed of discolored or black hydroseed and a dead lawn.

Herbicide Pretreatment

• Weeds are competitors for the nutrients and moisture that the grass also needs to grow rich and thick. It is important to minimize their presence early in the grasses establishment. A pre-emergent herbicide may be applied prior to hydroseeding. If the formula isn't chosen with care, or is broad spectrum, it can adversely affect the hydroseed mat. The herbicide can work up into the mat when watered and cause the germinating seedlings to blacken and die. The hydroseed mat appears discolored and the lawn does not sprout.

Watering

• Water is a component of the slurry, but is also an important part of aftercare. The seeds must be kept wet to germinate, though they cannot be allowed to sit in puddles of water. Moisture needs are a finely balanced issue that can cause moldy black spots or dead brown or black areas in the germinating grass if not properly applied. The hydroseed needs to be watered twice per day in hot weather and once in average temperatures.

Slurry Mixtures

• The slurry is the sprayed-on mix that carries the seed, moisture and nutrients necessary to produce a lawn. It is combined with a thin mulch to help hold the seed in contact with the soil and conserve moisture. The two main types are paper and wood. The wood mulch breathes better than the paper. The paper forms a crust over the soil that may discolor as the plants begin to germinate. It seals in the soil better than the wood but can also invite mold to form underneath when excess moisture is present. This leaves you with a black crust on the bed surface.