What are hydroseeding and hydromulching?

Hydroseeding and hydromulching involve spraying water-based mixtures to help establish grass or prevent erosion. Hydromulching uses water, mulch and a substance to help it stick. Hydroseeding adds seed and fertilizer to the mix. Hydroseeding can be used on yards, but is more often used on slopes. The method is generally less expensive than sod but more expensive than seeding.