Improving Poorly Draining Clay Soil with Organic Amendments and Gypsum

Improving Poorly Draining Clay Soil with Organic Amendments and Gypsum

A percolation test showing 12″ hole draining 2″ and 6″ hole draining 1″ in 24 hours indicates severe clay compaction.

Amendment Strategy

• Dig as deep as possible.
• Mix excavated clay with organic amendment at 1 part clay : 2 parts amendment (more amendment than the standard 1:1).
• Amendment recipe: peat moss, compost/humus, cedar bark mulch.
• Spread granular gypsum over the excavated area before backfilling; also mix some into the blend.

Depth Requirements

• 10–12″ of amended soil sustains grass while gypsum works deeper over years.
• 8″ suffices for most groundcovers.

Alternative: Shallow-Rooted Groundcovers

If you prefer not to amend deeply, plant wet-tolerant, shallow-rooted groundcovers (some evergreen, some flowering, 4–10″ tall, mowable). They thrive in 8″ of loose soil while gypsum improves subsoil.

This approach solves drainage without massive excavation.