Fixing Drainage Over Buried Parking Lot Sub-base

A Charlottesville native garden project over a former asphalt lot hit an impermeable stone layer at 8 inches. Water stood for 3+ days; a steel rod to 3 feet didn't help.

Diagnosis & Solution

1. Rent a power auger and bore 4-foot holes every 4 feet to map layers.
2. Likely finding: 6–8 inch gravel base from the old lot.
3. Drill through it with the auger; backfill holes with washed coarse gravel to create drainage columns.
4. Add 6–8 inches of soil/compost blend over the entire area and till deeply.
5. Monitor pH—limestone base may raise pH, locking up nutrients.

Root Zone Depth

Perennials need >8 inches of workable soil. The auger columns plus amended top layer create a functional root zone.