Planting Between Slate Patio Stones in a Wet Seattle Climate

A Seattle homeowner has an 8-year-old Montana slate patio on a sand base. Cracks were filled with potting soil, but moss dominates. Baby tears and sedum fail. They want a crack filler that supports low plants.

Why Previous Plants Failed

• Sedum needs full sun and sharp drainage—Seattle shade and moisture are opposite.
• Baby tears (Soleirolia) wants deep shade and constant moisture—may get too much sun or dry out between rains.
• Potting soil holds too much water, compacts, and encourages moss/algae.

Better Crack Filler Mix

Use a 1:1:1 blend of coarse sand : loam : peat (or coconut coir). This drains well, resists compaction, and holds enough moisture for establishment.

Plant Recommendation: Dichondra repens

Also called kidney weed or dichondra. It:

• Tolerates sun to part shade.
• Handles moderate foot traffic.
• Forms a dense, low mat (1–2 inches).
• Stays green year-round in mild climates.
• Outcompetes moss once established.

Alternatives for Seattle: Leptinella squalida (brass buttons), Pratia pedunculata (blue star creeper), or native Sagina subulata (Irish moss, not true moss).

Moss Management

Moss indicates shade, moisture, acidity, compaction. Improve drainage, prune overhead branches for light, and apply lime if soil pH < 6.0. But Dichondra will largely displace it.

Expert: Jonathan Radford | www.ecologicagardens.com