Pick a Groundcover for Flagstone Joints Based on How Much Sun Each Spot Gets

The Problem

A single groundcover planted across every joint in a flagstone patio or terrace ignores that sun exposure usually varies a lot across one surface — a corner shaded by a house or tree gets nothing like the light a spot in the open gets. Plant one thing everywhere and it thrives in some joints and struggles or dies in others.

The Main Types and When to Use Them

Irish moss — for the shadiest, dampest joints, where little direct sun reaches. It spreads slowly between the cracks and stays low and mossy; it won't tolerate a full-sun spot the way the other two can.

Mazus reptans — for the transition zones, roughly 50-50 part sun and part shade. Unlike moss, it produces a small flower in spring as it establishes, and it spreads over time to fill in the joints it's planted in.

Creeping thyme — for joints in direct sun all day. Originally a Mediterranean plant, it's built for heat and handles foot traffic well; it has small leaves, a light fragrance from being part of the thyme family, and is notably resilient once established.

All three knit into the stone joints as they spread, gradually softening individual pavers into one continuous planted surface rather than a grid of hard lines.