Repotting guide

When & how to repot Spike Moss (Selaginella kraussiana)

Also called Spike moss, Krauss' clubmoss, Krauss' spikemoss, African clubmoss, Japanese moss, Trailing Irish moss, Spreading club moss.

More about spike moss

About Spike Moss

Selaginella kraussiana · also called Spike moss, Krauss' clubmoss · houseplant

Spike moss (Selaginella kraussiana) is a low, creeping fern relative grown for its fine, feathery emerald foliage and mat-forming habit, ideal for terrariums. It demands constant moisture, very high humidity, and shade from direct sun. The ASPCA lists it as non-toxic to dogs, cats, and horses, making it pet-safe.

Mature size: Around 2-4 in (5-10 cm) tall, spreading 12-18 in (30-45 cm) or more; trim to control its rapid spread.

Watch for — Root rot and mushy stems: Result from waterlogged, poorly drained soil with standing water. Keep soil moist but never soggy and ensure the pot drains freely.

How to tell spike moss needs repotting

Repotting on a calendar is less reliable than reading the plant. For spike moss, watch for these signs:

Roots poking out of the drainage holes or coiling visibly around the inside of the pot.
You are watering far more often than you used to because the rootball dries out within a day or two.
Water runs straight through and out the bottom without soaking in.
Top growth has slowed or new spike moss leaves are noticeably smaller than older ones despite good light.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot spike moss

Every 12–18 months — sooner if roots show fast. Spike Moss's growth habit — low, creeping, mat-forming evergreen with dense, horizontally spreading stems of tiny scale-like leaves; spreads to form a soft ground-cover carpet. — sets the pace. Spike moss (Selaginella kraussiana) is a low, creeping fern relative grown for its fine, feathery emerald foliage and mat-forming habit, ideal for terrariums. It demands constant moisture, very high humidity, and shade from direct sun. The ASPCA lists it as non-toxic to dogs, cats, and horses, making it pet-safe.

What size pot to step spike moss up to

Step up one pot size — about 2–3 cm (an inch) wider. Spike Moss grows fast, so it will fill that space within a season, but jumping several sizes at once still backfires: the unused soil stays soggy and rots even a vigorous root system. One size at a time, every year or so, is the rhythm.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot spike moss

Early spring, just as new growth restarts, is the ideal window for spike moss. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting spike moss

Time it for spring. Repot spike moss in early spring as growth restarts so it re-roots quickly into the fresh soil.
Choose one size up. Pick a pot about 2–3 cm wider with drainage holes. One step only — a much bigger pot stays soggy and rots roots.
Ease the plant out. Water lightly the day before, then tip spike moss out and gently loosen any roots circling the bottom of the rootball.
Repot at the same depth. Put a layer of fresh rich, humus-heavy, moisture-retentive mix with good drainage in the new pot, set the plant so its soil line is unchanged, and backfill, firming lightly.
Water and pause feeding. Water once to settle the soil. Hold off fertiliser for about a month — fresh mix already has nutrients and feeding now burns new roots.

Aftercare

Water spike moss once to settle the soil, then let the surface dry before watering again — fresh mix around the roots stays wetter than the old compacted ball, so the commonest post-repot mistake is overwatering. Keep it out of direct sun for a week or two while roots re-establish. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for spike moss

Spike Moss wants rich, humus-heavy, moisture-retentive mix with good drainage. Use a peat- or coir-based potting mix amended with organic matter to hold moisture, blended with perlite or fine bark so excess water still drains. Slightly acidic to neutral pH (around 5.5-7.0) is ideal. A shallow, wide container suits its spreading, shallow root system. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting spike moss — frequently asked questions

How often should you repot spike moss?

Every 12–18 months — sooner if roots show fast for spike moss. Repot spike moss roughly every 12–18 months, in early spring as growth restarts. It grows fast and circles its pot quickly, so step up one size (about 2–3 cm wider) into fresh rich, humus-heavy, moisture-retentive mix with good drainage. Don't jump several sizes — that soggy excess soil is what rots vigorous roots.

What size pot does spike moss need?

When is the best time of year to repot spike moss?

Can you put spike moss straight into a much bigger pot?

No. Even a fast-growing spike moss should only go up one pot size at a time. A vastly oversized pot holds a reservoir of wet soil the roots cannot reach, which stays cold and soggy and rots the roots — the opposite of what you wanted.

Should you fertilise spike moss after repotting?

Not immediately. Wait about 4 weeks after repotting spike moss. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.