Repotting guide

When & how to repot Cobweb Spiderwort (Cyanotis arachnoidea)

Also called Cobweb Spiderwort, White Grass of the Dew, Grass of the Dew.

More about cobweb spiderwort

About Cobweb Spiderwort

Cyanotis arachnoidea · also called Cobweb Spiderwort, White Grass of the Dew · houseplant

Cyanotis arachnoidea is a creeping, softly hairy perennial from tropical Africa and Asia, bearing cobalt-blue or pink three-petalled flowers. Its prostrate stems root freely at nodes, making it an excellent groundcover or trailing basket plant. It needs bright light, well-draining soil, and warm, humid conditions.

Mature size: 5–15 cm tall; stems spreading to 60 cm

Watch for — Root and stem rot: Overwatering or poor drainage causes soft, blackened stems at the base. Always use pots with drainage holes and allow the surface of the soil to dry slightly between waterings.

How to tell cobweb spiderwort needs repotting

Repotting on a calendar is less reliable than reading the plant. For cobweb spiderwort, 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 cobweb spiderwort 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 cobweb spiderwort

Every 12–18 months — sooner if roots show fast. Cobweb Spiderwort's growth habit — prostrate, creeping perennial herb with branched, fleshy stems that root at nodes. forms a low mat or trails in hanging baskets. — sets the pace. Cyanotis arachnoidea is a creeping, softly hairy perennial from tropical Africa and Asia, bearing cobalt-blue or pink three-petalled flowers. Its prostrate stems root freely at nodes, making it an excellent groundcover or trailing basket plant. It needs bright light, well-draining soil, and warm, humid conditions.

What size pot to step cobweb spiderwort up to

Step up one pot size — about 2–3 cm (an inch) wider. Cobweb Spiderwort 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 cobweb spiderwort

Early spring, just as new growth restarts, is the ideal window for cobweb spiderwort. 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 cobweb spiderwort

Time it for spring. Repot cobweb spiderwort 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 cobweb spiderwort out and gently loosen any roots circling the bottom of the rootball.
Repot at the same depth. Put a layer of fresh moist, well-draining organic mix 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 cobweb spiderwort 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 cobweb spiderwort

Cobweb Spiderwort wants moist, well-draining organic mix. Prefers a rich, airy potting mix with good drainage — combine general compost with perlite or coarse sand. Ideal pH is 5.5–7.5. Avoid heavy clay-based composts that retain too much moisture. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting cobweb spiderwort — frequently asked questions

How often should you repot cobweb spiderwort?

Every 12–18 months — sooner if roots show fast for cobweb spiderwort. Repot cobweb spiderwort 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 moist, well-draining organic mix. Don't jump several sizes — that soggy excess soil is what rots vigorous roots.

What size pot does cobweb spiderwort need?

When is the best time of year to repot cobweb spiderwort?

Can you put cobweb spiderwort straight into a much bigger pot?

No. Even a fast-growing cobweb spiderwort 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 cobweb spiderwort after repotting?

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