Repotting guide

When & how to repot Sweet alyssum (Lobularia maritima)

Also called sweet alyssum, sweet alison, carpet of snow.

More about sweet alyssum

About Sweet alyssum

Lobularia maritima · also called sweet alyssum, sweet alison · flowering

A low-growing, mat-forming annual or short-lived perennial smothered in tiny, intensely honey-scented white, pink, or purple flower clusters from spring to autumn. Thrives in full sun to partial shade in well-drained soil. Drought-tolerant once established. Excellent for edging, containers, and hanging baskets; self-seeds prolifically.

Mature size: 8–15 cm tall (3–6 in); 20–30 cm spread (8–12 in)

Watch for — Root rot: Overwatering or poor drainage causes rapid crown and root rot, particularly in containers. Ensure excellent drainage and allow the top layer of soil to dry before rewatering. Raised planters with drainage holes are recommended for container growing.

How to tell sweet alyssum needs repotting

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

Roots circling the bottom of the module or pot, or poking out of the drainage holes.
The seedling dries out within a day and growth has visibly stalled.
Roots are white and matted in a tight spiral when you tip the plant out.
It has outgrown its current container for the stage of the season — pot sweet alyssum on before it becomes hard root-bound.

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 sweet alyssum

Pot on seedlings as they grow; not a perennial repot. Sweet alyssumis grown for one season, so the question is really “how often to pot on” — keep moving it up before the roots circle. Low-growing, spreading, mat-forming annual.

What size pot to step sweet alyssum up to

Pot sweet alyssum on gradually — a seedling jumped straight into a huge pot sits in cold, wet, airless soil and stalls. Step up one or two sizes at a time as the roots fill each container, finishing in a large final pot or the ground. The aim is roots that never circle and never check.

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 sweet alyssum

Pot sweet alyssum on through the active growing season, whenever roots fill the current container — there is no single date, just "before it becomes root-bound". Avoid potting on during a cold snap.

Step-by-step: repotting sweet alyssum

Pot on before it is root-bound. Check sweet alyssum regularly; move it up as soon as roots reach the edge of the cell or pot, not after they have circled.
Step up one or two sizes. Choose the next container up — not a giant one. Cold, wet, unused soil around a small root system stalls seedlings.
Knock it out gently. Support the stem, tip the pot, and ease the rootball out without breaking it. A little teasing of circled roots at the base is fine.
Pot into rich mix. Set it into fresh well-drained loam, sandy, or mixed; ph 6.0–7.0 at the same depth (tomatoes are the exception — they can go deeper to root along the stem).
Water in and grow on. Water well, keep it in good light, and resume feeding once it is established and growing again.

Aftercare

Water sweet alyssum in well and keep it in bright light; a freshly potted-on seedling can wilt for a day while roots settle, so do not overcompensate by drowning it. Do not fertilise for about 1 week — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for sweet alyssum

Sweet alyssum wants well-drained loam, sandy, or mixed; ph 6.0–7.0. Thrives in average to moderately fertile, free-draining soil. Does not require rich compost but does need drainage — waterlogged soil causes rapid crown rot. Works well in sandy soils, gravel mulched beds, and container mixes with 20–30% added perlite. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting sweet alyssum — frequently asked questions

How often should you repot sweet alyssum?

Pot on seedlings as they grow; not a perennial repot for sweet alyssum. Sweet alyssum is a seasonal crop, so you pot it on as a growing plant rather than repotting a perennial. Step seedlings up gradually into well-drained loam, sandy, or mixed; ph 6.0–7.0 so the roots never circle the cell, ending in a large final container. A root-bound transplant stalls and never fully recovers.

What size pot does sweet alyssum need?

When is the best time of year to repot sweet alyssum?

Can you put sweet alyssum straight into a much bigger pot?

No. Even a fast-growing sweet alyssum 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 sweet alyssum after repotting?

Not immediately. Wait about 1 week after repotting sweet alyssum. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.