Repotting guide

When & how to repot Mountain Alyssum (Alyssum montanum)

Also called Mountain Alyssum, Mountain Madwort.

More about mountain alyssum

About Mountain Alyssum

Alyssum montanum · also called Mountain Alyssum, Mountain Madwort · flowering

Mountain Alyssum is a low-growing, silver-grey cushion perennial native to rocky slopes and cliffs of central Europe. In spring it is smothered in dense clusters of bright yellow, honey-scented flowers. Exceptionally hardy and drought-tolerant, it suits rock gardens, dry stone walls, and raised beds. Often confused with Aurinia saxatilis but smaller and more refined.

Mature size: 10–20 cm tall, 30–50 cm spread

Watch for — Legginess after flowering: Without pruning, plants become woody and open in the centre. Trim back by one-third immediately after flowering to stimulate fresh compact growth; avoid cutting hard into old wood.

How to tell mountain alyssum needs repotting

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

Roots growing out of the drainage holes, or the rootball lifting the plant proud of the rim.
Soil that has shrunk away from the pot sides and no longer holds water.
The pot is unstable because the plant has grown top-heavy.
Old, compacted, broken-down mix that stays wet too long — for a succulent that is a rot risk, so refresh it even if the pot size is fine.

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 mountain alyssum

Every 2–3 years, into bone-dry mix. Mountain Alyssum's growth habit — low-spreading, mat or cushion-forming perennial subshrub — sets the pace. Mountain Alyssum is a low-growing, silver-grey cushion perennial native to rocky slopes and cliffs of central Europe. In spring it is smothered in dense clusters of bright yellow, honey-scented flowers. Exceptionally hardy and drought-tolerant, it suits rock gardens, dry stone walls, and raised beds. Often confused with Aurinia saxatilis but smaller and more refined.

What size pot to step mountain alyssum up to

Use a pot only one size up — or even the same pot with fresh gritty mix if the roots have room. Mountain Alyssum stores water and rots in a large pot of slow-drying soil. A tight terracotta pot that dries fast is far safer than a generous plastic one. Never up-pot a succulent by several sizes.

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 mountain alyssum

Spring or summer, while mountain alyssum is in active growth and warm, is best — roots recover fastest then, and the plant is not sitting in cool damp soil. Avoid repotting a succulent in winter dormancy.

Step-by-step: repotting mountain alyssum

Repot dry. Do not water mountain alyssum for several days first. Working with dry roots and dry mix dramatically lowers the rot risk for a succulent.
Pick a snug, fast-draining pot. Choose terracotta one size up at most, with a drainage hole. Have gritty lean, sharply drained, neutral to alkaline soil ready.
Tip it out and clean the roots. Slide the plant out, crumble off the old soil, and trim any black, mushy or dead roots with clean snips.
Pot into dry mix. Set mountain alyssum at its original depth in dry gritty mix, firming gently. Do not bury the stem deeper than it was.
Wait a week before watering. Leave it completely dry and out of harsh sun for about 7 days so any damaged roots callus. Only then water lightly.

Aftercare

Keep mountain alyssum completely dry and out of fierce sun for about a week so any nicked roots callus before they meet moisture; watering a freshly repotted succulent is the classic way to rot it. Then resume the normal lean, dry rhythm. Do not fertilise for about 3 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for mountain alyssum

Mountain Alyssum wants lean, sharply drained, neutral to alkaline soil. Best in a gritty, low-fertility mix with pH 6.5–8.0. Thrives in limestone-based soils. Mix coarse grit into planting areas to enhance drainage. Avoid rich composts. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting mountain alyssum — frequently asked questions

How often should you repot mountain alyssum?

Every 2–3 years, into bone-dry mix for mountain alyssum. Repot mountain alyssum every 2–3 years into a snug pot of lean, sharply drained, neutral to alkaline soil, ideally in spring or summer. Let it sit in dry soil and do not water for about a week afterwards so any nicked roots can callus. Over-potting and watering straight away is what rots succulents.

What size pot does mountain alyssum need?

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

Should you water mountain alyssum after repotting?

No — not straight away. Repot mountain alyssum into dry mix and wait about a week before the first watering so any damaged roots callus over. Watering a freshly repotted succulent is the single most common way to rot one.

Should you fertilise mountain alyssum after repotting?

Not immediately. Wait about 3 weeks after repotting mountain 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.