Tufa Trough: An Alpine Garden in a Wide Glass Basin

An alpine trough is the terrarium for growers who kill things with kindness. Every choice here — sloping drainage, a gritty open mix, a limestone scree surface — is made to reproduce the conditions of a mountain scree slope, where water leaves fast and roots travel deep. It is also the only build in this collection designed to be overwintered outdoors in a cold climate.

By The Terrarium DeskPublished 2026-11-01

Stratum by stratum

Sloped crocks

Four centimetres of broken crocks topped with 2 cm grit, deliberately sloped so one end of the trough is twice as deep as the other. That slope is a drainage gradient, and the alpine species you place at the shallow end will be the ones that most resent winter wet.

No filter layer

Unlike every moss build here, there is no charcoal layer. Alpines want an uninterrupted root run from the surface to the drainage zone, and a charcoal barrier interrupts the capillary column that keeps the deep roots supplied in summer.

Alpine mix

Grit, loam and leaf mould at roughly 5:3:2, to 7 cm. This is a lean mix — the loam holds the minerals, the grit provides the air, and the small amount of leaf mould feeds the plants slowly rather than pushing soft growth that winter will kill.

Scree surface

Two centimetres of tufa chips and limestone scree, worked in around each plant collar with a spoon. Tufa slowly releases calcium and is porous enough for saxifrage roots to colonise it directly, which is why it is worth sourcing properly.

Planting for a mat

Place Raoulia and thyme toward the front where they can spread over the scree, Sempervivum at the shallow, driest end, and Saxifraga at the deep end. Water with a rose at the rim, never overhead, and stop entirely once the plants close their mats.

Growing on

Raoulia australis is the plant that makes an alpine trough look established, and also the one that most often dies in cultivation — it needs sharp drainage, full light and above all dry winter air around its crown, which the scree surface provides. Thyme is the workhorse and will tolerate the most. Sempervivum needs the shallowest, driest corner and will rot in a season if placed where water collects. Saxifrage is the most demanding and rewards a position where its roots stay cool and moist while its crown stays dry.

Upkeep rhythm

Water thoroughly whenever the mix is dry 3 cm down — in summer that may be every third day for a trough this shallow and this wide. Stop watering entirely from late autumn until the plants show signs of growth, since winter wet is what kills alpines, not cold. Top-dress with fresh scree every spring to keep the plant collars above the damp line. Shear thyme and Raoulia lightly after flowering to keep the mats tight; an unpruned Raoulia mat will lift and die in the centre.