Alpine plants

Alpine plants grow above the tree line and are adapted to extreme weather conditions, surviving drought, high winds, intense sunlight and poor soils. Find out more about them here.

The alpine zone

Growing in the mountains of the world, alpine plants are adapted to extreme weather conditions, surviving drought, high winds, intense sunlight and poor soils. The alpine zone is found above the point at which trees can survive, known as the tree line. The altitude of the tree line varies and can be at 4000 metres in the Himalaya and near sea level towards the north and south poles.

Iris lineolata in the Armenian mountains

Habitats

The habitats in the alpine zone vary enormously. Rocky slopes and cliffs may not have much soil so the alpines that grow there usually have long taproots that delve deep down to search for moisture and nutrients. Valleys eroded by glaciers will often have only thin soils with exposed rock and debris left by the retreating ice. Erosion of mountain peaks and ridges, particularly by repeated freezing and thawing of water in cracks in the rock, creates steep piles of rubble called scree slopes. Plants that grow on scree slopes are adapted to growing in loose, shifting rock and they have long searching roots to find water. In winter all water is frozen, so alpines must be able to survive drought, often becoming dormant or retreating underground as bulbs or tubers until the spring melt water arrives.

Red hot pokers on the Rock Garden at Kew

Defining alpines

The plants that grow in these habitats above the tree line are true alpines. However, many of these habitats also occur below the tree line, in the subalpine zone, and the plants that grow here are similar to alpines. This is where the common definition of alpine becomes unclear. A steep-sided gorge or rocky slope below the tree line will support a range of plants that are just like the true alpines higher up the mountain and they are equally suitable for growing on a rock garden or in an alpine house. This means that, in horticultural terms, an alpine is classed as any hardy plant that is a suitable size for growing on a rock garden, alpine trough garden or raised bed. This vague definition covers an assortment of plants, including bulbs (e.g. white hoop petticoat daffodil), cushion-forming plants (e.g. Saxifraga burseriana), meadow flowers (e.g. cotton daisy), small shrubs (e.g. Vallea stipularis) and woodland perennials (e.g. snow trillium).

Where to see alpines at Kew

At Kew you can see a range of alpine plants in the Davies Alpine House and on the surrounding Rock Garden. They are mostly grown in free-draining soil to mimic their natural environment but the rock garden provides a range of habitats, from sunny slopes to shady gullies. Streams and waterfalls represent the cascading melt water found in the mountains, and along the water’s edge are more moisture-loving species.

Want to learn more? Follow Kew's Alpine and Rock Garden Team blog.