Angela Lambert
16th April 2013

hose on sedum roof

Watering a sedum roof

As a nation of gardeners, we are generally quite enthusiastic about watering our plants to keep them in good health.  The trouble is, it’s very easy to get it wrong.   I’ve lost count of the number of houseplants I’ve killed with kindness and the number of vegetable plants that have produced pathetic crops because I’ve been lazy with the watering can is probably well into double figures.

Water requirements of sedum roofs

A sedum roof is a different animal altogether.   Think of it as a giant sized butler sink crammed with alpine plants but lifted high off the ground – too high for everyday access.

An outdoor, container grown alpine garden at ground level is very self-sufficient, provided that it has the right soil type and the right drainage.  It rarely needs watering, the British weather does all that and although it relishes a light feed in spring time, it more or less cares for itself.

A sedum roof is just the same.  Provided that the right drainage and growing medium have been used, the roof slope is not too steep and the plants are given the right food in springtime, an established sedum roof will care for itself without a water-guzzling irrigation system.   In fact too much water is worse for the sedum plants than too little water.

Sedum plants are very drought tolerant because of a built-in metabolism called CAM  or crassulacean acidic metabolism.  In terms of green roofing, this means that sedums can thrive in a shallow layer of growing medium where other plants struggle to survive.  This provides a bonus in that on a normal year, any weeds that manage to germinate on a shallow substrate sedum roof,  will generally die of thirst - provided that we humans don’t alter the conditions and make the roof weed-friendly.

When to water a sedum roof

Like all plants, an Enviromat sedum roof will need watering until it is established, but will be independent after that.  Too much water will encourage weeds. Only water your Enviromat roof if your roof is very windy and dries out quickly, if the slope is greater than around 10 degrees, or if, during a drought, the leaves start to look like wrinkled balloons.  Other than that, let nature do the work for you.