What are succulent plants?
The word “succulent” comes from the Latin word sucus, meaning juice, or sap. Which gives us a hint that these plants somehow contain a lot of liquid.
A selection of succulent plants. There’s a big variation in leaf size, shape and colour but each leaf is a water storage vessel. A thick waxy coating on the surface of the leaf helps prevent water from being evaporated by sun or wind.
In fact, succulent plants are plants that have specially adapted leaves or stems so that they can store water. They tend to have fat or fleshy leaves and are very drought tolerant. In the wild, they grow where the soil is poor or dry, where there may be low rainfall or where hot sun quickly dries up surface water.
Cacti are classed as succulents, so are sedums, house leeks, agaves and ice-plants.
Why are succulents used on green roofs?
The thing about green roofs is that they add weight to a building. Consequently, any structure that is going to support a green roof needs a fairly robust construction. The heavier the roof, the more the total construction costs will be. Architects are keen to keep construction costs affordable, so they want the green roof to weigh as little as possible.
That means using the minimum depth of growing medium, a lightweight growing medium and avoiding waterlogging.
Add this to the fact that drying winds and hot summer sun will evaporate water from a roof very fast. And you have the exact conditions that succulents will love.
A dense carpet of Sedum Spurium that clearly loves growing where it is. Sedums like sunshine and are happy to grow in as little as 20mm of well drained soil.
Any gardener will tell you that it’s cheaper and easier to grow the plants that are best suited to the growing conditions. So it’s logical that succulents are used on green roofs.
Are all succulents suitable for green roofing in the UK?
That depends on how much work you want to be doing. Some succulents won’t grow out of doors all year round in the UK. If you’re planning a living roof, it’s always best to find frost-hardy plants. Unless of course you are prepared to bring them indoors for the winter.
Which succulents are frost hardy in the UK?
A great many plants in the Sedum family are perfectly happy to live outdoors all year long in the UK. Some are even evergreen.
Sempervivums or houseleeks are also good candidates for green roofing. Mesembryanthemums are beautiful and will survive a mild frost – but not a sharp one. They’re worth trying if you live in the Southern counties but don’t get your hopes up if you live North of Birmingham.
Where can I buy succulents for green roofing?
The absolute easiest way to plant succulents on a green roof is to unroll a blanket of sedum plants – something like Enviromat sedum matting.