Environmentally-friendly green roofs attract wildlife and help insulate buildings in winter and keep them cool in summer. The easiest way to install one is with sedum matting, which you can buy by the yard.
When to Start: Spring
At Its Best: All year round
Time to Complete: 2-3 hours, or longer, depending on roof size
If you want to cover a roof on your house, it is best to consult an expert first to ensure that the proposed area can take the weight of the planting and growing medium, and that it has sufficient drainage. Green roof specialists can be found on the internet or in local directories.
For flat or gently sloping shed roofs or similar garden structures, sedum matting is the best option for because it is easy to lay and maintain. Sedum mats come complete with mature plants already established on a special material and in growing medium, and should be laid soon after delivery. The matting is heavy, especially when wet, and will require two people to lift it onto the roof.
First, lay a heavy-duty plastic sheet, such as a pond-liner, over the roof to create a waterproof root barrier, then add a layer of sand or gravel, or a custom-made underlay sold by the suppliers. Ensure that the surface is even to prevent puddling when it rains since the plants do not tolerate waterlogging.
Place your sedum matting on the roof and trim with a sharp knife. The matting has an extra flap of material at each side. To butt up two sections of matting, unfold this flap on the first piece, and lay the second on top of it. This creates a perfect seam and anchors the matting. Don’t use small pieces of matting at the edge of the roof because they will dry out quickly and the plants may die.
To ensure that the plants thrive, don’t walk or kneel on them when installing the matting. Water plants during dry spells until they are fully established. After the first year they will require extra irrigation only during severe droughts. Apply a slow-release granular fertilizer each spring, and replant any bald patches with young plants. Some green roof suppliers offer specialist fertilizers, but one formulated for succulents and drought-tolerant plants will also do the job. Most weeds find it difficult to survive in the thin, dry soil, but remove any that do appear as soon as you see them.
Although sedum mats come already planted up, you can add plants of your own as bald patches appear. Choose from the following to create a sea of color throughout the year.
Image 1: Thymus 'Doone Valley'; 5 inches high, 14 inches wide
Image 2: Sedum acre 2 inches high, 24 inches wide
Image 3: Scabiosa lucida; 8 inches high, 12 inches wide
Excerpted from How to Grow Practically Everything
© 2010 Dorling Kindersley Limited