Make an alpine green roof
Alpines are the perfect plants to grow on top of your garden shed
I’s great fun to make a little green roof using alpines, whether on top of a shed, log store or even a rabbit hutch. Just make sure the structure is strong enough to support the weight of soil and plants on top. You need only have a depth of 5-8cm (2-3in) of gritty soil over a waterproof membrane. There’s plenty of more detailed information in my book ( Alpines – An Essential Guide) or on the internet on just how to go about it.
When it comes to choosing the plants they need to be tough as they have to be able to withstand the extremes of sun, drought, wind, rain and winter weather, so here are a few that will do just that!
Traditionally people often start with sedums on a green roof and they’re hard to
beat, even tolerating complete drought for a short while. There are many to choose from but some good ones to try are Sedum kamtschaticum, with green leaves and golden flowers, sedum ‘Golden Queen’, with very neat, creamy yellow foliage and sedum ‘Dragon’s Blood’.
Another drought-tolerant choice, available in many colours, are sempervivums. With their fleshy rosettes forming compact clumps and stout stems of usually pinkish flowers, they’re instantly recognisable. Sempervivum ‘Virgil’ has grey-pink foliage, S. nevadense a zingy yellowy-green and S. arachnoideum has rosettes covered in white hairs, giving it the common name of cobweb house leek. Flowering during early summer, Erysimum kotschyanum is a lovely lemon-yellow mini wallflower. It makes a striking combination grown alongside the exquisite blue-flowered Gentiana verna, which will seed around if happy and is one gentian able to withstand shallower soils on account of its diminutive dimensions.
You might think you know your onions but have you come across a little blue alpine allium? Allium sikkimense is useful for adding a bit of height among generally low level alpines and it mildly self sows to make casual drifts of blue pom-poms in the summer months.
If pink’s your thing then the brilliant cerise flowers of phlox ‘Crackerjack’ are hard to beat in summer. It makes a neat clump and, like all alpines, the flowers are very popular with pollinating insects. Equally beloved of bees and butterflies is an intense red alpine
thyme ‘Red Elf’ which is also neater than most thyme varieties and when flowering has a lovely honey scent. A really delightful, and non-invasive campanula is Campanula
portenschlagiana, with its neat hummocks of grey-green foliage and masses of bright purple flowers all summer.
No alpine garden is complete without a saxifrage, of which there are literally hundreds of species and varieties. Not all are suitable for a green roof, but one that does really well is named ‘Doctor Clay’. It’s particularly nice for
the evergreen, silver-grey leaves formed into compact rosettes which look great all year and in summer has 20cm (8in) wiry, reddish stems with clusters of billowing white flowers.
Even though these alpines can stand it quite dry, like any plants they don’t want to be completely dry so make sure to keep an eye on watering in any periods of hot summer sun.