How and Why to Choose Plants for a Green Roof

Plants are unique and wonderful (rather like humans) and they sometimes grow where they shouldn’t and often don’t grow where the conditions are perfect. Pop them on a roof and they behave with even more variation. I shall endeavour to explain further. On the ground plants have a wealth of soil depth at their disposal, which can be enriched where needed to give them exactly the mixture they require. They can be tended, protected from weather not conducive to their wellbeing and generally crooned over and nurtured. On a green roof they need to be much tougher to survive both the finite soil depth (substrate) and being much more at the mercy of the elements. However many wild flowers thrive in this environment, growing best in nutritionally poor soil so long as it is free draining and there is enough depth for their roots to spread.

The two most common planting schemes used on green roofs are sedum and/or wildflower. However which ever plants you choose they will behave differently every year depending on the climatic conditions that occur during the various seasons e.g. temperature and rainfall in the spring when plants are thinking about coming back to life. If you think of a green roof as it really is – a Living Roof – then it is much easier to embrace the year on year variations that occur.

Whilst some people opt specifically for either a sedum or wildflower roof (both laid as a turf which is always my recommendation for ease of establishment), it is perfectly possible to have the low growing neatness of a sedum roof and plant wild flowers both individually or in little clumps to provide added visual interest and increase bio-diversity. It is also possible to plant small bulbs in the substrate such as snowdrops or tete-a-tete daffodils. Nothing too big mind, as the depth of substrate will only be enough to support the smallest bulbs.

The following is a list of wildflowers that in my experience usually do very well on a roof whatever conditions get thrown their way. This comes with the caveat, of course, that plants have their own agenda and sometimes the best laid plans don’t always work out. There are many more that can be found, often self-seeded, so this is no way a comprehensive list but rather a place to start. I also always encourage trying plants out that wouldn’t typically be in green roof mix but you know they have every possibility of surviving.

Plantago media (Hoary Plantain)

Plantago lanceolata (Ribwort Plantain)

Silene latifolia (White Campion)

Silene dioica (Red Campion)

Silene vulgaris (Bladder Campion)

Leucanthemum vulgare (Ox Eye Daisy)

Armeria maritima (Thrift)

Trifolium pratense (Wild Red Clover)

Lotus corniculatus (Birdsfoot Trefoil)

Geranium pratense (Meadow Cranesbill)

Achillea millefolium (Yarrow)

Lychnis flow-cucuii (Ragged Robin)

Vicia sativa ssp. Segetalis (Common Vetch)

Prunella vulgaris (Self-heal)

Leontodon hispidus (Rough Hawkbit)

Scorzoneroides autumnalis (Autumn Hawkbit)