THERE’S MORE TO PLANTING GREEN ROOFS

With the right substrate and plant specification, green roofs can look vibrant and exciting without high maintenance, says Boningale GreenSky’s leading plant expert.

Maggie Fennell, manager of the innovative Shropshire-based company that pioneered the development of SkySuperstrates and SkyPlugs for green roofs, said that the range of plant species commonly used on green roofs can adapt to a lot of challenging situations, which is important when considering aesthetics and your maintenance programme.

Maintenance of green roofs is a key issue, but with the right planning, growing medium and the right species, the maintenance programme does not have to be a challenging or laborious task. And it doesn’t mean that your green roof has to be boring either.

When green roof designers use 150mm deep substrate, it opens up the types of suitable species that can be planted because there is room for extra root growth and more capacity for water storage.

For example, extensive green roofs are traditionally dominated by sedums because they are extremely drought tolerant, or by wildflowers because they are a good support for biodiversity

These are natural candidates for any green roof because they can cope with extreme weather conditions and poor soils.

However, there are also many more species that are suitabe for sites that are dealing with shade, high aesthetic demands and tight maintenance access. Using ferns, alpines, Mediterranean herbs and evergreen plants with a wide variety of forms and flowering times help to meet a broad variety of challenging urban conditions.

Mediterannean herbs such as lavender, rosemary and thyme can be used on extensive roofs when they might otherwise struggle in a wet, winter landscape. The sharp drainage is beneficial as long as the plants have enough sunlight. It is a very attractive option but requires slightly higher maintenance for the shrubby plants – they need trimming back correctly to maintain their form.

Hardy and drought-tolerant alpines and cultivars, such as Petrorhagia saxifraga and Delosperma and Mesembryanthemum species thrive brilliantly on lighter weight, extremely low maintenance extensive green roofs too, as long as they have a sunny position.

Ferns are increasingly used alongside other shade tolerant plants for lower level green roofs which might be overlooked but where su

nlight is so restricted that traditional sedums and many wildflowers would struggle.

Of course, in depths of 100mm or more bulbs should also be planted to boost seasonal and all-year colour.

With all this choice, there’s certainly no excuse for a boring, high maintenance, green roof.

Boningale GreenSky is the award-winning green roof division of Boningale Nurseries and a member of BALI and GRO. The company has developed market-leading horticultural products and guidance in partnership with the technology experts at the University of Sheffield’s Green Roof Centre. This research is translated into award-winning design tools that are freely available at www.boningale-greensky.co.uk