Growing Wild Flowers on a Green Roof

What is a green roof?

Green roofing is one of the most effective things you can do to help the environment.  Its way up there alongside recycling, double-glazing your windows and walking to work.

What green roofing does is it allows you to use every single possible surface for growing plants.  Plants soak up carbon dioxide, they filter dust from the air, they support whole ecosystems and they help to keep our planet cool.  Plus – they look good.  When friends, neighbours, customers etc see that you’re growing a green roof, they’ll know that you’re doing your bit for the environment.  It’s great PR.

traditional scandinavian house with wildflower turfed roof

Traditional scandinavian houses have turf and wildflowers on the roof for insulation.  This might not work on a suburban semi in the UK but could easily be adapted for a garden shed or a flat-roofed extension.

A green roof sits atop standard waterproofing on a building.  It can be as big as a warehouse or as small as a front porch.  There are no rules regarding size or shape, but you do need to be sure your building can support the weight of growing medium and plants.  Sloping roofs can be a bit more challenging to green up than flat roofs – but where there’s a will – most things are possible.

Different types of green roof

Some people like to have a green roof that is managed like a garden.  Maybe growing vegetables and herbs up there or using it as a venue for family gatherings.  That’s known as an intensive green roof.

Others prefer a lower maintenance option. An extensive green roof, once it’s established more or less looks after itself.  It’s like a nature reserve that just gets visited once or twice a year to make sure that everything is healthy.

Wild flowers make for a really good extensive green roof.  They don’t need a lot of attention and they do a great job of supporting wildlife.

Which wild flowers are suitable for green roofing?

Not all wild flowers are suitable for green roofing.  The conditions on a roof tend to be a lot harsher than on the ground and if you’re intending to stake, protect and water the plants they’re going to need to be very independent.

Perennial plants will make your life easier than annual wild flowers.  They don’t need to be sown every year and they’re happiest if you don’t disturb the ground around them.

 

Colourful wild flowers in Meadowmat Roof and Garden

Meadowmat Roof and Garden is a pre-grown mat of wildflower plants and grasses that will thrive on a living roof.

Choose tough, relatively short-stemmed plants that can cope with windy conditions, baking hot summers and very cold winters.  There is very little shelter on a roof and temperatures tend to be exaggerated.  If it’s hot in your garden it’s going to be even hotter on the roof.  When it’s frosty, the roof temperature will be one or two degrees lower than the ground temperature.

Go for a good variety of plants.  The more species there are, the wider the variety of creatures your roof will support. 

How do I establish wild flowers on a green roof?

First of all you will need to make sure you have the right layers of material on the roof to support your wildflowers.

  1. Waterproofing – doesn’t matter what sort but it MUST be intact and in tiptop condition.  If it’s roofing felt, protect it from root damage with a layer of thick polyethene.
  2. Drainage – excess rainwater needs to be helped off the roof otherwise you’ll end up with a muddy puddle where you want your wildflower meadow to be.   Install a layer of drainage matting (the egg-cup type is good for wildflowers) and make sure there are lots of drainage outlets
  3. Edging – you don’t want everything falling off the edge of the roof now do you?  Your green roof edging needs to be at least 12cm deep.  That’s equivalent to the depth of the drainage mat and the growing medium.
  4. Growing medium – aka substrate.  ALWAYS use a specially engineered green roof substrate.  Topsoil is no good for green roofs because the fine particles are easily washed into the drainage outlets.  Most topsoil is also too high in nutrients for wild flowers so stay clear of it.  You will need at least 100mm plus an irrigation system for growing wildflowers on a roof.  150mm is better – you’ll have less need to water the meadow if you have deeper growing medium.
  5. Meadowmat Roof and Garden.  This is soooo easy to install.  It’s a pre-grown mat of wildflowers and grasses that will live happily on a roof.  All you need to do is unroll it and water it in.  Keep it watered for the first month or so while the roots get established. After that you’ll need to do very little maintenance. 
  6. You can even place some spring flowering bulbs beneath your Meadowmat so that you get colour earlier in the year.  Crocus are great because bumblebees just love them.

How to look after wild flowers on a green roof

Manage your wildflower meadow in the sky the same way as you would if it were on the ground.  Click here to learn about meadow maintenance.

 

Learn about Wild flower matting for green roofs


Sedum green roofs – a lighter alternative to wild flowers

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