Summer is when green roofs really do have a lot to offer. Here’s what to expect from your green roof in summer along with some simple maintenance tasks.
- Insulates your building against heat
- Helps cool the rooms
- Combats the Urban Heat Island Effect
- Absorbs rainwater from sharp summer showers
- Looks amazing
- A haven for wildlife
- Adapts to weather conditions
- Very low maintenance
The benefits of a green roof in summer
The benefits of a green roof vary enormously between different projects depending on their design, their location, their age and how they have been maintained. But all of them should help to keep the building cool on hot days. A deep substrate wildflower roof will be a more effective insulator than a light weight sedum blanket but then the initial building costs would have been higher. Like so many other things in life, green roofing is a balancing act.
As well as cooling the inside of a building through evapotranspiration, a living roof cools the wider environment too. Meaning that your beautiful roof terrace will be more comfortable to sit on in hot weather. If there are enough green roofs in close proximity, the air will be a little cooler in the whole area. Great news for anyone living or working in cities.
Ever been caught in a sudden summer shower? Green roofs help our drainage systems to cope by absorbing up to 80% of the water that falls on them. Most of the water is stored for the plants to use. Any excess filters slowly into the drain.
What will your green roof look like in summer?
The way that your green roof looks depends on the type of plants growing on it, the way they are maintained and the good old British weather.
In early summer when the days are sunny, nights are cooler and rain is fairly regular. Expect to see lush growth as the plants prepare to flower.
A wildflower roof in mid-June will likely be resplendent with blooms. A well fed sedum roof will have plenty of foliage. If you are lucky enough to have Sedum Album plants on the roof, they will push out pinky-white flowers that look like clouds of candy floss.
All manner of insects will be making the most of the undisturbed space on your roof. There’ll be several species of bee collecting pollen and nectar. You may even have some solitary bees nesting in the substrate.
Some of the insects will become food for birds who are busy raising their young. It truly is a haven for wildlife.
As the temperature rises and the growing medium dries out you may see changes in the plants. On a shallow substrate roof with predominantly sedums, expect the foliage to turn red. That’s perfectly normal and it’s part of the plants’ stress management system. It’s how they cope with drought.
In terms of fauna, there’ll still be a big buzz with bees, butterflies and other insects making the most of what’s on offer.
In late summer, as the rains return your sedum roof will gradually green up. Depending on the species present, you may be lucky enough to witness Sedum Spurium in bloom. Stunning big flower heads in various shades of pink. These flowers often last well into the winter time.
Your wildflower roof on the other hand will be getting ready to set seeds. If there are grasses on the roof, they will be a lovely shade of honey-beige. You may see some flowers but for the main, you’ll be looking at graceful seed heads. A vital part in the life of a wildflower roof.
Now is the time to start thinking about a haircut for your roof – more on that later in the article.
Green roof maintenance jobs for summer
If you didn’t manage to feed your roof in early spring, it’s not too late. Sedums growing in a shallow substrate will benefit from an application of plant food. For a sloping roof, I’d advise feeding in spring and then again in early summer. That way you’ll get a much better show of flowers and the plants will be better able to cope with drought.
An established sedum green roof will only need watering if we have four weeks or more with no rain. These little plants are very resilient.
Look out for signs of severe stress. It’s normal for the foliage to turn red and for leaves to look like little hard beans. If however the foliage looks more like a saggy baggy deflated balloon, then the plants are in trouble. Give the whole roof a really good soaking – keep on watering until you reach the point of runoff and repeat twice a week until the rain comes.
New sedum roofs must be kept moist until they establish – but beware of overwatering. You’ll simply encourage weed growth.
Wildflower roofs are a little more sensitive to drought than sedums. Look out for limp, floppy plants, pale leaves and leaf-drop. With wildflowers it’s best if you can anticipate drought and just not let the roof become too arid. It definitely helps to have an irrigation system in place.
Just like sedums, a newly planted wildflower roof needs plenty of water to help it establish.
Weeds are rarely a problem on green roofs but you may find a few opportunists popping up. A shallow substrate green roof system is usually self-weeding. Imposters simply don’t survive the hot, dry summer conditions. On a wildflower roof – well – what is a wildflower if it’s not a weed?
If you see any plants you really don’t want on your roof, simply pull them out. Pay special attention to tree seedlings – if they get too big they are a threat to the integrity of your waterproofing.
A sedum roof doesn’t need mowing at all. By late summer/early autumn you may see lots of spent seed heads but you’ll find that they just blow away on the wind. They’re not a bother at all.
A wildflower roof however, may need a bit of a haircut towards the end of summer. Dry grasses and foliage don’t look attractive. Plus when they eventually collapse, they could kill the plants beneath them.
Simply chop all the foliage down until it’s only around 10cm high (no lower or you’ll damage the growing parts of the flowers). Then, and this is the important bit, let all the debris lie on the roof for a couple of days. That gives any seeds a chance to drop down into the growing medium. Free plants for next year —yaay! It’s vital though that all of that dried stuff gets brought down off the roof. Which could be tricky, depending on what equipment you have to hand. Those builders bags are great for collecting debris but not so good for dragging into the lift for the journey down to ground level.