Living roof... what to plant in a super dry, but still middle-German climate??

Hey Guys,

We are preparing our green roof and we're wondering what to plant on top... We live in aplace where summers got recently so dry and hot that some of the trees died and the grass turned yellow quite qickly last year... I am dreaming about agreen roof with a semi-long, grass, as I've seen in Norway, but I am afraid the grass will need some watering and it will not survive the heat. Do you have any ideas which plant would be suitable for that purpose? We live in Germany so we have rain, snow, frost, -10 degrees.... but summers have been quite desert-like lately...

The earth is 6-8 cm deep so we are limited with the amound of things we can put there.

Best wishes!
Marta

I think it will depend on how thick your soil can be. I have used 5cm perlite/earth mix with moderate success. More would be better.
Until the grass is established, you will also need something to hold the soil in place. (Rain washed most if mine away.)
How much load can the roof handle? The worst case would be wet soil and snow on top.

https://fenix.tecnico.ulisboa.pt/downloadFile/3779580646989/Basel%20Switzerland%20Building%20regulations%20for%20green%20roofs.pdf

Check their recommendations, they are not that far away.

In short: use local soil, and native species.

We are in a similar climate, with droughty summers, wet all other times of the year, zone 7b. We have a green roof that is stunning fall-spring, and pretty crispy in summer, BUT we have a lot of seedums/succulents on it and they always look good. I really recommend those types of plants. When my partner made the roof, he started with cut sod which I think would have the benefit of reducing soil erosion while it gets established. The roof has gone through phases since then and ended up a mixture of moss, grass, wildflowers, random weeds and succulents. Everything but the succulents die off in summer (they are dead now) but they either reseed, or the roots survive until the rains come. When we go up on the roof, we will often propagate the succulents around (as easy as pulling pieces off and poking them in holes) and try to slowly get better coverage, especially on the south facing slope where it is driest. I'll post a couple pics of our roof tomorrow if I remember :)

I just wanted to say what a beautiful building!

Charli Wilson wrote:I just wanted to say what a beautiful building!

Thank you! I will pass that to our pagoda constructors

How much load can the roof handle? The worst case would be wet soil and snow on top.

Yea... that's the big question. We reinforced the building lately and it should hold 6-8cm of earth and some snow but we will be checking every now and then if all is good and solid..

Karla Jaeger wrote:We are in a similar climate, with droughty summers, wet all other times of the year, zone 7b. We have a green roof that is stunning fall-spring, and pretty crispy in summer, BUT we have a lot of seedums/succulents on it and they always look good. I really recommend those types of plants. When my partner made the roof, he started with cut sod which I think would have the benefit of reducing soil erosion while it gets established. The roof has gone through phases since then and ended up a mixture of moss, grass, wildflowers, random weeds and succulents. Everything but the succulents die off in summer (they are dead now) but they either reseed, or the roots survive until the rains come. When we go up on the roof, we will often propagate the succulents around (as easy as pulling pieces off and poking them in holes) and try to slowly get better coverage, especially on the south facing slope where it is driest. I'll post a couple pics of our roof tomorrow if I remember :)

Thanks ! that's helpful.  Please post the photos :) What we thought about in first place were also the seedums and succulents and I guess that's what we will put there first, especially after reading your post.. Not sure what to put on the roof to keep the earth from sliding down but that cut sod sounds good! For now we just put some branches on it to hold the earth in case of rain.

Thyme,  Rosemary, and Ceanothus can handle dryness, and heat, and full sun; these also all have cultivars that are "creeping" and so would cover more sqft over time(although the branches wouldn't be re-rooting, so maybe a soil retention issue?)

Beautiful building!
I have used sedum on 2 buildings now with great success.

You can get it  in the the form of plugs, a blanket roll, or ready planted in interlocking modular trays with reservoirs in the bottom, to store excess water, which the plants can then use in a dry period.
The last is the most expensive system, but seems to work really well for me in the UK.

For sedum, the substrate should be very low in nutrients...it needs very little to survive, as it is a mountain plant that grows naturally on barren rocks and in crevasses.  A mix of perlite and very little soil is best.  I weed it once a year, and spray it with a hose pipe only after about 2 weeks of drought. Lovely flowers all summer.

As other viewers have said.... you need to check that the roof structure can bear the weight! I'm strong, but can barely lift a tray when it's throughly soaked.

Cath Brown wrote:Beautiful building!
I have used sedum on 2 buildings now with great success.

You can get it  in the the form of plugs, a blanket roll, or ready planted in interlocking modular trays with reservoirs in the bottom, to store excess water, which the plants can then use in a dry period.
The last is the most expensive system, but seems to work really well for me in the UK.

For sedum, the substrate should be very low in nutrients...it needs very little to survive, as it is a mountain plant that grows naturally on barren rocks and in crevasses.  A mix of perlite and very little soil is best.  I weed it once a year, and spray it with a hose pipe only after about 2 weeks of drought. Lovely flowers all summer.

As other viewers have said.... you need to check that the roof structure can bear the weight! I'm strong, but can barely lift a tray when it's throughly soaked.

Thanks a lot! it looks stunning.

The weight is a bit of a topic for us.. The guy who build the roof can't say if it can bare the weight but he mentioned that already before he started, that he has no experience with that. So we had some people and father of my partner who's a professional in constructing wooden houses and he suggested some reinforcing here and there... so we did it but I have to be honest... I don't have full trust towards it But my friends decided to put earth on the roof and then measure if the wood is bending and if something is changing in the structure. In the worst case we take the earth off and cover it with tiles... but 2 tons of earth to take off... I would be happy if the roof can handle it

If it was totally up to me I would've done the homework of doing the calculations before we build but it was not me constructing it and deciding whether we will put earth there or not... sadly

Thanks! It's a good thing you're testing the roof...fingers crossed, it might be fine. Good luck!

Here are some pics. It’s still looking really green on the north side. The south side has had most of the little weeds and wildflowers die. I will try to remember to take a pic in August :)

This is gorgeous. I really love green roofs. Succulents are a good way to go, but eventually nature takes over and shows us what will survive. I have a friend who had a green roof in Turkey. Green in the winter, and dry straw in summer, but it still protected the house from the sun's heat.

I love the idea of a green roof, we have a barn that needs fixed up and would love to do this instead of simply replacing tiles. Not sure wether or not planning permission is required. We are in the south of France and I have read that no planning permission is needed. Fingers crossed that’s true. Could anyone tell me what the cost of a green roof is, is it expensive.

Cheers

I would say it's more labour intensive.
You need the following
1) strong supporting roof structure
2) waterproof membrane
3) root barrier membrane
4) growing medium (shallow for extensive roofs, deeper for intensive roofs)
5) edge barrier to keep growing medium in place but allow excess water to drain
6) some maintenance....it   is a garden after all.

It can be very cheap if you find reclaimed materials and build everything yourself, or expensive if you go with ready built instant systems.
There is a lot of information online.
Good luck

Cath Brown wrote:This is gorgeous. I really love green roofs. Succulents are a good way to go, but eventually nature takes over and shows us what will survive. I have a friend who had a green roof in Turkey. Green in the winter, and dry straw in summer, but it still protected the house from the sun's heat.

Yes, the roof offers wonderful insulation!
One aspect of the roof that we think about in summer is fire risk. The past couple of years here in western Canada have had crazy forest fires, and while they don’t usually reach us here on the coast, it’s possible. A floating spark could set our house on fire when the roof is basically tinder. So this year we are installing sprinklers for peace of mind.

Marta, I think it would be good to broadcast some seed over your roof to get some roots established and hold the soil on, as long as you’re still expecting some rain or can irrigate. I’m really impressed at the ability of succulents to propagate (and we have one native variety that seems to be self seeding everywhere) but still, coverage is slow. Getting some clover or grass started will help hold the earth in place, and you can still plant into it, especially after it all dies in summer.

Wildflower mix is nice too! My partner threw down some wildflower seeds at some point, and some of them come back every spring.