Forum home› Problem solving
This Forum will close on Wednesday 27 March, 2024. Please refer to the announcement on the Discussions page for further detail.

DIY Green Roof Substrate

AverageNoodleAverageNoodle Posts: 8
in Problem solving
Hi all,

I'm looking for some advice on making my own substrate for a green roof please.

I'm putting a green roof on a small bike shed.  It's 2x1m, with a 10cm depth and it's sloped, so drainage won't be an issue. There's a mix of sun and shaded areas, so I'm thinking of using a mix of alpines and small drought-tolerant ferns.

I've been looking online for substrate mixes but as we don't need a lot, I'm not sure this is going to be cost effective. On some websites, the delivery cost is more than the actual material!  The shed is very sturdy but I'd rather not risk the weight of standard soil just in case. 

Has anyone made their own substrate before?  Any tips on composition greatly appreciated!

Posts

  • DovefromaboveDovefromabove Posts: 88,147
    Never done it myself, but this 

     http://www.bbc.co.uk/gardening/basics/techniques/gardenstructure_greenroof1.shtml

    suggests a mix of potting compost and a high proportion of perlite

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • wild edgeswild edges Posts: 10,497
    What plants are you planning to grow? The pic below was on top of our rabbit hutch and the substrate was 1200 gauge DPM with 15-20mm of gravel on top, terram root barrier, 2 bags of John innes No2 with a bag of sharp grit mixed in and a layer of gravel on top to cover the soil. The plants are all easy going sedums and some drought tolerant saxifage. Given the choice again I'd replace the lower layer of gravel with plastic egg crate (the suspended ceiling light diffuser stuff) or expanded clay balls if I could find any cheap enough. Even broken up polystyrene would work as a base as it's just a drainage layer to stop the roots sitting in water.

    Perlite is also a good choice because it's much lighter than grit. If you go for really drought tolerant plants like sempervivums then you could mix it 50/50 with john innes.

    If you use some bigger rocks and logs on top it adds wildlife value and you can make deeper areas of soil for alpine bulbs or herbs.


    If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
  • lovegardening77lovegardening77 Posts: 332
    Wow that's impressive!
  • AverageNoodleAverageNoodle Posts: 8
    Lovely hutch Wild Edges!

    Thanks for the advice all. Looks like John Innes, perlite and clay balls will do the trick for the substrate layer. 

    I haven't decided on the exact plants yet. I've bought a copy of Nigel Dunnett's Planting Green Roofs and Living Walls and there's a good list of plants in it that I'm reading through. The part shade area is a bit of a challenge but Maidenhair Spleenwort and Irish Moss might work. 
  • davidcraig11955620davidcraig11955620 Posts: 1
    I’m just diving in on learning about green roofs and appreciate all of your wonderful posts AverageNoodle. I live in Atlanta and have a flat shady roof area on my home about 20 x 20 (feet) that I want to plant. I saw your plant recommendations in another post and have just ordered Neil Dunnett’s Green Roofs and Living Walls.

    The roof is currently covered with stone pebbles so I know it can handle the weight of a garden using planting trays. Do you have any suggestions on how to design a space that large? I’m trying to figure out if I can mix moss, sedum and ferns and get a good look through all four seasons. 

    Just want to say thank you for all your helpful suggestions. 
  • FairygirlFairygirl Posts: 55,117
    Hi @davidcraig11955620 - it might be a good idea to see what works in your local area, due to the climate differences, but many saxifrages will take some shade. 
    You might just need to experiment a bit - I wonder if you could have a slightly deeper 'box' on the roof so that you'd have more scope for planting? If it's got pebbles/gravel, then it would seem to be substantial enough, but plants can also be very heavy. 
    If you get low, or intermittent rainfall, you'll also need plants that can manage that, but the extra depth would help a bit. 
    Erigeron is popular in areas of the UK as it copes with very dry conditions, and next to no soil, but I don't know how well it manages shade. It's not something I grow. Some Gentians also manage shade, so that might be worth a look.  :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • bédébédé Posts: 3,095
    Hard Fern, Blechnum spicant, is a native that lives on mossy trees and dry stone walls in the damp West-Country. It doesn need damp roots exceept for germination of spores.  It should be good for your more shady side.
     location: Surrey Hills, England, ex-woodland acidic sand.
    "Have nothing in your garden that you don't know to be useful, or believe to be beautiful."
  • McRazzMcRazz Posts: 440
    edited 11 March
    Here you go...

    Intensive roof garden substrate
    You'll just need to up the organic matter content slightly
  • bédébédé Posts: 3,095
    I have Sempervivums and Sedums growing in my house and greenhouse gutters.  I just threw them there.  Initial substrate, non.  Any substrate  has blown in or been dropped by birds since.
     location: Surrey Hills, England, ex-woodland acidic sand.
    "Have nothing in your garden that you don't know to be useful, or believe to be beautiful."
Sign In or Register to comment.