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by Darren
(London, UK)

Hi I am doing some research on Sempervivum & Sedum which seem to be the most hardy of plants for my project needs.

I have a bin shed cover with a rather boring looking roof top the roof surface is roughly 6 feet long by 3.5 feet wide and just 4 feet from the ground.

The roof top is waterproofed with felt type roof material.

My main goal is to build a plant box or at least a wooden edging to hold in soil and grit for the sedums and Sempervivum.

I wondered if you have any advice on how many plants I should buy for this space?
I may wish to add some flat rocks to try and provide a natural environment for the plants too and for decoration purpose.

I understand they need well drained soil with grit and not a lot of soil depth needed. I have sunshine all morning in the location.

I want to make my wooden bin shed cover look pretty attractive to passers by which now looks really boring.

Any tips, where I can order from etc would be appreciated.

Drought Smart Plants reply:

Hi Darren, I’ve posted your question here so other people can have the information too.

Your project sounds wonderful – and you will bring lots of pleasure to people due to the fact that as the shed isn’t very high, they’ll have a birds eye view of the plants.

My one concern is that the roof should be covered with some kind of waterproof membrane, especially if this is roll roofing or some kind of roofing with joins. If you don’t want to cover it with anything else, make sure all the joins are covered with some kind of roof patching compound.

The box idea is great, that way you could remove it to renovate the plants. I would do several boxes that all fit together with a couple of extras, making it really simple to replace or renovate if any plants die.

You can pretty much figure on two to three plants per square foot, as they will spread over time. If you want to really fill it quickly you can of course plant them closer.

It depends a lot on which types of Sedum and Sempervivum you want to use; the Sedum for groundcovers that I recommend are all well behaved and compact, and if you want some really small carpeting hens and chicks, look for the Sempervivum arachnoideum, otherwise known as cobweb houseleeks. These stay very small and make a little colony of many plants clustered together. Among your decorative rocks you can use a pebble or lava rock mulch to hold in the moisture.

There are several suppliers in the UK, but I have never ordered from them.

Fernwood Nursery is a well known mail order supplier in the UK.

Also, alpine plant nurseries will sometimes have some of these plants, and alpine plant societies and rock garden societies.

Links to Sites of Botanical Interest.

Make sure you check out these pages too:

Green Roofs

Green Roof Soil

Green Roof Sedum

Good luck in your search; I would love to see some pictures when it’s done!