Friday, 5 October 2012

grow your own sedum roof

Sedum roofs are very much in vogue.

They look beautiful and so for aesthetic reasons alone they are increasingly chosen.

sedums have diverse colours and forms
But they are now favoured for more practical reasons too.

The use of sedum or green roofs can help slow the flow of rainwater from a roof into the drains that quickly become overfull. during heavy rain, UK storm drains become overfull and result in discharges of raw sewerage into our rivers.  Slowing the flow of rainwater reduces pressure on storm drains, reducing the flows of untreated effluent into our watercourses and seas.

In cities, sedum or green roofs can contribute to a cooler temperature as they absorb sunlight in the summer rather than radiating it into the already-too-hot summer city climate.

And for wildlife they are a bonus offering a food source to invertebrates when flowering and to birds when they seed.

Our architect has designed our new home with a 20 degree roof slope on the north side of the building that will be a sedum roof. This is very much in tune with our low energy, sustainable ethos.

But dagnabbit, those sedum roofs are expensive!

We have 125m2 of roof to cover with sedum and will need:

Reservoir board @£8.00 m2
Filter fleece
Growing medium 2x25 litre bags per m2 @ £6.80 bag
Aluminium trim
Cobbled or gravel edging 1.5 @25 litre bags per linear metre

grit, sieved peat free compost, sieved builders' rubble
Plus the plants themselves. And then we have Judith and Rogers bungalow to cover too!

So time to have-a-go at growing our own sedums.

Sedum plants have evolved to thrive in conditions that other plants hate. They have waxy leaves and stems to limit water loss and are usually ground hugging to limit water loss through wind movement.
Jill recalls visiting a site where the ground contained high levels of heavy metals. Only sedums coped.

So, the trick with sedums is to avoid any particularly vigorous species or varieties and to plant them into a growing medium that is very low fertility.

We chose to grow cuttings in mini-modules. Our sedum was sourced from a local garden centre and we excluded one pot of sedums because it looked very much like vigorous Sedum sarmentosum. Selection of too-vigorous sedums will result in prettier, dwarf forms being swamped.

Plants are used on roofs at a rate of 25 per m2 - so, over 3000 to produce for a 125m2 roof!!

Our growing medium for modules was a third each of horticultural grit, sieved peat-free compost and sieved builders' rubble.

Once the plants were potted into their individual modules they were dressed with a final sprinkling of the sieved builders' rubble and watered. The plants need a low fertility regime when on the roof, but to get them going in their modules we have included peat free potting compost. And we are watering them occasionally with highly dilute leachate taken from our wormery.

Finally, they will be housed in a mini-cloche to speed their growth in these final days of sun and warmth.

Commercial  sedums are grown in trays or cut as rolls rather like turf. I will post regular updates on the growth of our sedum roof over the coming months.

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