I have a green roof covered with sedum plants and I noticed that in the late spring and summer many sedum plants turn red. The same plants placed in our garden (in the shade) stay green all summer. I suspect the cause of the sedum turning red is either a lack of nutrition (fertilizer?) or water.
The red sedum does survive but I'm worried that it may cause problems in the long run. Can sedum turning red every summer become a problem, and if so what can I do about it?
It's not a problem, just the reaction of the plant to sunny conditions. The best colour to absorb energy for photosynthesis is green. If you are getting so much you cannot use it many xeriscape plants produce other pigments as a sunscreen. As wikipedia states
In direct sunlight, plants face desiccation and exposure to UV rays, and must expend energy producing pigments to block UV light, and waxy coatings to prevent water loss.
Nothing to worry about and no reason to do anything unless the plant coverage on the roof is thinning. In this case conditions may not be optimal and you could consider different species.
