Can You Install Sedum Green Roofs in Winter?
by Dr. Anna Zakrisson on Wednesday, November 27, 2019
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Extensive sedum green roof installations
There are about 400 different species of sedum plants, of which a handful are well-researched for use on extensive green roofs. Sedums are incredibly resistant to stress, especially drought and extreme temperatures. This is, of course, is a useful characteristic for extensive green roof conditions where the plants will be exposed to a considerable variety of stressors throughout a year.
In most climates, sedums will remain evergreen throughout winter, perhaps with a color change from green to reddish-brown. They may also undergo some interesting morphology changes as the leaves often go from being fleshy, thick, and water-filled in summer to a more hardy, less fleshy morphology in winter that with lower water content and thus with a lower propensity for freezing.
Most installations of sedum roofs are done in spring and summer, but often there isn’t any reason for this seasonality other than habit as it is possible to install extensive sedum green roofs in winter in most climates.
Installing sedum roofs in winter
Winter installations of sedum roofs can be very successful. However, there are a few items that you need to consider when doing this.
Also, note that any reliable and sincere plant supplier will provide a guarantee for your winter installation to ensure it can be done without any risk for your project. The supplier will also be able to advise you on specifics for your climate.
What to consider when installing winter sedums roofs
So what should you consider when installing a sedum roof in winter? Firstly, it is vital to use sedums that have been pre-grown outdoors and in a similar climate to ensure that the plants have been acclimatized to the relevant temperatures. Just imagine being dragged from a pleasant warm place, where you were well fed and rested and forced to stay outdoors in an icy and cold environment with a too-thin jacket and bad food. No one would be expected to thrive after such a rapid and harsh change. We all need some time to acclimatize to new conditions. Even plants.
Secondly, it is critical to use mature plants to ensure high survival rates. Young plants have not developed hardiness due to, for example, immature root systems, and are thus more likely to display low survival rates.
Thirdly, if you are installing the roof in fall, it’s important to ensure that your newly planted sedum roof isn’t covered by falling leaves as this may restrict the plant’s access to light and will reduce growth- and survival rates.
One benefit of installing a sedum green roof in winter is that the shelf-life of the sedum mats is much longer than in spring and summer, where you need to unroll and water the sedum mats within 24h of delivery.
Once the sedum mat has been rolled out or installed it does need to be watered very well, even soaked.
Winter installation of sedum roofs: mats vs. plugs vs. cuttings
A sedum mat contains creepers that will keep the mats covered through winter. These sedum creepers filled in the space temporarily vacated by the dormant broadleaves.
Plugs cannot be installed because the different soil density will cause freeze/thaw problems which can make the plugs get pushed upwards and out of the soil which causes winter dehydration.
Cuttings will blow away.
If you install Sedum mats in December or even January they can freeze / thaw in winter with no or little damage. It’s like a blanket that can move up or down without any harm to the plants. In spring, when warm weather hits, the plants suddenly “realize” the plumbing is not intact and will use their reserves to establish roots very fast. They will rebound within 2-3 weeks.
When is the best time to install a sedum green roof?
Well, whenever it is most suitable for you, but it is important to consider the differences in requirements between the seasons. Also, ensure that you have good communication with your supplier to guarantee correct installation.
Guide: How to select sedum plants for your vegetated roof!
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