If you are caring for a sedum roof, you will probably notice seasonal changes in the way it looks. Dry weather can trigger a change in the plants. Here’s what to expect and how to care for your sedum roof in hot dry weather.
Sedum plants are incredibly drought tolerant. They are not, however, drought-proof. At the time of writing (early July 2018) the UK is basking in a heatwave. Some parts of the country have had no rain for a month and farmers are warning of a possible potato shortage. It’s inevitable that green roofs will start to react and change appearance due to the hot dry weather. But is there anything you can do about it?
This sedum roof has an array of problems. The plants you can see are quite healthy, however, coverage is sparse. The cause? inadequate feeding and lack of irrigation when it was installed.
Recognising signs of heat stress on a sedum roof
Sedums are part of the plant family known as Crassulaceae. They are cousins to the pineapple, the Aloe vera and Sempervivums. These plants are all characterised by thick fleshy leaves which act as water storage vessels. They also have a waxy coating on the outside of the leaf to help prevent evaporation and have adapted their metabolism to minimise water loss. Compared to many herbaceous plants commonly grown in the UK they are remarkably resilient to drought.
Whilst lettuces, geraniums and potato plants are wilting in the heat, sedums deploy their unique anti-drought mechanism. Chemical processes within the plant are altered. We don’t need to go into the science of it for the purpose of this blog. Suffice to say that you will see a difference in the plants. The leaves turn from looking large, plump and green to becoming smaller, red and turgid.
When your sedum roof changes from green to red, there is nothing to worry about. The plants are coping with the weather in their own way.
If however, the plants on your sedum roof start to look “wrong” then you may have a problem. If the leaves become pale or ashen looking and take on the texture of a deflated balloon, the plants are struggling to cope with drought and they need emergency assistance.
Does your sedum roof need to be irrigated in hot weather?
The whole principle behind sedum roofs is that they are low maintenance and virtually self-sustaining. Apart from an annual feed and an occasional weeding session, they should look after themselves.
Sedums are remarkably resilient little plants and ideally suited to green roofing. However, in extreme conditions, they may need a little extra TLC!
If your sedum roof turns red, but the leaves are still glossy and turgid, there’s no need to water it. The changes are cosmetic and temporary. Keep an eye out for any changes though.
The brilliant thing about the sedums’ survival mode is that unwanted plants, just don’t have it. Hot dry weather will kill off the weeds so you don’t have to. So look upon this time as a free maintenance session. Unless of course, the plants you want are truly suffering.
When sedum leaves look like wrinkled balloons it’s time to take action. And that means irrigation.
How to help a sedum roof suffering from drought stress
Robert Allen the Production Manager at Enviromat advises watering a stressed sedum roof only when absolutely necessary. Water in the evening as the sun is beginning to set. That way less of the precious resource will be lost to evaporation. And water thoroughly – to the point of runoff. Really really soak the roof.
Because green roof substrate (growing medium) contains only a small percentage of organic material, it can take a while to rehydrate. Repeat the irrigation every day for at least a week.
At the end of the first week, apply a green roof feed to help boost the plants’ recovery. Water it in, then reduce the frequency of watering to just twice a week until the drought ends.