Green Roof Maintenance in Autumn

Summer 2013 was a challenging year for many sedum roofs.  Sedums are a brilliant choice for green roofing because they are drought tolerant and can withstand high temperatures, but this summer was challenging even for such well adapted plants.

Problems arising from the dry summer

grass on green roofAt Enviromat we tend to discourage people from over-watering their sedum roofs.  In general, we find that over relatively short periods of time, too little water is better than too much.  An excess of water or nutrients will result in weeds and grasses thriving on the roof and spoiling the visual effect.  However, the long, hot dry days during summer 2013 have left some sedum roofs stressed out.

Weeds and grass are often a result of
over-watering a sedum roof 

Drought stress

sedum roof in summerSedums are very good at coping with drought due to a special metabolism that is unique to plants from the crassulacae family.  Typically, in drought conditions, a sedum plant will change from being green leaved, vibrant and succulent to having browny-red coloured foliage and small, tight, bead-like leaves.  This is perfectly normal and the plant will go back to its robust self when the weather is more friendly.

If however, the leaves look dried, wrinkled or baggy – like a deflated balloon – the plants are in trouble and need a good soaking to help them out of a muddle.

A typical sedum roof after prolonged drought

Other summer problems

If plant coverage has disappeared over the summer either all over or in large patches, then there may be a problem with nutrient levels or with red spider mite.

Autumn Feeding

While the weather is still mild, plants are quite capable of taking in the nutrients they need to help them survive the winter months.  Apply Nutrifusion Green Roof Feed in September, particularly if your roof was not fed during spring or summer.  But beware, after September there is a risk that this formulation may result in excessive growth that is less frost-hardy than it ought to be.  If in doubt – contact our expert.

Red Spider Mite

These small but voracious pests are more frequently associated with greenhouses because they like hot dry conditions.   Unfortunately, conditions on a green roof this summer have emulated the environment inside a hothouse, and on some roofs, particularly pitched roofs that are super-dry, the sedum plants have been attacked.

Symptoms of red spider mite include dry-looking roofs with very poor plant coverage, sorry looking vegetation and if you get really really close you can see very small creatures scurrying across the substrate.  You may also notice fine white webs – like miniature spider webs on the roof.

If you think you have Red Spider Mite, the best treatment is to water the roof really well every day for at least a fortnight to get rid of the mites.

If you have any worries at all about your green roof, please don’t hesitate to contact us for free advice. 


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