Moss on roofs

This wonderful spring-like weather gives the ideal opportunity to get up on to green roofs and check see if they’re in good condition.

robust coverage of healthy green roof plants

A basic green roof check list includes making sure that drains are working properly, that fall restraints, edgings and walkways are securely fixed and that there is a good coverage of robust, healthy plants, ideally ones that should be there and not weeds or moss.

It’s not unusual to see moss on extensive green roofs, especially if the weather during the previous twelve months was challenging to plants, or, if the maintenance regime hasn’t quite met the needs of the plants.  Moss is an opportunist, if there are bare patches in the vegetative layer, you can bet your bottom dollar that moss will fill the gaps. Excessive moss though, is not a good thing.

Why is moss undesirable on a green roof?

On this green roof, the moss is in better shape than the sedums. Time for some maintenance!

A green roof needs green plants for it to provide the maximum benefits to the building below. Moss is a plant, but it may not give the same amount of ecological interest, wildlife habitat, ability to cool the building or substrate stabilisation that is created by sedums, herbs or wild flower plantings.  In general, moss is a sign that your green roof may not be working properly….if you have moss, the original plants have probably died….and they’re most likely to have died for one of four main reasons;  poor drainage, shade, mechanical damage, or lack of nutrients.

Controlling moss on a green roof

First address any issues with water….are the drainage outlets blocked? If not, could there be a problem with the installation – an expert will be able to judge if water management needs improving.

If the moss is growing in a shady area, find out how deep the growing medium is and investigate what plants could be established there.  Sedums hate shade but you may find that there are other shallow rooted plants that will thrive in low-light conditions.

Could the plants have been damaged by being walked on? by wind scour? or by birds pulling out plug plants.  Establish what has happened, take steps to ensure it won’t happen again and replace the plants by whatever means is practical and cost effective (choices include seeding, plug plants or sedum cuttings)

spreading plant food on a green roof needs the right equipment to ensure the correct rate of fertiliser is applied

Finally, feed the plants.  A green roof is essentially a giant planter.  The nutrient levels need to be topped up from time to time because green roof ecosystems are not quite the same as on the ground and besides….have you ever tried to garden without using fertiliser of any sort? believe me, plants do much better with a little bit of the right feed (not too much, we’re not breeding triffids here) than they do when left to fend entirely for themselves.

Confused?  Don’t be.  Enviromat can assess your roof, offer advise and carry out all of these jobs for you. An assessment is free (for roofs throughout mainland UK) and you might be surprised at how little it costs for a simple maintenance visit.  Our assessors are horticulturists, not salesmen, they want what’s best for the plants, for the environment and for your budgets in other words, we won’t rip you off.

Contact to arrange your free green roof assessment


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