During very wet seasons green roofs can have problems retaining the plant nutrients. If the flowers have been in short supply then it may be time to apply a sort of fertilizer.
If there are an abundance of flowers, this may be that the plants are heading for exhaustion and may need a pick me up ready for the winter.
Too much rain or cold conditions can cause the Sedum to change colours:
Red indicates a sign of the plants going dormant. Typically seen during the winter months.
If this is the case the Sedum roof will be fed with an organic fertilizer during spring and summer.
Basic Maintenance: The 7 Point Plan
Procedures carried out during maintenance of the green roof will be as follows:
1. Removal of unwanted plant material, ie grasses etc.
2. Correction of any localised plant system problems that may have occurred post installation.
3. Replacement of any naturally failed plants not exceeding 5% of total plants installed.
4. Application of nutrient source.
5. Removal of dead flower heads (if required).
6. Inspection of rainwater outlet chambers and surrounding vegetation breaks.
7. Replenishment of any areas of settled substrate
General Green Roof Maintenance
General maintenance will normally be carried out annually during springtime. However, certain tasks such as the removal of weeds or accumulated leaf litter will be done during the Autumn.
All debris and leaves will be removed from the roof surface, rainwater outlets, chutes, gutters,
All debris from the roof will be removed to avoid suffocation of the sedum plants.
Any planting, which has encroached into drainage outlets, walkways and the vegetation barriers (pebbles), should be removed. This removed vegetation will be used to repair any bare patches if required. If movement/settlement of the pebble vegetation barrier has occurred, then additional washed stone pebbles (similar to the existing) will be added.
Sedum blankets will at times include moss and grass. If considered excessive, provision should be made to remove any unwanted vegetation, e.g. weeds/ grasses/ saplings. These can be removed manually by hand, or by using a ‘spot weed wipe’. Weeds are a problem of aesthetics rather than damaging the roof, but large areas of weed or grass should be removed, as should saplings. After removal of weeds treat area as if it were a bare patch (see below).
Bare patches should be repaired only during the growing season (March/April or late August until the end of September). Take clumps of Sedum from areas of abundant growth and place on bare patches pressing gently into the soil. They can then have a light sprinkling of sand mixed with compost. The Sedum cuttings will grow best if this is carried out during spring maintenance and kept moist and free of temperature extremes (frost and intense sun).
An annual application of fertiliser should be applied for the sedum plants to remain healthy. Fertiliser to be applied during March/April. This helps to prepare the plants for extreme weather conditions and flowering and also because it allows the different species to gain all their nutrients without competing against each other. A good organic fertiliser applied at the rate of 80gm/m² using a hand held spreader or strewn by hand from a bucket.
Avoid fertiliser pellets settling on damp leaves as this may have a detrimental effect i.e. burning the leaves. The fertiliser should be lightly ‘watered in’ immediately after application.
Dung based organic fertilisers are to be avoided.
To chat about your green roof maintenance issue or forthcoming project contact RIEFA Green Roofs on 0844 057 0359. We’re happy to give advice and can supply everything you’ll need for your green roof including a root resistant membrane, your sedum and importantly your lightweight, organic green roof growing medium.
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