Green Roof Valuation Durban

A brief evaluation of the Green roof trials conducted in Durban over a period of ten years.

Early in 2009 I became involved in the eThekwini Municipality Green Roof Pilot Project at which time I started the trial of a number of species of local plants at Mount Moreland north of Durban.

Delosperma lineare green roof durban

Delosperma lineare 

As from 1987, prior to becoming involved in the eThekwini Municipality Green Roof Pilot Project I had considerable exposure to green roof construction in Germany. Therefore, it was natural to copy as closely as possible the methods employed in green roof construction in Germany. Using drainage and engineered growing medium consisting of materials such as light weight expanded clay granules, perlite and vermiculite. In addition, we incorporated very little organic material as done in Germany with the percentage not exceeding 5%.

Ledebouria apertifolia green roof durban
 
Ledebouria apertifolia

For many reasons it was decided to limit our research to exclusively local indigenous plants that occur naturally within 50 of the test site. In regards to my own testing I have added a few plants collected in the very hot and dry Ndumo area.
 
This evaluation has been done after most of my test plants had been grown for ten years with virtually no attention, being left almost completely on their own with no watering, no fertilising, no addition of soils to the trays or mulching with compost.

images/gladiolus_cruentus.jpg

Gladiolus cruentus

Ten years later the evaluation of the projects has proven that many of the practices carried out in Europe to not be true for our circumstances.

Firstly, drainage appears to not be essential because the drainage very soon becomes invaded by plant roots which decrease or completely prevents its operation. The reality is that during periods of heavy rain the majority of the water leaves the roof via surface drainage.

Specially engineered soils appear to not be essential other than they are a little lighter a factor that can very easily be mitigated during the design stage of the roof to allow it to carry a little more weight.

orbea longidens green roof durban

Orbea longidens

As observed in nature many of the plants that we trialled grow in humus rich soils on rocky slabs in nature. In literature found on the internet it is generally recommended not to add more than 5 percent organic matter to the growing medium mix. Experiments have proven that most of the plants that we did trials on grow better with considerably more compost. Recently since the end of the ten-year testing period I have found great benefit in heavily mulching the plants with fresh sheep manure just before the onset of the first rain in the spring time.

Clearly a great range of South African plants are extremely suitable for use on green roofs growing in shallow relatively nutrient poor soils
Many indigenous orchids are ideal candidates for growing on nutrient poor green roofs, especially orchids from the genus Eulophia, in particular the very showy Eulophia speciosa.

eulophia speciosa green roof durban

Eulophia speciosa

All of the local indigenous bulbous plants trialled have been an overwhelming success, one of the main reasons for this appears to be that during the period of maximum growth there is sufficient moisture for good growth from the rain with a dry period during the winter when they are naturally dormant.

A number of new plants have established themselves from seed that was blown in or brought in by birds. Of particular note are Bulbine natalensis, Cyanotis speciosa, Delosperma lineare, Drimiopsis maculata, the orchid Eulophia speciosa and a Plectranthus sp collected at Ndumo.

Below are lists of plants that I have trialled at my home in purpose manufactured planting trays most of which have been in trialled for ten years the minimum period that plants have been grown is 4 years.

Plants trialled that have done well
Adenium multiflorum
Aeollanthus parvifolius
Agapanthus campanulatus
Agapanthus praecox
Albuca fastigiata
Albuca setosa
Aloe arborescens
Aloe greenii
Aloe tenuior
Anthericum saundersiae
Ceropegia nilotica
Ceropegia stapeliiformis
Crassula expansa
Crassula lanceolata
Crassula multicava
Crassula obovata
Crassula ovata
Crassula pellucida
Crassula perfoliata
Crassula sarmentosa
Cyanotis speciosa
Cyrtanthus sanguineous
Delosperma lineare
Delosperma tradescantioides
Dipcadi viride
Drimia delagoensis
Drimia elata
Drimia flagillaris
Drimiopsis maculata
Drimiopsis maxima
Eulophia speciosa
Eulophia leitchii
Eulophia citellifera
Eulophia clavicornis
Eulophia parviflora
Eulophia unidentified Ndumo
Cheilanthus viridis
Gasteria croucheri
Gladiolus cruentus
Huernia histrix
Huernia zebrina
Hypoxis costata
Kleinia fulgens
Ledebouria apertifolia
Ledebouria revoluta
Murdannia simplex
Orbea longidens
Ornithogalum sp. Dwarf bought
Ornithogalum sp. Minute kloof
Pelargonium alchemilloides
Plectranthus neochilis
Plectranthus creeping sp. Ndumo
Scadoxus multiflorus
Scilla natalensis
Selaginella dregei
Vera-duthiea zebrina
Zingela pooleyorum   

Plants that have self-established
Scadoxus puniceus
Aloe maculata
Aloe ferrox
Euphorbia tirucalli
Plectranthus madagascariensis
Tetradenia riparia
Kalanchoe rotundifolia

Plants freely spreading from seed
Agapanthus praecox
Bulbine natalensis
Crassula expansa
Cyanotis speciosa
Delosperma lineare
Drimiopsis maculata
Eulophia citellifera
Eulophia speciosa
Murdannia simplex
Orbea longidens
Ornithogalum sp. Dwarf bought
Pelargonium alchemilloides
Plectranthus creeping sp Ndumo
Plectranthus neochilis

Weeds
Bidens Pilosa established from windblown seed although they are aesthetically unwanted, they complete their life cycles or die from drought before they produce seed. Weeds have not been a threat to the growth or the health of the plants.
 
Under normal conditions weeds would need to be controlled mainly for aesthetic reasons as well as to keep the plantings purely indigenous.

Establishment of grasses
In addition to unwanted annual agricultural weeds the grass Melinis repens has established in some of the trays during the rainy growing season dying off during the dry winter leaving seed to resprout with a onset of spring rains. Melinis is probably a good and certainly an attractive addition on most extensive green roof plantings.

Cyrtanthus sanguineus green roof Durban

Cyrtanthus sanguineous

Conclusion and recommendations

The vast majority of the plants tested did extremely well.
Soil similar to the soils that the plants are naturally found growing in produced the best results however all plants grew satisfactory in a general fairly open well drained growing medium.

Occasional watering and the removal of unwanted weeds would be of great benefit.

An annual mulching with either a well-rotted and leaf mould of bark compost or animal compost such as sheep dung appears to be of great benefit.

I would not recommend the addition of inorganic fertilisers because they would promote weak rapid growth of the plants

Michael Hickman
18.11.20


Weed




Contact


Rehabilitation




Green Roof


Company Profile




hlengiwe luthuli environmental managemet blog

ecoman



Google logo



but google chrome browser
Designed, Developed & Maintained by Michael Hickman
18.11.20
This page was last updated on 18.11.20