Green Roof Trials

 


Green roofs need more than just succulents if they are going to fulfill all the goals and benefits wanted from a podium enviroment. Research from Australia including a paper from the University of Western Sydney and a USA Texas study has shown many of our native plants do as well, if not better than introduced succulents. They also show that organics are a viable low maintenance option for green roofs. These changes allow designers to create a far more functional and visually appealing green roof.

1. List of recommended plants

Plants recommended for:
NSW
QLD
VIC
SA
WA
ACT
TAS
NATIVES - Strappy Leaf
Shara*
Tanika*
Katrinus Deluxe & Katrinus
Nyalla
Sungold
Katie Belles* & Tropicbelle
Aranda* & Little Jess*
Cassa Blue
Lucia
Tasred
Revelation & Baby Bliss
NATIVES - Grasses
Pennstripe*
Mingo*
Nafray & Purple Lea
NATIVES - Shrubs
Naringa & Blue Gem
Aussie Box & Grey Box
Better John & Green John
NATIVES - Groundcovers
Mundi*
Yareena*
Aussie Rambler
NATIVES - Screening Trees
Slim
Pinnacle
EXOTICS - Strappy Leaf
Isabella*
Amethyst & Just Right
Sweet Mist* & Flamin
EXOTICS - Shrubs
Blush
Cosmic White & Cosmic Pink
EXOTICS - Groundcovers
Double Gold
Flirt

* = used in trials

2. List of Top 5 Performing Plants

1. SharaTM Lomandra fluviatilis ‘ABU7’PBR
2. MundiTM Westringia fruticosa ‘WES05' PBR
3. YareenaTM Myoporum parvifolium ‘PARV01’PBR
4. Tanika® Lomandra longifolia ‘LM300’ PBR
5. Double GoldTM Gazania hybrid ‘GT20’ PBR (replacement for Tiny Tom)

3. Recommendations for different depths based on this trial

80/20 mix = 80% organics, 20% mineral
50/50 mix = 50% organics, 50% mineral
Mineral mix = 100% mineral
Note: see full paper for more mix details

10cm - if a slow release fertiliser is used and watered at least once per week in hot months:

  • 80/20 mix - no plants recommended.
  • 50/50 mix - Mundi, Tanika, Gazania, Yareena and Shara.
  • Mineral mix - Tanika and Shara.

20cm - recommended to fetilise at least once per year with slow release fertiliser:

  • 80/20 mix - Katie Belles, isabella, Mundi, Aranda, Little Jess, Tanika, Mingo, Tiny Tom, Sweet Mist (only if irrigated), Yareena and Shara.
  • 50/50 mix - Mundi, Tanika, Mingo, Tiny Tom, Sweet Mist (only if irrigated), Yareena and Shara.
  • Mineral mix - Mundi, Shara.

30cm

  • 80/20 mix - Katie Belles, Aranda, Isabella, Mundi, Tanika, Mingo, Tiny Tom, Sweet Mist (only if irrigated), Yareena and Shara. If fertilised - Sedum, Pennstripe and Little Jess.
  • 50/50 mix - Mundi, Tanika, Mingo, Tiny Tom, Sweet Mist (if irrigated), Mingo, Yareena, and Shara. If fertilised: Katie Belles, Aranda, Little Jess, Sedum, Isabella, and Pennstripe
  • Mineral mix - Mundi, Mingo, and Shara.
    If fertilised: Sedum, Yareena, and Sweet Mist (if irrigated)

4. Overall Observations

  • Organic mixes promote better health. In the past advocates of mineral substrates used an argument that you cannot use organics because they slump, and the water runoff would be unclean. This research proves both these assumptions to be incorrect.
  • No shrinkage in the two organic mixes that differed from the mineral mix.
  • First flush water quality showed differences, less difference after the first flush with lower values.
  • Reuse of drainage water for irrigation could be feasible, based on long term water qualities.
  • Bare substrate temperature exceeded base of the planter box by 15 – 25 0C.

How is it possible that organics didnt slump?

1. Stabilised organics were used. They are composted much better than normal organic mixes and use organics that are extremely slow to break down. Including extremely well composted pine bark and coir. DO NOT confuse this specialised mix with standard organic potting mixes.

2. Most of the plants used in this trial have highly fibrous root systems, which helps to stablise the mix more. Used together stablised organics and plants with fibrous roots will prevent slumpage.

3. 100% organic mixes WERE NOT used in this trial! The organic mixes in this trial had either 20% mineral or 50% mineral components to help stablise the mix. Results for a 100% organic mix would probably be much different.

IMPORTANT NOTE: Standard potting mixes are not going to have the same effect as the specialised organic mixes that were used in the trial. For mix details please refer to the full paper.

 

To read the entire paper, download the pdf.

Australian Native Plants for Harsh Green Roofs | 4.5MB


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