Australian native plants for harsh green roofs Roadway to rooftop By Todd Layt 2011
Can green roofs learn from roadside landscape plantings?
Contents Introduction .......................................................................................................................................2 Research and options; Green life for green roofs .............................................................................3 Lawns for green roofs .............................................................................................................3 USA study ................................................................................................................................5 Evaluation of Western Sydney green roof test plots ........................................................................7 Background to original study ..................................................................................................7 Key findings from the original study .......................................................................................7 Post evaluation for plant health ..............................................................................................8 Results for the three mixes .....................................................................................................8 Discussion ........................................................................................................................................24 Choosing a substrate .............................................................................................................24 Plant evaluation.....................................................................................................................25 Recommendation of plants to use in various depths and substrates ...................................25 Plant comparison and roadside plants ..................................................................................26 Conclusion ........................................................................................................................................27 References ........................................................................................................................................27 Annexure A .......................................................................................................................................28
Australian native plants for harsh green roofs | By Todd Layt 1
Choosing plant types and substrates that perform in Australia Todd Layt is a well‐known turf and plant breeder, who specialises in breeding functional, no fuss, plants and turf for commercial landscaping in Australia, the USA, Europe, Asia and New Zealand. Many of the plants and turf he has developed are used on harsh roadside projects. Now these same plants are finding a home in roof top gardens and green roofs around the world. He is currently involved in green roof research, plus other research projects including the quantifying of carbon sequestration of many Australian native plants. Many Australian native plants are providing answers, not just for Australia, but for the USA as well. Green roofs need more than just succulents if they are going to fulfil all the goals and benefits wanted from a podium environment. 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, and also show that organics are a viable low maintenance option for green roofs. These changes allow designers to create far more functional and visually pleasing green roofs.
Introduction Green roof is made up of two words. For green life the rooftop indicates a harsh, hard to access place for maintenance, and in Australia a windy, exposed and hot environment. The definition of a garden (green) is a planned space, set aside for the display, cultivation, and enjoyment of plants and other forms of nature. Modern green roofs have moved on from rooftop gardens, but they still hold some of the main principles. They must be beautiful, green, vegetative, healthy and low maintenance. To achieve most of the benefits of a green roof, or a rooftop garden, the plants need to be healthy and look good. Sterile mineral based substrates not only limit the health and look of plants, they greatly limit the types of plants that can be used. Even if plants are found that can survive for a couple of years in shallow mineral based substrates on green roofs, it is doubtful that such gardens will survive after five or ten years and more unlikely that they will continue to look good. The plants that manage to work overseas in cold climates find Australia's heat, and in many regions humidity, difficult. Australia is on a steep learning curve when it comes to plant selection for green roofs, especially for shallow extensive green roofs. A great deal can be learned from plants that thrive in roadside conditions, as a roadside is often as harsh as a rooftop. Green roofs are cooler than surrounding areas, but healthy plants with lots of foliage are far cooler than bare soil with small plants that are struggling to grow. In a recent study1 on a 40 degree day, bare soil temperatures were taken for gravel; in full sun the temperature was 77.78°C, whilst the gravel next to a Lomandra was down to 53.9°C. Bare soil was 68.5°C and turf was 45.65°C. Dense foliage from healthy green life is critical to maximising one of the major benefits of a green roof; that of its cooling effect. Another benefit often touted by green roof advocates, is the health benefits to people. There is extensive research that proves green life is good for peoples health.2 On the other hand desert looking environments may not have the same impact. So the concept of brown roofs or rooftop gardens that look sickly or relatively bare may not have the same psychological health benefit of a healthy green space. Architecture is enhanced more with a healthy green roof, rather than a struggling one. A good substrate profile that promotes healthy vigorous plants is integral in helping green roofs better achieve their objectives. Plants and turf are excellent water quality improvers. Turf and grasses are well known to improve water quality. Further research is needed to compare the ability of different plant types like grass, succulents, Lomandra, ground cover plants and small shrubs. It would be reasonable to assume some types will clean water better than others, and a healthy garden would be better than a struggling garden. Growth media for green roofs3 by E. Charles Morris from the University of Western Sydney clearly shows the benefits of better substrate profiles to plant health. This paper evaluates the plots from Australian native plants for harsh green roofs | By Todd Layt 2
this study at a later date. For the first year in the study little differences were found between plots, but some time into the second year differences were clearly evident. In this evaluation period, we look at these plots as a post evaluation almost two full years after the study commenced. The differences between plant health in the plots is now far more evident, and the differences between species is also more obvious. Interestingly it was the commonly used roadside plants that generally did best. Back in the mid 1990's small native grasses and forbes were widely planted on roadsides by the millions. These days other plants are used instead. The reason why the installation of plants like Danthonia, Bothriochloa, Dichelachne and forbes like Wahlenbergia are rarely planted these days on roadsides, is because they were not successful in the long term. They worked well for the first year, and regularly for part of the second year, but by the end of year two, three, and four they had almost always failed. They are just too short lived. Plants like Poa and Themada worked better, but the public preferred evergreen plants. Dianella and Lomandra provided this for roadsides. Today the most popular plants for roadsides are Lomandras, and tough small shrubs. Will the same thing occur on green roofs in Australia? People in general want low maintenance, drought tolerant evergreen plants. Can we look at what other plants do well on roadside conditions and use them on green roofs? Research in Western Sydney has identified how Lomandra and Westringia are some of the most successful plants for green roofs. They are also some of the most successful roadside plants. The top 5 plants in the study are regularly used on roadsides. Roadside conditions and green roofs have a lot in common. Roadside plants have to survive on low water, low nutrients, cope with the heat of a road, the wind of cars passing, and only receive very little maintenance input. Landscape professionals in different cities have a list of plants they often use on roadsides. Is it time to look at those lists for green roofs? Has the green roof research already been done for us with the tens of millions of plants installed on roadsides every year? Another aspect to roadside plant selection that green roofs could learn from is that certain varieties of a species do better than others. Eg; Some Lomandra and Dianella types perform far better than others, so it is not just getting the genus and species right, but also the appropriate cultivar. Humidity is another factor. Plants that work in Victoria or NSW often succumb to humidity in Queensland.
Research and options; Green life for green roofs Lawns for green roofs Many green roofs use lawns for public spaces. Maintenance of lawns on green roofs is difficult. Fortunately these days there are lawns or lawn alternatives that require little mowing. Zoysia turf varieties like Empire have been shown by research to require half to a third the mowing of other lawns.4 Nara, a new Australian Native Zoysia has similar attributes and is naturally adapted to exposed windy sites. Zoysia works in full sun or up to 40% shade. Zoysia is fast becoming the lawn of choice by roadside departments. If shade is an issue Buffalo turf has shown to be best for up to 70% shade. A recent study by the Department of Primary Industries5 showed Sapphire Buffalo to be the top performer in shade, but most other Buffalo types performed far better than other grass types in the trial. If an area has very high wear, and is in full sun, then a turf may need to be chosen that requires more regular mowing. A new Kikuyu called Kenda has four times as many rhizomes as common Kikuyu, and is proving to be far more wear tolerant than other Kikuyu, however weekly mowing in summer will be required on this type of turf. Another alternative is to use pavers for traffic, and to plant a mow once per year plant like Isabella. This plant makes a dense lawn for passive areas, and tolerates heavy shade and full sun. It is the only fine leaf Liriope that is fast spreading and low growing. It requires mowing every year at the end of July or early August. It is far more spreading than Mondo or Mini Mondo. Another alternative is Zoysia tenuifolia, or Australian native plants for harsh green roofs | By Todd Layt 3
Japanese temple grass. This is not for traffic areas, but is a lawn that needs mowing about every 18 months or more. The only issue is that after trimming it can look brown for many months before it reshoots, as it thatches profusely.
Image 1: Zoysia tenuifolia
Image 2: ISABELLA® Liriope muscari ‘LIRF’ PBR Australian native plants for harsh green roofs | By Todd Layt 4
Image 3: NARA™ Australian Native Zoysia Turf: Zoysia macrantha ‘MAC03’ PBR
USA study In a recent study in the USA at Texas A & M University by Dr. Anthony Camerino, Dianella and Lomandra plants from Ozbreed were tested and compared to other plants in a green roof trial. In early 2009, a season‐long trial had begun near Houston, led by Texas A&M with the cooperation of Jacob White Construction, to evaluate the potential of several plant "mixes" for green roof applications: native wildflowers (from seed), butterfly Iris (from one gallons), native grasses (from seed) and the Ozbreed Plants (from 2.5‐in plugs). There were both irrigated and non‐irrigated plots. The Ozbreed plants fared much better without supplemental water which earned them the highest quality ratings in the study, roughly a 7 out of 10. The plants used were Lomandras Tanika, Katrinus Deluxe and Tropic Belle and Dianellas Cassa Blue, Little Rev, Revelation, Tasred, and Baby Bliss.
Australian native plants for harsh green roofs | By Todd Layt 5
Image 4: A picture of the trial plots at the end of summer. Ozbreed plants at back and centre left; also in front right. You can see the drip irrigation on the front section and none in the rear. Chart 1: Average quality ratings of the Aussie mix, Butterfly Iris, Wildflower mix, and US native grass mix
Australian native plants for harsh green roofs | By Todd Layt 6
Evaluation of Western Sydney green roof test plots Background to original study In December 2009 test plots were established in Western Sydney to compare different types of substrates for green roofs. The aim was to compare the effect of these different substrates on a variety of plants, as well as water quality, slumpage effects, and temperature variations between these substrates, and bare substrates. Table 1: Recipe for three types of growing mixes. A) 80:20 Mix Recipe Product Coir Composted Pine Bark Clinker Ash B) 50:50 Mix Recipe Product Coir Composted Pine Bark Fines Scoria ≤ 6mm Clinker Ash C) Standard Mix Recipe Product Scoria ≤ 6mm Bayswater Sand (ash) Coarse Sand
35% 45% 20% 25% 25% 40% 10%
15m³ 5.25 m³ 6.75 m³ 3 m³ 15m³ 3.75m³ 3.75m³ 6m³ 1.5m³ 15m³
50% 40% 10%
7.5m³ 6m³ 1.5m³
Key findings from the original study
There was little difference between the standard mineral mix, and the two organic mixes used, on plant survival or growth over the period of measurement (17 weeks). In the post‐trial period up to 90 weeks, there was more plant death in the 100mm substrate depth, especially if not fertilised. A greater difference in plant growth was observed amongst the mixes with plant survival/health being best in the 50:50 mix, followed by the 80:20 mix and then the standard mix. There were initial differences between mixes and depths for some measurements of water quality, but these lessened and disappeared as the ‘first flush’ effect (high initial values) was replaced by longer‐term, low values of the variables. Longer‐term values for water quality parameters are under standards for irrigation water; reuse of drainage water for irrigation could be feasible, given the low concentrations of the inorganic chemical indicators of water quality The two organic mixes did not show shrinkage or movement that differed greatly from the standard mix There was a substantial daytime temperature difference between bare substrate and the base of the planter boxes (at 100 mm depth), with the bare substrate temperature exceeding that of the planter box by 15 – 25 0C (October measurement period).
The main reasons advocates for mineral substrates use to deter the use of organics on green roofs are that the organics slump, and that the water quality can be poor. This study shows both those assumptions to be incorrect. What the study also shows is that the health of plants are greatly enhanced by organics. Australian native plants for harsh green roofs | By Todd Layt 7
Post evaluation for plant health In September 2011 the plots that were originally studied by E. Charles Morris from the University of Western Sydney, were again re‐evaluated. No new maintenance had occurred other than the maintenance outlined in the first paper. The only maintenance during the first period was establishment watering. The establishment period ended on 17 January 2010 (end of week 6); watering was withdrawn. The only other maintenance was an addition of an organic fertiliser to one of the two blocks in August 2010. Peter Abell (Ass. Dip. Hort.) with the assistance of Katrina Layt were engaged to perform a post evaluation of the plant health of the various plant types in the three different substrates, and the three different substrate depths. Peter Abell is an experienced horticulturist, with decades of experience in TAFE teaching. He has also had years of experience in evaluation of plants for Plant Breeders Rights, and is a Qualified Person for Plant Breeders Rights trials, and was once a field evaluator for Plant Breeders Rights Australia. Katrina Layt is a final year Landscape Design student in the Horticultural department. Each plant was given a rating for health. 0 was for dead plants, and 10 was for how the plant looks at its peak condition growing in a well maintained garden. Both observers have seen the plants in well maintained gardens at other sites. Note; unhealthy does not necessarily mean diseased, it includes nutrient deficiencies and poor plant growth. Also it must be noted that in a real green roof, it is recommended to apply 8 to 9 months slow release fertiliser each year. It is reasonable to assume with two applications of this, the plant health would have improved. It was decided to only use a quicker release organic fertiliser on one block, and no fertiliser on the other, to better show the effects of the different substrates. The fertilised plants in general were better. A future test comparing yearly slow release fertiliser applications would be beneficial.
Results for the three mixes A mix (80% Organic 20% Mineral), B mix (50% Organic 50% Mineral), C mix (100% Mineral) Top 5 plants through all plots SHARA™ Lomandra fluviatilis ‘ABU7’ A MUNDI ™ Westringia fruticosa ‘WES05’ A YAREENA ™ Myoporum parvifolium ‘PARV01’ A TANIKA ® Lomandra longifolia ‘LM300’ A TINY TOM™ Gazania tomentosa ‘GT10’ A Top 5 plants for A mix MUNDI ™ Westringia fruticosa ‘WES05’ A YAREENA ™ Myoporum parvifolium ‘PARV01’ A ISABELLA® Liriope muscari ‘LIRF’ A & SHARA™ Lomandra fluviatilis ‘ABU7’ A TANIKA ® Lomandra longifolia ‘LM300’ A & TINY TOM™ Gazania tomentosa ‘GT10’ A ARANDA ™ Dianella caerulea ‘DC150’ A Top 5 plants for B mix SHARA™ Lomandra fluviatilis ‘ABU7’ A YAREENA ™ Myoporum parvifolium ‘PARV01’ A & TINY TOM™ Gazania tomentosa ‘GT10’ A Themeda australis ‘Mingo’ A MUNDI ™ Westringia fruticosa ‘WES05’ A TANIKA ® Lomandra longifolia ‘LM300’ A
Australian native plants for harsh green roofs | By Todd Layt 8
Top 5 plants for C mix SHARA™ Lomandra fluviatilis ‘ABU7’ A MUNDI ™ Westringia fruticosa ‘WES05’ A TANIKA ® Lomandra longifolia ‘LM300’ A YAREENA ™ Myoporum parvifolium ‘PARV01’ A & Themeda australis ‘Mingo’ A SWEET MIST ® Phormium tenax ‘PH0S2’ A
Table 2: Averages of plant ratings
A‐10cm (plots 3 & 12)
B‐10cm (plots 6 & 9)
C‐10cm (plots 15 & 18)
A‐20cm (plots 5 & 8)
B‐20cm (plots 14 & 17)
C‐20cm (plots 2 & 11)
A‐30cm (plots 13 & 16)
B‐30cm (plots 1 & 10)
C‐30cm (plots 4 & 7)
Average (to 2 dp)
Plant average rating /10
1
2
2
5
3.5
2.5
5.5
4.5
1.5
3.06
0
0.5
1.5
3.5
3
2.5
3
3.5
2
2.17
KATIE BELLES™ Lomandra hystrix ‘LHBYF’ PBR
Anigozanthos hybrid ‘Gold Velvet’ PBR Sedum pachyphyllum ARANDA ™ Dianella caerulea ‘DC150’ PBR ISABELLA® Liriope muscari ‘LIRF’ PBR MUNDI ™ Westringia fruticosa ‘WES05’ PBR LITTLE JESS ™
2.5
2
1.5
2
1
2.5
0
3
3.5
2
2.5
3.5
3
5.5
3.5
2.5
5
4.5
2.5
3.61
5
3.5
2
5
3
2.5
5.5
3.5
2
3.56
1.5
4
3
8
5
4
7.5
5
5
4.78
Dianella caerulea ‘DCMP01’ PBR
2
2.5
1
4.5
1
2
3
3
2.5
2.39
TANIKA ® Lomandra longifolia ‘LM300’ PBR PENNSTRIPE™
1
4
4
6.5
5.5
3.5
7
4
3
4.28
Pennisetum alopecuroides ‘PAV300’ PBR
0
1
0.5
2.5
3.5
2
3
3
2.5
2
0
3
1
7
5
3.5
5.5
6.5
5.5
4.11
1.5
1.5
2
1.5
2.5
1
3.5
1.5
1
1.78
TINY TOM™ Gazania tomentosa ‘GT10’ PBR SWEET MIST ®
3.5
4
2
4.5
5
3.5
6.5
6.5
2
4.17
Phormium tenax ‘PH0S2’ PBR
0.5
2.5
2.5
5.5
4.5
2.5
5.5
6
3.5
3.67
3.5
4.5
3
5.5
5.5
3.5
7
5.5
3.5
4.61
2 6 4.5 7 6.5 4 6.5 7 1.77 2.97 2.23 4.9 3.87 2.8 4.93 4.47 NB: Pennstripe ratings were based on spring colour (brown)
4.5 2.97
5.33 3.43
Themeda australis
‘MINGO’ PBR Test Succulent: Echeveria hybrid
YAREENA ™ Myoporum parvifolium ‘PARV01’ PBR
SHARA™ Lomandra fluviatilis ‘ABU7’ PBR Average (to 2 dp)
Australian native plants for harsh green roofs | By Todd Layt 9
Table 3: Averages of percentages of plants dead and unhealthy in each mix type and depth Average of % dead in each mix A mix: 10cm 36.2% A mix: 20cm 7.0% B mix: 10cm B mix: 20cm 15.5% C mix: 10cm C mix: 20cm Average of % unhealthy in each mix A mix: 10cm 86.6% A mix: 20cm B mix: 10cm 79.3% B mix: 20cm C mix: 10cm 93.8% C mix: 20cm
1.8% 3.5% 5.2%
A mix: 30cm
6.9% 1.7% 0.0% 29.6% 44.1% 82.8%
B mix: 30cm C mix: 30cm
32.4% 55.4% 93.1%
A mix: 30cm B mix: 30cm C mix: 30cm
Table 4: Percentages of plants dead/alive and unhealthy/healthy in each plot Plot no. % Dead % Alive % Unhealthy % Healthy 1 (B ‐ 30cm) 0.0% 100.0% 31.0% 69.0% 2 (C ‐ 20cm) 0.0% 100.0% 86.2% 13.8% 3 (A ‐ 10cm) 31.0% 69.0% 85.0% 15.0% 4 (C ‐ 30cm) 0.0% 100.0% 100.0% 0.0% 5 (A ‐ 20cm) 3.6% 96.4% 40.7% 59.3% 6 (B ‐ 10cm) 3.6% 96.4% 74.1% 25.9% 7 (C ‐ 30cm) 0.0% 100.0% 65.5% 34.5% 8 (A ‐ 20cm) 0.0% 100.0% 24.1% 75.9% 9 (B ‐ 10cm) 10.3% 89.7% 84.6% 15.4% 10 (B ‐ 30cm) 3.4% 96.6% 57.1% 42.9% 11 (C ‐ 20cm) 10.3% 89.7% 100.0% 0.0% 12 (A ‐ 10cm) 41.4% 58.6% 88.2% 11.8% 13 (A ‐ 30cm) 6.9% 93.1% 18.5% 81.5% 14 (B ‐ 20cm) 0.0% 100.0% 55.2% 44.8% 15 (C ‐ 10cm) 17.2% 82.8% 87.5% 12.5% 16 (A ‐ 30cm) 6.9% 93.1% 40.7% 59.3% 17 (B ‐ 20cm) 6.9% 93.1% 55.6% 44.4% 18 (C ‐ 10cm) 13.8% 86.2% 100.0% 0.0% Totals: 8.6% 91.4% 66.3% 33.7% NB: Unhealthy does not necessarily mean diseased, it includes nutrient deficiencies and poor plant growth NB: There were not enough test succulents to go around all of the plots. Two missed out (plots 5 & 6)
Australian native plants for harsh green roofs | By Todd Layt 10
Chart 2: Comparing percentages of plants that died in the three mixes 40.0% 35.0%
36.2%
30.0% 25.0% A mix
20.0%
B mix
15.0%
C mix
15.5%
10.0% 5.0%
7.0%
1.8% 3.5% 5.2%
0.0% 1 10 cm 10cm
6.9% 1.7% 0.0%
2 20cm 20cm
330cm 30cm
Chart 3: Comparing percentages of plants that were unhealthy in the three mixes 100.0% 90.0% 80.0% 70.0%
93.8%
93.1%
86.6% 79.3%
82.8%
60.0%
A mix
50.0%
55.4%
B mix
40.0%
44.1%
30.0%
32.4%
C mix
29.6%
20.0% 10.0% 0.0% 1 10 cm10cm
2 20cm 20cm
330cm 30cm
Chart 4: Comparing averages of plant ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 6.00 5.00 4.93
4.9
4.47
4.00 3.87
A mix
3.00 2.97 2.00
2.8
2.97
B mix C mix
2.23 1.77
1.00 0.00 1 10 cm 10cm
2 20cm
330cm 30cm
Australian native plants for harsh green roofs | By Todd Layt 11
Chart 5a: Comparing averages of all plant ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between the average ratings of all plants (excluding the succulents) to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 6 5.42
5.38
5
4.81
4
A mix: All plants
4.19
B mix: All plants
3
3.15
A mix: Succulents
2.31
2
C mix: All plants
3.08
2.96
2.252.25 2
1.73
1.751.75
1.751.751.75
1.75
B mix: Succulents C mix: Succulents
1
0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 5b: Comparing averages of all plant ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between the average ratings of all plants (excluding the succulents) to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 4 3.5
3.67
3 2.5 2
1.89
1.5 1 0.5 0 Average (to 2 dp) All plants Succulents ulents
Australian native plants for harsh green roofs | By Todd Layt 12
Chart 6a: Comparing averages of Lomandra ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between the average ratings of Lomandra's (TANIKA® Lomandra longifolia ‘LM300’ PBR & SHARA™ Lomandra fluviatilis 'ABU7' PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 8 7 6.75
6.75
6 6
A mix: Lomandra's
5.5
5
B mix: Lomandra's
5
4
C mix: Lomandra's
4.25 3.75
A mix: Succulents
3.75
3
B mix: Succulents C mix: Succulents
2 2
1
1.5
2.252.25 1.751.75
1.751.751.75
1.75
0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 6b: Comparing averages of Lomandra ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between the average ratings of Lomandra's (TANIKA® Lomandra longifolia ‘LM300’ PBR & SHARA™ Lomandra fluviatilis ‘ABU7’ PBR) to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 6.00
5.00 4.81 4.00
3.00
2.00
1.89
1.00
0.00 Average (to 2 dp) Lomandra's Succulents
Australian native plants for harsh green roofs | By Todd Layt 13
Chart 7a: Comparing averages of Shara ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between SHARA™ Lomandra fluviatilis ‘ABU7’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 8 7 7
7 6.5
6
6.5
6
A mix: Shara
5
B mix: Shara 4.5
4
4.5
C mix: Shara
4
A mix: Succulents
3
B mix: Succulents C mix: Succulents
2 2
2
2.252.25 1.751.75
1.751.751.75
1.75
1 0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 7b: Comparing averages of Shara ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between the average ratings of SHARA™ Lomandra fluviatilis ‘ABU7’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 6.00
5.00
5.33
4.00
3.00
2.00
1.89
1.00
0.00 Average (to 2 dp) Shara Succulents
Australian native plants for harsh green roofs | By Todd Layt 14
Chart 8a: Comparing averages of Mundi ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between MUNDI ™ Westringia fruticosa ‘WES05’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 9 8 8 7.5
7 6
A mix: Mundi B mix: Mundi
5 5
5
5
C mix: Mundi
4 4
A mix: Succulents
4
B mix: Succulents
3 3
C mix: Succulents
2 2
1
1.5
2.252.25 1.751.75
1.751.751.75
1.75
0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 8b: Comparing averages of Mundi ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between MUNDI™ Westringia fruticosa ‘WES05’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 6.00
5.00 4.78 4.00
3.00
2.00
1.89
1.00
0.00 Average (to 2 dp) Mundi Succulents
Australian native plants for harsh green roofs | By Todd Layt 15
Chart 9a: Comparing averages of Yareena ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between YAREENA ™ Myoporum parvifolium ‘PARV01’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 8 7 7
6 5.5 5.5
5
B mix: Yareena 4.5
4 3
A mix: Yareena
5.5
C mix: Yareena
3.5
3.5
A mix: Succulents
3.5
B mix: Succulents
3
C mix: Succulents
2 2
2.252.25 1.751.75
1.751.751.75
1.75
1 0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 9b: Comparing averages of Yareena ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between YAREENA ™ Myoporum parvifolium ‘PARV01’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 5.00 4.50
4.61
4.00 3.50 3.00 2.50 2.00
1.89
1.50 1.00 0.50 0.00 Average (to 2 dp) Yareena Succulents
Australian native plants for harsh green roofs | By Todd Layt 16
Chart 10a: Comparing averages of Tanika ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between TANIKA® Lomandra longifolia ‘LM300’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 8 7 7 6.5
6
A mix: Tanika
5.5
5
B mix: Tanika C mix: Tanika
4 4
4
4
A mix: Succulents
3.5
3
B mix: Succulents
3
C mix: Succulents
2 2
2.252.25 1.751.75
1.751.751.75
1.75
1 1
0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 10b: Comparing averages of Tanika ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between TANIKA® Lomandra longifolia ‘LM300’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 4.50 4.00
4.28
3.50 3.00 2.50 2.00
1.89
1.50 1.00 0.50 0.00 Average (to 2 dp) Tanika Succulents
Australian native plants for harsh green roofs | By Todd Layt 17
Chart 11a: Comparing averages of Tiny Tom ratings to Succulent ratings in the three mixes Note: these numbers are based on the averages of ratings out of 10 between TINY TOM™ Gazania tomentosa ‘GT10’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 7 6.5 6.5
6 5 5
A mix: Tiny Tom
4.5
4
B mix: Tiny Tom
4
3
C mix: Tiny Tom
3.5
3.5
A mix: Succulents B mix: Succulents
2
2.252.25 2
2 1.751.75
1.751.751.75
2
C mix: Succulents
1.75
1 0 1 10cm 10 cm
2 20cm 20cm
330cm 30cm
Chart 11b: Comparing averages of Tiny Tom ratings to Succulent ratings Note: these numbers are based on the averages of ratings out of 10 between TINY TOM™ Gazania tomentosa ‘GT10’ PBR to the average ratings of Succulents (Sedum pachyphyllum & Test Succulent: Echeveria hybrid) 4.50 4.00
4.17
3.50 3.00 2.50 2.00
1.89
1.50 1.00 0.50 0.00 Average (to 2 dp) Tiny Tom Succulents
Australian native plants for harsh green roofs | By Todd Layt 18
Chart 12: Comparing averages of plant ratings in the three mixes: Fertilised vs NOT fertilised Note: these numbers are based on the average rating out of 10 for all of the plants in the fertilised and non fertilised plots 6.00 5.6
5.47
5.00
5.13 4.5
4.00
4.4
A mix: Fertilised
4.13
3.00
3.4
3.2
3.8
3.73
3.6
B mix: Fertilised C mix: Fertilised
2.93 2.33
2.00
A mix: Not fertilised
2.53 2.2
2.2
C mix: Not fertilised
1.93
1.00
B mix: Not fertilised
1.2
0.00 1 (B ‐ 30cm) 10 cm 10cm
2 (C ‐ 20cm) 20cm 20cm
3 (A ‐ 10cm) 30cm 30cm
Chart 13: Comparing ratings of Katie Belles in the three mixes: Fertilised vs NOT fertilised Note: these numbers are based on the ratings out of 10 for KATIE BELLES™ Lomandra hystrix ‘LHBYF’ PBR in the fertilised and non fertilised plots 7 6 6 6 5 5
5
5
A mix: Fertilised B mix: Fertilised
4 4
C mix: Fertilised A mix: Not fertilised
3 3
3
3
B mix: Not fertilised
2 2 2
2 2
2
C mix: Not fertilised
2
1 1
1
1
0 1 (B ‐ 30cm) 10cm 10 cm
2 (C ‐ 20cm) 20cm 20cm
3 (A ‐ 10cm) 30cm 30cm
Australian native plants for harsh green roofs | By Todd Layt 19
Chart 14: Comparing averages of fertilised A mix vs non‐fertilised A mix Note: these numbers are based on the averages of ratings out of 10 for all plants and plot depths for fertilised A mix and non‐fertilised A mix 5.00 4.50 4.00
4.47 3.37
3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00
A mix: A mix: NOT fertilised Average (to 2 dp) Fertilised
Chart 15: Comparing averages of fertilised B mix vs non‐fertilised B mix Note: these numbers are based on the averages of ratings out of 10 for all plants and plot depths for fertilised B mix and non‐fertilised B mix 4.50 4.00 3.50
4.16 3.44
3.00 2.50 2.00 1.50 1.00 0.50 0.00
B mix: B mix: B mix: NOT fertilised B mix: NOT Average (to 2 dp) Fertilised Fertilised
Australian native plants for harsh green roofs | By Todd Layt 20
Chart 16: Comparing averages of fertilised C mix vs non‐fertilised C mix Note: these numbers are based on the averages of ratings out of 10 for all plants and plot depths for fertilised C mix and non‐fertilised C mix 3.50 3.00
3.22
2.50 2.11 2.00 1.50 1.00 0.50 0.00
C mix: C mix: NOT fertilised Average (to 2 dp) Fertilised
Image 5: 10 cm depth, C mix (mineral substrate). The worst performing plot for plant health.
Australian native plants for harsh green roofs | By Todd Layt 21
Image 6: 20cm depth, A mix (80/20 substrate).
Image 7: 20cm depth, B mix (50/50 substrate).
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Image 8: 30cm depth, C mix (mineral substrate).
Image 9: 30cm depth, A mix (80/20 substrate).
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Image 10: 30cm depth, B mix (50/50 substrate).
Discussion Choosing a substrate When choosing a substrate for a green roof, this trial and the plant health ratings clearly show organics help greatly improve plant health. Based on this research, the minimum substrate depth should be 20cm and should include at least 50% organics. The study shows however a depth of 30cm will provide the best option, with at least 50% organics. At 30cm and with the 80% organics, the number of unhealthy plants was only 29.6%. Compare that to the 82.8% unhealthy plants in the 30cm mineral mix, and it is easy to see why organics are so important for green roofs. The 50/50 blend at 30cm only had 44.1% unhealthy plants. 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 those assumptions to be incorrect. One hypothesis for the lack of slumpage in this trial, and in real world situations is that any slumpage due to organic decomposition is replaced by the roots of plants growing in the substrate, or the binding properties of those roots. Based on this research, it is reasonable to argue that organics should be part of every green roof in Australia. Many believe that fertilising green roofs is too difficult. On the contrary, a single application of 8 to 9 month slow release fertiliser is a very simple task. A 20kg bag will do a large area, and the carrying of 20kg to a roof via and elevator or stairs is not difficult. The average rating of plant health in mix A without fertiliser was 3.37, and with fertiliser was 4.47. For mix B it was 3.44 without fertiliser, and 4.16 with. This was only with an organic fertiliser that does not have the longevity of an 8 to 9 month slow release fertiliser. It would be reasonable to predict that if a slow release fertiliser was used, the results would have been enhanced. The fertiliser used in this study was a pelletised compressed manure product, that is far lower in nutrients and quicker to release than a good quality 8 to 9 month slow release product. To date after almost two years slumpage has not occurred on these plots. The organics chosen in these substrates have very minimal Australian native plants for harsh green roofs | By Todd Layt 24
slumpage over a longer period. If in the unlikely event over a 5 to 10 year period minor slumpage did occur, a simple maintenance solution is at hand. Bags of mulch could without too much difficulty be carried to the roof, and spread over the garden. This would be no harder than say replacing parts on an air‐conditioner on a roof.
Plant evaluation Based on this research, below are lists of plants that performed best in each type of substrate and depth.
Recommendation of plants to use in various depths and substrates 10cm depth plant recommendations 10cm depth for all mixes, if unfertilised and not irrigated at all, no plants are recommended based on this study. If fertilised each 9 months with 8 to 9 month slow release fertiliser, and the plants are watered at least once per week in the hot months, then the following plants would however be the best option based on this research. 80/20 mix at 10cm no plants recommended. 50/50 mix at 10cm Mundi, Tanika, Gazania, Yareena, and Shara. Mineral mix at 10cm Tanika and Shara However based on this research it would be much better to not use a depth of 10cm at all. A 20cm depth produced much better plant health, particularly with organics added. Weight is often the reason why a shallow substrate depth is needed. Mineral substrates per square metre at a depth of 10cm equates to 135kg and at 20cm 270kg. 270kg may be too heavy, but an 80/20 blend only weighs 190kg at a 20cm depth per square metre. Based on this research the plant health at 20cm in the 80/20 blend is far higher than the 10cm mineral substrate. For an extra 55kg plant health is greatly improved. The percentage of unhealthy plants in a 10cm mineral mix was 93.8%, whilst the 20cm 80/20 blend was 32.4%. That means the 80/20 blend at 20cm was 61.4% better at providing healthy plants compared to the 100% mineral mix. At 10cm the 80/20 blend is not an option, as it performed the worst of all mixes at that depth. A 50/50 blend has some other benefits, so if weight allows this could also be an option. Remember to consider plant weight when specifying plants. Trees and shrubs will be heavier than plants under 1m and strappy leaf plants will weigh less than shrubs. 20cm depth plant recommendations For 80/20 substrate, mix A at 20cm. Katie Belles, Isabella, Mundi, Aranda, Little Jess, Tanika, Mingo, Tiny Tom, Sweet Mist (only if irrigated), Yareena and Shara. For 50/50 substrate, mix B at 20cm. Mundi, Tanika, Mingo, Tiny Tom Gazania, Sweet Mist (only if irrigated) Yareena, Shara. For 100% mineral substrate, mix C at 20cm. Mundi, Shara. At these depths it is recommended to fertilise at least once per year with slow release fertiliser. 30cm depth plant recommendations For 80/20 substrate, mix A at 30cm. Katie Belles, Aranda, Isabella, Mundi, Tanika, Mingo, Tiny Tom, Sweet Mist (if irrigated), Yareena and Shara. These all did well without fertiliser. If fertiliser is added Australian native plants for harsh green roofs | By Todd Layt 25
by using 8 to 9 months slow release fertiliser each 12 months, Sedum, Pennstripe and Little Jess can be added to this list. Little Jess did much better in this trial in the fertilised plot. This is another lesson we can learn from roadsides. In general Dianella require slightly better soils as far as nutrients are concerned compared to Lomandra. For 50/50 substrate, mix B at 30cm. Mundi, Tanika, Mingo, Tiny Tom, Sweet Mist (if irrigated), Mingo, Yareena, and Shara. If fertilised Katie Belles, Aranda, Little Jess, Sedum, Isabella, and Pennstripe could be added to this list. For 100% mineral substrate, mix C at 30cm. Mundi, Mingo, and Shara. If fertilised each year with slow release fertiliser, then Sedum, Yareena, and Sweet Mist (if irrigated) could be added to the list.
Plant comparison and roadside plants A few plants were real standouts in this trial. Mundi, a groundcover Westringia, and Shara, a compact form of Lomandra worked well in almost all substrate plots. Shara was rated at 8 for the B 30cm mix, and Mundi was rated a 9 in the 30cm A mix when fertilised. Considering a rating of 10 is for a very healthy plant growing in a well maintained garden, to get a rating of that in these harsh conditions shows how well these plants did. All the top plants are regularly used on roadsides. Shara, Tanika, Mundi, Yareena, and Tiny Tom or similar cultivars are all used on roadsides. Although the Dianella types did well in the fertilised 20cm and 30 cm organic substrates, they did not do well in the mineral substrate, or as well in the organic blends without fertiliser. The same happens on roadsides. Dianella does not do as well in very poor compacted roadside soils. Soil for Dianella needs to be reasonable for good long term viability. Provided the depth is 20cm or more, organics are in the substrate, and the green roof is fertilised yearly with 8 to 9 month slow release, then the plants that can be used based on this study are; Katie Belles, Aranda, Mundi, Tanika, Mingo, Tiny Tom, Yareena, Shara, Sedum, Pennstripe and Little Jess. Sweet Mist a compact Phormium, and Isabella a spreading Liriope also did well but in general these need some irrigation. It must be noted that Tiny Tom has now been replaced by another Gazania, namely Double Gold. Double Gold is just as tough, but it has the added advantage of not producing viable seed, and has more flowers. Gazania, Isabella, Sweet Mist and Sedum are not natives, but all the others in the list are. It must be noted that the Kangaroo Paw did not receive the maintenance recommended for them, either did any of the true grass species. All these type of plants should be pruned annually for good performance. Roadsides are wonderful proving grounds for plants. Often varieties of a plant genus and species perform differently, so you cannot assume just because one variety does well that all plants of that species will. For example, LITTLE JESS™ Dianella caerulea 'DCMP01' PBR performs very well in most parts of Australia on roadsides, where BREEZE® Dianella caerulea 'DCNC0' PBR needs far better conditions and better soils to do well. The experience with what plants work on roadsides in different regions can help specifiers choose plants for green roofs for their region. Another example is Lomandra. People think of Lomandra as bullet proof, but if the wrong variety is used in the wrong region, problems can occur. For example in high humidity regions like Queensland, Lomandra hystrix performs much better than Lomandra longifolia. With this in mind, and from roadside plant research, trials in poor soils at various locations, and with the research conducted in this green roof trial, lists have been compiled for recommended plants for green roofs in various states (see Annexure A). Sedums are widely used overseas on green roofs. In Australia they have been less reliable, and in this trial they performed worse than most other plants. It was only in the 30cm organic mix that they were barely acceptable. In fact, over all plots the succulents scored only 1.89 for health ratings, where the average of all other plants over all plots was 3.67. Over all plots Shara had a rating 3 times better than the succulents. Australian native plants for harsh green roofs | By Todd Layt 26
Conclusion If weight is not an issue, based on this study it would be best practise to install a green roof in a 30cm substrate of either 50/50 organics to mineral, or 80/20 of organics to mineral based substrates. If weight is an issue then 20cm depth of either of the blends will work, particularly if fertilised, and some maintenance occurs. Substrates of less than 20cm should be avoided. Many Australian plants such as Lomandra, Dianella, and Westringia have done well in green roof trials. Many other Australian native plants have potential. Native plants that work on roadsides have a lot to offer for planting in green roofs. They need to be drought tolerant, long lived, adaptable, low maintenance, and preferably evergreen.
References 1) http://www.ozbreed.com.au/download/landscapenews08_10/its_too_hot.html 2) http://www.ozbreed.com.au/download/NewsletterArticles/turf_vs_fake.html 3) Growth Media for Green Roofs: a trial for The Hills BARK BLOWER™ Company 2009‐10 E. Charles Morris School of Natural Science Hawkesbury Campus University of Western Sydney 4) http://ozbreed.com.au/research‐papers/mowing‐trials.html 5) Duff, A.A. and Loch, D.S and Colmer, T. (2009) Adaptation and management of Australian buffalograss cultivars for shade and water conservation. Project Report. TU04013. Horticulture Australia Limited, and the Department of Primary Production Qld.
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Annexure A
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