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Mixed Group Plantings: ACT Focus!

By Todd Layt

There has been a trend recently to use more plants in smaller group plantings rather than in large mass scale plantings. If the right plants are used this can work well, but if weaker plants are used, then the concept is only as good as the weakest plant. So when designing mixed group plantings what do you need to do to make the project work long term?

Firstly, design with a decade of performance in mind as a minimum. Make sure the right soil is being used for the plants chosen. If you want more diversity, use organics in the soil to promote better plant growth. Remember, someone will need to maintain the landscape, so choose plants and mulch that will reduce future maintenance inputs. Too much diversity impacts greatly on the cost of maintenance.

Pruning or weed control becomes very costly with too much diversity – getting the balance right with enough range to be interesting, but not so much that the cost of maintenance sky rockets is a juggling act. The best ways to lower maintenance costs include: opting for large scale mass planting with plants that perform for at least a decade that need less pruning, using plants and mulch that help reduce weed pressures and equally as important is being very clever with plant selection for smaller group plantings.

The first and probably most important aspect is to get the soil preparation right; a good soil will help all plants perform far better, but it is not always that simple. Budget constraints often require the use of site soil. In this case, it comes down to plant selection, making sure you only use plants that can cope with the poor soils. Drainage is another important aspect; if the planting is on the lower side of a path, wet conditions will make that side damp for longer periods, so it is necessary to use plants that can cope with wet feet.

If the site is non-irrigated, which is often the case, the plants also need to cope with drought. Mulch selection is one of the most important decisions for the project. On a commercial landscape, the key role of mulch is to reduce weeds and its secondary role is to help add organics to the soil. Only chunky mulch with close to zero fines achieves the first goal. Mulch with small pieces or lots of fines actually acts as a potting mix and aids the germination of weed seeds.

Avoid tub ground site mulch with fines, as this not only helps weed seeds germinate, it also is often full of disease and can kill most of the plants in a landscape. If you are forced to use this, make sure the plants can cope really well with Phytophthora and other diseases. Ozbreed has a number of plants that cope with this type of mulch, so if you must use it call Ozbreed and a list of those plants can be provided.

Plant selection is the other really important aspect. Smaller group plantings are only as good as the weakest plant and the maintenance level is often set by the plants that need the most upkeep, so choose plants that need less maintenance. There are enough good plants available for your region to choose long lasting, low maintenance options and still have good diversity in the project.

Ten different plants installed in smaller groups of say 3 to 10 square metres per variety will provide a diverse landscape. ACT has a very cold climate, so it is important to make sure the plants chosen work in the region. Below is a list of the best 10 plants for ACT in general for low growing group plantings that will not only provide diversity, but also great companion planting, low maintenance and a long lasting landscape.

Top 10 Native Plants for ACT Group Plantings

Mixed Group Plantings: a Dangerous Trend or Great Design? ACT Focus! - Native Plants for ACT Group Plantings
^ Plants are described from 1-10 from left to right

1) Shara™ Lomandra – The only compact, fine leaf Lomandra that looks like a compact Poa but stays evergreen in drought, cold or periodic wet feet.

2) Green John™ Callistemon – Tough as nails, Myrtle Rust resistant and smaller than ‘Little John’. Crisp, clean green foliage that contrasts nicely with its red flowers in spring and autumn. A lot more tidy and less woody compared to ‘Little John’. Can handle periodic wet feet better than ‘Little John’.

3) Grey Box™ Westringia – Small, compact Westringia that is longer lived and handles drought well, yet copes very well with wet feet and cold.

4) Tanika® Lomandra – The most drought tolerant, tidy looking Lomandra. Many have been used in ACT with great results. With less brown through its foliage and a clean crisp green, Tanika® Lomandra is one of a kind.

5) Little Jess™ Dianella – Needs better soils than the rest of the plants on the list, but provided the soil is good and organics are used, Little Jess™ Dianella spreads and fills in gaps, is low growing and looks great. Avoid for poor site soil situations, but if the soil is improved it will be one of the best plants in the project.

6) Tasred® Dianella – This has been a consistent performer in ACT for over a decade and does well in full sun, shade, hot, dry and cold.

7) Cassa Blue® Dianella – This is the best performing blue foliage plant in ACT that grows really well in dry conditions. Avoid using in areas that regularly get wet feet. E.g. use on the top side of a path and use something else on the lower side of the path where the water runs off.

8) Low Horizon™ Westringia – This ground cover Westringia has performed well in ACT in both dry and periodic wet feet areas. A great non fussy, low growing Westringia that handles the cold of Canberra.

9) Macarthur™ Callistemon – Ideal if you want a plant that is a little taller, but not too tall. Copes well with cold, heat and dry, and is highly Myrtle Rust resistant.

10) Little Rev™ Dianella – Compact, blue-grey foliage that is well suited to Canberra’s climate, as it was born and bred in the region. Ideal for roadsides, median strips, round abouts, carparks, golf courses and ornamental gardens needing a modern, compact plant.

Top 5 Exotics for ACT Group Plantings

Mixed Group Plantings: a Dangerous Trend or Great Design? ACT Focus! - Exotic Plants for ACT Group Plantings
^ Plants are described from 1-5 from left to right

1) Just Right® Liriope – The only Liriope that does not burn in full sun. It is smaller than ‘Evergreen Giant’ and much tougher.

2) Obsession™ Nandina – With red foliage for 9 months of the year this compact shrub is a great plant for mass planting, or in rows if a more formal look is required. New growth is always red when normal Nandina has green new growth.

3) Blush™ Nandina – More of a traditional Nandina look, but with red new growth in spring, summer and autumn.

4) Cosmic White™ Rhaphiolepis – An unbelievably tough plant. Dark green foliage and large white flowers twice per year, and best of all it rarely if ever procures a berry, so it will not become weedy.

5) Cosmic Pink™ Rhaphiolepis – Just like Cosmic White™Rhaphiolepis, but large pink flowers and a smaller, more compact form.

Best 5 Shade Plants for ACT Group Plantings

Mixed Group Plantings: a Dangerous Trend or Great Design? ACT Focus! - Shade Plants for ACT Group Plantings
^ Plants are described from 1-5 from left to right

1) Isabella® Liriope – This low growing, spreading Liriope is the ideal ground cover for shade gardens in ACT. It can be mown once per year in August and is a great low maintenance, very shade tolerant lawn alternative.

2) Katie Belles™ Lomandra – This plant copes with heavy shade, and even copes with wet heavy shade.

3) Amethyst™ Liriope – Excellent in shade gardens with its deep purple flowers that sit well above the foliage. It also looks great in mass planting.

4) Just Right® Liriope – One of the best shade plants for ACT that also does really well in full sun. It is smaller than ‘Evergreen Giant’, but big enough for the mass planting effect.

5) Silverlawn™ Liriope – If you want a little colour contrast in a shade garden, this variegated Liriope will provide that in spades.

Remember, we are dealing with live plants and sometimes things go wrong in life, so have a follow up maintenance plan and at least one replanting phase if possible after one year to replace any dead plants. Landscape Architects and Designers often face a grim reality that the project did not quite turn out as planned after all the construction has been completed. Some areas may be wetter than planned, the mulch not as good, the soil preparation was not as planned, or weed invasion was worse than envisaged.

One or two of the plants may not have performed due to the changed circumstance or unforseen problems, so it may be necessary to replace underperforming plants with ones that worked on the project. If you are unsure of the conditions, choose plants that work in most conditions, but do not lose sight of specialised plants for specialised conditions. Slopes need very drought tolerant plants and wet feet is usually not an issue here, or gullies need plants that cope with wet feet, but also a little drought.

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