www.landscapegardeningplants.co.nz

Playground plant and mulch trial

By Fiona Robbé and Katrina Layt

NOTE: This trial was conducted in Sydney, Australia

The aim of this trial is to systematically determine the optimal growth conditions for non-woody plants in playground mulch.

Ozbreed is undertaking this trial on behalf of Fiona Robbé Landscape Architects because there is demand and interest in growing non-woody plants in playground mulch in and around play equipment, including fall zones.  This will allow playgrounds to look more natural, and reduce the open, bare appearance of equipment in mulch, without compromising safety.

Two different methods are being trialled in two garden beds of Pine bark mulch and Port Stephens Soft fall 300mm in depth, supplied by the Hills Bark Blower:
a)     Plants in pure mulch -
1. The plants have been planted directly into the mulch
2.  A small amount of slow release fertiliser was mixed into the planting hole at the same rate for each plant.

b)     Plants with soil underneath (soil base method) -
1. A planting hole was made, and then a bottomless pot was placed in the planting hole. Depending on the pot size of the plant used, an amount of soil was placed at the bottom of the planting hole to make the plant level with the top of the mulch. Some soil was placed around the outside of the plant within the bottomless pot.
2. A small amount of slow release fertiliser was mixed into the planting hole at the same rate for each plant.
3. The mulch was then replaced around the outside of the bottomless pot and the pot removed.

The plants used in the trial are Naringa™ Westringia ‘WES01’ PBR (requires some pruning in playgrounds to ensure it doesn’t become woody) and Tanika® Lomandra longifolia ‘LM300’ PBR and the pots sizes used are 200mm, 300mm and 140mm. There are two controls of each pot size and plant in normal soil to monitor the differences.

The trial will last for at least 12 months, and then Ozbreed will circulate the results through various industry websites and magazines. Early results show promise for the soil base method over direct planting in mulch. The full results and information on planting methods will be available when the trial has concluded, for now below are some preliminary results.

Preliminary results as of 18.11.10

The plants with soil underneath have shown that they establish and root out much quicker than the plants planted straight into the mulch. This could be felt and seen, as any plants tugged around with soil underneath would not budge while plants with no soil had room to move within two months of planting. The Naringa has shown how growth is affected by having soil compared to no soil. The photos show how with soil, growth has been abundant while without it has seemed to stay the same since planting (see Naringa photo above). The Tanika also has a better growth habit with the base method and the foliage looks a lot cleaner as well.
As for the difference in mulch material, the plants in Port Stephens Soft Fall have rooted out much quicker and all look cleaner than in the pine bark mulch. This may be because of extra watering as the location surrounding had establishing turf or the finer texture of the mulch mimicking structure of soil a little better. This would have to be further tested.

Results as of 3.02.2011

After five months of being in mulch the plants are still thriving, the interesting thing is that they seem to be even healthier and have grown slightly more than the control plants in ground (the soil in the area is very heavy clay so this may be why). Again the Port Stephens soft fall has grown more than the pine bark mulch, this will have to be further tested now turf is established. One plant seems to be failing in the pine bark mulch, a Tanika without soil. Two seem to be failing in the Port Stephens soft fall, both Tanika, one with soil and one without.

A joint initiative between Fiona Robbé Landscape Architects, Ozbreed Pty Ltd, The Hills Bark Blower and Sydney Environmental Soil Laboratory

Kids love playing with plants, we should consider them as playthings for children, not just for the background.

Naringa growth differences in Port Stephens soft fall

Tanika without soil failing in the Pine Bark soft fall

Control plants (front) slightly smaller than trial plants in Port Stephens soft fall