Indigenous plants for a degraded site

Our local Friends group asked me to work out plant lists for autumn/winter plantings along the river. How to work out a plant list? With all the changes wrought since colonization, and further coming with climate change, what species are appropriate?

Once all of the plain at Bacchus marsh was some kind of redgum swamp, with billabongs, and rivers and streams frequently changing course across the floodplain. There’s still a billabong down at the Parwan end, near where the Werribee and Lerderderg rivers meet, but it’s on private land so most won’t have seen it.

In the section we planted on April 3, near the main Grant St bridge over the Werribee River, the river has been artificially deepened to prevent flooding. As the story goes, the farmers held title to the middle of the river, but the river kept moving so this caused some friction between landowners. At some point, they banded together and dug a deeper, permanent channel.

DSC_0022
Before.

Most of the time now, the river is about 4m below the top of the bank, so it rarely floods (which I won’t complain about, living just near it), but the top of the bank is now a considerable vertical distance from the water table. It’s a free draining sandy loam which dries out rapidly in warm dry weather.

For these reasons, I didn’t select a bunch of species typical of a redgum swamp! Redgums, woolly tea-tree, tangled lignum, river bottlebrush, common tussock grass, reeds, sedges, and rushes might be expected in a well-drained alluvial floodplain. But now that this area has become a terrace above the river I had to find local (indigenous) plants that grow in deep, dry sandy soil.

soil scraping
Site preparation

We found the soil still dry and hard as rock when we planted! But we had a firehose from a pump in the river, so we were able to flood irrigate at the end of the day’s work. We also had a contractor prepare the site by removing about 2cm of topsoil (with a lot of the weed seeds in it), and loosening the surface with the bobcat blade. Hopefully these measures will help overcome the difficulty of the site.

The planting list is below, with notes as prepared for a handout to volunteers on the day. Only time will tell if I chose well! All these are fairly common species in the area

.* * *

Grasses

Plant grasses in open areas away from trees (except Poa sieberiana), in groups with 3-5 (or more) of the same species together. Plants should be spaced about 30cm apart.

  • Feather spear-grass Austrostipa elegantissima, Rough spear-grass Austrostipa scabra. Prefer dry, open position with full sun or light shade.
  • Tussock grass Poa sieberiana Grows best with some shade, under trees.
  • Silky bluegrass Dichanthium sericeum Summer growing grass, likes full sun.

Wildflowers (herbs/forbs)

Small plants. Plant 30cm or more apart in open areas along with grasses. Plant in groups with 3 or more per species. Mulch lightly, especially for Pussy tails. Guards not needed.

  • Common everlasting Chrysocephalum apiculatum Daisy. Will spread in time.
  • Lemon beauty-heads Calocephalus citreus Small tufted, non-spreading daisy.
  • Common bluebell Wahlenbergia communis Spreads to form low clumps 30-50cm across.
  • Austral tobacco Nicotiana suaveolens Small bush, survives dry exposed positions well.
  • Austral stork’s bill Pelargonium australe Small bush. May grow to 50cm across.
  • Pussy tails Ptilotus spathulatus Prostrate ground cover,  do not bury in mulch!

Trees & shrubs

Plant singly or in groups of about 3. Space 1m or more apart, with trees about 2m or more from grasses and herbs (except Poa sieberiana). Use tree guards, except for fragrant saltbush. Mulch well.

  • Lightwood Acacia implexa Summer flowering wattle, grows to 5m or more, on dry & exposed sites.
  • Drooping sheoak Allocasuarina verticillata Tree 5m or more. Good shade and wind shelter when grown, copes with dry & exposed sites.
  • Hedge wattle Acacia paradoxa Shrub, grows 1-2m tall & wide. Very spiny, wear gloves. Not to plant right next to the path.
  • Fragrant saltbush Rhagodia parabolica Shrub spreading to about 1m tall by 2m across. Part shade or full sun on dry, exposed areas. No tree guard needed.

 

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The result.
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