Ask a Plant Nerd: Grass

Ask a Plant Nerd: Grass

Flora, Plant Nerd, The Scoop

I am the grass,
Let me work

Carl Saundberg

I recently received an email from a former colleague, Pierre, who has a property over near Gloucester and was curious about what different grasses represented regarding different soil conditions and land use history.

This is a very good question, it’s not just grasses but lots of other plants can tell us a lot about soil type, fertility, moisture, land use, fire history, salinity and so on, it’s not an exact science but knowing plants and some of their ecological requirements helps us to understand our sites better and to better manage them. 

For example, Banksia serrata is often killed by fire with seeds being released onto the freshly burnt ground and germinating. It will then take around 8 years for those Banksia seedlings to grow and set seed so fire periods of less than 8 years can see local extinctions of that species, other species can germinate, set seed and die off again very quickly so will need fire before their seed stored in the soil becomes unviable so it can be a balancing act, but I’m getting off track here so I’d better get back to Pierre’s question.

Now, these are, for the most part generalisations and you will often have a site containing many of these species, the trick is to figure out which is the dominant species and then have a look at other possible indicators round the site.

  • Blady Grass (Imperata cylindrica), generally prefers softer soil (often sandy or rocky), loves fires, hates compaction
  • Plains Grass (Austrostipa aristaglumis) is a great indicator of black, basalt derived soils.
  • Slender Bamboo (Austrostipa verticillata) germinates best under trees and can survive decades after the tree has gone, a great indicator of holes and stumps (don’t drive through it). (the closely related and similar looking Austrostipa ramosissima likes areas that are moist but well drained) 
  • Couch (Cynodon dactylon) fairly universal however if you have an area which is just about all couch then it may be an indicator of compaction and/or salinity
  • Anything lush, leafy and dark green will generally indicate fertile, moist (often wet) soils (Paspalum, Kikuyu, Water Couch), (avoid driving through these too)
  • Weeping Grass (Microlaena stipoides), generally prefers moist, well drained and fertile sites
  • Giant Red/Giant Blue Grass (Bothriochloa biloba), likes drainage ditches and regularly moist areas
  • Red Grass (other Bothriochloa spp), fairly generic, can handle a variety of conditions, moderate fertility clay soils.
  • Wallaby Grasses (Rytidosperma spp) and Blue Grass (Dichanthium sericium), moderate to high fertility, moderate moisture soils.
  • Parramatta Grass (Sporobolus spp), Wire Grass (Aristida spp) and Love Grass (Eragrostis spp), can indicate low fertility compacted soils (or even sandy soils)
  • Phalaris has a high phosphorus requirement so a big lush patch of that can indicate high soil Phosphorus in that spot.
  • Kangaroo (Themeda triandra) and Native Sorghum (Sorghum leiocladum) are generally found in moderate fertility, non compacted soils and are susceptible to overgrazing so an area with lots of these hasn’t been overgrazed/overmowed/compacted.