Weeds can be used as indicators of soil conditions and as environmental indicators. You can then use this information to help create the best possible conditions for lawns and your turf grass.

 
What weeds are present has a direct effect on what herbicides to use. This is a key factor that impacts herbicide selection in turfgrass management.
 
Weeds help indicate soil conditions. Using them as indicator weeds is the first step in getting an idea of what may be affecting turf growth. Don’t make any decision based solely on the presence of one weed. For example, some weeds like Sorrel like multiple soil conditions.
 
When you see weeds your first reaction should be why are they there? This is much better than simply reaching for the spray bottle and applying a pre-emergent weedkiller or post-emergent herbicide!
 
 
Indicator weeds are plants whose presence is due to the soil type, soil moisture, soil fertility, pollution, or soil disturbance.
 
 
First, identify a weed with the turf weed ID chart. Then you can use the tables below to discover what conditions favour it. For example, if Bindweed is present it shows that the soil is compact. So if you carry out a soil aeration program, this will create less favourable conditions and so you won’t possibly need to use a weed killer in the future.
 
 
When it comes to sports turf, many weeds can provide insights into turf management and environmental conditions.

Weeds as indicators of wet soil conditions.

Plants like cat-tails, bulrushes (Cumbungi), and sedges show wet soils.

  1. Yellow Nutsedge.
  2. Common Purslane.
  3. Horsetail.
  4. Mallow
  5. Speedwell
  6. Scarlet Pimpernell
  7. Oxalis sp
  8. Knotgrass
  9. Sorrel
  10. Buttercup
  11. Mosses
  12. Bittercress or Flickweed and
  13. Rushes
 

Weeds and what they tell us about soil fertility.

Indicators of poor soil

  1. White Clover is a weed indicator of low fertility soil. It is a nitrogen-fixing plant that thrives in low-nutrient soils.
  2. Inkweed.
  3. Black Medic thrives in low-nutrient soils.
  4. The presence of redroot pigweed means that the Fe-Mn ratio is out of balance.
  5. Summergrass shows low levels of Ca and P and high levels of Mg and K.
  6. Dandelions show low Ca and very high levels of K.
  7. Oxalis sp shows low levels of Ca, and high levels of Mg.

Indicators of rich soil

  1. Stinging Nettles are weed indicators of nitrogen-rich soils.
  2. Chickweed shows nitrogen-rich soil. It also indicates very low Ca and P levels and very high K and Na levels.
  3. Chicory favours high nitrogen soils and so do lambs quarters
  4. Knapweed shows high soil K.
  5. Both Mustard and Purslane indicate high P levels.
  6. Speedwell.
  7. Shepherds purse
  8. Henbit
  9. Dandelion
  10. Canada thistle
  11. Fat Hen thives in high K soils.
 

Indicator weeds for disturbed soils.

Weed indicators of disturbed soils, include fireweed.

  1. Common Ragweed
  2. Shepherd’s Purse
  3. Field Thistle
  4. Japanese Knotweed
  5. Red root Pigweed
  6. Knapweeds
  7. Prickly Lettuce
  8. Horsetail
  9. Wild Mustard
  10. Bittercress or Flickweed and
  11. Ox-Tongue

Environmental indicators:

Certain plants, such as mosses and lichens, are useful bioindicators of air quality and pollution. For instance, lichens are sensitive to air pollution.

Indicators of Soil pH.

Some weeds prefer acidic or alkaline soils. For example, mossy stonecrop (Sedum acre) grows well in acidic soils. In contrast, alkali grass funnily enough loves alkaline soils.

Acid soils (low pH)

  1. Oxalis.
  2. Plantain.
  3. Summergrass.
  4. Velvet weed.
  5. Ox-eye daisies.
  6. Pearly everlasting.
  7. Sheep sorrel.
  8. Wild radish and
  9. and prostrate knotweed.

Alkali soils (high pH)

  1. Chickweed.
  2. Chicory.
  3. Wild mustard and
  4. Black medic
 

Compaction:

  1. Broadleaf plantain is a weed indicator of compact soil
  2. Ground Ivy.
  3. Dandelion.
  4. Crowsfoot is found on compact sports turf in warm-season grasses.
  5. Burdock has deep tap roots and likes compact soil.
  6. Bindweed.
  7. Chickweed
  8. Chicory.
  9. Knotweed is an excellent indicator of compaction.
  10. Inkweed will grow in heavy clay or compact soil.
  11. Bindii.
Indicator weeds can tell us about the soil and act as environment indicators
jerry spencer senior turf agronomist
Senior Turf Agronomist at Gilba Solutions Pty Ltd | 0499975819 | Website

Graduated from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) as a turf agronomist before emigrating to Australia in 1993.

He followed this by gaining a Grad Dip in Business Management from UTS. He has worked in a number of management roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.

He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions as an independent sports turf consultancy in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.