What weeds tell us
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.
- Yellow Nutsedge.
- Common Purslane.
- Horsetail.
- Mallow
- Speedwell
- Scarlet Pimpernell
- Oxalis sp
- Knotgrass
- Sorrel
- Buttercup
- Mosses and
- Rushes
Weeds and what they tell us about soil fertility.
Indicators of poor soil
- White Clover shows low fertility soil. It is a nitrogen-fixing plant that thrives in low-nutrient soils.
- Inkweed.
- Black Medic thrives in low-nutrient soils.
- The presence of redroot pigweed means that the Fe-Mn ratio is out of balance.
- Summergrass shows low levels of Ca and P and high levels of Mg and K.
- Dandelions show low Ca and very high levels of K.
- Oxalis sp shows low levels of Ca, and high levels of Mg.
Indicators of rich soil
- Stinging Nettles prefer nitrogen-rich soils.
- Chickweed shows nitrogen-rich soil. It also indicates very low Ca and P levels and very high K and Na levels.
- Chicory favours high nitrogen soils and so do lambs quarters
- Knapweed shows high soil K.
- Both mustard and purslane indicate high P levels.
- Speedwell.
- Shepherds purse
- Henbit
- Dandelion
- Canada thistle
Indicator weeds for disturbed soils.
Weeds that indicate disturbed soils, include fireweed.
- Common Ragweed
- Shepherd’s Purse
- Field Thistle
- Japanese Knotweed
- Red root Pigweed
- Knapweeds
- Prickly Lettuce
- Horsetail
- Wild Mustard and
- 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)
- Oxalis.
- Plantain.
- Summergrass.
- Velvet weed.
- Ox-eye daisies.
- Pearly everlasting.
- Sheep sorrel.
- Wild radish and
- and prostrate knotweed.
Alkali soils (high pH)
- Chickweed.
- Chicory.
- Wild mustard and
- Black medic
Compaction:
- Broadleaf plantain prefers compact soil
- Ground Ivy.
- Dandelion.
- Crowsfoot is found on compact sports turf in warm-season grasses.
- Burdock has deep tap roots and likes compact soil.
- Bindweed.
- Chickweed
- Chicory.
- Knotweed is an excellent indicator of compaction.
- Inkweed will grow in heavy clay or compact soil.
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