UConn Extension — “Weeds as Indicators of Growing Conditions in Landscapes”

This resourc organizes common weeds according to what they may indicate:

• Low soil fertility

• Acidic soil

• Excess moisture or poor drainage

• Dry soil

• Compaction

• Shade or insufficient light

It includes photographs and both common and botanical names, so gardeners can identify a weed and then examine the conditions that may be favoring it. (Integrated Pest Management)

For Pennsylvania-specific identification, you could use Penn State Extension’s “Weed Identification and Control” library first, then consult the UConn indicator guide for interpretation. (Penn State Extension)

The important qualification to remember is:

“A weed is a clue, not a laboratory result. One plant proves very little, but a dominant community of plants can tell us where to investigate.”

For example, a concentration of plantain and knotweed may suggest compaction; sedges may point toward wet conditions; sheep sorrel may suggest acidity or low fertility. But plants tolerate ranges of conditions, so observations should be confirmed with a Penn State soil test before adding lime or fertilizer. Extension specialists explicitly caution that indicator weeds are a starting point rather than a foolproof diagnosis. (Ask IFAS - Powered by EDIS)

Before asking how to kill a weed, ask why that particular plant is succeeding there.