Indicator plant

An indicator plant is a usually weedy plant that grows in some specific environment, allowing an assessment of soil and other conditions in a place by simple observation of vegetation.

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Much useful knowledge can be obtained about our land by observation of the wild plants and cover crops that are growing, and their condition. These include indicating fertility levels and potential nutrient deficiencies, waterlogging or compaction problems, pH levels and so on. When assessing land by observation of indicator species however it is good practice to observe plant communities or consistent populations of indicator species rather than individual specimens which may not be typical. Perennial weeds which may have colonised an area for some time are also a more reliable form of indicator than annual weeds which may have only been there for that year and thus indicate a temporary condition.

Examples

• Fertile soil supports plants such as nettles, chickweed, groundsel and fat hen.

• Nitrogen-deficient conditions are indicated by the presence of nitrogen fixing legumes such as clovers or vetches.

• Bluebells are very competitive, in other words whenever they occur, they occur frequently.

• Bracken, plantains, sorrel, knapweeds, rhododendron and cranberries are amongst the plants that favour acidic conditions, while alkaline conditions tend to support populations of perennial sow thistle, bladder campion, henbane and mustard.

• Waterlogged or poorly drained land is indicated by the presence of species such as mosses, creeping buttercup and horsetail, or bog loving plants including sedges, rushes, marsh marigold, marsh orchid or flag iris.

See also: Organic gardening