Indicator plants in the garden

What are indicator plants?

Indicator plants are important bioindicators. This means that they can be used to detect environmental changes such as climate change, soil or air pollution. They are better adapted to certain conditions than many other plants. For example, if the soil is too acidic or moist, only those (indicator) plants that do not mind these less optimal conditions will grow there. By observing carefully, you can get an overview of the different microclimate zones in your garden.

Indicator species reflecting your soil

But what exactly does this have to do with gardening? Wild plants only occur naturally in places to which they are adapted. Species with similar site requirements thrive in their neighborhood. By closely observing the species that occur, you can gain insightful information about the location. These plants, which "show" you what kind of location it is, are called indicator plants. If you want to create a new garden or reuse an old fallow one, they can help you to characterize your soil. Air and light conditions are also reflected in the species present. This will tell you which plants can thrive in your soil or which measures you should take to improve the soil. The goal here is a loose, humus-rich soil with a relatively neutral pH value. This corresponds to the average optimum conditions for most crops. Tips for a fertile garden soil can be found here!

Indicator plants: Overview and examples

In the following, I would like to introduce you to some soils with suitable indicator plants. When determining the soil using indicator plants, it is important not to draw conclusions about the soil conditions based on just one plant species. Only when several indicator plant species are present can the soil be characterized with sufficient certainty. So if you see soil on which a few dandelions are growing, this does not necessarily mean that the soil is heavy and compacted. It can be helpful to carry out the simple soil test in advance to get an idea of the type of soil in your garden.

Indicator plants for sandy, light soil

A sandy soil has relatively large particles and is usually a well-aerated, loose soil. Sandy soils have several advantages: The loose soil can be worked well all year round, weeds can often be removed effortlessly, there is hardly any waterlogging and the soil warms up quickly in spring. However, the soil is less good at storing water as it seeps away quickly through the large pores. Organic matter can also hardly bind to the large particles, which means that the soil is quite poor in nutrients and humus. Not a happy starting point for many vegetables. However, the site is ideal for some herbs. You can find measures to improve sandy soil in this article.

Indicator plants: Table with examples for sandy soils

Indicator plants: Examples of very dry, sandy soils

Sandy soils are often very dry, depending on the location and water supply. To find out whether you have a very dry location, you can look out for the following indicator plants:

• Dyer's chamomile(Anthemis tinctoria)
• Spring feverfew(Erophilia verna)
• Field croaker(Lycopsis arvensis)
• Quender(Thymus pulegioides)
• Hare's clover(Trifolium arvense)
• Heather(Dianthus deltoides)

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Indicator plants for heavy, compacted garden soil

Heavy and therefore often compacted soils have a high clay content. This means that many of the soil particles belong to the smallest size fraction. This creates tiny fine pores, which only allow a small amount of oxygen into the soil. The small particles are strongly bound together, making it difficult for many plant roots to work their way through the solid soil. Compacted soil is also a challenge for gardeners. It is often almost impossible to work the soil with a spade. Especially when it is damp, the soil soaks up a lot of water, making it very heavy. However, the high storage capacity can certainly be an advantage: Nutrients and organic matter can bind to the small particles much more easily, which means less fertilizer is washed out. You also need to water less, as the water can be kept in the soil for longer. However, the higher water content also means that the soil warms up much more slowly in spring, which means you can get started with your crops later. Tips for improving heavy soils can be found here in the article.

Pointer plants: Table with examples of heavy soil

Table: Indicator plants for moist, heavy soils

The many small pores in heavy soils store a particularly large amount of water. Here are some wild plants that indicate a moist location with heavy soil:

Our tip: Heavy soils tend to be waterlogged, which can lead to oxygen-depleted conditions in the soil and therefore at the plant roots. Most crops cannot cope with this. So if you want to grow vegetable plants, you definitely need to improve the soil and, depending on the moisture level, possibly install drainage.

Indicator plants: Examples of nitrogen-rich soils

A high nitrogen content means that plants with a high nutrient content in particular can thrive. Nitrogen-rich sites are often dominated by a few plants that are particularly competitive. These soils provide the best conditions for growing a vegetable patch. In this case, you do not need to apply any improvement measures.

Table: Indicator plants for nitrogen-rich soils

Examples of indicator plants: Nitrogen-poor soils

Nitrogen-poor soils need more organic matter or other, preferably organic, fertilization measures. Every plant needs sufficient nitrogen in order to thrive. Most crops often have a particularly high requirement. Some weak growers can still thrive on low-nitrogen soils if you combine them with legumes such as beans. Some Mediterranean herbs even prefer soils low in humus and nitrogen.

Table: Indicator plants of nitrogen-poor soils

Indicator plants: Acidic soil

Some soils are naturally acidic. Acidic means that the pH value of the soil is low. However, the soil can also become acidic due to environmental influences. In humid climate zones, soils acidify naturally. A lot of precipitation dissolves the naturally occurring lime particles and washes them out. Acid rain, CO2 that comes from the respiration of soil organisms or protons excreted by plant roots are other natural factors that affect the pH value of the soil. Agriculture also contributes to soil acidification through soil cultivation and acidic fertilizers. To improve acidic soil, it can help to lime your garden soil regularly. You can find tips on liming garden soil and an overview of different lime fertilizers in this article. Many vegetables prefer a slightly acidic soil pH. However, if the following plants are growing in your garden, the soil is a little too acidic for a successful vegetable harvest.

Indicator plants for acidic soils: a table

Indicator plants for calcareous soil

Lime-rich soils have a high pH value (over 7). A lot of lime in soils ensures that the nutrient salts are dissolved in the water, which quickly leads to leaching. This is why calcareous soils tend to be poor in nutrients. Plants that grow on them can suffer from deficiency symptoms such as chlorosis or stipple, which can be attributed to a lack of nutrients. Soil that is too calcareous is therefore also problematic for some plants. Soil that is too calcareous can be improved and the soil pH lowered with acidic rock powders. You can find tips on using rock powders in the article on this topic.

Table: Examples of indicator plants for calcareous sites

Now you have some information about indicator plants. I hope I have been able to give you a better understanding of the subject so that the next time you go for a walk in nature, you might even recognize what kind of location it is. But you can now also find out what the conditions are in your garden.

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