Selenium

Selenium (Se) is a plant nutrient that easily falls into the “too much of a good thing can be a bad thing” category.

If you grow a lot of your own food and your soil lacks selenium, you might, too. In fact, selenium deficiencies are a global dietary problem. On the flip side, if your soil has too much selenium, it can make you very, very sick.

Selenium in sandstone (James St. John) CC BY 2.0

People and animals must have a little selenium to be healthy. The same is true of some plants. Let’s see what selenium does, which plants use it, and how to tell when there’s too much selenium in the soil.

How plants use selenium

Selenium isn’t considered an essential plant nutrient. For some plants, such as poplar trees, selenium is useful. Selenium is believed to stimulate plant growth and to counteract stress, pests, and disease. [In the human body, selenium makes antioxidant enzymes that prevent cell damage.]

Plants grown on selenium-depleted soils end up being less nutritious for us. The Pacific NW, New England, the Great Lakes, and certain areas around the New Mexico and Arizona state line are traditionally low in selenium. But, as we all know, each yard has its own characteristics.

Indicator species

You won’t see selenium listed in a soil test report unless you specifically ask for it. The presence of certain weeds and other plants may. In some cases, high selenium levels are needed for growth. These plants will accumulate toxic levels of selenium in their tissues. These plants are referred to as obligate and include:

• Goldenweed (Oonopsis sp.), sunflower family
• Hairy goldenrod (Solidago hispida), sunflower family
• Hydrangeas (Hydrangea)
• Locoweeds (Astragalus sp.), legume
• Prince’s plume (Stanleya sp.), cucurbit
• Snake willow (Salix matsudana; S. reichardtii)
• Woody Asters (Xylorhiza sp.), sunflower family

Woody Asters (Stan Shebs) CC BY-SA 3.0

Facultative selenium accumulators do not need selenium to grow, but will accumulate it anyway:

• Gumweed (Grindelia sp.)
• Saltbush (Atriplex sp.)
• Sideranthus sp.
• Tansy asters (Machaeranthera sp.

Curlytop gumweed (Cory Maylett) CC BY-SA 3.0

Prince’s plume (Kip E. Panter) USDA Public Domain

Most other plants are referred to as passive selenium accumulators. These plants can absorb too much selenium and suffer toxicosis. This is especially true for grasses and cereals, such as barley.

Toxic soil can be corrected with something called phytoremediation. Phytoremediation takes advantage of the fact that some plants absorb toxins through their roots. Before plants can cough those toxins into the atmosphere through their stems and leaves (transpiration), the plants are harvested and disposed of safely.

Signs of selenium toxicity

Selenium toxicity appears as stunting, early leaf death, and chlorosis. Leaves of affected plants may wither and dry up. High selenium levels in the soil can also cause copper, iron, and zinc deficiencies. Of course, these symptoms can mean several other things, as well. You will have to consider symptoms, location, and the presence of the aforementioned plants in your analysis.

Too much selenium in the soil can make your edible plants toxic. This can be the result of native bedrock. It can also be caused by industrial runoff. If you suspect high selenium levels in your soil, contact your local County Extension Office or Department of Agriculture.