March Weed of the Month: Edible and Dangerous

Minnesota Department of Ag Logo In Minnesota, we have some poisonous plants commonly growing in home and community gardens of which we can safely eat certain parts (like tomatoes or other nightshades). In this article we will focus on a few of these vegetable and fruit crops that have poisonous parts—Nightshades, Prunus species, and Rhubarb.

The Solanaceous family, also known as the Nightshade family, includes such plants as tomato, potato, pepper, and eggplant. These plants all contain the toxin solanine in varying amounts in the green plant parts. The leaves of Solanaceous plants usually must be ingested in large quantities to produce harmful effects in humans and animals. Potatoes have the potential to be the most dangerous; tubers that have turned green and/or sprouted due to sunlight exposure or improper storage have high amounts of solanine, and should never be eaten. A small percentage of the population is allergic to Solanaceous fruits. For some with sensitive skin, brushing against the hairy and resinous leaves can cause irritation or rash.

 The Prunus (stone fruit) family includes plum, cherry, apricot, almond, and native fruit trees like chokecherry, black cherry, and wild plum. These trees all have trace amounts of cyanolipids in the leaves and amygdalin in the seeds. These compounds can be converted into the toxin cyanide when the leaves are crushed and exposed to air (as after mulching or chipping) or upon chewing and digestion. After this decomposition process, poisonous amounts of cyanide may be released. Accidental poisoning may occur in humans, especially by curious children, but it most commonly occurs in livestock and pets. The smaller size of dogs and cats can make them particularly susceptible.

Edible and dangerous, all at the same time

There are toxic compounds in the leaves of a rhubarb plant, but humans must ingest large amounts to be dangerous. However, small animals like cats and dogs wouldn’t have to ingest much to be toxic. (contributed photo)

Rhubarb (Rheum rhabarbarum) is a beloved vegetable grown in Minnesota’s home and community gardens. An herbaceous perennial with thick rhizomes, it is grown for its tart, fleshy stalks. Most people do not realize that rhubarb’s leaves contain oxalic acid, among other unidentified poisonous substances. The stalks contain trace amounts of this compound but are obviously safe for consumption. There are a number of references to accidental poisonings occurring in Europe during World War I, as the rhubarb leaves were apparently recommended as food during the scarcity of wartime. People must ingest large quantities of leaves to experience the toxic effect, but small animals like cats and dogs can fairly easily ingest too much. 

Edible and dangerous, all at the same time.

The leaves of the potato plant contain a toxin called solanine, which much be ingested in large amounts to be toxic. However, a potato that’s turned green or sprouted due to too much sunlight or improper storage will contain high amounts of the toxin, and should never be eaten. (contributed photo)

 We clearly are intimately linked to these plants and will continue to grow and harvest from them in our home and community gardens. With the knowledge that specific plant parts can be harmful to pets or children if ingested, we should use them with precaution. Please contact Minnesota Poison Control with any concerns about potential human poisoning at 800-222-1222poisonhelp@hcmed.org, or www.mnpoison.org.

MDA weed of the month: Garlic Mustard

Garlic Mustard is the MDA weed of the month

Garlic Mustard is a highly invasive, noxious weed that is prevalent in southern Minnesota and rapidly making it’s way north. (Photo from MN Department of Ag)

January’s Weed of the Month is garlic mustard (Alliaria petiolata).

Garlic mustard is an edible, biennial herb that emits a strong garlic odor. It was brought to the United States from Europe as a culinary herb. It has naturalized in many eastern and midwestern states.

In Minnesota, it is widespread in the south and is spreading north.  The bad news is garlic mustard is highly invasive. It grows in woodlands, and along trails and waterways. It outcompetes native plants, becoming detrimental to wildlife habitat and biological diversity.

Garlic mustard forms rosettes after seed germination in early spring. In its second year, it forms upright stems that produce flowers in May and June. Seeds begin to develop in slender pods shortly after flowering and are the plants’ primary means of spread.

The plant has distinctive characteristics to distinguish it from other woodland MDA-logoplants. In the rosette stage, the leaves are heart-shaped with toothed margins. When it matures, the leaves along the stem are triangular and the small, white, four-petaled flowers are produced in clusters at the tops of the stems. The plant produces slender seed capsules. Seeds can be spread by water and soil movement on boots and equipment.

Garlic mustard is a restricted noxious weed and cannot be transported, sold, or intentionally propagated in Minnesota. It is recommended that this species be prevented from spreading to new areas and that smaller populations be eradicated.

Managing garlic mustard takes persistence and a focus on preventing flowering, making timing a key component to management.

  • Regular site monitoring for several years will be required to ensure that new seedlings are destroyed and the seedbank is depleted.
  • Hand pulling may be practical for small infestations. Pull plants prior to flowering to prevent seed production. Flowering plants can continue to set seed following removal of soil.
  • Mowing of bolted plants prior to flowering can prevent seed production. All equipment should be inspected and cleaned prior to moving into new areas.
  • Foliar herbicide applications may be effective. If using herbicide treatments, check with your local University of Minnesota Extension agent, co-op, or certified landscape care expert for assistance and recommendations.