Growing Green

By Robin Trott, Extension Educator

I spent Saturday working outside, only to find red spots all over my legs by the end of the day. Many plants in Minnesota can cause skin irritation, and it seems I encountered one of them. To help you avoid the same fate, let me introduce you to several plants to watch out for this summer.

Wild Parsnip (Pastinaca sativa) is a toxic plant with an edible root that has invaded many roadsides. The flowers are yellow and arranged in an umbrella shape. The leaves are coarse with saw-toothed edges, and the stem is hairy. Wild parsnip grows two to five feet tall and resembles the ornamental Queen Anne’s Lace. Several herbicides can control wild parsnip, but repeated applications may be necessary.

Giant Hogweed (Heracleum mantegazzianum) is a biennial or perennial herb in the carrot family that grows 15 to 20 feet tall. It has stout, bristly, dark reddish-purple stems, and spotted leaf stalks. The white, umbrella-shaped flowers can be 2 to 2.5 feet in diameter. Giant hogweed is on the Minnesota Department of Agriculture early detection list. While it is not yet present in Minnesota, it is making its way here via Wisconsin.

Cow Parsnip (Heracleum maximum) is a large-leafed plant that can reach heights of more than seven feet and has white, umbrella-shaped flowers. Cow parsnip is present throughout Minnesota, often seen in late spring and early summer along roadsides and in wet ditches. It is the native counterpart to the highly invasive non-native giant hogweed. The stems and leaves of all these plants contain furocoumarins, a photosensitive chemical that can cause rash and blisters on some people after exposure to ultraviolet light.

Stinging Nettle (Urtica dioica) and Wood Nettle (Laportea canadensis) are both native plants that cause minor skin irritation. The stems and leaves of these plants are covered with long, stinging hairs. At the slightest touch, the hairs break off, their sharp points penetrate the skin and release sap that inflames the skin. Both nettles grow 2 to 7 feet tall. Wood nettle grows in shaded, wooded areas, while stinging nettle grows in full sun.

Poison Ivy (Toxicodendron radicans and T. rydbergii) can be found in many places and in many forms. It can grow as a shrub or a 12-foot vine. New leaves are often shiny and reddish, while older leaves have a dull green cast. The adage “Leaves of three, let it be” is good advice. Roots, leaves, and stems contain an oily resin called urushiol, which typically causes an irritating rash, blisters or swelling when exposed to human skin, and occasionally on livestock. Burning poison ivy is extremely dangerous, as the smoke can contain urushiol and cause serious respiratory or other systemic health problems if inhaled.

For more information about any of these plants, please contact the Douglas County Extension Office at 320-762-3890.

Until next time, happy gardening!