Gardening in Larimer County

by Elizabeth Wuerslin
 Colorado State University Cooperative Extension Master Gardener
 Larimer County

Euphorbia is an exciting and diverse genus of over 2,000 plants distributed worldwide. They offer something for everyone, and range from woodland spurges to tropical trees to an extensive collection of succulents. Our familiar holiday poinsettia is a member of this family of plants. Discerning home gardeners have had the happy pleasure of finding an increasing selection of Euphorbia plants which are suitable for the Colorado landscape.

The genus dates back to Greco-Roman times when it was used as a digestive. The name spurge evolved in Middle Ages due to the medicinal use of the milky white sap which can be a topical irritant or poisonous when ingested. All Euphorbia have this sap and care must be taken when handling the plant.

The foliage of Euphorbia is what makes it exceptional. The plants do not carry true flowers but rather form a fused bract called a cyathium, which forms a cup around the insignificant version of a flower. The colorful petal-like parts of the poinsettia plant (E. pulcherrima) are such bracts. Often these bracts in woodland species are a contrasting color of lighter green, which make for texture and interest.

Wooodland spurge (E. amygdaloidesi), is a perennial and can tolerate sun and shade, and mixes well with hostas in the dappled shade garden. Hybrid ‘Helena Blush’ adds purple and variegation to the leaves, whereas ‘Kalipso’ has contrasting green interplay for interest. You can find plantings of these hybrids plus ‘Efanthia’ at the CSU Trial Gardens on College Ave in Fort Collins.

Euphorbia have found their container plantings as well with ‘Diamond Frost’ as a good example. This plant was popular this summer for its spray of delicate white flowers which resemble baby’s breath. E. marginata, also known as Snow-on-the Mountain, is an annual whose tall spires of green and white bracts contrast with the bright orange and red colors of summer cutting flowers. ‘Summer Icicle’ works well when planted from seed. Cut stems should be seared with a flame or dipped in boiling water to prevent the latex from bleeding and to prolong freshness.

Though many Euphorbia species are nice additions to the garden, some introduced as ornamentals have escaped, creating many problems. An example is donkeytail or myrtle spurge (E. myrsinites). This attractive succulent was introduced as an excellent rock garden plant that thrives on heat and little to no water. Because of its tolerance to various conditions, it has also become a noxious weed and is currently a List A weed. List A weeds must be eradicated by law. This creeping plant has started to invade natural areas. If there are small infestations, you can pull the plant by hand, but wear gloves as the caustic sap is a skin irritant.

Another List A Euphorbia weed species is cypress spurge. A List B species includes leafy spurge. Take caution when you purchase Euphorbia plants and always handle the plants with care. Contact with the sap is irritating to the skin, and if mucous membranes are involved, a doctor should be consulted. Keep children and pets away from these plants.