If you have a dog that grazes on backyard vegetation, it's a good idea to check out landscaping plants for possible toxicity. Even common vegetables like tomatoes and rhubarb can affect your pets if they eat the leaves. In the case of creeping myrtle (Vinca minor), also called lesser periwinkle and running myrtle, the plant contains toxic compounds that can affect dogs if eaten.
Most animals won't choose to eat creeping myrtle even if it is available because it doesn't taste good. If they do eat it, it is usually in small enough quantities that the amount of chemicals in the ingested leaves and stems won't cause severe poisoning. Usually symptoms are restricted to gastrointestinal upsets, and the dog vomits up the plant material. According to the American Kennel Club, periwinkle is listed as possibly causing hallucinations. The Pet Poison Helpline advises that periwinkle has a generally mild to moderate level of toxicity, depending on the amount eaten. The possible symptoms they list are a drop in blood pressure, incoordination, tremors and seizures.
If your dog is eating creeping myrtle, take your pet away from the plant and remove any plant material that is still in its mouth. Call the veterinarian, and be prepared to estimate how much plant material your dog ate. Often dogs begin spontaneous vomiting, but your veterinarian may wish to induce vomiting if the dog hasn't already done this. There is no real antidote against the toxic compounds in creeping myrtle, and usual treatment is to soothe and coat the stomach and intestines and to make sure your dog has plenty of fluids.
A wide array of toxic alkaloids such as vincristine, yohimbine and vinblastine are present in creeping myrtle, and all the actions of the various chemicals are not fully understood. Some of them are used in human medical treatments. These compounds are also present in other vincas and vinca relatives used in landscaping, such as greater periwinkle (Vinca major) and Madagascar periwinkle (Catharanthus roseus, formerly Vinca rosea).
Creeping myrtle is a low-growing ground cover that reaches 4 to 8 inches tall. It grows in U.S. Department of Agriculture plant hardiness zones 4 through 9 and spreads quickly. In the spring, blue pinwheel-shaped 1-inch-wide flowers appear just above the foliage. It tolerates full sun as well as partial or full shade. A number of varieties exist, some with variegated green-and-white foliage. Greater periwinkle is very similar, but is a larger-scale plant that can grow 12 inches high and has 2-inch-wide blue flowers. It is also hardy to USDA zones 7 through 9. Madagascar periwinkle is frost-tender, hardy in USDA zones 10 and 11. It is widely grown as a summer annual because of its large flowers in a wide color range and its ease of care. All these plants are common landscaping subjects, so familiarize yourself with their appearance so you can help your dog avoid eating them. They are rampant growers and are considered invasive in some areas of the country.