Generally unwelcome plant blows into the yard
Q: A piece of a plant blew into my yard during a storm a few months ago. I left it there and it took root. I pruned it hard — I took about a foot off all around because it was growing too big. It has a sort of minty smell, and I wonder what it is and whether it can be used in cooking. If so, I'll try drying it.
Carolyn Gold, Clearwater
A: From evaluating the leaves and the fragrance, my colleague Andy Wilson, senior horticulturist at the Pinellas County Extension Service, nailed it as common ragweed, Ambrosia artemisiifolia.
I hope that no one in your household has any allergy problems. Common ragweed pollen is the principal cause of hay fever and a single plant in full flower is said to produce more than a billion pollen grains!
The plant does have several medicinal uses. The essential oil is used as an antimicrobial and antifungal, and the leaves can be crushed and rubbed to help soothe an itch from insect bites or poison ivy, to name a couple.
However, if I were you, I would prune it again — about 4 inches underground — and do not let it go into flower.
Carolyn: No one in my family suffers from any outdoor-generated allergies. I can tell you that I haven't had mosquitoes in the front yard since that thing made its appearance, and I am strongly tempted to keep it for that sake alone, but I will be good and pull it out.
Dr. Hort: Carolyn, it will grow as an annual and die off in the winter. Just keep it from flowering, through pruning, and enjoy its fragrance and you might just be onto something about the mosquitoes. Perhaps some of its essential oils would act as a mosquito repellent.
Use your family as guinea pigs in a mosquito-heavy area: Have them rub some leaves on their skin, and wait to see if the mosquitoes stay away. The natural oils would probably be a whole lot better than DEET, the active ingredient in most repellents.
Identifying a Pasco mystery plant
Q: I have seen a certain plant in west Pasco for a few years. Most of the time I see it on the side of the road. It does not seem invasive because it is not everywhere. Local nurseries around me don't seem to know exactly what it is but they don't speak highly of it either.
Cortney King, Trinity
A: The daisy-looking flower in the photo is a plant with many common names; Bolivian sunflower, Honduras sunflower, Japanese sunflower, shrub sunflower, tree marigold, but most commonly, Mexican sunflower (Tithonia diversifolia). It grows very fast, reaching heights of 15 feet by 6 feet wide in just a couple of years, blooming from late spring to late fall with 6- to 7-inch golden yellow flowers. A good idea is to cut it down to a foot or so after flowering to keep it in bounds.