How to Identify and Avoid Ragweed

Ragweed, a common culprit for fall allergies in North America, might not be easily recognizable due to its nondescript appearance. Unlike plants with colorful berries or distinctive flowers, ragweed lacks such features, making identification challenging. Blooming from late summer (typically August) through November, with peak pollen levels in September, ragweed comes in two main types: common ragweed (Ambrosia artemisiifolia) and giant ragweed (Ambrosia trifida). Common ragweed, often confused with plants like mugwort, can reach up to 6 feet in height, while giant ragweed dwarfs it at an impressive 15 feet tall. Identifying these plants involves observing their leaves and blooms.

Common Ragweed Leaves

The common ragweed plant is characterized by compound leaves composed of multiple leaflets, giving them a fern-like appearance. These “twice compound” or “double compound” leaves consist of miniature versions of the overall leaf structure. The leaflets are approximately 6 inches in length and 4 inches in width. When left undisturbed, the common ragweed plant can reach a height of up to 6 feet.

An additional identifying feature of common ragweed is visible in its initial leaves, which emerge after the seed germinates. These leaves often exhibit purple speckling. However, it’s essential to exercise caution, as other weeds, such as lamb’s quarters (Chenopodium album), also display purple markings. Careful observation is necessary to distinguish between different plants with similar characteristics.

Common Ragweed Blooms

Ragweed, belonging to the Ambrosia genus within the aster family, contrasts sharply with the vibrant blooms of flowers like the New England aster. The flowers of ragweed are exceptionally unobtrusive, appearing as small yellowish bumps that may go unnoticed by casual observers.

Being monoecious, a single ragweed plant possesses both male and female flowers. The male flowers form a spike, as seen in the image below, with each flower containing five stamens, which can be observed with the aid of a magnifying glass. The female flowers of ragweed are even more inconspicuous, concealed in the upper leaf axils—the angles between the upper side of a leaf or stem and the supporting stem or branch.

Following the flowering stage, ragweed produces fruits classified as “achene,” which are small, dry, and single-seeded. These brownish fruits, akin to the flowers, maintain a discreet presence on the plant.

Giant Ragweed Leaves

Giant ragweed is characterized by its “palmate” leaves, resembling the shape of a hand. These leaves come in two varieties: one with five segments, more closely resembling a hand, and the other with three segments. Encountering a tall weed with leaves resembling either of these configurations likely indicates giant ragweed.

The leaves typically feature serrated edges, and their green stems are adorned with tiny white hairs. Additionally, the smaller leaves near the base of the plant often have hairs on their undersides. Overall, the leaves can reach up to a foot in length and span 8 inches across.

Giant Ragweed Blooms

Giant ragweed flowers closely resemble those of common ragweed. The plant produces flower spikes that are cylindrical in shape, growing on many upper stems and measuring approximately 3 to 6 inches in length. Additionally, smaller flower spikes are often present closer to the base of the plant.

Similar to common ragweed, the blooms are inconspicuous, appearing as small bumps. Each flower is around an eighth of an inch in length, initially green but transitioning to a yellow-green and eventually a yellow-brown color as they mature.

How to Control Ragweed

To prevent ragweed from taking over your yard, it’s crucial to maintain regular fertilization and mowing, while keeping flower beds well-maintained and free of weeds. If ragweed is already present, controlling it can be achieved through natural and organic methods. Hand-pulling ragweed plants before they bloom is an effective approach, especially if done before the plants go to seed. This prevents the spread of new seeds in your yard and garden beds.

Alternatively, you can opt for a weed-killer herbicide application during mid-spring to early summer when the ragweed plants are still in their immature stage. This helps to control their growth and minimize their impact on your yard.