Happy spring, south Minneapolis! Welcome to another growing season and another season of the City Gardener. As I’m writing this column, it’s 75 degrees out. By the time you read this, it will probably be back in the 40s – but summer is quickly approaching!
Towards the end of last season, a couple of readers reached out and asked me to write about ragweed, the bane of Minnesotan allergy sufferers. I decided to wait until the spring because that’s when the plant is emerging and easier to control. Read on for information about ragweed, including why you might want to remove it from your yard despite its pretty flowers – and what you might plant in its place.
Ragweed refers to several species, with common ragweed (Ambrosia artemisiifolia), western ragweed (Ambrosia psilostachya), and giant ragweed (Ambrosia trifida) being the most widespread in Minnesota. These plants thrive in disturbed soils, so they are common along roadsides, agricultural fields, construction sites, and urban lots. Ragweed tends to emerge quickly in newly disturbed areas and outcompete native vegetation.
Giant ragweed grows up to 17-20 feet tall and is less common in urban areas. Common and western ragweed reach a height of 1-4 feet and will likely be the types you encounter in your yard. Each type of ragweed looks somewhat different, although all types have small, yellowish-green flowers in the fall. Common ragweed’s leaves are thin and deeply lobed, and early in the season will look like a small mound of fern or marigold-type leaves. Western ragweed’s leaves are a similar fern-like shape, but thicker, a bit fuzzy, and often have a grey-green look.
One of the defining characteristics of ragweed is its method of pollination. Unlike flowering plants that rely on insects, ragweed is pollinated primarily by the wind. As a result, it produces massive quantities of lightweight pollen that can travel long distances, making it difficult to avoid even if the plant is not nearby. In fact, according to air sampling conducted by the Minnesota Department of Health, ragweed represents almost 60% of pollen in the air at some times of the year.
Effective ragweed management begins in the spring, long before allergy season arrives. Ragweed seedlings emerge in late spring, and removing them at this stage prevents them from maturing and producing pollen later in the season. Hand-pulling is the best approach for small infestations, especially in a home garden.
Avoiding soil disturbance can also help. If you tend to till your garden beds each year, try no-till gardening methods to reduce the growth of ragweed and other weeds (with the additional benefit of building soil structure, reducing erosion, and improving water retention!). Similarly, maintaining a healthy lawn and minimizing bare soil can help prevent ragweed establishment. Anytime soil is exposed, ragweed will likely be one of the first plants to take hold.
There are herbicides that can be used on ragweed, although some ragweed populations have become immune to various herbicides, causing a particular problem for farmers. If you do use herbicides on ragweed, make sure to check the label carefully to ensure the product is intended for the particular species you’re dealing with and you are applying it according to the instructions. Applying herbicides early, when plants are small, is generally more effective than treating mature plants later in the season.
Ragweed is a significant allergen in Minnesota, substantially impacting many people’s day to day lives. Between 10% and 20% of Americans are allergic to ragweed pollen, making it one of the most common seasonal allergens. In Minnesota, ragweed season is particularly intense because it coincides with the high season for other weed and grass pollens. Additionally, climate change has extended the ragweed season over recent decades, increasing the length and severity of symptoms for many individuals.
If you remove ragweed from your yard and are looking for an alternative, consider planting native goldenrod! This plant blooms around the same time as ragweed, providing fall color, but has even brighter yellow flowers. It’s a great food source for late-season pollinators. And, it produces significantly less pollen than ragweed.
In conclusion, ragweed is more than just a common weed – it is a significant environmental and health concern in Minnesota. Although its fall flowers are pretty, consider replacing it with less problematic alternatives to help protect native plants and allergy sufferers in our community.
For more information, check out the University of Minnesota Extension Yard and Garden website. Extension resources are written by experts and contain the latest and most reliable research-based information. Happy gardening!
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