Common Ragweed

Common Ragweed (Ambrosia sp.)

This is a summer to fall annual that spreads by seed.
It can also reseed as a perennial.

There are about 40 types of Ambrosia species and technically about 15 are 'Common'.

Amongst these 15 species of, they are all fairly similar with slight differences.

For example, the one strain that is most famous allergy culprit is Ambrosia artemisiifolia, which grows up to 4 feet. It prefers poor quality, dry soils but can adapt well to many types of soils. Giant Ragweed (A. trifida) can grow up to 12 feet tall and although it likes moist areas, it can also adapt to other soils.

Ragweed is an upright, rough weed with branched hairy stems. Stems have fern like, lobed leaves divided into 3 to 5 lobes and are similar in appearance to marigold leaves but are a lighter greenish-gray color.

The cluster of flowers on top are also upright.
Flower heads are green spikes with seeds running up and down.

Ambrosia species are monoecious, which means it has both male and female flower heads.

A yellow-green male flower is rested in a bract, or a leaf designed specifically for reproduction, with the cream color female flower heads resting beneath it.

After pollination, the female flower develops into a wood-like encasement housing the seed inside. When encasement is mature it is a light to dark brown.

Ambrosia artemisiifolia
Photo: Gerald Tang

Many states consider ragweed noxious due to the severe and widespread allergies caused by its pollen. It's everywhere - grassy plains, river banks to roadsides and is the top cause of fall allergies where close to 85 percent of people allergic reactions from it.

Ragweed is common in most regions of the United States from mid-august through the first frost. Pull or dig weed out. It's likely there will be plenty of seeds that fall off. Pull or hoe ragweed after the final winter frost in spring. The goal is to get it before it flowers.

Mulch area but before doing so it is a good idea to burn seeds on ground with a propane torch.

Using post-emergent herbicides with these common weeds should be done in spring when the leaves are still tender and vulnerable. Common ragweed is not easy to remove all of.

Is there anything good about common ragweed?

  • Maybe not for humans but for our feathery friends, pigs and cattle ragweed is a tasty treat.

  • It is an excellent soil preserver and conditioner.

  • Don't confuse Ambrosia species with Kochia scoparia, which is also known by the name Ragweed, also known as bitterweed. This is a shrub that has recently been introduced to North America from Europe and Asia.

Related Articles

          Growing Plants from Seed -
               Benefits and suggestions of removing weed seeds.

Back to Weed Identification

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