An average size plant produces roughly 275 seeds. Newly matured seed is usually dormant and requires a cold, moist period to germinate. Most germination in the field occurs early to mid-spring and at soil depths to 16 cm, optimal 2 cm. Germination rarely occurs on the soil surface. Seedlings emerging from shallow depths are most likely to survive.
Plants effectively compete other species for light.
Cultivation to prevent seed production can help control infestations. Its foliage is similar to that of annual bursage , but its burs are shaped like those of giant ragweed . Unlike annual bursage and giant ragweed , western ragweed can reproduce vegetatively from creeping roots and leaves are mostly 1-pinnatem divided , with irregularly toothed margins.