Season: Crabgrass seeds have a very lengthy germination time and will grow anytime between late spring and early fall, and are most commonly seen in early to late summer. Being an annual plant, a crabgrass plant will only survive one year and usually dies off in late fall.
Environment: Crabgrass needs an empty space with bare dirt to grow, they often do well in dry soil or in patchy areas where lawn grasses are struggling. The will often spring up in places where the soil has been disturbed or in areas that are very warm (near side walks, pavement, and rocks).
Habit: Crabgrass is a low growing plant that is best identified from above, it has an almost circular growth with stems radiating from one center point in a star pattern.
Leaves: Crabgrass has broad, flat leaves that are perpendicular to the stem, with tips that point up slightly.
Auricle: An auricle is a small ear shaped projection on the interior side at the base of a leaf , Crabgrass has a membranous auricle that is easily seen.
Collar: A collar is the area on the back of the leaf where it connects to the stem, Crabgrass has a divided collar that is easily recognized by its two distinct sections on either side of the leaf/stem junction.
Leafbuds: Leaf bud are where the new leaf blades are emerging from the stems. Crabgrass has rolled leafbuds, which have a spiral shaped cross section. These leaf buds unfurl slowly and flatten out as they mature.
Flowers: Crabgrass flowers are one of the most recognizable parts of the plant and are the reason crabgrass is sometimes referred to as finger-grass. The flowers consist of between 2 and 13 long thin purple spires (approximately 4-6 inches in length) extending from the top of a long vertical stem. Crabgrass typically flowers in August and September.
Seeds: Crabgrass produces approximately 150,000 seeds, the seeds form on the stalks of the flowers in an alternating pattern that resembles a zipper. The seeds start as a light green and turn a tan to light brown color as the mature.
Types of Crabgrass: Two main types of crabgrass exist in the midwest: smooth crabgrass and large crabgrass. Smooth crabgrass tends to be short reaching between 3 and 6 inches in height, it is a very light green color. Large crabgrass tends to be taller and with some flowers reaching 2-3 feet high, it can easily be identified by the slight purple color at the base of its stems and leaves.