Keep in mind that crabgrass is a weed. In simple words, it is any undesirable plant growing in your garden or lawn. Furthermore, there are certain weeds that actually add to the beauty of a garden but removing them is important to ensure the health of rest of the plants in the garden. The same holds true for crabgrass.
Once you have established that the plant you are observing is a weed, observe its general appearance. Crabgrass plants have numerous branches and both large and smooth crabgrass grows in either an upright or in a prostate direction. Furthermore, it is a characteristic of large crabgrass to grow into the form of a mat to a height of about 3 feet. However, the height of smooth crabgrass generally does not exceed 15 inches. One of the most evident factors that can be relied upon for identification purposes is that the stems of large crabgrass are purple in colour.
The structure of a weed’s leaves is another factor that can be taken into account for identifying crabgrass. The colour of the leaves of large crabgrass is generally pale blue green while it is dull green for smooth crabgrass leaves. If the leaves under observation are sharply pointed and margined, there are high chances that the plant under scrutiny is crabgrass. Moreover, the length of large crabgrass leaves can vary from 2 to 6 inches, while for smooth crabgrass leaves, it is 4 inches. The width of both crabgrass types is the same i.e. 1/4 inches.
The exact location where a weed grows in your garden or lawn can point to it being crabgrass. Weeds growing in moist, warm areas of the garden or lawn and if they have all the characteristics detailed above, they are crabgrass for sure.