It may be tempting to ignore crabgrass, especially since it has “grass” in its name, but crabgrass is among the most troublesome lawn weeds. It can invade poor turf and, if allowed to develop through its complete lifecycle, a single plant is capable of producing thousands of seeds before dying off in the fall. Crabgrass management can be intensive, but it is an important practice in maintaining a healthy lawn.
Crabgrass plant | Photo Jake Louwsma

Crabgrass is an annual weed, which means it germinates from seed, matures, flowers and produces seed in one season before it dies off during frosty fall weather. In contrast, most lawns in northern climates are cool season perennial grasses, meaning they go dormant over the winter but continue to grow year after year. Turf grasses that become stressed or thin can provide the foothold that crabgrass needs to establish. It is common to see crabgrass invade along curb, driveway, or sidewalk edges where damage from the adjacent surfaces occurs, but crabgrass can become problematic in any lawn area where desirable grasses are less competitive. Crabgrass seeds can even lie dormant in soil for a number of years, sprouting new plants when germinating conditions become favorable.

Crabgrass exploiting and invading an area of stressed grass | Photo Jake Louwsma

In addition to its ability to exploit openings in the lawn, crabgrass is a durable plant that is able to survive repeated mowings and isn’t bothered by being stepped on. It can thrive during the high heat of summer when turf grasses sometimes go dormant. In fact, you will often see crabgrass growing in sidewalk cracks under the harshest conditions – heavy foot traffic, low water, minimal nutrients, and extreme heat. These characteristics make crabgrass an aggressive weed that will spread quickly if given the chance to complete its life cycle and produce seeds.

Many lawn care practices and products have been developed to manage crabgrass. In most cases prevention is sufficient to keep crabgrass and other weeds in check. Healthy, dense lawns can outcompete opportunistic weed establishment, so proper mowing, fertilization, adequate water and aeration are critical. Mowing should be done at frequent intervals and the blade height should be adjusted to the highest setting recommended for the dominant type of turf grass in the lawn. Fertilizers should be applied judiciously to increase lawn vigor. Irrigating in long intervals and only as needed encourages deep rooting and healthy, dense turf grasses. Aeration reduces compaction and encourages the exchange of air, water and nutrients into the soil root zone. Finally, seeding over bare spots in a lawn will prevent weeds from establishing a localized presence.

Sometimes even the most carefully managed lawns suffer from drought, pest damage, poor soils or other growth limiting factors. When mowing, watering, and fertilizing aren’t enough or other problems come into play, herbicides are another method to either prevent or contain a crabgrass population. There are several herbicides on the market that control crabgrass and they are generally split into two groups: pre-emergence and post-emergence products. As the name suggests, pre-emergence herbicides work by preventing weeds from emerging. Application timing is important to ensure the product’s ingredients are available during the spring window of time (once the soil is warm enough) when overwintering crabgrass seeds actively germinate. However, crabgrass seeds can continue to germinate throughout the summer, so pre-emergents are not necessarily a cure-all to heavy crabgrass pressure. In that case, selective post-emergence herbicides (those that target specific pest plants with minimal damage to turf grasses) can kill crabgrass plants that have matured past germination. All pesticides should be used according to their labeling.

As with many weeds, crabgrass can be a chronic problem that lawn owners encounter year after year. With patience and perseverance, crabgrass can be beat.

Dustin Wolff | Account Manager
Posted 5/2/2022

Resources consulted for this post:
https://www.agry.purdue.edu/turfnew/pubs/AY-10.pdf
https://outagamie.extension.wisc.edu/files/2010/05/Crabgrass.pdf