Types of Crabgrass: Understanding the Different Varieties

Crabgrass (Digitaria spp.) is an invasive, warm-season grass classified as a weed. Key species include smooth crabgrass (Digitaria ischaemum), distinguished by its smooth, hairless leaves, and large crabgrass (Digitaria sanguinalis), which is hairier and can reach up to 2 feet in height. Southern crabgrass (Digitaria ciliaris) grows up to 3 feet tall with longer, hairy leaves, while tropical crabgrass (Digitaria bicornis) is noted for its unique seed head branches. Effective management requires identification and understanding of these species’ morphological traits and habitat preferences. Further insights will detail habitat adaptation and control methods.

What is Crabgrass?

Crabgrass, an annual warm-season grass, is classified as a weed due to its invasive growth habit and its ability to rapidly colonize and dominate lawns and gardens. Belonging to the genus Digitaria, crabgrass species exhibit a wide range of physical characteristics and ecological adaptations, making them formidable competitors in various environments.

Primarily, crabgrass is spread by seeds and stems that root at the nodes, allowing it to quickly establish and proliferate, especially during the summer months when conditions are favorable.

Among the various types of crabgrass, smooth crabgrass (Digitaria ischaemum) and large crabgrass (Digitaria sanguinalis) are the most prevalent. Smooth crabgrass, characterized by its smooth, hairless leaves and stems, typically grows close to the ground and can reach heights of up to 6 inches if unmowed. In contrast, large crabgrass, also known as hairy crabgrass, can grow up to 2 feet tall and has distinctive hairy leaves and stems.

Other notable crabgrass varieties include southern crabgrass (Digitaria ciliaris), which features long, hairy leaves and is sometimes used as livestock forage, and tropical crabgrass (Digitaria bicornis), prevalent in warmer southern regions.

Understanding these annual and perennial crabgrass species is essential for effective management and control of these pervasive summer weeds.

Most Common Crabgrass Varieties

Among the various types of crabgrass, smooth crabgrass (Digitaria ischaemum) and large crabgrass (Digitaria sanguinalis) are the most prevalent and problematic varieties in North American lawns. Both crabgrass species are summer annual grasses that present significant lawn weed problems due to their aggressive growth patterns and extensive seed production.

Characteristic Smooth Crabgrass Large Crabgrass
Scientific Name Digitaria ischaemum Digitaria sanguinalis
Common Names Small crabgrass, Low crabgrass Hairy crabgrass, Purple crabgrass
Growth Pattern Grows close to the ground Spreads more aggressively
Leaf and Stem Features Smooth, hairless Hairy leaves and stems

Smooth crabgrass is characterized by its smooth, hairless leaves and stems, and typically reaches a height of 6 inches if left unmowed. In contrast, large crabgrass can grow up to 2 feet tall, with wider, hairy leaves and stems that exhibit a more vigorous spreading habit. Despite these differences, both crabgrass varieties thrive in similar environments, making crabgrass identification important for effective management.

With over 30 crabgrass species, smooth and large crabgrass dominate when it comes to distribution and impact on lawns. Their prolific seed reproduction and adaptability to various conditions underscore the significance of understanding crabgrass characteristics to mitigate their spread effectively.

Types Of Crabgrass

Invasive and prolific, several key species of crabgrass dominate North American lawns, posing significant challenges to turf management. Understanding the various types of crabgrass is essential for effective control and management.

The primary crabgrass species found in North America include:

  1. Smooth Crabgrass (Digitaria ischaemum): This species, also known as small or low crabgrass, is one of the most prevalent crabgrass varieties in North America. It grows close to the ground, featuring smooth, hairless leaves and stems, and can reach heights of up to 6 inches if unmowed.
  2. Large Crabgrass (Digitaria sanguinalis): Commonly referred to as hairy or purple crabgrass, this variety exhibits more aggressive growth. It can grow up to 2 feet tall if left unmowed and has hairy leaves and stems.
  3. Southern Crabgrass (Digitaria ciliaris): Native to the Americas, Asia, and Africa, this species can grow up to 3 feet tall. It is characterized by long, hairy leaves and is sometimes used as forage for livestock.
  4. Tropical Crabgrass (Digitaria bicornis): Prevalent in warmer southern regions of the U.S., this species, also known as Asian crabgrass, has seed head branches that join at the same point on the stem.

Other less common types include blanket crabgrass and India crabgrass, each with distinct morphological traits, contributing to the diverse crabgrass classification.

Where Does Crabgrass Grow?

Understanding the diverse types of crabgrass is fundamental for effective management, but equally important is knowing the specific environments where these species proliferate. Crabgrass exhibits remarkable adaptability, colonizing a variety of habitats globally. Its geographical range extends from approximately 50°N to 40°S latitude, encompassing temperate, subtropical, and tropical regions.

Crabgrass habitat includes both cultivated and uncultivated areas. It thrives in disturbed sites such as roadsides, vacant lots, and waste places, as well as managed environments like lawns, gardens, crop fields, orchards, and vineyards. Crabgrass growth conditions favor compacted, low-fertility soils, especially in thin, weak, or bare spots where it can outcompete desirable grasses.

Crabgrass preferred environments are typically characterized by full sun to partial shade and moist to slightly dry soil conditions. The species exhibits notable regional variations: large crabgrass (Digitaria sanguinalis) is more common in gardens and landscapes, while smooth crabgrass (Digitaria ischaemum) dominates turfgrass lawns. Southern crabgrass (Digitaria ciliaris) is prevalent in the southeastern U.S., and tropical crabgrass (Digitaria bicornis) is found in warmer southern regions.

Crabgrass’ global presence is a confirmation of its ecological niche adaptability, making it a persistent challenge across diverse landscapes. Accurate identification and understanding of crabgrass thriving locations are essential for targeted management strategies.

Crabgrass Control Methods

Effective crabgrass control methods encompass a combination of cultural practices, pre-emergent herbicides, and post-emergent herbicides to manage and mitigate the proliferation of this pervasive weed. Crabgrass management necessitates a strategic approach that incorporates both preventive and remedial actions.

Cultural Practices: Maintaining a robust, healthy lawn is foundational to crabgrass prevention. Proper mowing, fertilization, and irrigation are critical. Mowing at a height of 2.5-3 inches helps shade the soil, reducing crabgrass germination. Deep, infrequent watering fosters deep root growth, enhancing lawn resilience.

Pre-Emergent Herbicides: Timing is pivotal in applying pre-emergent crabgrass herbicides such as prodiamine, dithiopyr, or pendimethalin. These should be applied in early spring when soil temperatures reach 55-60°F for several consecutive days to preclude crabgrass seed germination. Products combined with fertilizer can concurrently nourish the lawn.

Post-Emergent Herbicides: For controlling crabgrass post-emergence, herbicides like quinclorac, fenoxaprop, or mesotrione are most efficacious when applied to young crabgrass before tillering. Multiple applications may be required to achieve optimal results.

Mechanical Removal: Hand-pulling, particularly in small infestations, and solarization using plastic or mulch can be effective crabgrass removal techniques.

Preventing Crabgrass Infestations

Preventing crabgrass infestations requires a thorough approach that integrates cultural practices, precise timing of pre-emergent herbicide applications, and consistent lawn maintenance. Understanding the crabgrass life cycle is pivotal for effective crabgrass control.

Crabgrass, a warm-season annual weed, germinates when soil temperatures reach 55-60°F. Applying pre-emergent herbicides, such as prodiamine or pendimethalin, 2-3 weeks before expected germination, can greatly reduce crabgrass lawn problems. Pre-emergent applications are most effective when soil temperatures have consistently reached 55°F for several days—often coinciding with forsythia bloom.

Maintaining a dense, healthy lawn can mitigate the establishment of lawn crabgrass. Mowing at the appropriate height, typically between 2.5-3 inches for most grass types, helps shade out emerging crabgrass seedlings. Regular fertilization promotes vigorous turf growth, which competes effectively against lawn weeds. Deep, infrequent watering fosters robust root systems, enhancing overall lawn resilience.

Cultural controls, such as annual dethatching and aeration, alleviate soil compaction, further deterring crabgrass proliferation. Organic options, like corn gluten meal, can serve as a pre-emergent alternative. Combining these strategies with timely interventions is paramount, as crabgrass control becomes much more challenging once the weed is established.

The integration of these practices provides a thorough defense against crabgrass infestations.

Crabgrass and Lawn Care

To effectively manage crabgrass and maintain a healthy lawn, integrating cultural practices with precise herbicide applications is crucial. Crabgrass (Digitaria spp.) thrives in thin, bare, or weakened areas of lawns, outcompeting desirable grasses by spreading prolifically and producing thousands of seeds. Effective lawn care strategies hinge on a combination of preventative and control measures.

  1. Prevention: Maintain lawn density through proper mowing height, fertilization, and deep infrequent watering. These practices reduce the likelihood of crabgrass establishment by crowding potential germination sites.
  2. Pre-emergent Herbicides: Apply pre-emergent herbicides such as prodiamine or dithiopyr in early spring when soil temperatures reach 55-60°F. Timing is critical, often coinciding with 4-5 days of soil temperatures at 55°F or the blooming of forsythia.
  3. Reseeding: Regularly reseed bare or thinning areas to eliminate potential germination sites for crabgrass, thereby reinforcing the lawn’s resilience against weed invasions.
  4. Post-emergent Control: For existing crabgrass, use post-emergent herbicides containing quinclorac or fenoxaprop. Apply these treatments when crabgrass plants are immature to maximize efficacy.

Implementing these strategies ensures a robust lawn ecosystem that minimizes crabgrass infestations and promotes healthy turfgrass growth.