Crabgrass

Crabgrass (Digitaria spp., mainly large crabgrass D. sanguinalis and southern crabgrass D. ciliaris) is a warm-season annual grass increasingly used as a fast-establishing summer cover that also doubles as quality forage. Growers choose crabgrass for its quick soil cover, strong fibrous root system, drought tolerance, and ability to produce significant biomass and suppress summer weeds between spring and fall cash crops. (Virginia Tech Extension, 2024; UF/IFAS EDIS)

• Erosion Control: As a non-legume grass cover crop, crabgrass provides a dense canopy and residue that can dramatically reduce erosion. Across studies of grass cover crops, soil loss has been reduced by 31–100%, with average sediment-loss reductions of 20.8 tons/acre in conventional-till, 6.5 tons/acre in reduced-till, and 1.2 tons/acre in no-till systems. (SARE Ecosystem Services—Erosion)
• Weed Suppression: High-biomass grass residues can reduce weed emergence 75–90% when sufficient mulch is present; crabgrass’ rapid summer growth and shading help suppress light-sensitive annual weeds until termination or frost. (UConn IPM)
• Soil Structure Improvement: Crabgrass develops an extensive, fibrous root system with roots documented to 6.5 ft (≈2 m), which enhances soil aggregation and porosity. Recent USDA-ARS research confirms cover crops improve aggregate stability and reduce erodibility—key to better tilth. (Cornell CALS Weed Profile; USDA-ARS 2024)
• Water Management: Grass cover crops increase water infiltration; literature syntheses report >6× increases in some systems and 8–462% increases for non-legume covers, which lowers runoff and improves soil moisture availability during dry spells. (SARE—Infiltration; SARE Overview)
• Disease/Pest Break: As a summer grass cover, crabgrass is a documented non-host for several key nematodes in soybean systems—soybean cyst nematode (SCN), southern root-knot nematode (Meloidogyne incognita), and guava root-knot nematode (M. enterolobii)—providing a pest break between broadleaf crops. (NC State Extension)
• Nitrogen Management: Like other non-legume grasses, crabgrass scavenges residual soil N during summer. Grass cover crops commonly retain 25–70 lb N/acre in aboveground biomass, and with high biomass the N captured can exceed 100 lb N/acre (e.g., cereal rye at 3% N captures ≈180 lb N with 6,000 lb DM/ac). Expect reduced nitrate leaching—median 48% reductions reported for cover crops. Plan for slower N release if residues are mature/high C:N. (Penn State Extension—Rye; UNL CropWatch; SARE—Off-farm Impacts)
• Biomass Production: Typical crabgrass forage/cover biomass is 2–5 tons DM/acre depending on rainfall and fertility; improved varieties (e.g., ‘Red River’, ‘Quick-N-Big’) can reach 8,000–10,000 lb DM/acre under optimal moisture and N. (UF/IFAS EDIS; Missouri Extension; Virginia Tech Extension, 2024; NC State Extension trials)

• Seeding Rate (drill AND broadcast):
• Drill: 3–5 lb PLS/acre gives reliable stands in clean, firm seedbeds; some guides list 5–8 lb/acre when using coated seed or less-ideal conditions. (UT Beef & Forage Center; Alabama Extension; Virginia Tech Extension, 2024—Table 3)
• Broadcast: 5–8 lb PLS/acre with immediate cultipacking for seed-soil contact; uncoated seed can establish at 3–6 lb/acre on a well-prepared, firm seedbed. (NC State Extension—Burke County; UT Beef & Forage Center; Virginia Tech Extension, 2024—Table 3)
• Seeding Depth:
• 0.25–0.5 inch maximum; deeper planting (>0.5 inch) reduces stands. Firm seedbeds and cultipacking help. (UF/IFAS EDIS; UT Beef & Forage Center; Virginia Tech Extension, 2024)
• Soil Type and pH:
• Best on well-drained sands, sandy loams, loams, and silt loams; less productive on heavy clays. pH tolerance is broad (≈5.5–7.5), with optimum near 6.0–6.5. (Virginia Tech Extension, 2024; UF/IFAS EDIS)
• Planting Time (seasonal windows by region; always wait for warm soils):
• Deep South/Gulf (AL/FL Panhandle and similar): Late February–April (after last frost; warm soils). (Alabama Extension)
• Mid-South (TN): May 1–July 1. (UT Beef & Forage Center)
• Lower Mid-South (MS): April 15–June 15. (Mississippi State Extension)
• Mid-Atlantic (VA): Start in early May when soil ≥60°F. (Virginia Tech Extension, 2024)
• Central Midwest (MO): April, weather/soil temp permitting. (Missouri Extension)
• General rule: plant after frost risk when soil temps are 60–65°F for quick germination; emergence begins around 55°F but is slower. (Virginia Tech Extension, 2024; UT Beef & Forage Center)
• Termination (methods and timing):
• Natural winter-kill: Crabgrass is frost-sensitive and generally winterkills at first hard frost—common termination in temperate regions. (Cornell CALS)
• Early termination: For a clean seedbed or to prevent reseeding, terminate 2–3 weeks before planting the next crop using tillage or a non-selective herbicide (e.g., glyphosate or glufosinate) applied when plants are actively growing and temps are favorable (daytime ≥55°F). Roller-crimpers are less relevant for summer-annual grasses like crabgrass but can manage residue; always follow label and preplant intervals. (UMN Extension; UNL CropWatch; Iowa State Extension)
• Rotational Considerations:
• Nematodes: Because crabgrass is a non-host to SCN, southern RKN and guava RKN, it can be a strategic summer cover ahead of soybeans to help reduce nematode pressure (coupled with weed control to remove alternate hosts). (NC State Extension)
• N cycling: Mature grass residues have higher C:N and can temporarily immobilize N; if terminating late or leaving heavy residue, consider starter N for the following heavy-feeding crop or pair with a legume cover to balance C:N. (UNL CropWatch; SARE—Conservation Tillage Systems)
• Volunteer risk: If you do not want volunteers next year, avoid allowing seedhead formation; mow/terminate before heading. If reseeding is desired, allow 2–3 weeks before first frost for seed set. (Virginia Tech Extension, 2024)
• Water Requirements and Drought Tolerance:
• Crabgrass is drought tolerant relative to cool-season grasses, thrives in heat (C4 physiology), and rebounds quickly after rainfall; deep roots help access subsoil moisture. (NC State Extension—Sampson County; Cornell CALS)
• Grass cover cropping generally increases infiltration and reduces runoff, improving in-season moisture retention and drought resilience. (SARE—Infiltration)

Practical notes:

• Fertility: As with other summer annual grasses, crabgrass responds to split N applications; typical forage systems use 40–80 lb N/ac at establishment with additional N after first harvest, adjusted to goals and soil tests. (Missouri Extension; Virginia Tech Extension, 2024)
• Establishment tips: Mix small seed with a carrier (e.g., dry fertilizer) for even distribution; calibrate equipment and cultipack after seeding to ensure shallow placement and seed-soil contact. (Virginia Tech Extension, 2024)

This guidance draws on recent extension bulletins, SARE syntheses, and USDA research to provide actionable, region-specific recommendations for using crabgrass as a high-performing summer cover.