Forage Collards / Kale / Cabbage

Forage collards, kale, and cabbage (all Brassica oleracea types) are cool-season brassicas valued as fast-establishing, high-biomass cover crops and dual-purpose forages. Growers choose them to rapidly protect soil, scavenge residual nitrogen, alleviate surface compaction with strong taproots, and provide high-quality fall/winter grazing or green chop. These traits are well documented for brassica cover crops broadly, including B. oleracea types such as forage kale/collards and rapeseed relatives used similarly in U.S. systems (SARE—Brassicas and Mustards; Ohio State—Brassica Crops). (sare.org, agcrops.osu.edu)

• Erosion Control: Across many systems, cover crops cut sediment losses dramatically; non-legume covers reduced soil loss by 31–100%, and mustard (a brassica) reduced soil loss by up to 82% compared with no cover. Meta-analyses also report average reductions of 20.8 tons of sediment per acre under conventional till compared with no cover (SARE—Covering the Soil to Prevent Erosion). (sare.org)
• Weed Suppression: Rapid fall canopy and glucosinolate-rich residues suppress small-seeded annuals. Trials have documented 73–85% reductions in weed infestation after rapeseed and up to 80–87% reductions in weed biomass after brassica cover crops in perennial systems; fall-planted mustards suppressed in-season weed biomass by >50% in 90% of site-years (Agronomy Journal—rapeseed volunteer study, citing prior work; HortTechnology—brassicas in orchards; Agronomy Journal—mustard weed suppression; SARE—Brassicas and Mustards). (acsess.onlinelibrary.wiley.com, journals.ashs.org, sare.org)
• Soil Structure Improvement: Brassicas produce stout taproots that can penetrate compacted layers and “bio-drill” up to about 6 feet, leaving macropores that enhance subsequent root growth and infiltration (UMass—Brassica cover crops; SARE—Brassicas and Mustards). (umass.edu, sare.org)
• Water Management: Cover crops substantially increase rainfall infiltration; reviews show increases ranging from 8% to >400% depending on system. Better infiltration and residue cover help conserve moisture in dry spells and reduce runoff in storms (SARE—Increasing Infiltration; USDA—cover crops and drought). (sare.org, usda.gov)
• Disease/Pest Break: When incorporated as green manure, brassica tissues release isothiocyanates that suppress certain soil-borne pathogens and nematodes. University/extension reports show suppression of Rhizoctonia, scab, and Verticillium in potatoes, and Phytophthora blight in cucurbits with mustard/rapeseed programs; trap-crop and biofumigation effects are documented but site- and timing-dependent (UMass—Brassica cover crops, pest section; SARE—Brassicas and Mustards; SARE project report with nematode data). (ag.umass.edu, sare.org, projects.sare.org)
• Nitrogen Management: Brassicas are excellent N scavengers (they do not fix N). Late-summer/fall brassicas commonly capture 80–120 lb N/ac; controlled comparisons found rape averaged 111 kg N/ha (~99 lb/ac) in shoots by late fall, and forage radish captured 119 kg N/ha in shoots plus additional N in fleshy roots (SARE project LNE03‑192; UMass—radish N capture). (projects.sare.org, umass.edu)
• Biomass Production: Forage brassicas routinely produce 2–4 tons dry matter (DM)/ac in 60–120 days under U.S. conditions, with 3.1 ton DM/ac at 90 days typical in PA trials; kale can exceed 4–6 ton DM/ac with 150+ days. Variety and season drive performance (Penn State—use of brassicas; Alabama Extension—Forage Brassicas; UMass—Brassica fodder yields). (extension.psu.edu, aces.edu, umass.edu)

• Seeding Rate (straight stand):
• Drill: 3–4 lb/ac for kale/rape-type brassicas (same seed size class as forage collards); many state guides use this rate for B. oleracea and related forage brassicas (Penn State Extension; Ohio State Agronomic Crops Network). For broader “brassica (rape, turnip, kale)” cover-crop category, Mississippi State lists 8–14 lb/ac for broadcast and notes drilled rates can be 20–30% lower, aligning with ~6–11 lb/ac if broadcasting is the baseline (MSU—Cover Crops Seeding Rates & Depths). (extension.psu.edu, agcrops.osu.edu, extension.msstate.edu)
• Broadcast: 8–14 lb/ac for “brassica (rape, turnip, kale)” single-species plantings; reduce to 3–6 lb/ac in blends. As a rule of thumb, increase broadcast rates 20–50% over drilled to ensure stands (MSU—Cover Crops Seeding Rates & Depths; Midwest Cover Crops Council—Planting). (extension.msstate.edu, midwestcovercrops.org)
• Inference note: Forage collards (a B. oleracea type like kale) are managed at the same rates as kale/rape in extension forage brassica guides; if using a collard variety with larger seed or in a wildlife/grazing objective, adjust within the stated ranges. (Based on OSU and Penn State rates for kale/rape.) (agcrops.osu.edu, extension.psu.edu)
• Seeding Depth: Place seed 1/4–1/2 inch deep into a firm, moist seedbed; up to 3/4 inch is acceptable on lighter soils with good moisture. Row spacing 6–8 inches is common for monocultures or narrow drilling (Ohio State—Brassica Crops; MSU—Forage Brassicas; MSU—Cover Crops Seeding Rates & Depths). (agcrops.osu.edu, extension.msstate.edu)
• Soil Type and pH: Brassicas establish best on well-drained soils; avoid saturated or ponded areas. Optimal pH is roughly 5.3–6.8 for forage brassicas; rapeseed (a common analog) tolerates 5.5–8.0. Ensure adequate sulfur and nitrogen fertility for vigorous growth (MSU—Forage Brassicas; Penn State—Brassica forage bulletin; OSU—Rapeseed cover crop; eOrganic—Brassicas). (extension.msstate.edu, extension.psu.edu, ohioline.osu.edu, eorganic.org)
• Planting Time (seasonal windows):
• General rule (most regions): Establish 4 weeks before the average first 28°F fall freeze to maximize fall biomass and N capture; minimum soil temperature ~41°F (5°C) and avoid >85°F for establishment (UMass—Brassica cover crops). (umass.edu)
• Northeast/Mid-Atlantic (example PA latest fall seeding dates): Rapeseed/canola and turnip by Sep 1–15 depending on region; forage radish by Sep 1–15; annual ryegrass earlier. Use the Penn State guide’s small-grain areas as a reference (Penn State—Recommended Fall Cover Crop Planting Dates). (extension.psu.edu)
• Ohio Valley/Great Lakes: Reliable rapeseed establishment window (state average) July 25–Oct 19; kale also listed among covers that can be planted through mid–late October with increased frost risk (OSU—Rapeseed as a Cover Crop; OSU—Cover Crops in the Garden). (ohioline.osu.edu)
• Southeast: For winter growth and grazing/cover, plant early fall (September–October); in some systems, early spring plantings are also used, but fall plantings generally produce more biomass and are more reliable (eOrganic—Brassicas). (eorganic.org)
• Termination (methods and timing):
• Winter-kill varies by species and temperature; some B. oleracea types can overwinter in mild climates. Where winter-kill is unreliable, terminate before seed set via herbicide, mowing plus tillage, roller-crimping at reproductive stage, or full tillage, depending on system and goals (NC State—Termination Methods; VT Extension—Herbicide Options to Terminate Winter Cover Crops; SARE—Termination of Cover Crops). (covercrops.ces.ncsu.edu, pubs.ext.vt.edu, sare.org)
• If using rapeseed/cole types and terminating chemically, small plants are easier to control; research in DE/VA showed glyphosate+2,4‑D and similar programs provided >80–90% control 28 days after early termination, but large/tall plants were difficult for any herbicide program—plan timely termination or use mechanical methods if needed (Weed Technology—rapeseed termination). (cambridge.org)
• For biofumigation objectives (disease suppression), mow/chop at flowering and immediately incorporate, then seal with a roller/cultipacker and irrigate or time with rain to retain isothiocyanates (UMass Vegetable Notes—biofumigation steps). (ag.umass.edu)
• Rotational Considerations:
• Avoid tight rotations with brassica cash crops (cabbage, broccoli, cauliflower, canola, radish). Brassica covers share diseases and can increase risk of issues like clubroot or black rot; SARE advises not rotating brassica covers with brassica cash crops in close sequence (SARE—Brassicas and Mustards). (sare.org)
• Herbicide carryover: Brassicas (especially radish/mustards) are among the more sensitive cover crops to residual Group 2, 5, 14, and 27 herbicides; atrazine >1.0 lb ai/ac, mesotrione, flumetsulam, and clopyralid often injure fall-seeded brassicas. Check labels and rotation intervals; reduce risk by allowing more time/rainfall between application and seeding (Iowa State—residual herbicides; Univ. Minnesota Extension—herbicides & cover crops; Purdue Pest&Crop). (crops.extension.iastate.edu, extension.umn.edu, extension.entm.purdue.edu)
• Water Requirements and Drought Tolerance:
• Brassicas need moisture for establishment and do poorly on saturated soils, but once established, they’re rated good for drought tolerance relative to many cool-season broadleaf covers; rapeseed in particular is rated “good” for drought tolerance and grows deeply to access subsoil moisture (MSU—Forage Brassicas establishment; OSU—Rapeseed cover crop; USDA Climate Hubs—cover crops improve infiltration). (extension.msstate.edu, ohioline.osu.edu, climatehubs.usda.gov)
• Additional Notes for Use in Mixes:
• Brassicas can dominate in mixtures due to rapid growth; reduce their seeding rate when mixing with small grains or legumes to avoid outcompeting companions (UMass—Brassica cover crops, mixtures). (ag.umass.edu)

Practical targeting by region and goal:

• Northern/Upper Midwest/Northeast grain rotations: Drill forage kale/collard-type brassicas 4–6 weeks before first 28°F freeze, or follow Penn State latest dates (e.g., rapeseed/turnip by early–mid September depending on zone) to maximize fall biomass/N capture; plan chemical or mechanical termination before cash-crop planting in spring (UMass; Penn State dates). (umass.edu, extension.psu.edu)
• Ohio Valley/Great Lakes vegetable/grain rotations: OSU lists a July 25–Oct 19 establishment window for rapeseed with similar timing suitable for forage kale/collards; drill 1/4–1/2 inch deep and target early fall for most growth (OSU—Rapeseed cover crop). (ohioline.osu.edu)
• Southeast grazing + cover goals: Plant early fall (Sept–Oct) for winter grazing and spring green manure; ensure good drainage and fertility (N+S) for rapid establishment; terminate via grazing-out plus mowing/tillage before replanting spring crops (MSU—Forage Brassicas; eOrganic—Brassicas). (extension.msstate.edu, eorganic.org)

Why growers choose Forage Collards/Kale/Cabbage:

• They provide the brassica family’s hallmark services—fast ground cover, N scavenging, compaction relief, and flexible termination options—while fitting short late-summer planting windows ahead of corn/soybeans or vegetable crops. Used thoughtfully with rotation and termination plans, they reduce erosion, suppress weeds, improve infiltration, and build resilient soil structure at practical seeding rates and depths familiar to U.S. growers (SARE—ecosystem services; SARE—Brassicas and Mustards). (sare.org)

Notes:

• Forage collards are B. oleracea types biologically similar to forage kale; where collard-specific extension sheets are limited, seeding/management guidance from kale/rape-type forage brassicas is used by extensions and is appropriate for cover-crop objectives. Always adjust within the ranges above and confirm herbicide carryover and termination plans for your field conditions. (Inference based on OSU and Penn State rates and management for kale/rape.) (agcrops.osu.edu, extension.psu.edu)

If you’d like, tell me your field location and next cash crop and I can tailor dates, rates in mixes, and a termination program specific to your planting window and equipment.