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Cover Crop Seed Looking for more than 200 lbs?
Sorghum-Sudangrass Seed
Sorghum bicolor × S. bicolor var. sudanense | SKU: PG-SOSU
What is Sorghum-Sudangrass?
Sorghum-sudangrass is an interspecific hybrid between grain sorghum (Sorghum bicolor) and sudangrass (S. bicolor var. sudanense). The cross was developed to combine grain sorghum’s massive yield potential with sudangrass’s faster regrowth and finer stem structure. The result is the highest biomass-producing warm-season annual cover crop in commercial agriculture. Plant breeders began developing sorghum-sudan hybrids in the mid-20th century specifically for forage and soil-building applications. The hybrid vigor from crossing these two closely related species produces plants that out-perform either parent in growth rate, root mass, and total dry matter per acre under most field conditions. Agronomically, sorghum-sudangrass is valued for three overlapping properties: its sheer volume of aboveground biomass that feeds soil biology when terminated and incorporated; its deep fibrous root system that physically penetrates and fractures compacted soil layers; and its allelopathic compounds that inhibit weed germination. These three traits working together make it one of the most productive single-species cover crops available to row crop and vegetable farmers across the warm-season growing window.
Specifications
Seeding Specs
Water Needs Low to Moderate (drought-tolerant once established)
Soil Preference Tolerates a wide range of soils including clay, sandy loam, and compacted subsoils. Performs best in well-drained soils but handles moderate clay. Avoid waterlogged conditions.
Soil pH pH 5.5–7.5
Planting Depth 0.5–1 inch
Establishment Specs
Height 6–12 feet in 60–90 days
Color Green foliage; purple-tinged stems common
Uses Cover Crop, Biomass, Compaction Remediation, Weed Suppression, High-Residue No-Till
Native/Introduced Introduced — hybrid derived from crops originating in Africa
Why Choose This Seed?
Unmatched Biomass Production
Under normal summer conditions, sorghum-sudangrass produces 4–8 tons of dry matter per acre in a single 60–90 day window. That’s the highest output of any common warm-season cover crop. When that residue is terminated and incorporated, it feeds the soil microbial community, improves water infiltration, and builds organic matter in a way that takes legumes multiple seasons to match. For high-residue no-till systems, this single crop can establish the residue base needed for cash crop planting in one shot.
Deep Compaction Busting
The root system on sorghum-sudangrass isn’t typical of a grass. A dense, fibrous network drives down 3 feet or more, physically penetrating hardpan layers that a cover crop with a shallow root system simply cannot reach. Farmers managing plow pans and wheel-track compaction from heavy equipment use this grass as the first step in transitioning degraded fields to reduced-till or no-till production. The roots also create biopore channels that improve drainage and subsoil aeration after the crop is terminated.
Natural Weed Suppression
Sorghum-sudangrass is allelopathic—it releases chemical compounds into the soil that inhibit the germination of weed seeds. Combined with the shading effect from a 6–12 foot canopy, weed pressure in the season following incorporation is measurably lower. This is especially useful before transplanted vegetables and small grains, where early-season weed competition has the biggest economic impact. The allelopathic effect is strongest in the season immediately after incorporation, when soil residue breakdown is at its peak.
Fast-Establishing Summer Window
Sorghum-sudangrass germinates in 5–7 days in soil at 65°F or warmer and reaches usable height inside 30 days. That speed makes it the practical choice for summer cover crop windows between spring harvest and fall planting. Most other high-biomass summer crops take longer to establish or produce less total residue in the same timeframe. If you have 60–90 days of warm weather available between cash crops, this grass will fill that window efficiently.
Honest About Limitations
Sorghum-sudangrass produces dhurrin, which converts to prussic acid (hydrogen cyanide) under plant stress. Do not graze plants under 18 inches tall, do not graze drought-stressed growth, and do not graze within 7–10 days of frost kill or until drought stress is relieved—this is a documented livestock toxicity risk, not a theoretical one. Both prussic acid and nitrates can reach toxic levels under drought or heavy nitrogen. This crop requires warm soil (65°F minimum) and cannot survive frost; it is strictly a summer annual in all zones. Terminating and managing the heavy biomass requires equipment capable of handling 6–12 foot material. And it is strictly allelopathic—allow full residue decomposition before planting small-seeded crops directly into the soil.
How to Plant Sorghum-Sudangrass
Site Prep
Sorghum-sudangrass will grow in most soils, but a firm, weed-free seedbed gives you the best stand. If following a spring harvest crop, mow or disc residue first, then wait for soil temperature to hit 65°F at 2-inch depth. Light tillage or a field cultivator pass is enough to prepare a seedbed. No special amendments are needed unless your soil is severely acidic (below pH 5.5) or deficient in basic nutrients.
Seeding
Drill at 25–40 lbs/acre at 0.5–1 inch depth for best results. Broadcast at 40–60 lbs/acre followed by a drag or cultipacker pass to improve seed-to-soil contact. Germination happens in 5–7 days when soil is warm. Do not plant when soil is below 65°F—germination will be erratic and the stand will be thin. Planting window is late May through early July for most of the continental U.S.
Establishment
Once germinated, sorghum-sudangrass establishes rapidly with minimal intervention. It will out-compete most summer weeds by canopy closure within 3–4 weeks of emergence. Moisture is critical in the first 10–14 days; after that the crop is drought-tolerant. If targeting maximum biomass, apply 50–80 lbs/acre of available N at planting or as a side-dress. The crop does not require irrigation in most regions but will respond to supplemental water during dry spells.
Termination / Management
Terminate before the crop reaches the boot stage if you need finer residue that breaks down faster. Let it reach 6+ feet for maximum biomass and weed suppression residue. Mow and incorporate, or roll-crimp for no-till systems. Do not graze until plants exceed 18 inches, and never graze drought-stressed growth. After a frost kill or once drought stress is relieved, wait 7–10 days before grazing to allow prussic acid to dissipate; note that nitrates can also accumulate under drought or heavy nitrogen and do not dissipate in cured hay. Allow 3+ weeks of residue breakdown before planting small-seeded crops into the terminated field.
Helpful Resources
Cover Crop Planting Guide
Questions & Answers
What is the best soil temperature for planting sorghum-sudangrass?
65°F at 2-inch depth is the minimum you should plant into. Below that threshold, germination is erratic, seedling emergence is slow, and you risk a patchy stand that never catches up. In most of the U.S., you reach that temperature in late May to early June in northern zones (5–6) and late April to May in southern zones (7–11). Use a soil thermometer rather than guessing by calendar date—air temperature fluctuates too much to be reliable. A few extra days of patience waiting for warm soil is worth it for a strong, uniform stand.
Is sorghum-sudangrass safe to graze with livestock?
It can be grazed safely, but only under specific conditions. Never graze plants under 18 inches tall—young sorghum-family plants contain dhurrin, which converts to prussic acid (hydrogen cyanide) under stress. Do not graze drought-stressed plants either; wait 7–10 days after drought stress is relieved, and the same 7–10 days after a killing frost. Prussic acid poisoning in cattle and sheep is a documented risk, not theoretical. Sorghum-sudangrass can also accumulate toxic NITRATES under drought or heavy nitrogen fertilization—a separate hazard from prussic acid. Most prussic acid dissipates as hay cures, but nitrates do NOT break down in hay, so hay from drought-stressed or heavily fertilized stands should be nitrate-tested before feeding. When managed correctly it is productive summer forage; when grazed or fed recklessly it is dangerous.
How much biomass will sorghum-sudangrass actually produce?
Under good summer conditions—adequate moisture, warm temperatures, and 50+ lbs of available nitrogen—expect 4–8 tons of dry matter per acre in a single season. The lower end of that range is typical in drier conditions or on nutrient-depleted soils without supplemental nitrogen. The upper end is achievable with irrigation and good soil fertility. That biomass, when incorporated, translates to meaningful organic matter improvement over multiple seasons. For comparison, a typical legume cover crop might produce 1–3 tons of dry matter in the same window.
How does sorghum-sudangrass break up compaction?
The fibrous root system generates significant mechanical pressure as it grows, physically penetrating compacted soil layers. Unlike a single taproot, the dense network of fine and coarse roots creates thousands of micro-channels through hardpan layers up to 3 feet deep. When the crop is terminated and roots decompose, those channels remain as biopores that improve drainage, reduce bulk density, and allow subsequent crop roots to penetrate soil that was previously impenetrable. Results vary by the severity of compaction and soil type, but measurable improvements in soil bulk density have been documented in university extension research after a single sorghum-sudangrass cover crop season.
Can I plant sorghum-sudangrass in Zone 5?
Yes, as a summer annual. You will not get a full 90-day season in Zone 5—your window from 65°F soil to first frost may only be 70–80 days depending on the year. Plant as early as the soil allows (typically late May to early June), and you will still get substantial biomass and root development before frost kills the crop. The crop cannot overwinter anywhere in the continental U.S. It is frost-killed at first hard freeze. In Zone 5, focus on biomass and compaction goals; you may not reach the 8-ton upper end of the yield range due to the shortened season.
How do I terminate sorghum-sudangrass for a fall cash crop?
The most common termination methods are mowing and incorporation, rolling with a crimper for no-till systems, or herbicide application. For no-till planting into heavy residue, roll-crimp at the boot to soft dough stage for best mat formation. If incorporating with tillage, plan for the sheer volume of material—a 6–12 foot crop creates a heavy load for any tillage implement. Allow at least 3 weeks of decomposition time before planting small-seeded crops directly into the residue, and longer if soil temperatures are cool. The allelopathic compounds in the decomposing residue can inhibit germination of small seeds; transplants are less affected than direct-seeded crops.
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