When to Cut Sorghum-Sudan Grass for Hay: 4 Reliable Signals

Sorghum-sudan grass produces the best hay when cut at the boot stage or before it reaches 40 inches tall. This guide covers cutting timing, prussic acid risk, drying methods, stubble height, and regrowth rules. I walk through the field signs I watch for on my own Kansas farm each summer.

Cut sorghum-sudan grass for hay when it reaches 30 to 40 inches tall or enters the boot stage, whichever comes first. Leave a 6-inch stubble to protect regrowth. Wait at least 7 days after a killing frost to avoid prussic acid poisoning.

What Is Sorghum-Sudan Grass?

Sorghum-sudan grass is a warm-season hybrid forage bred from grain sorghum and sudangrass. It grows fast in hot weather, handles drought better than corn, and delivers two to three cuttings per season. Farmers use it for hay, haylage, silage, and summer grazing.

The stems grow thick and the leaves stay broad. That combination gives high tonnage but slows drying compared to most grasses.

When to Cut Sorghum-Sudan Grass for Hay

The best cutting window falls between 30 and 40 inches of plant height, which matches the late boot stage. At this point, the plant holds peak protein and digestibility before the seed head pushes through.

Cut too early, and you lose tonnage. Cut too late, and the stems harden while crude protein drops. Forage data from Penn State Extension places protein near 12 to 15 percent at boot stage, then under 9 percent after full heading.

First Cutting Timing

The first cut usually comes 45 to 60 days after planting, depending on heat units. Watch the tallest stems, not the average canopy. Once those stems hit the boot stage, cutting time has arrived.

Follow-Up Cuttings

Regrowth reaches cutting height again in 30 to 45 days during hot weather. Leave 6 to 8 inches of stubble on every cut. The plant stores sugars in that base, and cutting lower slows regrowth sharply.

Time of Day to Cut

Cut in the late morning after the dew lifts. Afternoon sugars peak and leaf moisture drops. I avoid cutting late in the day because the windrow then sits wet through the cool night.

How to Judge the Right Cutting Stage

I check three field signs before I start the mower:

1. Plant height: 30 to 40 inches on the tallest stems.
2. Boot stage: the seed head swells inside the flag leaf but has not emerged.
3. Weather window: three clear days ahead with low humidity.

If heading has started, cut right away. Quality drops fast once pollen shows. For broader timing cues across forages and row crops, I walk through the signals I watch in my notes on knowing when to harvest crops.

How to Cut and Dry Sorghum-Sudan Hay

Thick stems hold water. The cutting and drying plan matters as much as the cutting date.

Step 1: Set the cutter height to 6 inches. Shorter stubble stresses the crown and delays regrowth.

Step 2: Use a mower-conditioner with rollers. Crimping cracks the stems so water leaves faster. Without conditioning, hay can take 5 to 7 days to dry. With it, 3 to 4 days is realistic.

Step 3: Lay wide windrows. A wide swath catches more sun across the full mat. I aim for windrows near 70 percent of the cutter width.

Step 4: Ted the hay within 24 hours. Spreading the mat evens moisture across thick and thin spots.

Step 5: Bale at 15 to 18 percent moisture. Large round bales need the lower end of that range. Small squares tolerate 18 percent. Above 20 percent, you risk mold and heating. My guide on post-harvest handling covers moisture targets in more detail.

Prussic Acid and Nitrate Safety

Sorghum-sudan grass contains prussic acid precursors. Young regrowth, frost-damaged plants, and drought-stressed stands carry the highest risk. Proper curing as dry hay reduces the hazard, but drought hay still needs testing for nitrates.

Follow these cutting rules:

• Do not cut or graze plants under 24 inches tall.
• Wait 7 to 10 days after a killing frost before cutting.
• Test drought-stressed hay for nitrates before feeding.

The USDA Agricultural Research Service and state extension labs provide nitrate and prussic acid testing guidance.

Common Mistakes to Avoid

• Cutting too short. Stubble under 6 inches starves the regrowth crown.
• Baling wet. Thick stems trap moisture and drive mold or bale heating.
• Skipping the conditioner. Uncrimped stems dry unevenly and bleach on top.
• Cutting right after frost. Prussic acid spikes for several days in damaged leaves.
• Waiting past heading. Protein drops and stems turn woody by mid-head.

Troubleshooting Slow-Drying Hay

If the windrow sits wet past day three, ted it again and widen the swath. Check stem moisture by twisting a handful. A wet twist that foams or drips means at least one more day in the sun.

Humidity above 70 percent stalls drying. I wait for a drier window rather than bale hot and hope. Hay stored above safe moisture can reach 150°F inside the bale and catch fire days later.

Storing Sorghum-Sudan Hay

Store bales off the ground and under cover when weather allows. Round bales shed rain better in end-to-end rows. Check core temperature for the first 10 days using a hay probe. For longer-term care, see my notes on crop storage methods.

FAQs about Cut Sorghum-Sudan Grass for Hay

Final Thoughts

Cutting sorghum-sudan grass at the right stage drives both quality and safety. I aim for 30 to 40 inches, boot stage, and a clear weather window ahead. I hold off after frost and test drought-stressed fields before feeding. With a sharp mower, a good conditioner, and patience on moisture, this forage cures into reliable hay season after season.