Sudangrass Cover Crops: Growing Sorghum Sudangrass In Gardens

Sudangrass Cover Crops: Growing Sorghum Sudangrass In Gardens

By: Bonnie L. Grant, Certified Urban Agriculturist

Cover crops like sorghum sudangrass are useful in the garden. They can suppress weeds, thrive in drought, and may be utilized as hay and forage. What is sudangrass, though? It is a fast-growing cover crop that has a broad root system and can grow in many areas. This makes the plant excellent at rejuvenating areas that have been over-cropped and compacted or low in nutrients. Learn how to grow sudangrass and take advantage of all its many benefits along with its ease of care.

What is Sudangrass?

Sudangrass (Sorghum bicolor) may grow from 4 to 7 feet (1 to 2 m.) in height and is grown as pasture, green manure, hay, or silage. When it is hybridized with sorghum, the plants are slightly smaller and easier to manage with superior high heat tolerance. In addition, sorghum sudangrass care is minimal, as the seed needs little moisture to germinate and the seedlings thrive in heat and low water regions.

The biggest need for this versatile grass is at least 8 to 10 weeks of fine weather before harvest. Sorghum sudangrass has been shown to reduce weeds when planted thickly as well as suppress root nematodes. The plant has also been shown to be extremely efficient in water absorption with twice as many roots as corn but less leaf surface, which allows evaporation. It is also grown for its seed, as the grass is a prolific seeder, economically providing the next generation of the crop.

Good soil management ensures future crops, prevents erosion, and is part of the ecological wheel of sustainability. Sudangrass cover crops are an essential part of soil management in many areas of North America and are widely used as one of the highest yielding forages too.

How to Grow Sudangrass

The best soil for sudangrass is warm, well-tilled, moist, and clod free. Fertility is not the most important consideration, as this grass requires little nitrogen; however, in heavily used lands, additional nitrogen will enhance its growth.

Early seeding is important when growing sorghum sudangrass. Seed in warmer regions can be planted as early as February, but most of us must wait until the soil is evenly warmed to at least 60 degrees Fahrenheit (16 C.). A general rule of thumb is to seed July through August.

The correct timing of planting is important if harvesting the entire plant, such as in the case of sudangrass cover crops. Till young plants under only as older plants create clumps that can be difficult to break down. Crops that are mowed for hay can be cut at 4 to 7 inches (10 to 18 cm.) to allow for recovery and another harvest.

Management of Sorghum Sudangrass

This grass is one of the easier varieties to manage. Early mowing is crucial to sorghum sudangrass care that is being used as forage since older leaves have lower protein content and become fibrous, thus harder to digest.

The plant must be harvested at the vegetative stage, as it contains as much protein as mature alfalfa and can be harvested at least one more time, producing more usable product. Mow when plants are 20 to 30 inches (51 to 76 cm.) tall, leaving 6 inches (15 cm.) of stubble.

Once late summer approaches, the entire plants should be tilled under to decompose and a suitable winter crop sown. Sudangrass is useful as a summer cover crop where a long mid-summer period is available.

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Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

John A. Guretzky, Dep. of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915, Lincoln, NE 68583‐0915, USA.

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

John A. Guretzky, Dep. of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915, Lincoln, NE 68583‐0915, USA.

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

Department of Agronomy and Horticulture, Univ. of Nebraska‐Lincoln, 279 Plant Science, P.O. Box 830915

Reasons for Hot Weather Cover Crops

I can think of 5 big reasons to grow cover crops in your summer garden.

Reason 1: Vacation

I know so many gardeners who have left on vacation for a couple of weeks and come back to find their beautiful gardens devoured by insects and weeds. That’s because even if you only spend a few hours in the garden each week, you are constantly picking off pests, keeping up with the water, removing small weeds, and more to maintain your beds.

Without that routine care, weeds get big, water runs out, and pests move in to take advantage of stressed plants. Rather than letting your garden get overrun with problems, harvest what you can, pull up your more needy crops and start fast-growing cover crops. This will keep your soil in good condition even when you can’t care for it.

Most hot weather cover crops are fast germinating and require only a week or two of care to get started. So, plant 1 to 2 weeks before your scheduled vacation to make sure your cover crops take off and will work their magic while you are away.

Reason 2: Mid-Season Crop Failure

It happens to even the very best gardeners. You plant something, it grows for a while, then suddenly the plants die or disappear.

Pests get them. The plants become diseased. Your significant other mows over your winter squash with the riding mower or whatever else happens. So, then you’ve got this empty space in your garden.

If it’s early in the season you may just replant with more vegetables. But what if happens when you only have a 6-10 week window for growing before it’s time to plant fall crops?

You might not have sufficient time to get to harvest. So, rather than just leave that space open, this is a perfect time for cover crops to come to the rescue and save your soil from heat damage.

Reason 3: Increase Soil Fertility

You may also want to intentionally plant hot weather cover crops to increase your soil fertility ahead of your fall planting. There are various nitrogen adding legumes, such as cowpeas or bush green beans, that work well as a hot weather cover crop.

All you need to do is grow them using a legume inoculant until they begin to flower. Then you can mow them down and turn the soil lightly to expose the roots and dry them out.

While the plants decay, they will add nitrogen to the soil. Also, you can even plant new seeds as the legume residues decay.

Just push aside some of that plant matter and drop in your seeds. Then, as your seedlings emerge, side-dress those new plants with the decaying leaves as both a mulch and nitrogen source.

Reason 4: Scavenge Nutrients

Sometimes we blow it and over-fertilize our gardens. Maybe our math was wrong or we didn’t use this most awesome fertilizer calculator. Or maybe we used homemade amendments and overestimated the amount of nitrogen we’d need.

Excess nitrogen is a boon to some plants like corn or cabbage, but it can be detrimental to light feeders. So, for example, if you planned to put some beets in next and discovered you had too much nitrogen, you could plant a cover crop to draw out some of that nitrogen quickly before you start your beets.

Things in the grass family such as sudangrass-sorghum, or even extra corn seeds grown and mowed when they reach knee height, can draw out nitrogen in hot weather. Then, you can add that green matter to your compost pile using our compost calculator.

Reason 5: Compost Maker

One of the most famous organic gardeners, John Jeavons, author of How to Grow More Vegetables advocates devoting 60% of your garden beds to growing cover crops for compost. By doing this, you can grow a lot of green matter for your compost, manage minerals, and avoid having to buy as many external inputs to nourish your soil.

Even if you don’t dedicate that much space to making compost greens, growing cover crops in summer whenever you have an open space in the garden can increase your compost creation abilities while making sure you don’t leave extra nutrients in the ground to wash away every time it rains.

What is Soil Health – an interactive infographic

Soil health plays an essential role in raising healthy, productive crops and livestock. With this interactive infographic, learn how practices such as cover crops, no-till, crop rotation and the integration of livestock work in concert to improve soil health.

Product Description

Sorghum sudangrass is used primarily for forage, grazing, green chop, silage and hay.


Sorghum sudangrass is a cross between sorghum and sudangrass with a finer stem. It is a warm season annual grass and will regrow after each harvest. The maximum growth height is 15 feet tall and typically has small seed heads. The leaves are similar to corn like many sorghum varieties but are shorter and sometimes wider. There are approximately 21,000 seeds per pound.


Sorghum sudangrass is adapted throughout the United States and southern Canada. However, it performs best in moderate to well drained soils. This variety with grow best in soil with a pH between 5.5 and 7.5. Drought tolerance is high with the water requirement being approximately 1/3 less than corn.

Land Establishment

Planting rates vary from 20 – 40 lbs/per acre depending on whether the seed is broadcast or planted in rows. Seeding depth should be 1 inch. Planting usually occurs from May to July but can be earlier in the deep South with little chance of frost. Soil temperature needs to be a minimum of 60 degrees Fahrenheit for germination.

Perfect Management

For optimum forage production, moderate fertility is suggested although sorghum sudangrass will grow on lower fertility soils with better results than corn. Fertilize using soil test recommendations. If a soil test is not available, fertilize at similar rates to other annual grass crops.

If you would like graze sorghum sudangrass it should begin when the plants are between 18 to 30 inches tall and grazed down to 8 inches within 10 days. To ensure the highest quality forage after grazing, the residue needs to be clipped to a minimum uniform height of 8 inches. If this is done then the next grazing period could be in 3 to 4 weeks. If there is a killing frost do not graze for 7 days or until the plants turn completely brown. If there was early frost damaged, wait until the regrowth is at least 18 inches high before grazing again.

Green chop harvesting should begin when the sorghum sudangrass is 18 inches tall and should be completed before the plants begin to head out. If you are harvesting for silage it should be done when the plants are 36 to 48 inches tall or in the boot to early head stage. After harvesting at this stage, moisture is usually too high and the plants should be allowed to partially dry in the field before ensiling. Rapid, uniform drying is critical for sorghum sudangrass hay to prevent spoilage. For best results, delay feeding silage 6 to 8 weeks after ensiling to allow prussic acid to dissipate. Never feed sorghum sudangrass to horses.


When cover cropping for long periods of time, combine a small grain (think cereal ingredients like oats, barley, rye) and a legume (nitrogen-fixing plant like peas or vetch) for best results.

When cover cropping for shorter periods of time, consider green manure crops, or tender, quick-growing crops that will outcompete weeds and, when finished, will provide some easily-digested, supple foodstuff for the soil microorganisms. Examples include buckwheat and field peas.


This work was supported by the Nebraska Agricultural Experiment Station, the USDA National Institute of Food and Agriculture, Agriculture and Food Research Initiative Competitive Grants Program project 1009080, and the USDA National Institute of Food and Agriculture Hatch/Multistate NC1182 project 1005435. The USDA project 1009080 funded a 10‐week Undergraduate Research and Extension Experiential Learning Fellowship Program in Integrated Agronomic Systems, which supported the lead author's participation the Hatch/Multistate NC1182 project (1005435), with an objective focused on legume establishment, provided stipend assistance for this author while she developed the project into an M.S. degree in Agronomy at the University of Nebraska‐Lincoln.

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