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The Summer Annual Manual

Summer annuals have unique benefits, like filling a small space in the rotation with multiple cuttings of big yields. They also bring some unique challenges and considerations. Here’s what you need to know.

Step 1 is waiting for warm soils.

These crops are adapted to hot climates and won’t germinate consistently until soil is at least 65 degrees F. For most of the Northeast, this is late May at the very earliest, though there can be great variation across years. Watch out for a false warm-up in May – seeds that are in the ground and tricked into germinating early can die off in the seedling stage.

Harvest summer annuals to optimize not only quality and yield, but also manageability.

Many of the most productive summer annuals are grasses – millets, sorghums, sorghum-sudans, sudangrasses, and teff. These grasses are staples in wet hay and grazing scenarios and play a starring role in most summer forage mixes, providing highly digestible fiber. However, remember that they are stars in yield because they grow several inches a day during the peak of summer. You should start harvesting most of these varieties between waist and chest height, or the growth may get ahead of you and become difficult to mow and dry. Grazing can usually start at knee height. If you start the grazing or cutting rotation soon enough, it won’t be too tall by the time you reach the end.

Dry hay is possible but the options are limited.


Teff is the best choice to dry for hay, but with good management, millet and sudangrass can work too, since they have the next thinnest stems. The more stemmy they become, the harder to dry, so cut millets and sudangrasses by waist height for dry hay. Millet is a little easier to dry than sudangrass, and dwarfs are easier still because they have a greater leaf-to-stem ratio. Sorghum-sudans have thicker stalks and hold moisture in their stalks, so they will typically not dry fast enough to make dry hay. Conditioning and tedding several times will be necessary to make dry hay out of these products. Wide-swathing (at least 80 percent of cutter bar width) is also highly recommended for rapid drying. Optimized rapid drying, especially in sunny weather, keeps sugars high in the plant, because the more it has time for respiration after cutting, the greater its loss of sugars and dry matter.

Dwarf varieties have many unexpected advantages.

Brachytic dwarf varieties may look smaller, but they compensate with leafiness – the most digestible part of the plant and also the easiest to dry. Dwarf millets and sudangrasses are especially great for grazing because they can be grazed down a little shorter while still maintaining the excellent regrowth that is characteristic of these crops. Dwarfs also have reduced risk of lodging.

Take advantage of the great strides that have been made in digestibility.

BMR, or brown midrib, is a non-GMO trait in sorghums and millets that started as a gene mutation and was incorporated and improved through generations of natural plant breeding. BMR millets have become especially popular in recent years, and even teff, which has not been developed as a BMR, is very high in fiber digestibility (about 8-10 points higher in TTNDFD, translating into 3 lbs of milk) and averages about 16 percent protein.

Decide if multicut is right for you.

Multicut or multigraze products include millets, sudangrass, sorghum-sudan, and teff. Whether you want to get all your tonnage at once or spread out the harvest over 2-3 cuttings over the course of the summer depends on your forage needs and equipment availability. There are some excellent single cut forage sorghum products out there, especially long season dwarfs. Earlier non-dwarf sorghums tend to have more issues with standability. Often, these products are used at a higher seeding rate for a boot stage cut and wilt harvest instead of direct cut soft-dough stage harvest. Forage sorghum planted for intended boot stage harvest is advantageous because this is the point in the plant’s growth that whole plant sugars are highest. After this point, the plant begins to send its resources into grain head production.

Understand what makes sorghum unique.

Unlike corn, sorghums have adapted to extremely hot and dry climates. They have the ability to shut down their growth when conditions get too dry or too cool (their best growing temperatures are 70 degrees F – 90 degrees F). This can throw off your harvest planning, since these delays can cause it to shift its typical maturity dates.

Spoon-feed fertility. 

Give it about 1 lb of N/A/day, at planting and after every cutting. The goal is to avoid putting down too much at once.

They are luxury N consumers.

Use caution during a rain following a drought period. Along with the extra moisture, the plants will pull up extra N, and can’t convert all this excess to protein right away, leaving you at risk of high nitrate content. Nitrates do not dissipate during ensiling if you cut too soon after this drought-ending rain, so wait at least a week.

Knowing seed size, planting depth and timing is critical.

This is important to seed germination and emergence. A small seed planted too deep is at risk of not emerging. Small seeds are frailer in terms of ability to absorb and retain moisture as well as in energy reserves to spring up out of the soil once they have germinated. With seeds the size of grains of table salt, teff is the smallest seeded summer annual and is very susceptible to being planted too deep (this is its Achilles heel and the major reason for teff complaints). It needs to be seeded just at surface level on very well packed soil – either with a Brillion seeder or broadcast and cultipacked into well-prepped soil. Sorghums and millets also need to be planted according to seed size and timed to get the seed into moisture at the depth it needs to be planted. Sorghum-sudans have an advantage here because they have larger seeds and can be planted 0.75 up to 1.5 inches deep. More caution is needed with the smaller seeded sudangrass, which can go in at 0.5 to 0.75 inches. Millet is the smallest of these, and should be planted ¼” to ½” deep. Because of its shallow depth requirement, millet is among the riskiest for late planting – as the summer progresses, the soil dries out from the surface down.

Most summer annuals prefer well drained soils.

If your soils are a little on the wetter side, millet or teff can handle these conditions the best.

For mechanical harvest, these products need to be crimped for better drying.

The stalks are thicker than traditional grasses and need to be crushed to aid in the drying process.

Higher stubble means faster regrowth.

Non-dwarf products have their growth point higher than most cool season grasses, so leave at least a 6-8 inch residual. This will ensure that plants regrow from the stalk as opposed to solely from tillers. Dwarfs can be taken down to about 4 inches.

Watch out for prussic acid.

As long as there is green tissue, sorghums, sorghum-sudans, and sudangrasses can accumulate prussic acid, or cyanide, with a killing frost. This is toxic to livestock and you should wait at least two weeks before grazing. If you’re mechanically harvesting it, two-three weeks before feeding should be enough time for it to dissipate during fermentation. Millet has no prussic acid danger.

Roundup Ready varieties might be a handy idea for the farmer, but they don’t exist here.

Sorghums would cross-pollinate with their wild relative, johnsongrass, spreading herbicide resistance to a weed – not good.

Start small on products you have not grown before, and understand that mastering summer annual management is a learning curve. Practice makes perfect!

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Genevieve Slocum
Genevieve Slocumhttp://www.kingsagriseeds.com
Genevieve provides forage and cover crop research and marketing support for King's AgriSeeds Inc. in Lancaster County, PA. She has also worked on organic vegetable farms and as an intern in agricultural field trials at the Rodale Institute.

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