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Diverse Yet Smart Cover Crop and Forage Mixes: 4 Rules for Perfect Pairings

When you make a mix or interseed one crop in another for a “relay effect”, you’re looking for the most bang for your diversity buck. Taking care to mix a few carefully selected species that are well matched always trumps throwing together a hodgepodge of random selections. The species you choose will depend heavily on your goals for the crop and whether you plan to seed all the species together or at staggered times (i.e. interseeding).

Ray’s Crazy Fall Mix in North Carolina, one of King's Agriseeds' newer and more popular mixes where diversity performs
Ray’s Crazy Fall Mix in North Carolina, one of King’s Agriseeds’ newer and more popular mixes where diversity performs

King’s AgriSeeds and Southeast AgriSeeds continually look for ways to make better mixes. Combining products for unusual applications have given us invaluable information that we use for both the commercial mixes that we have available and the carefully formulated custom mixes we make on demand. Here are a few lessons learned over the years”

  1. Mixing annuals and perennials can be done, but use caution when mixing two species with different growth speeds (and in some cases, similar growth speeds too). You probably know that annuals grow faster than perennials, since they accomplish all their vegetative and reproductive growth in one season. Taking advantage of that quality can make good sense, for example, by growing oats or another small grain as a nurse crop for alfalfa.

Interseeding a fall cover crop in standing corn planted in 30-inch rows is another case where these lines are blurred and you can use crop differences to your advantage. This works perfectly since slower-growing crops like perennial clovers and winter annuals are used so they can begin growing without offering too much competition to the corn. The corn is usually unharmed by this form of competition, precisely because it grows so rapidly in the summer heat and dry spells while the cover crops hang back and wait for the corn to come off and for the arrival of cooler, wetter weather. Broadcaster Mix has proved to be a perfect fit for this scenario; its mix of clovers, annual ryegrass, and Daikon radish each contribute to soil health and start off slowly in the heat of summer

However, planting clovers or another perennial crop in combination with a heat-loving summer grass like millet or sorghum-sudan makes little sense, because these grasses are usually planted in 7 inch rows and would quickly smother the perennial. Plus, their multiple harvests would likely do damage to the intended relay perennial crop.

Likewise, interseeding a crop with TOO similar a lifecycle to corn can present too much competition, such as seeding summer annual Ray’s Crazy Mix into corn. Both crops will grow rapidly in the summer heat and compete heavily for moisture and nutrients.

  1. Know how each species grows and adjust for differences with the right seeding rates. Whether your mix will be for a cover crop or a forage, every component  will grow a little differently and have different demands. Account for differences in competitiveness and growth habit. Brassicas grow outward in an aggressive, leafy pattern and need to be kept to a low seeding rate in a mix, while many grasses generally grow upward, confined to a small area around their original seeding spot. Combining varying heights and structural growth is a great way to maximize the benefits from diversity, but it also has to be planned in such a way that each species has space and ability to express itself.
A custom summer pollinator mix made to attract beneficial insects and pollinators in time for late summer pumpkin bloom.
A custom summer pollinator mix made to attract beneficial insects and pollinators in time for late summer pumpkin bloom.

It may seem obvious, but seed size also has a big impact on the final mix. Smaller seeds mean more seeds per pound, and a lower seeding rate is needed for those species to be expressed in the mix as much as a larger-seeded crop.  Plus, if everything is planted together from the large box of the drill, you have to be able to plant at a seeding depth that will be acceptable for all the seed sizes in the mix. If you can’t, you may have to seed smaller-seeded products separately from the small box. (If very small seeded species are planted at the depth needed by larger seeds, they will have poor emergence and there is little point in including them.) For this reason and the limited early vigor of very small-seeded plants, teff is difficult to fit well in a mix because its seed size is so much smaller than most other species.

Think about the most competitive species in the mix. Limiting its seeding rate should be your priority. This could be your oats nurse crop, since oats grow faster than alfalfa and could be overly competitive if the rate is not kept low (about one bu/A, depending on location). It could be a tall species like sunflowers or sunn hemp with more nutrient and water demands, and perhaps some shading. Or it could be a very leafy crop like brassicas, buckwheat or sunflowers that will physically shade out plants in its vicinity that grow the same speed or a little slower. Competition takes the form of both growth to fill physical space and the more subtle “hogging” of water and soil resources.

Some species are more easily outcompeted, while vining crops like cowpeas and hairy vetch adapt and climb other species to find the sun. Balancing these two types will be very important.

  1. Make sure every species is being used in the correct growth window. You may have two components that can be classified in different seasonal windows yet still overlap, which is fine. Back to the interseeding example, many fall cover crop species are pushed up to fit this June planting date because of the circumstances – they are suppressed a bit, growing in the shade of the corn canopy for most of these extra months until they can take off, and because of that slow initial growth, this doesn’t detract from their natural growth cycle.

Then there are other situations where certain components would be completely out of place. Using sorghum-sudan in a fall mix would be a waste, since it will kill off with the first frost (and be toxic to grazing animals at this point). However, summer annuals like this are sometimes used as nurse crops to keep weeds back in winter annuals that grow a little slower in the fall, but again, the rate would have to be kept low.

Most of the time, it’s not advisable to combine a summer annual with a winter annual, but cool season fall and spring crops like oats, spring small grains, spring peas, and brassicas can generally cross those lines more readily.

Clover is quite versatile and can be planted at almost any point throughout the year (including late winter frost-seeding), but most cool season perennial grasses and alfalfas must be planted in early spring or late summer for good success. It’s often not recommended to try to establish them in the heat of summer regardless of what you plant them with.

Again, nurse crops are common examples, but this is one of the few times you should consider planting an annual with a perennial. In many mixes, where these are combined at normal seeding rates (as opposed to the reduced nurse crop rate), perennials don’t have the early vigor to compete with an annual.

  1. Consider the lifecycle of each species in the mix and the method of harvesting or termination. Will they all reach maturity within the same time frame? You may not care as much if you plan to plow the mix under as a green manure, but if you plan to harvest for baleage, you want the correct maturity for every species, and the right moisture level in each species for ensiling. You also won’t want one species going to seed as you wait for the others catch up. If the crop will be grazed or hayed, will every species regrow? If not, you’ll have gaps after the first harvest where weeds can invade. If you want primarily a pollinator mix, you want each species to be able to reach bloom within your time constraints, and preferably for the blooms to be staggered enough to lengthen the total period of bloom and create a “relay bloom effect”.




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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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