Planting Cover Crop Seed

Methods and Best Practices

From sourcing seed to planting, many factors influence successful cover crop establishment. What do seeds need to germinate? The essentials are moisture, good seed-to-soil contact, appropriate planting depth, and suitable soil temperatures. Beyond these basics, your planting method, equipment settings, and timing all play crucial roles. Establishing a successful cover crop isn't just a matter of throwing seed out and hoping it grows. With proper planning, you can set yourself up for success.

Method 1: Direct Seeding

Direct seeding with a drill, air seeder, or planter ensures the best seed-to-soil contact, giving seeds access to moisture while protecting them during their first stages of life. These implements provide more control over seeding depth, row spacing, and seed placement.

Equipment Considerations

When seeding with a drill, make sure you have enough down pressure to match the texture of your soil. Proper down pressure ensures consistent seed placement and good soil contact across varying field conditions. Drills give you precise control over seeding depth and row spacing, making them ideal for diverse cover crop mixes.

Seeding Depth Considerations

Several variables influence the depth at which you should plant your cover crop seed. As a rule of thumb, smaller seeds need shallower planting depths as they have less stored energy to push through the soil, whereas larger-seeded species can be planted much deeper. But how do you decide planting depth for a diverse cover crop mix containing various seed sizes?

Most of our cover crop mixes work well at ¾-inch depth. The large-seeded species emerge first, creating pathways through the soil that small-seeded species can follow. These pathways reduce the energy required for small seeds to reach the surface, and the species work together in symbiotic relationships to achieve successful germination and growth. If the mix contains a large percentage of small-seeded species, consider planting slightly shallower.

Planting depth is also influenced by soil moisture and weather conditions. If your soil lacks moisture, planting seed deeper into the soil profile allows you to place seed where moisture remains. If you're expecting rainfall shortly after planting, you can place seed at a shallower depth.

Finally, consider the amount of residue on top of the soil because your seedlings will have to make their way through this layer as well. Heavy residue may require shallower planting to prevent seedlings from expending too much energy reaching sunlight.

Seeding Rate Guidelines

Seeding rate varies depending on the species you're planting. We discuss seeding rates in terms of pounds per acre, but it can be helpful to consider seeds per pound and then calculate plants per acre. This approach helps you understand the actual plant population you're establishing and adjust rates accordingly for your goals.

Calibrating Your Drill for Planting

There's nothing worse than getting almost done with the field and running out of seed. Luckily, there is a simple exercise that you can do in about 15 minutes to calibrate your drill and ensure proper seeding rate before planting the entire field.

Often we get asked about separating small seeds from larger seeds in mixes to plant them at a more species specific seeding rate and depth. We've found that a diverse mix of seeds works quite well planted together. The small seedlings follow the paths of the larger seedlings and they all work together, forming symbiotic relationships to achieve successful germination and growth.

Method 2: Broadcasting

Broadcasting is another option for establishing cover crop seed, but it requires particular conditions to be successful. This method works best when you have limited time, are planting into standing crops, or want to cover large acreages quickly.

When to Choose Broadcasting

Small-seeded species like brassicas or clovers are the most ideal candidates for broadcasting as they have a small surface area, making it easier to achieve optimal seed-to-soil contact. In addition, most cereals broadcast well, with the exception of oats and barley which have hulls that absorb moisture and delay germination.

Broadcasting Equipment and Methods

There are several methods for broadcasting seed:

• Aerial application: Using an airplane or drone to apply seed over large acreages or into standing crops.
• Ground equipment: Using a spreader or boom air machine for more precise application.
• Livestock distribution: Mixing seed into livestock minerals so they consume it, pass it through their rumen, and deposit it in their manure. Seed distributed this way receives moisture and beneficial microbial inoculation. However, seed distribution will be spotty and germination rates unpredictable, making this only cost-effective with inexpensive seed. Consider this a supplemental method for diverse pastures where perfect uniformity isn't critical.
• Frost seeding: Broadcast seed in late winter to utilize freeze-thaw soil cycles. As the soil freezes and thaws, it creates small openings that pull seed into contact with the soil. Timing is critical: seed when snow is still present or when daytime temperatures are just beginning to rise above freezing to catch the final freeze-thaw cycles before spring green-up. Small-seeded clovers and other legumes work best for this method.

Incorporating Broadcast Seed

Ideally, incorporate broadcast seed into the soil to ensure seed-to-soil contact. Incorporate seed into the top half-inch of soil while limiting disturbance to prevent excessive moisture loss and avoid planting seeds too deep. Methods for incorporation include light harrowing, chain dragging, or allowing livestock to trample the seed with their hooves. Note that frost seeding and livestock distribution methods incorporate seed naturally and don't require additional steps.

Success Factors for Broadcasting

Having success with broadcast seed depends greatly on rainfall timing. Ideally, you would receive not just one but several good rains shortly after broadcasting seed. If seed is broadcast and receives a single rain followed by warm or hot conditions, it will likely germinate and then die shortly after from moisture stress.

You will also want to consider the amount of residue on your soil, as heavy residue can inhibit germination of broadcast seed by preventing adequate seed-to-soil contact. Light to moderate residue is ideal—enough to protect soil moisture but not so much that it prevents seed from reaching the soil surface.

Troubleshooting: Why Isn't My Cover Crop Germinating?

Sometimes, despite our best efforts, seed simply does not emerge. When dealing with this situation, it's important to observe what's happening both above and below ground to understand why the seed may not have survived and how to avoid this situation in the future.

Ask yourself these diagnostic questions:

• Is there residual herbicide in the soil? Some herbicides can persist and damage emerging cover crops, especially sensitive species like brassicas and legumes.
• Is there optimal seed-to-soil contact? Dig up some seed and check if it's in contact with soil or suspended in residue or air pockets.
• Is there enough moisture? Seeds need consistent moisture to germinate and establish. A single rain may not be sufficient.
• Are rodents or birds eating your seed? Surface-sown seed is vulnerable to wildlife predation, especially sunflowers and larger seeds.
• Did the seed germinate but lack resources to continue? Sometimes seed will germinate but die shortly after due to drought stress, soil crusting, or depleted seed energy.
• Were soil temperatures appropriate? Warm season species need 55°F+ soil temps, while cool season species need cooler conditions.

Learning From Failure

Not every crop or cover crop is a huge success. While it's extremely difficult to experience a failure of this sort, it's usually these experiences that offer the most valuable learning opportunities. Observing and understanding poor germination is crucial to having success in the future. If you have a cover crop that doesn't germinate well, make notes, take pictures, and talk with others who have experience. These records will help you avoid similar problems and make better decisions going forward.

Remember, even the most experienced farmers have occasional establishment failures—what matters is learning from them and improving your practices.

Special Application: Corn Interseeding

Corn interseeding is a popular and highly debated practice. This method allows you to introduce diversity into your crop rotation during the growing season by seeding cover crops between corn rows, often with goals of fixing nitrogen or growing high-quality forage to be grazed after harvest. Context is important, as this method will look very different from farmer to farmer depending on available moisture, equipment, and goals.

There are two primary timing windows for interseeding into corn: the V3-V4 growth stage and the V5-V6 growth stage. You cannot plant too early because corn plants will not tolerate competition from other plants during early development. However, you also cannot wait too long, as the corn will eventually grow so rapidly that it canopies completely and blocks all available sunlight, preventing cover crop establishment.

The V3-V4 window offers more time for cover crop establishment but requires careful species selection to avoid competing with the corn. The V5-V6 window is safer for the corn but gives the cover crop less time to establish before canopy closure.