Which Cover Crops Should I Plant?

Ever struggled with decision paralysis? Maybe while choosing an entrée at a restaurant, or selecting traits for your cash crop. We live in a world filled with options, and cover crops are no exception. With over 100 species to choose from, how do you make the right decision? Your planting window, location, and rainfall will help narrow your options, but you still need to decide which species or mix to use. These guidelines will help you navigate the choices and create a plan that achieves your goals.

The Decision Framework

Selecting the right cover crops involves three key considerations: your goals, the seasonality of different species, and strategic diversity. By working through each of these factors, you'll be able to confidently choose species that fit your operation.

Step 1: Define Your Goals

First, you need to consider your goals. You might have lots of goals for your cover crop. In fact, you may be looking for a silver bullet that will solve all the problems with your soil. Instead, choose your top two or three goals and start to make decisions based on those criteria. Focusing on two or three makes the decision-making process much easier and streamlines your thoughts and motives for the cover crop. Here are common cover crop goals to consider. Mixing cover crops can help you achieve multiple goals, but remember there is no such thing as a silver bullet.

• Increase Soil Organic Matter
• Erosion Reduction
• Nutrient Cycling
• Nitrogen Fixation
• Provide Lasting Residue
• Weed Suppression
• Compaction Breaking
• Supplemental Grazing
• Diversify Introduced Perennial Pasture
• Attract Beneficial Insects
• Salinity Tolerance
• Mycorrhizal Fungi Growth
• Nematode Control
• Winter Stockpiling
• Interseed into Corn (V3-V6)
• Introduce Annuals into Warm Season Perennial Pasture
• Introduce Annuals into Cool Season Perennial Pasture
• Grazing with Regrowth
• Establish New Introduced Perennial Pasture

Goals should be SMART, an acronym standing for Specific, Measurable, Attainable, Relevant, and Timely. For example, instead of "improve soil health," try "reduce soil compaction in Field 5 by planting daikon radish this fall, measured by penetrometer readings next spring."

• Specific: clearly define what you want to achieve
• Measurable: track progress with quantifiable criteria
• Attainable: set realistic and achievable objectives
• Relevant: align goals with your broader priorities
• Timely: establish a deadline to create urgency

Step 2: Understand Seasonality—Warm Season vs. Cool Season

Plants can be split into two categories based on when they grow best:

Warm Season Plants (C4 Species)

Warm season plants such as sorghum-sudangrass, millet, cowpeas, and sunflower require soil temperatures of 55°F or higher and will die in the first frost. These plants are also known as C4 plants, which means they are highly efficient at growing in hot conditions. These are ideal plants to use in summer cover crop mixes.

Cool Season Plants (C3 Species)

Cool season plants can germinate at much lower temperatures and they have varying cold tolerances. The cool season grass cereal rye, for example, will continue to photosynthesize at 38°F. God designed these plants to thrive in cool conditions, making spring and fall their optimal growing seasons. They can also succeed in summer mixes where warm season plants provide shade and cooler microclimates. This diversity creates synergy that benefits all species.

Step 3: Add Strategic Diversity

Adding diversity is one of the six soil health principles, but it's important to do so with intention. Don't just throw out 20 different species without purpose to see what will grow. You don't want to spend money on seed that won't germinate, and you don't want to plant anything that could cause issues down the road. Focus on at least 4-6 different species and add as much diversity in plant families as possible.

Each plant species belongs to a certain plant family. These plant families associate with different soil microbes such as fungi and bacteria. Increasing the diversity of plant families in a mix will greatly increase the diversity of soil life. Different plant families also develop different root structures, have different growth patterns, and access different micronutrients from the soil. Targeting at least 4-6 plant families in a cover crop mix will increase biological activity in the soil. A mix with 7 or more families will be highly effective at building and healing the soil.

The Legume Family (Fabaceae)

Key Features: nitrogen fixers, protein rich forage, great for wildlife and livestock, support soil biology, fuel for microbes and mycorrhizae.

Examples: clovers, vetch, peas, cowpeas, etc.

The Grass Family (Poaceae)

Key Features: biomass builders, tons of biomass above and below ground, fine root structure improves soil structure and reduces erosion, scavenges nutrients (especially nitrogen).

Examples: ryegrass, oats, sorghum, teff, millet

The Brassica Family (Brassicaceae)

Key Features: deep rooted taproot to break compaction and bring nutrients to the surface, fast growing, great for quick cover and weed suppression, great forage for grazing, 2-4lb/ac is plenty.

Examples: radish, mustard, turnip, collards

The Broadleaves (represent lots of different plant families)

Key Features: increase diversity, nutrient cycling, great for pollinators.

Examples: sunflower, buckwheat, flax, phacelia

Pro Tip: Working With Weeds

Many common weeds share the same family as certain cover crop species. This information can be helpful when formulating a cover crop mix for your operation. If you struggle with certain weeds in a particular area, that weed is likely contributing an important function to that soil. If you can replace that weed's function with a desirable cover crop, you can provide the soil ecosystem what it needs while also alleviating weed pressure from your crops.

Common Mistakes to Avoid

• Planting too late: Cool season species need time to establish before winter; warm season species need adequate growing season.
• Too much nitrogen fixation: Excessive legumes can lead to nitrogen overload and this imbalance can cause soil health issues.
• Ignoring termination timing: Plan ahead for how and when you'll terminate your cover crops.
• Poor seed-to-soil contact: Cover crops need good contact with soil for germination; don't just broadcast on hard ground.

Putting It All Together

Choosing your cover crop species all boils down to context. What are your growing conditions? What are your goals? When are you planting the cover crop? When would you like it to terminate? When you've evaluated your context, you can start to lay out a plan for your cover crop and narrow down the options you have.

Here's a Simple Decision Process:

1. Identify your planting window. (determines warm vs. cool season)
2. Select your top 2-3 goals.
3. Choose 4-6 species from different plant families that match your goals and season.
4. Plan your termination method and timing.

Over time you will likely find certain species that you really like and will be consistently in your lineup. You might also plant some species that you decide you don't want to try again. Learning what works in your specific context is part of the journey of building soil health and becoming a better steward of the land entrusted to you.