Cover Cropping | Part 3
Part 1 | Part 2 | Part 3
Timing
The National Resource Conservation Service (NRCS) has established four fundamental principles that lead to healthy soil. These are:
Keep the soil covered as much as possible.
Keep living roots growing throughout the year.
Manage more by distributing soil less.
Diversify soil biota with plant diversity.
Cover crops can play a big role in supporting these guiding principles of soil management and successfully integrating cover crops into your gardening or farming system means thinking through three main elements: type, timing and techniques. I previously covered the types of cover crops and now it’s time to focus on timing.
Timing is one aspect of cover cropping that you can’t overlook, or things can definitely go awry. Anyone who has sown a popular rye-vetch cover crop mix in the fall and forgotten about it until May knows what I’m talking about. Just about the time the weather is pleasant enough to go transplant your tomato starts, your rye is about eight feet tall and the vetch is a big, tangled jumble of viny flowers with fat bumblebees hanging off them. How’s a gardener supposed to plant tomatoes in that?
With respect to cover cropping, there are two parts to getting the timing right.
First, you need to think about how cover crops will fit into the larger system or plan of your growing system. This means getting very clear about what you’re trying to accomplish. If you’re not sure exactly how you want or need to include cover crops in your garden, then read my previous post on types of cover crops. Also, review the four basic principles to soil health I listed above. Which of these four presents the biggest challenge to your garden aspirations?
Are there times of year your soil sits bare? Or have you grown tomatoes in the same spot for four years running and you are worried that pest or disease issues are catching up with you? Maybe you like to plant a fall/winter garden and you don’t like having muddy, compacted pathways between your rows of kale? These are just ideas to help you narrow down what you are trying to accomplish by using cover crops.
Once you have figured out specifically how you want to use cover crops, that will naturally determine the windows of time you will need those crops to be sown, established and turned under, mowed, or mulched.
Generally speaking, this window of time means establishing: when to plant (what time of year- spring? Summer? Fall? Winter?) and for how long you need cover crops to be in place (Just a month or two? From late September to May? All year round? Or maybe even, as we do, multiple years to help the soil biota rest and restore from annual vegetable production).
Getting this piece figured out is like setting the cornerstones of your cover crop foundation plan. For example, if your goal is to grow a cover crop over the winter to protect the soil in your raised beds, then you need to think through what that specific period of time looks like. For instance, if your raised beds currently sit bare all winter, then your next step is to look at your garden plan and determine when the last harvest of crops are. Do you keep your tomato plants in your raised beds crossing your fingers those last green fruits will ripen before a late October frost kills them? Or do you only grow determinate tomatoes that set their fruit in early September after which time you promptly composted your plants by mid-September? And on the flip side, are you planning to transplant lettuce starts in that raised bed the middle of May next spring? Or do you wait until mid-June to direct seed carrots? Knowing where you’ve come from and where you’re headed will help create the framework into which your cover crops need to fit. Does your current gardening plan mean you need a winter cover crop from October to June or late August to March or ?
And this leads to the second piece: the intrinsic needs of the crops you choose. Just like squash, melons, and beans grow best at certain times of year, cover crops likewise have seasons. Some are perennials, some are annuals. Some like to be seeded in and grow best in cool weather, others need more growing degree days (heat) to thrive. Some grow fast and some take most of a year to become well established. You need to align the time period you have available with cover crops that fit that window nicely. Otherwise… we’re back to 8 ft tall rye and mega vetch.
With respect to timing, it helps to think broadly about cover crops in two distinct buckets:
Cool season grasses and broadleaf plants (usually planted in late summer/fall and grow well in cool weather, but some can be planted in early spring too)
Warm season grasses and broadleaf plants (usually planted in spring/summer and grow well in summer/fall)
As we discussed previously, within these categories are a whole host of plants with different superpowers. For instance, cool season broadleaf plants include red clovers that work with bacteria to fix nitrogen in the soil, but they also include mustards that can reduce nematode pressure and tillage radishes that can help with compaction. Thinking in terms of cool/warm season is helpful to make sure you are selecting crops that are naturally suited to grow at the time of year you intend to use them.
Here is a table I put together of cover crops that I use as a good reference guide when planning my cover crop rotations. Note: this is not a comprehensive list, but rather crops that I have ready access to in quantities I need to plant acres of cover crops. You home gardeners will have many additional choices because you don’t need 50 lb bags of seed. Again, refer to quality seed suppliers and regional land grand publications to learn more.
One thing to note about plant selection and timing. I like to reduce my risk of cover crop failure by making sure to use a diverse mix of cover crops. This is basically an insurance policy against uncertain weather patterns to make sure that no matter what I sow, something will establish and grow well. One example of this diversity is to utilize both grasses and broadleaf plants. Very common examples for our climate are oats and peas or winter wheat and clover. In addition, I also make sure to include multiple broadleaf varieties to ensure success. For instance, in my spring, short season cover crop mix, I include phacelia and buckwheat. These are both warm season broadleaf plants, but plants that have different rates of germination. That way, if we get hit with a late frost right after I’ve seeded my cover crop mix, maybe it kills off the buckwheat (3-5 days to germination) but it doesn’t hurt the phacelia (5-10 days to germination). Once again, functional diversity is a front and center in our strategic planning.
As I mentioned last week, cover crop planning is an iterative practice. Now that you have a clearer sense of the structure of cover crop timing, you can loop back and start to hone in on specific plant varieties that will be a good fit for these windows of opportunity to utilize cover crops in your system.
I encourage you to check out the very informative soil health guides from Organic Farming Research Foundation. I currently serve as a board member of OFRF because I believe so deeply in their mission. I’m really proud of the depth and quality of OFRF’s work to support organic farmers and gardeners too. Many of the practices I use came from information I learned via OFRF publications. Their research is available free of charge to us all, thanks to generous contributions from supporters like you and me. OFRF’s technical team has done an incredible job pulling together all the available research about specific organic farming practices into very concise, scientifically rigorous guides that are easy to read. This is no small feat.
Here’s a link where you can download OFRF’s guide to cover crop selection. Of specific interest is Table 1, which identifies specific soil health goals you want to achieve on the left column and then gives suggestions for crops that will help fulfill that need. Once you’ve identified a few potential crops, think about what time of year those potential contenders are naturally suited to growing (cool or warm season?). How does that align with when you need to have cover crops working in your garden?
Remember, timing is not just about when you plan to seed the cover crop, but also about how the life cycle of the cover crop fits into growing food for your table. Will your cover crops grow alongside your garden harvest (interplanting)? Or after the cover crop is finished growing (succession planting)?
Big ag uses the term ‘terminated’ when discussing the senescence / end of life cycle of the cover crops. I prefer the term harvested because it is less violent and more accurate to think of this phase not as an obliteration or vanishing of the cover crop but rather a transformation of energy from one form to another. The grower is actively determining how to maximize the benefit of her cover crops. This means proactively thinking through the end of life. Will the cover crop be turned under to feed the soil? Rolled and crimped to provide a mulch to plant through? Or mowed short and left living as a low growing ground cover?
Which leads me right into the upcoming discussion on cover cropping techniques. More accurately I could refer to this third leg of the cover crop planning as Tools and Techniques. Next, we’ll dive into the available options to sow, grow, and harvest your cover crops with minimal effort based on what methods and materials you have at hand. ~AJ
Fall Beauty at AJF | “Joe-Pye weed (Eutrochium spp.) are early fall blooming wildflowers that colonize roadside ditches in sunny, moist sites. These native perennial plants grow to 4 – 6 feet tall and bloom along with goldenrods (Solidago spp.), ironweeds (Vernonia fasciculata), and native grasses. The flowers are mildly fragrant and very attractive to butterflies and other beneficial insects.” ~Clemson University Fact Sheet
“Movements are born of critical connections rather than critical mass.”