Talking yourself into sacrificing a cash crop for a cover crop is a hard thing to do on a small-scale operation where every square foot counts. When done well, cover crops can have multiple benefits like improved soil, fewer weeds, and reduced pest pressure. But there are risks with cover crops when they don’t germinate, grow, or terminate as planned. When done poorly, they can be more troublesome than they’re worth.
I’ll explain how we at Moonlighter Farm have had success with warm season, “quick-turn” cover cropping on a 1/3 acre plot in the Sonoran Desert. This process has worked for us for the past three summers, so hopefully, some of what we’ve learned will apply to you wherever you’re growing.
Prepping the soil for a quick-turn cover crop. When clearing, we just flail mow any crops still in the ground. In the first week of July, we power harrow in 5 cubic feet of composted pig manure per 50-foot by 30-inch bed, sourced from a local farmer. This is a good time to mix in any needed amendments so your soil will be topped-off for your first cash crop.
Our farm’s context: Moonlighter Farm is located in Tucson, Arizona, in hardiness zone 9b. We have thirty-two 50-foot by 30-inch beds with a sandy loam soil texture. Our primary irrigation source is drip irrigation with three drip lines per bed at 4-inch spacing on emitters. We grow all outdoors except for five beds in our greenhouse. Tucson’s summers average 105°F with sporadic monsoon rains giving about 2 inches of rain in each summer month (on a good year).
Why we do it: Tucson summers can be pretty miserable. All that heat is what spurred the idea for a “quick-turn” cover crop. It allows us to take a brief vacation during the farming high season, reducing market pressure for farmers in our area and reducing heat exhaustion for us. The cover crops also provide us with our own fertility and organic matter, which is useful because it has been a challenge to get good compost here in the desert.
Compost companies mostly use native landscape trimmings, which are high in salts, in their mixes. If I can take a vacation while building my soil, that’s a win-win.
As a small, intensive market farm, we grow four to five crops per bed per year. We focus mainly on salad greens and quick-maturing roots like radishes and scallions. This lack of crop diversity means we need to focus on reducing potential pest problems. Moonlighter is usually just an ocean of asteraceae and brassicas. Cover cropping the entire farm acts as a reset button for any pest build-up during our growing year from September through June.
A four-week-old cover crop.
Lastly, it’s quick. That heat and rain I mentioned really lend themselves to speeding up cover crop growth. On average, we can get a 5-foot tall, dense cover crop in four to five weeks, meaning there is reduced downtime and reduced risk for the entire process. As much as I’d like to take the entire summer off to camp and surf, it’s not financially worth it for the farm to spend three months out of production.
How we do it: I was taught to treat a cover crop like a cash crop in terms of care and attention, especially during establishment. That has served us well in getting a good stand of cover crops that does its job. We clear beds of previous crops by the end of June each year.
When clearing, we just flail mow any crops still in the ground. In the first week of July, we power harrow in 5 cubic feet of composted pig manure per bed, sourced from a local farmer. (My soil specialist recommended pig manure based on my soil tests, so use what’s best for your soil.) This is a good time to mix in any needed amendments so your soil will be topped-off for your first cash crop.
We then seed an eight-species mixture of pearl millet, sorghum sudangrass, cowpeas, lablab, hairy vetch, sunflower, sesbania, and sunn hemp. We inoculated seeds with the appropriate inoculum the first year and haven’t felt the need to inoculate again. This mixture helps build up as much soil carbon and microbe diversity as possible while also removing any brassicas from the field.
Seeds for the eight-species cover crop mix. If you want a diverse stand of cover crops, dial back the grasses to about 50 percent of the seed supplier’s lower recommended seeding rates to hit a better balance. Here’s how it pencils out for each 50-foot bed: millet = 0.6oz; sorghum = 1.0oz; cowpeas = 1.8oz; lablab = 0.7oz; vetch = 1.2oz; sunflower = 0.8oz; sesbania = 0.6oz; sunn hemp = 0.7oz.
If you want to focus more on alleviating soil compaction or attracting beneficial organisms to fight certain pests, you can easily tailor your cover crop mixture to fit your farm’s needs. For seed suppliers, Territorial Seed and Hancock Seed usually have a good selection of cover crops and bulk pricing.
We use the Jang JP1 seeder with the N-6 wheel set to ½ inch depth and geared at 5.5 inch spacing with the brush UP. We use the double-disk opener when seeding anything, but it is especially handy if there’s any debris left in the soil after the power harrow. We start with the lower recommended sowing rates from the seed companies and then reduce it to 75 percent since we’re mixing so many species.
Here’s how it pencils out for each 50-foot bed: millet = 0.6oz; sorghum = 1.0oz; cowpeas = 1.8oz; lablab = 0.7oz; vetch = 1.2oz; sunflower = 0.8oz; sesbania = 0.6oz; sunn hemp = 0.7oz. To get the desired coverage and seed output, we make four passes with the Jang on each bed. Sometimes these rates feel a bit high, but we’re more concerned about poor germination and less concerned about another $50 in seed cost. Operations growing on a larger scale or working with a heavier soil that doesn’t dry out as fast as mine may want to experiment with lower seeding rates.
As a side note, we’ve done a simple two-species cover crop mix of sorghum and cowpea. Here’s the lowdown on that: Jang N-6 wheel, ½ inch deep, brush DOWN, geared at 7-inch spacing and three passes per bed. This will give you 2oz/bed of sorghum and 3oz/bed of cowpea.
We overhead irrigate or rely on monsoon rains to keep the top inch of soil moist until the cover crop has emerged and put on a couple of leaves, at which point we switch to running only drip irrigation. In the past, we have used silage tarps with the white side up to help with germination, but it may not be worth the trouble of dragging out and pinning down tarps for just three or four days of use (these seeds pop fast). Then, we’re off to the races.
In about four weeks, our cover crop hits the sweet spot at 4 to 5 feet tall and is still fleshy and easy to mow. At this point, we remove drip irrigation and use our flail mower on our BCS to cut it to the ground. Once mowed, we power harrow everything 2-inches deep and put down silage tarps with the black side up for seven to ten days. We prefer the power harrow over a tiller because it is gentler on the soil biology we’ve built up. With our heat and the black tarp, we’ve never had a cover crop survive termination to give us any grief. This final tarping also gives us a stale seedbed to plant into with minimal weed pressure.
Flail mowing a three-week-old cover crop. Once mowed, we power harrow everything 2-inches deep and put down silage tarps with the black side up for seven to ten days. We prefer the power harrow over a tiller because it is gentler on the soil biology we’ve built up. All images courtesy of the author.
That’s it. From bed prep to cash crop it takes just five to seven weeks. This break in production pays for itself in multiple ways: all the cover crop benefits, a brief summer vacation, and reduced market competition with fellow farmers during a typically high season.
Troubleshooting: Don’t let it grow too big. One summer I tried a seven-week cover crop, which was a mistake. We ended up with 6- to 7-foot tall plants with giant, carbonaceous stalks that were very difficult to mow/terminate, and they tied up some nitrogen upon termination. It was cool (literally) to get cover crop mulch for the bed surfaces.
7-feet tall, 7-week old mixed-species cover crop in a hoophouse.
Still, the headache of mowing over each bed multiple times, the 14 day tarping that followed, and the nitrogen deficiencies made it more of a traditional cover crop method instead of a quick-turn cover crop. It was not worth the trouble for us.
Tarping a cover crop after mowing to ensure complete termination.
Don’t introduce weed seeds. Once we mistakenly used semi-composted horse manure as a soil amendment instead of fully composted manure. I still have nightmares about seeing the tiny Bermuda grass shoots coming up with the cover crop (wince). We were still able to let the cover crop get to 3 to 4 feet tall and terminate.
Luckily, the combination of terminating everything before the Bermuda started forming thick rhizomes and the stale seedbed method was enough to kill most of the Bermuda plants and seed. A bit of extra weeding the following year kept us from having any major weed issues.
Limit grass-type cover crop species. My sorghum and millet seeding rates are a bit lower than the other cover crop species because these grasses can easily outcompete the other species. If you seed them at equivalent rates as other, less vigorous cover crops, you’ll end up with a bed of only grasses with maybe a few token sunflowers and vetch on the outer edges of each bed.
How it looks after a cover crop is mowed and power harrowed. Blue survey whiskers are nailed into the ground at the corner of each bed- they can be mown over with the flail mower, which is nice.
If you’re just going for biomass, this would be fine. If you want a diverse stand of cover crops, dial back the grasses to about 50 percent of the seed supplier’s lower recommended seeding rates to hit a better balance.
Conclusion: The first two cash crops that followed our cover crops were spectacular. We saw very little pest pressure, our sandy soil held moisture and nutrients well from the added organic matter, and there were practically no weeds for those first couple of months. Granted, there are other factors at play — there aren’t many noxious weed seeds blowing around in the desert and the composted pig manure can be credited for some of the excellent yields. Still, I truly believe that the quick-turn summer cover crop method can be given the lion’s share of the credit. That’s why this is a practice we’ll continue using every year to support our intensive system.
Tommie Burch is the Owner/Operator of Moonlighter Farm. He does small-scale farm consulting as well as traveling ‘farm-sitting’. Due to family troubles, Moonlighter Farm is for sale at the time of this publication. Feel free to contact Tommie at [email protected] (Instagram @moonlighterfarm).
