Now that the rainy days of May are gone, and the humid, dusty days of June are here, it is really feeling like Summer. Despite the May 14th hail damage, it doesn’t appear that our tomatoes will be late. We think perhaps our switch to Vermont Compost potting soil might even be pushing them a little early. We start our earliest tomatoes in mid-February, so we don’t ever get fruit until July, and we’re not expecting any until then. But some of the cherry tomatoes have some full-size green fruit on them, so we’d better keep our eye out for color while we’re stringing them up.
[Follow-up to Growing cover crops as if they are cash crops] Now that we’ve tilled in that buckwheat and planted radishes, turnips, bok choi, arugula, and other mustard greens there, we can give you an update on the experience. The buckwheat worked well–we mowed it at the right time, just as it was flowering but before it set seed, and I used the discs on the same day, which helped break up the roots and cover up the mowed buckwheat to speed decomposition. Our discs are a little wimpy (but we got them for free–thanks Janet and Rob!) so I was worried they wouldn’t tear up the roots, but the soil looked fluffy and loose and the buckwheat was totally dead when I was finished. Then we waited a week and I disked again, and then a week later I rototilled for a nice flat seed bed, as we were direct seeding, not transplanting. There were some buckwheat stems still visible in the soil, but they didn’t slow down the precision seeder. The seeding was quick and easy.
That’s the good news. The medium news is that the sorghum-sudan grass is a little out of control. Seeding it in a mix with buckwheat worked well; we mowed the patch when the buckwheat started to flower and the sudan grass was still little. Well, at least we mowed where we could. The patch neighbours a melon planting whose vines had spilled over into the cover cropped area, so there was nothing we could do without damaging our melons. (Note to selves: plant sprawly viney things next to things that don’t need to be mowed!) So now we have tall woody grass that is trying to flower, which is bad–we don’t need another weed in the fields–so this week Heather went through and cut off the flower heads by hand. We will still have to deal with all of the slow-to-break-down plant material come fall, but luckily we tried sorghum-sudan grass in a non-crucial area of our fields, so (hopefully) it won’t slow us down too much next year. (Thanks to Michael and Arden of Great Day Gardens for the sudan grass seed–we promise we will try it again!)
And then there is the bad news: the area that didn’t get a cover crop at all, and, predictably, grew up in weeds. Just as predictably, that field looked really trashy even after I chisel plowed (that’s a deep plow that breaks up roots and compaction without turning over the soil) and disced twice. The weeds had grown tall and deep-rooted, and then they flowered, so their carbon-to-nitrogen ratio changed to favor more carbon, which doesn’t break down quickly. So we’ll most likely be kicking ourselves when we transplant kohlrabi into that bed in a couple weeks because we’ll have to move aside plant residues to get to actual soil.
So while we feel like we did a better job this year than last, this mixed bag of experiences serves to motivate us to continue to try to improve our crop succession planning for next year. We clearly still have a lot to learn.
We are making a concerted effort to grow more cover crops this year. Cover crops differ from our normal cash crops because we turn them back into the soil, rather than harvesting them for market. After attending the Pennsylvania Association of Sustainable Agriculture (PASA) meeting this winter, we came away with the message, “Treat your cover crops like cash crops,” which has helped us adjust our mindset and actually plan them into our crop rotations. Still, you might be wondering why we would bother growing something we can’t sell.
In the photo, you can see the first summer squash planting on the left, and a field of buckwheat, a quick summer cover crop, on the right. The buckwheat is growing where the strawberries and spinach grew in the spring. In the fall, we plan to plant radishes and turnips in this field. But between strawberries, which finish in early June, and turnips/radishes, which will go in early August, what is to be done with this field? We could totally ignore it, and it would grow up in weeds, which wouldn’t be the worst thing (I’ll explain why in a minute). We could till it every week or so, so that it remains more or less bare soil for two months. Or we could plant a cover crop that fits our time window of about two months.
Tilling frequently to control weeds may be appealing, but it is terrible for soil health. Healthy soil is alive with microbes and fungi, and it has a structure that allows it to hold water and provide a home for all the critters (insects, worms, microbes) that live in it. When we till, we disrupt the ecology of the soil. I attended a talk given by a soil scientist who said, “Bare soil is soil in agony,” meaning that all the underground life dies as it is exposed to the sun after tillage. Of course, soil that is healthy with a diverse ecology to begin with is quite resilient, especially in the summer months. Critters will recolonize quickly if the soil is left to rest after tilling, especially if there is fresh organic matter from a cover crop incorporated into the top layers of the soil.
Another soil scientist who gave a talk that I attended this spring at PASA said, “Grow a root 24/7,” and gave a cool demonstration to illustrate why. He had in a suitcase two dense clumps of grass that he had pulled up from somewhere. One was totally brown and dead and the other had only been pulled out a few days ago, badly wilted, but still mostly green and alive. When volunteers from the audience swished the clumps of grass in a plastic tub with a little water in it, an interesting thing happened. The water from the dead grass just looked like muddy water, but the muddy water from the living grass had a frothy white scum on the surface after about ten seconds of swishing. “What is this stuff?” he said, and I had no idea, but someone from the audience answered, “Exudates.” “Right,” he said, “Roots exude a sugary liquid that feeds the soil.” Normally we think of the purpose of a root as sucking nutrients from the soil to feed the plant, but in fact it is a two way street. Root exudates feed the microbes in the soil. This blows my mind every time I think about it, and leads to the answer of why a field grown up in weeds is not the worst thing. The roots of those weeds are feeding the soil by exuding sugars, organic acids, and other nutrients. Then, we till them under, the soil microbes break down the organic matter and voila! We have a nice healthy soil to plant into.
We like to think of cover crops as the best possible weeds. They break down quickly when you mow and till them at the right time, and they can have other benefits as well. Clovers (there are two side-by-side in the photo above) and other legumes “fix” nitrogen in the soil so that other plants can access it, and they are usually the best choice for farmers who want to graze animals on their cover crops. Sorghum-sudan grass and daikon radish have deep roots that can loosen the subsoil and bring up nutrients from down deep. Buckwheat and rye can suppress the germination of many species of weed seeds.
In nature, you rarely see one species growing by itself; they are almost always mixed in what ecologists call communities. Communities have synergistic properties that make them more resilient than the sum of their parts, so it might be reasonable to think that farmers could replicate some of these effects by combining cover crop species. This is another reason why letting a fallow field grow up in “weeds” is not the worst thing in the world. We don’t begin to understand everything that is going on, but that doesn’t stop us from trying. For example, in one field this year, we combined buckwheat and sorghum-sudan grass (it looks like corn in the photo); the buckwheat germinates quickly and facilitates the establishment of the slower-growing sudan grass. And earlier this spring, we tried oats and peas sown together as a cover crop, which also seemed to work well. We’re far from being cover crop experts, but we do see how cover crops are a powerful tool for the ecologically minded farmer, and we’re looking forward to learning more about them.