Organic No-Till Farming: The 2 Most Infuriating Weeds

We’re beginning to see fantastic soil improvements from our multiple seasons of cover crops!  However, trying to plant and grow successions of cover crops without herbicides or tillage (called “organic no-till”) isn’t easy.  For a new cover crop to grow well and confer all its benefits to the soil, the existing mature cover crop needs to die.  Unfortunately, mow-killing doesn’t work perfectly.  We don’t have livestock or the impressive roller-crimper tractor implement, both of which are probably better at organically killing cover crops.  Moreover, mowing opens up sunlight that encourages “weeds” to germinate, further complicating our cover-cropping scheme.  This post discusses these weeds and our prevention plan…

The baseline comparison, what all our cover crop fields could look like. We planted this cover crop into rotovated soil (no weed competition). Oats are knee-high. 11/6/2012

These 2 Weeds Aggressively Block Cover Crop Seedlings

Okay!  The two worst “weeds” for us are crabgrass and annual ryegrass.  When we mowed our summer cover crop cocktail in late August, the clippings disappeared pretty quickly and crabgrass and annual ryegrass started taking off like crazy, especially in spots where the summer cover crop was thin.  Both of these weeds are very aggressive, and I wouldn’t be surprised if they “engineer” their soil environment in order to stunt other plants.  When we drilled the new winter cover crop seeds in mid-September, these two weeds kept the new cover crop from germinating.  It’s a frustrating waste of seed money, especially given how beneficial a good winter cover crop can be for the soil.  Annual ryegrass is a decent winter cover on its own, but the variety we have is VERY difficult to control in the spring.  Crabgrass isn’t terrible either, but it dies at frost and leaves the soil without growing roots during the winter.

Green winter cover crop plants on left show where mow-killing our summer cover crop worked well. Brown shows crabgrass, where winter cover crop did not germinate. 11/6/2012

The Organic No-Till Solution:  More Mulch!

Good problem solving involves separating the true problem from the symptoms, right?  Maybe these two weeds are really symptoms, and the true problem is lack of mulch.  In contrast to our 2012 summer cover crop cocktail, our 2011 summer cover crop of sorghum sudan and cowpeas resulted in very thick mowed mulch from these high-biomass plants.  I’ve heard farmers say that Ben Franklin should have added “thick mulch suppresses weeds” to death and taxes in his list of life’s certainties.  We for sure did not have the crabgrass and annual ryegrass problem after mowing sorghum sudan and cowpeas last fall, nor any weed problems in our super thick vetch mulch last spring.  On the other hand, our 2012 cocktail contained a lot of brassicas.  Brassicas have many benefits, but high biomass/mulch is not one of them.  So our big conclusion is:  low biomass and poor weed suppression is a trade-off of very diverse cover crop cocktails.

Volunteer annual ryegrass competition. Lonely lupine and pea are growing, but nothing else.  11/6/2012

Our Plan

In spring 2013, we’re going to allow more time for mow-killing our winter cover crop and spring weeds.  If mowing continues into June, that’s okay.  We’ll then plant sorghum sudan and cowpeas again for their many benefits, including super-fast growth, weed suppression, and mega mulch.  We’ll then wait for frost (around Halloween) to kill the sorghum sudan to plant our final pasture grass mix.  Early November isn’t the best time to plant grass, but we know it will work okay from past grass-planting experience.    On the upside, we’re happy to be getting some experience that is starting to point us in the right direction.  Good education is never cheap!


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