Cultivating Questions Concerning the Bio-Extensive Market Garden

by Anne and Eric Nordell of Trout Run, PA

Grow-Your-Own Mulch – Part 4

We have relied exclusively on rye for the grow-your-own mulch experiment because it is such a perfect match for many of our spring and summer vegetables. Established in early-to-mid September at our northern Pennsylvania location, rye produces a prodigious amount of biomass by the end of the following May. Mowing the rye at this time eliminates the possibility of volunteer grain. And raking the conveniently grown straw next to the adjacent vegetables a week or two later coincides nicely with the soil temperature and moisture requirements of tomatoes, peppers, zucchini, onions, leeks and winter squash.

This year we branched out a little, trialing different cover crops for other growing windows. We learned that Japanese millet, planted the beginning of June, makes an ideal mulch for fall broccoli. Despite receiving only 2-1/2” of rain from planting (7/20) to the start of harvest (9/10), the crop never showed any signs of moisture stress and produced large, tight, deep green heads. However, while the millet was growing, it served as a magnet for every rabbit on the farm – not exactly the situation we want to encourage in the market garden as rabbits like young broccoli plants.

This was not a problem for the fall cover crop of oats we trialed in 2012 for mulching our 2013 crop of no-till garlic. On the other hand, designing the layout of this experiment was more of a challenge. We knew from past experience that planting the oats on ridges would facilitate no-tilling the garlic directly into the cover crop, but we did not think the ridges would be desirable for mowing and raking the additional cover crop mulch. The best way we could think of to seed the oats on ridges and flat ground in an efficient layout for mulching was to use the horsedrawn guidance system described in the Fall 2012 SFJ.

Rigging up nine closely-spaced teeth with two cross-brackets on the McCormick riding cultivator did a nice job of incorporating the Esker oats, broadcast on August 8. Working our way across this half-acre field with this setup also defined 21 low, flat planting beds. After laying out the beds, we replaced the straight shovels on the riding cultivator with two pairs of disc-hillers to form ridges on the middle 7 beds for direct planting garlic. We then used the cultipacker to level off the ridgetops and firm in the oat seed on the 14 low planting beds flanking the ridges.

On Oct. 15, we hitched the team to the cultipacker again, this time to roll down the headed-out oats on the 7 ridges in the middle of the field. As illustrated in the “Weed the Soil” video, the loose soil in the ridges makes it much easier to open up a no-till planting furrow for hand setting the cloves than no-tilling into flat ground.

Concerned that a snowstorm in the forecast might flatten the waist-high oats on either side of the garlic, we mowed the standing cover crop with the five-foot sicklebar and single horse on Oct. 25. Although this was earlier than we had intended to mow the oat mulch, it turned out to be timely since it took almost a month of fall weather to completely dry down the longstem straw before raking it into windrows with the team and moving the windrows by hand into the valleys between the rows of ridged garlic.

Compared to our normal practice of buying in wheat straw to mulch the valleys, the homegrown oat straw was a whole lot cheaper. Moving the oat windrows in place also turned out to be faster and easier than breaking up square bales of wheat. Most importantly, the oat mulch seemed to do a comparable job of preserving soil moisture. Although we received almost normal precipitation in May, June and July, we started to 2013 growing season with a 5” moisture deficit and received only 2” of rain in April. Nevertheless, most of the Rocambole and German white bulbs ended up 2 1/2 to 3” in diameter.

At this point the main weakness of this dryland system seems to be the dependence on rain to grow the mulch. The 2012 oat cover crop benefited from an abundance of soil moisture. By contrast, when we repeated the oat mulch trial in 2013, the cover crop headed out prematurely due to severe moisture stress in August and September. As of this writing on 9/28, it does not look like the oats will produce enough straw for the 2014 crop of garlic.

Even if we have to supplement with bought-in straw or recycled cover crop mulch, we will continue the oat-and-garlic experiment because one of the unanticipated benefits of using the mature oat top-growth for mulching the garlic was trouble-free seedbed preparation for early vegetables. The low, flat beds on either side of the garlic dried off quickly as soon as the frost went out of the ground and were easy to till shallowly with the riding cultivator due to the very short oat stubble. Even better, the lightly tilled oat stubble posed absolutely no problems for seeding the first two plantings of salad mix, beets and spinach with the walk-behind Earthway and Planet Jr. We wouldn’t be surprised if eliminating the challenges of planting into heavy cover crop residues turns out to be the most important discovery of the grow-your-own-mulch adventure.