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Food
‹‹ V.21 No.14 | April 5 - 11, 2012

Food for Thought

Green Mulch Makeover

Summer-proofing your vegetable garden

By Ari LeVaux
Ari LeVaux

Across the Midwest, New England and Canada, high-temperature records are being broken by the thousands—3,125 between March 12 and 18 alone. Meteorologists are scrambling to find anything comparable to weather that has been dubbed “summer in March.” Two days before the official end of winter, temperatures of 94° were recorded in South Dakota.

If we're having summer in March, what can we expect in July? Even in a normal summer, the process of mulching should be on every gardener's mind as we say "good morning" to our gardens. But this year, the idea of heat-proofing the garden is especially timely.

Mulching—covering the ground—helps regulate soil temperature and moisture while keeping the soil from blowing away in the wind. In addition to deflecting sun and wind, mulching can also block weed growth and prevent runoff from heavy rains, which many regions can expect more of in a warming climate. Mulching encourages a moist, healthy garden ecosystem, which is vital for healthy plant growth.

Straw, leaves, grass clippings, pulled weeds, compost and other organic materials are typically used for mulch, as are living plants such as vetch between corn rows or clover in the orchard. Such living mulch, aka green mulch, can do everything a layer of straw can, and oftentimes more. Most green mulches are legumes that add nitrogen to the soil as they protect and stabilize it. But edible living mulches can be employed as well, with obvious benefits.

Over the years, my garlic patch has functioned as a laboratory for edible mulch research.

Over the years, my garlic patch has functioned as a laboratory for edible mulch research. I used to mulch with straw, but I began seeing all that covered area between plants as wasted space.

I started experimenting with a proprietary technique I call "hurling random vegetable seeds at the garlic patch." I mixed together all the leftover seeds from previous gardens that I had saved in various baggies and crumpled envelopes. I threw handfuls of mixed seeds into the garlic to see what grew, how well it did and if it adversely affected the garlic.

Bushy plants like tomatoes began swallowing garlic plants in late June and had to be pulled before they could produce. Plants in the mustard family, like broccoli and kale, grew poorly, perhaps victims of garlic's well-known allelopathic behavior. Allelopathy is the ability of some plants to secrete substances into the soil via the roots, which inhibits the growth of neighboring plants.

Eventually, two categories emerged as edible green mulches for the garlic patch.

By the time the carrots are dug, I'll have harvested three crops in one season from the same piece of dirt: garlic, greens and carrots. The living mulch will have done a service for my topsoil by protecting it from the elements

One category, the early-season greens, includes lettuce, radicchio, escarole, endive, spinach and other leafy greens outside of the mustard family. During the early stages of the season, when the young garlic plants are just a few inches tall, these greens basically have the whole garlic patch to themselves. As soon as the leaves reach edible size, I start harvesting them—just the leaves, not the whole plants.

The other category is carrots, planted at the same time as the greens. During the early season, the fast-growing greens tend to crowd and shade the carrots (though not the garlic, which is usually about 6 inches taller). By June, most of the leafy plants will have run their course and gone to seed.

As the greens fade, the carrots begin to take over between the garlic plants. Carrots and garlic will grow side by side, rarely getting in each other's way. Underground, carrots and garlic don't butt roots, while above ground the bushy carrot tops guard the soil surface. Once the garlic is harvested in July, the carrots have the whole patch to themselves and can stretch out comfortably into their expanded space.

By the time the carrots are dug, I'll have harvested three crops in one season from the same piece of dirt: garlic, greens and carrots. The living mulch will have done a service for my topsoil by protecting it from the elements. And for what it's worth, the extra biomass will have sucked up considerably more carbon dioxide than a dead layer of straw. That makes my living mulch garlic patch, by my calculation, a win-win-win-win-win situation.

This kind of diversity-focused gardening falls into the broad category of agroecology, the practice of building diverse, sustainable agriculture systems based on ecological principles.

While dismissed as nonscientific woo-woo by many who favor industrial-style farming, the discipline of agroecology is being taught at about 20 universities worldwide, including UC-Santa Cruz, Iowa State and Penn State. A report commissioned by the UN Human Rights Council examined hundreds of peer-reviewed scientific papers and concluded that agroecology has the potential to double food production in marginally productive areas. These areas are often at risk of desertification, which happens when the soil is overexposed. Activities that stall or reverse desertification, such as planting trees, are like mulching on a grand scale. Reclaiming desert facilitates the absorption of carbon dioxide via the new topsoil, flush with microbes and plant roots.

Even if you're not a garlic grower, the principles behind my thrice-harvested patch can be applied to whatever you do grow. Given that this year is shaping up to be a hot one—with more likely to follow—now is a great time for this kind of mulchy thinking. Whatever you grow, and whatever you mulch with—living or dead—the game is essentially the same: Cover as much ground as possible. If an edible mulch can do the job, all the better.