How to heat-proof your garden
Across the Midwest, New England and Canada, high-temperature records are being broken by the thousands -- 3,350 of them between March 12-18 alone. Meteorologists are scrambling to find anything comparable to weather that has been described as "summer in March." Two days before the official end of winter, temperatures of 94 degrees Fahrenheit were recorded in South Dakota.
If we're having summer in March, what can we expect in July? For backyard gardeners, the idea of heat-proofing the garden is one way to cope with a changing and changeable climate. We know that covering the soil -- mulching -- helps regulate soil temperature and moisture, while keeping the soil from blowing away. Mulching can also block weed growth and prevent runoff from heavy rains, which many regions can expect more of as temperatures climb. Mulching encourages a moist, healthy garden ecosystem.
Straw, leaves, grass clippings, pulled weeds, compost and other organic materials are typically used for mulch, as are living plants such as vetch between cornrows, 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 consider this: Edible living mulches can also do the job. I used to mulch my favorite crop, garlic, but began seeing all that covered area between plants as wasted space. So I started experimenting with a proprietary technique you might call "hurling random vegetable seeds at the garlic patch." The results were definitely mixed.
Bushy plants like tomatoes began swallowing the garlic plants in late June, and had to be pulled before they could produce. Plants in the mustard family, such as 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 inhibit the growth of neighboring plants.
Eventually, two categories emerged as edible green mulches for the garlic patch. 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, though 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 six 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. Carrot and garlic will grow side by side, rarely getting in each other's way. Underground, carrot 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 can stretch out comfortably into their expanded space. By the time the carrots are dug, I'll have harvested three different 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 non-scientific woo-woo by many who favor industrial-style farming, the discipline of agroecology is currently being taught at about 20 universities worldwide, including the University of California, Santa Cruz, Iowa State and Penn State. A December 2010 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.
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 -- and who knows what the future will bring? -- now is a great time for this kind of mulchy thinking.
Ari LeVaux is a contributor to Writers on the Range, a service of High Country News (hcn.org). He writes about food and lives in Placitas, New Mexico (flash@flashinthe pan.net).