There are many people who believe, with some justification, that Santa Fe is in the twilight zone. According to the United States Department of Agriculture, however, Santa Fe straddles zones 6a and 5b, but mostly exists in zone 6a. Unlike the twilight zone—or Johannesburg's District 9—zone 6a imprisons only a range of temperatures and, more specifically, the plants likely to grow and produce well within it.
What it means concretely is that Santa Fe is a place where winter does not escape notice, and where temperatures are likely to drop below zero at least a few times a year.
USDA hardiness zones range from 1 to 11, with 11 being uncommonly tropical and 1 being so damn cold you want to cry, but can't because the tears will freeze to your eyeballs and blind you. As a climate gauge, a zone is not a particularly subtle or comprehensive tool. It doesn't account for factors such as wind, humidity, rainfall or even heat, and is strictly a measure of cold temperature extremes at which certain plants are all but certain to die.
On the map, most of the zones are logically narrow in reach from north to south. As individual zones stretch from east to west, each tends to take on the character of a crooked smile, so that Santa Fe sits in equal territory with northern destinations such as Maine or eastern Washington. If New Mexico is an incisor, Maine and Washington are molars. When you consider that these respective climates are as radically different as those same teeth—despite falling into the same theoretical zone—it's easy to understand that other qualities are as important as cold temperatures to plant survival. Soil quality, elevation, humidity and all the factors that determine micro-climates come into play when you want to be more specific about a plant's health than you can be by reading the zone recommendation on a seed packet and crossing your fingers.
The easiest way to give plants a little boost when the weather turns cold and you start thinking that, for a place with 300 days of sunshine, there sure is a short growing season here, is through simple, straightforward means. These include wind blocks, row covers, extra mulch, and positioning near mass to benefit from heat gain and release, and additional moisture. But when you want to get into serious geo-engineering and give winter the finger, it's time to get all mini-biosphere on your garden's ass.
This can be done using cold frames, hoop houses or greenhouses. In the last year, I've done all three, and here's what I think:
What are they? Cold frames are low garden enclosures with hinged tops that allow sunlight to feed plants and warm the environment within the frames. The simplest cold frames are wooden boxes with glass tops (often recycled windows). Think of a cold frame as a raised bed with a lid.
What’s good about them? Cold frames are cheap to assemble, especially if you’re handy or willing to trade greens with someone who is. A trip to the Habitat for Humanity ReStore (2414 Cerrillos Road, 473-1114) can usually net you all the supplies you need. Cold frames are a great way to begin experimenting with prolonging the growing season; you can start with a small box and test the feet with a few heads of spinach and some radishes, or another forgiving combination.
What’s bad about them? Small-scale geo-engineering requires some maintenance. The biggest problem with cold frames is that they heat up really quickly. On a cold, sunny day in the middle of winter, your plants can easily burn to death. The solution is to vent the cold frame with a hinge at the top, but this requires opening the cold frame in the morning and closing it at night before it gets too cool. There are automatic devices that can perform this function, but they increase the cost of construction and make it a little harder to access your plants for watering, harvesting and care.
What are they? Hoop houses are sort of greenhouses on the cheap. They usually are constructed with flexible piping, bent into an arch and then covered with thick plastic sheeting. Hoop houses can be as small as a single garden row and as large as you’re able to bend pipe (some hoop houses are as big as airplane hangers).
What’s good about them? They go up quickly and are relatively cheap. It’s easy to make a portable hoop house or two that can cover modest garden plots, and it’s also pretty simple to put together a hoop house big enough to stand up in. The bigger you go, however, the more effort and energy you’ll have to put into constructing the side walls that support and seal the ends of your arch. They’re easier to vent and control temperature in than a cold frame.
What’s bad about them? Even thick plastic sheeting degrades quickly in the New Mexico sun, and the unpredictable New Mexico wind can thrash the houses. If you’re thinking of building a large hoop house, it’s worth considering the investment in a greenhouse.
What are they? Greenhouses are more-permanent structures than either cold frames or hoop houses, although relatively portable kits are available.
What’s good about them? The structural rigidity of greenhouses allows them to withstand the elements better than hoop houses and, typically, allows for significantly more cultivation than a few cold frames. It’s also usually easier to insulate portions of a greenhouse or to include features such as Trombe walls, which can help keep the greenhouses warm at night, or even help heat your house if the greenhouses are attached. They allow the most stable environment for growing exotic plants. Lemon tree, anyone?
What’s bad about them? Greenhouses are generally pretty expensive. They are a commitment in terms of investment and the allocation of space. Even modular greenhouse kits are far more expensive than cold frames or hoop houses. Plus, you never know when the Drug Enforcement Agency will raid you for growing tomatoes in the winter.
These three garden tools can allow you to extend the sometimes-fickle Santa Fe growing season. You may be thinking it’s late in the year to tackle a project like this but, if you build your personal biosphere this winter, you can get your starts in that much earlier come spring. Next year, you’ll be ready to whip out fresh greens for that Thanksgiving meal.
But there's one big drawback: When you create a micro-climate capable of keeping your plants alive, you create a micro-climate capable of keeping pests alive, too.