Bozeman News

Sense of Place

Understanding Microclimates Helps To Grow Your Garden

By Susan Duncan, 5-28-08

Gardeners in the Intermountain West face two challenges: Short growing seasons and microclimates — even at the garden plot level.

Awareness of these factors allows gardeners to adapt their seed choices and garden layout to mitigate the affects.

Some vegetable plants grow best in cool, damp conditions – peas, lettuce, celery, spinach, cabbage, broccoli, onions, carrots, beets, and turnips. Some vegetable plants like heat – corn, tomatoes, cucumbers, beans, and squash. If heat-loving vegetables are sown in a cool damp location, they will not reach maturity (produce edible fruits) before frost. If cool season vegetables are planted in “hot” spots they “bolt” (go to seed, quickly) or don’t come up at all.

Therefore it is important to know the hot and cool parts of a garden plot or design a garden layout that modifies temperatures.

Since cold air sinks, any slope in a garden plot is important. Look at a garden plot from all sides. My 3200 square foot garden plot looks flat from the north side. But looking at it from the west side, it obviously slopes to the south and southwest. The southwest corner is the lowest spot. The “high” spots along the east and northeast sides are the “hot” spots. I plant corn, beans, squash, and cucumbers there.  The western third (that is lower in elevation and shaded by the windbreak) is cooler and wetter. I plant peas, lettuce, spinach, beets and onions there.

Memorial Day weekend is a very busy time for us. We flush the lines and get the irrigation going on the pasture and hayfields. We check fences and sort, weigh, and worm our cows and get them out with a bull. For the last two years, my garden didn’t get tilled and planted until June 15th to June 20th. We have a ninety day growing season at best – Memorial Day to Labor Day. Planting late means a loss of 2-3 weeks of an already short 12 –13 week growing season. Because I knew what to plant (and where) for best results, I could plant late and still get corn, cucumbers, squash, and beans.

Seed selection also plays a major role in success. I have searched seed catalogs for 30 years to find seeds that will mature in my short growing season. I am working with 54-day corn (Earlivee), 45-day beans (Contender), and 47-day zucchini (Greyzini). Since cool, wet weather can instantly turn to hot, dry weather, I choose a heat resistant pea variety (Wando). Almost any variety will do for cool season crops like leaf lettuce, radishes, beets, and spinach. Since the soil I have is shallow, I choose short varieties of carrots (Danvers Half-Long or Chantenay) rather than long, skinny ones.

Local gardeners use several strategies to modify temperatures. Some prepare their soil and cover it in black plastic. The black plastic captures heat, allowing them to plant earlier. Seeds and transplants are inserted through holes in the plastic. The plastic also controls weeds.

Some plant tomatoes, peppers, and eggplant in old tires. The black tires retain heat and radiate it back to the plant. My friend Daryl grows cucumbers in tires covered by clear plastic, to create a mini greenhouse.

Another favorite strategy is raised beds. Since even slight variations in elevation affect temperatures, raising plants even a few inches is helpful. Raised beds are often made from 2 by 6 lumber (wood, cedar, or plastic). Garden supply companies sell metal corners that hold the wood together (better and longer) than nails. (Search “Raised Beds” at www.gardeners.com for one source.) Raised beds can also be made from cinder blocks (the kind with 2 holes), in a single row or stacked 2 high, depending on how deep the bed will be. (See: Cinder Block Gardens by Lynn A. Gillespie, self published paperback book ISBN 1-929709-01-3.  Google Search “Cinder Block Gardens”. Reviews on Amazon.com)

Raised beds have advantages beyond modifying temperatures. The beds are more or less permanent. The entire bed (3-4 feet wide) is a growing area, eliminating wasted space between rows. Only the growing area is watered and fertilized. Plants shade each other to reduce weeding and moisture loss. Crops are rotated among beds from year to year. Since they are never compacted by foot traffic, yearly roto-tilling may be reduced. I have used (temporary) raised beds and liked the results. I plan to move toward permanent raised beds as my primary gardening plan as I get older and my body refuses to bend as well as it does now. In the meantime, I usually plant in wide rows (2-3 feet wide) for many of the same reasons.

Finding hot spots for key plants like tomatoes, peppers, and melons is crucial. (Test out hot spots with a thermometer.) But, “hot spots” can actually be too hot. The two-foot-wide bed along the white south wall of my garage is too hot for tomatoes. A white wall refracts too much light. I plant my tomatoes in big pots salvaged from nursery stock so I can move them – nearer or farther from a hot wall or indoors, if a freeze is predicted.

But, knowing this wall was “hot”, we planted a hardy grape vine near the end by the garage door. Watered by the downspout from the garage roof and sprawling over a piece of combination panel, we actually got enough pea-sized grapes to make 4 cups of jam last year! Who would have guessed I could grow grapes here?

Pay attention to the prevailing wind direction. Corn is wind pollinated. The wind has to blow at right angles to the rows to spread pollen evenly. Our winds are from the southwest, so my cornrows are laid out north to south. For the same reason, corn should be planted in blocks of 4 rows or more.

Harsh winds batter and dry tender plants. Protect young plants against prevailing winds by putting two cedar shakes (or thin boards) at right angles on the windward side. Shelter cucumber vines by planting corn or beans on the windward side. Late summer peas, lettuce, and broccoli do well in the afternoon shade of corn. The arrangement of garden plants can take advantage of sun for heat loving plants as well as create shade for cool season plants.

Every garden plot is different in its physical limitations. The microclimate in every plot varies. Pay attention. Only you can discover its potential. Unexpected discoveries are the best part of gardening. 

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