Know your microclimates: identifying your garden's pocket climates can help you grow the right plants in the right place - Garden

Sunset, Nov, 2002 by Jim McCausland

How can one gardener grow perfect plumerias year after year, while a close neighbor invariably fails? Or why does one vegetable plot produce tomatoes until October, while another just down the street nearly always freezes out two weeks earlier? Sunset's garden staff constantly fields such questions; the answers usually involve microclimates--small pockets that are seasonally colder, warmer, or windier than the rest of the garden or neighborhood.

Wherever you live in the West, your garden falls into one of the 32 Sunset climate zones mapped and defined in the Western Garden Book. But every garden also harbors a number of microclimates that make a world of difference to plants: the chill air that helps set buds on an apple tree can freeze orange blossoms.

The illustration above shows nine microclimates typically found in Western gardens. Each situation presents gardening challenges and opportunities.

Fall is a good time to start observing your own garden's microclimates and making notes about sun angle, wind direction, and daily minimum and maximum temperatures. It's also a good time to modify the microclimates where you can--by planting hedges for windbreaks or trees for shade--or to move struggling plants from an unfavorable area to a better one.

RELATED ARTICLE: Nine common microclimates

1 Exposure to wind For this part of the garden, choose wind-resistant trees, shrubs, and perennials such as daylily, lavender, and penstemon. Or block the wind: a hedge or a windbreak of closely spaced trees planted on the windward side can create a sheltered area extending 10 to 20 times its height (a 10-foot-tall hedge will shelter 100 to 200 feet of ground behind it). If your property has a breezeway--a narrow passage between a house and a detached garage or other structure that funnels wind--you can buffer the upwind side with a hedge or line the passage with conifers or other wind-tolerant plants.

2 South and west walls Masonry and stucco walls soak up solar energy and radiate it back at night. In cool-summer areas, that extra heat can help ripen summer vegetables like tomatoes, peppers, and eggplants. In hot-summer areas, plant trees to shade these walls, or screen walls with heat-loving vines like bougainvillea.

3 North wall Since it gets little direct sun, it's ideal for shade-loving plants like ferns. In warm climates, the north side of the house is the place for temperate plants such as hydrangea and viburnum that would burn up with too much sun exposure.

4 Sloping ground As it flows downhill, cold air mixes with warm air just above so it is a bit warmer than the still air on mountaintops or in valleys. That's why sloping ground is favored for growing oranges. Grapes planted on a south- or west-facing slope pick up extra heat that helps sweeten fruit.

5 Cold-air pockets Low-lying spots allow cold air to pool. Chill air can also be blocked behind structures and landscaping elements like hedges (some typical cold-air traps are discussed on page 93). Frost-tender plants like citrus and plumeria that need heat don't belong in cold pockets. But such spots can be used to advantage in mild climates, where the extra chill encourages lilacs to bloom and apples, apricots, cherries, peaches, and pears to set fruit.

6 East wall Although it can get up to a half-day of sunshine, the sun is less intense here than on a west-facing wall. This makes it perfect for plants that like plenty of light but not much heat, such as azaleas and fuchsias.

7 Overhanging eaves They protect delicate flowers like camellias from shattering or turning mushy in the rain. Eaves also provide a couple of degrees of frost protection for tender plants underneath. Remember to irrigate under overhangs.

8 Shade trees and overhead structures A canopy of leaves or the latticework from an arbor casts filtered shade preferred by hosta, impatiens, and many other plants. On frosty nights, the air beneath stays a few degrees warmer than the open ground.

9 Dry banks They have fast-draining soil that's prone to erosion. Cover these banks with heat- and drought-tolerant ground covers such as Acacia redolens, ice plant, or trailing lantana or rosemary; Mediterranean shrubs like rockrose or santolina; or Western natives like manzanita (Arctostaphylos), wild lilac (Ceanothus), penstemon, or salvia.

Check your property for cold-air traps

Like water, cold air runs downhill and pools in certain places in the garden, particularly in low spots and behind structures and plantings. Walk around your property on a morning when the temperature is around 32[degrees] and you'll see where frost has collected in these cold pockets. Keep tender or marginally hardy plantings away from these areas, or provide plants with extra frost protection.

Ironically, a hedge installed to block wind can also trap cold air if the planting runs across the contour of a slope. You can use such cold-air pockets to your advantage by growing chill-loving plants there. However, if you don't want to trap cold air, thin the existing windbreak to open up its base. That way, the hedge will allow cold air to drain through but still break the force of the wind.