Designing with Climate in Mind

A California gardener shares her solutions for dry summers and wet winters

by NORA HARLOW

photography by SAXON HOLT

Landscape design presents special challenges where rain, if it comes at all, falls only in winter months. In places where a Mediterranean climate dominates, such as the San Francisco Bay region, these challenges may include not only summer drought and waterlogged winter soils, but rugged topography with varied microclimates, cities and suburbs surrounded by open space, and a natural tendency toward periodic wildfires.

The climate also encourages outdoor activities almost year-round, so landscapes are used for many purposes. Gardens typically include areas for entertaining or relaxing outdoors, and many commercial and public landscapes feature spaces designed for the enjoyment of visitors or office workers.

DESIGNING FOR SUMMER DROUGHT

Landscapes in summer-dry climates must be designed to deal with many months without a drop of rain. Too often the default design response is irrigation. If we take our cue from the natural areas around us, we can create private landscapes that are functional and attractive year-round with little or no supplemental water. This doesn’t mean we can’t choose to have a pool or fountain, a lawn, or pots of thirsty annuals. The choice, however, should be conscious and deliberate: to add water to a landscape that could get by with none.

Two approaches to designing for summer drought are the liberal use of unwatered spaces such as paving, decks, or lightly tended natural areas and the selection of plants that are adapted to summer-dry climates. Paved areas and decks can provide usable outdoor spaces while minimizing or eliminating the need for irrigation. Areas left largely to their own devices can provide a pleasing contrast to groomed and tended planting beds. Plantings can be designed to thrive with occasional to no summer water.

The composition of patios, decks, paths, and other unwatered spaces can serve as a framework for the entire landscape design. There are many choices of materials—flagstone, wood or composite decking, bricks, concrete or adobe pavers, cobbles, gravel, decomposed granite, wood chips, even tumbled glass. Each material has its own advantages and disadvantages. Recycled materials, such as broken concrete or used bricks, can be attractive and environmentally sound, especially if they are reused on the same site or nearby.

Paving should be porous and open to the soil below whenever possible. The quantity and quality of storm-water runoff from roofs, roads, and parking lots is an increasingly important issue in urban and suburban areas. Porous pavings reduce runoff to storm drains and natural watercourses while helping to filter out water-borne pollutants before runoff reaches creeks and other waterways. Bricks or paving stones on sand with planted or unplanted spaces between the pavers are an attractive and ecologically friendly alternative to poured concrete or other impervious materials.

In Mediterranean climates, natural landscapes are green in winter, bursting with color in spring, and mostly subdued or dormant in late summer and fall. Plants native to, or naturalized in, local wild lands and untended open spaces have adapted to this seasonal pattern. Plants in designed landscapes can do the same.

There are dry-adapted plants that flower brilliantly in summer, but spring is when it really happens, and winter is when it starts. Summer in the San Francisco Bay region, for example, when many plants rest or go dormant, is a little like winter in areas of snow and sleet. Residents of colder climates don’t expect flowers or even leaves in winter; they appreciate and feature the striking silhouettes of bare branches and gray bark among their hardy evergreens. Here we can appreciate and feature the magnificent golds, gray greens, and rusty colors of summertime.

DESIGNING FOR WINTER WET

Winter can bring dramatic rainstorms and other challenges. Many Mediterranean and native California plants prefer good drainage, and some demand it. These plants may grow naturally on rocky outcrops or on sloping terrain where winter rains seep beneath the root zone or are carried away by seasonal watercourses. Many urban and suburban properties don’t provide this natural drainage, especially if the site is flat and the soil is mostly clay.

If your soil is heavy clay, you may decide to limit your choices to plants that thrive in clay soils. Or you may choose to install some artificial means of improving drainages such as terraces, raised beds, earth mounds, or swales. Raised beds and earth mounds are good solutions for poor drainage and can add visual interest to an otherwise flat landscape. Terraces not only serve as raised planters, but also help to control erosion and slow runoff on sloping terrain. Swales are wide, shallow, summer-dry streams or watercourses, vegetated or lined with cobbles and boulders that slow the flow of water on sloping land. Swales and dry streams can be designed to direct water away from plants that won’t survive in saturated soil and toward plants that benefit from some extra water. Be sure to consult a licensed professional before making any changes to your landscape that may affect site drainages. Ponding of water near foundations and oversaturation of unstable or compacted soils can have catastrophic consequences.

If your soil is heavy clay, amended topsoil can be added when making raised beds and terraces. Raised planting beds should be open to the ground below, so plant roots can reach deeply into cooler soil where some moisture may be retained. When constructing raised beds and terraces, it is important to mix any imported or amended soil with existing site soil to form a gradual transition between the layers. Otherwise, plant roots may never venture into the heavier soil beneath, and plants will need more summer water. Also, water may not drain freely into lower levels of soil, and the beds may become waterlogged in rainy winters.

Earth mounds or berms are another effective means of improving drainage while featuring special plants and adding visual interest into the landscape. As with raised beds and terraces, imported or amended soils should be mixed thoroughly with existing site soil to create a gradual transition between the layers. Groups of targe and small boulders set into the mounds make an attractive foil for leaves and flowers and give roots a cool place to run.

Good drainage can be provided in large ornamental pots. Plants in containers generally should be considered a high-water choice, since most will need almost daily summer water except in shade or right along the foggy coast.

Small, summer-dormant bulbs vulnerable to rodents and delicate ephemerals easily lost in open ground may be best grown in pots. These can be moved out of the limelight in their down season. Large containers with a specimen shrub or combination of flowering plants also can provide dramatic accents and an architectural or artful quality—a frame for a flower picture. H

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