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Orchestrating the Ideal Site for Succulents

by Timber Press on November 8, 2017

in Design, Gardening

All great gardens are light-and-shadow experiences, and Alex Geremia’s is no exception. The tree aloe is ‘Hercules’, the blue explosions with trunks, Yucca rostrata. Alex Geremia Garden, Santa Barbara, CA.

How to make succulents feel at home, from the author of Designing with Succulents.

Because they are the least demanding of all plants, succulents require very little from their owners. However, for succulents to look their best, they do need some consideration as you’re laying out your site. Imagine being rooted and unable to move, and then exposed to too much (or too little) light, wind, heat, rain, and cold. Landscape professionals and gardening enthusiasts who use succulents as a living palette make a point of providing the right sun exposure, microclimates, and soil mix.


Which way is the sun?

Every so often a homeowner surprises me by being uncertain where north is. Yet I admit that when I took possession of my yard more than two decades ago, I wasn’t sure either. I’ve since learned that orientation to the sun is a key factor in garden design and plant placement. Sun is essential for photosynthesis, which gives plants energy needed for growth and flowering. Although any succulent’s optimal sun exposure depends on numerous factors (among them the type of plant, whether it’s newly introduced to the garden, and if it’s actively growing or dormant), the rule of thumb is to locate a succulent garden where it will receive fi ve
or six hours of direct sun daily and bright shade for the remainder. As it happens, my sloping garden faces east. Plants bask in gentle morning sun and are in shade during the heat of the afternoon—a nice bonus for them and for me as well.

Also notice how the intensity , duration, and even location of the sun’s rays change gradually throughout the seasons. As your pinpoint on the planet rotates toward or away from the sun during the year, sunrise and sunset occur earlier or later and at slightly different places on the horizon. An area that is fully shaded in winter might have significantly more sun in summer and vice versa.

Rosette succulents (such as aeoniums and echeverias) grown in too little light will flatten to expose more of their leaf surface to the sun. This, and when a plant becomes elongated from seeking sunlight, is called etiolation. If the plant is in a pot, rotating it 180 degrees once a week or so helps prevent lopsided growth.

The sun also impacts a garden’s aesthetics. Sunlight cast on spiny plants makes them glow and creates intriguing shadows. Silhouettes and the sky are part of a landscape, as is the wind, which creates motion.

Narrow-leaved succulents such as Yucca rostrata are kinetic sculptures that shimmer when sunlit and ripple in the breeze.

If these succulents could speak, they’d say, “The sun is over there!”

Match the plant to the microclimate

My half-acre garden is in one of San Diego’s inland valleys, which tend to be several degrees colder in winter than surrounding hilltops. Frost-tender plants such as avocados, palms, and bougainvilleas, common elsewhere in the region, are seldom grown in these low-lying areas. Cold air, being heavier than warm, flows downward and pools. Most seasonal frosts are mild, so only leaf tips freeze, making the plants look singed—hence the term frost burn.

My across-the-street neighbors are slightly higher in elevation and give frost little thought. When it’s 30°F down in my garden, it’s a degree or two above freezing in theirs. For succulents such as kalanchoes, crassulas, and many euphorbias, a few degrees below freezing can mean death or deformity. If they’re exposed to 32°F or lower long enough, moisture in their tissues solidifies, expands, and bursts cell walls. Those few degrees also mean that their owner has to dash around covering them with bedsheets when a lingering frost is predicted—unless, of course, they’re already growing in the garden’s warmer microclimates.

A microclimate in your garden is any area with a distinct set of growing conditions that differ from those of your overall property. To identify your garden’s cold pockets, notice where ice crystals linger the longest after sunrise. Warm spots tend to be near boulders, structures, trees, hardscape, and asphalt, all of which absorb heat from the sun. Your garden’s warmest area, and the best place to grow frost-tender succulents in winter, is likely to be south facing—such as a slope backed by a fence or retaining wall.

Wind is a factor, too. Garden areas shielded by walls, hedges, or some other windbreak are warmer than those out in the open. Locations exposed to northerly winds tend to be colder. But wind isn’t always a problem; air that moves is less of a threat than air that’s still, because movement keeps cold air from settling around plants. Wind can make leaves more frost resistant because it has a drying effect, and drier leaves contain less water. Good air circulation also discourages pests and fungal diseases, to which succulents are prone in damp climates. Excessive wind will cause desiccation, however, and if you’re sheltering your plants within a cold frame, in a greenhouse, or beneath a cover, wind may cause greater heat loss by cooling the air around the structure.

Tree canopies, by providing bright shade in summer and a barrier against cold in winter, moderate the temperature beneath them, thereby shielding understory plants from both sunburn and frost.

A palo verde tree at the Ruth Bancroft Garden in Walnut Creek, California, is in full bloom, its fallen petals forming delicate yellow drifts. The tree’s canopy protects succulents underneath it from too much sun in summer and frost in winter—as does the structure at upper right. Photo: Saxon Holt

What roots want you to know

Although succulents aren’t fussy about soil, their lives depend on good drainage. Determine your garden soil’s consistency by digging a hole the size of a 1-gallon nursery pot and then filling the hole with water. If it drains in a few minutes or less, the soil is probably sandy and will benefit from the addition of organic matter. If the water takes an hour or more to drain, the soil likely is clay and inhospitable to succulents—indeed, to most garden plants—because waterlogged roots may rot. If you have heavy clay soil that drains poorly, you might want to remove it and replace it with a commercial cactus mix. Or simply plant in good soil mounded above the existing soil, or construct planters atop it—that is, raised beds. Made of block, stone, or pressure-treated wood, these function like large pots.

Since soil varies from region to region, and even within areas of a garden, amendment formulas vary. In general, though, succulents planted in average garden soils benefit from having the soil amended with equal parts crushed lava rock (pumice), organic matter (humus or compost), and coarse sand (like decomposed granite).

Also called sharp sand, coarse sand—unlike fine, silty sand—has grains that feel sharp when rubbed between the fingertips. Succulents generally prefer slightly acidic soil (pH between 6 and 7).

Botanical gardens, like homeowners, contend with native soil that’s not ideal for cacti and succulents, and amend it accordingly. At the Ruth Bancroft Garden in Walnut Creek, California, for example, rocky soil is used to build up mounds atop the existing clay, with lots of pumice added beneath the more sensitive plants, and compost used as mulch. At the Huntington Botanical Gardens in San Marino near Los Angeles, forest compost is added to the soil, plus pumice if drainage needs improvement. Heavy soil at the Arizona-Sonora Desert Museum in Tucson, which showcases cacti, is topped with 6 to 12 inches of well-draining soil mixed with enough sulfur to keep the pH between 6.5 and 8.

The only definitive method to find out which additives—such as agricultural lime and compost—will turn your soil into the perfect growing medium is to analyze it. Large nurseries, garden centers, and home improvement stores sell soil pH test kits. Your local agricultural advisories and Master Gardener associations can also provide guidance.

What goes on top of the soil is important, too. Inorganic topdressings—as opposed to wood chips and shredded bark—are best for succulents because they don’t harbor pests and diseases, nor do they keep the plants’ crowns overly moist. Moreover, organic topdressings break down over time and have to be reapplied. Crushed rock, available in a variety of colors and sizes at garden centers and landscape suppliers, offers aesthetic as well as practical advantages. By covering bare dirt it lends a finished look, and when applied to a depth of several inches, it keeps sunlight from the soil, thereby discouraging weeds from sprouting (and if they do, they’re easier to pull). Gravel also absorbs the sun’s warmth, allows rain to percolate into the soil, reduces evaporation, and keeps the ground insulated, thereby promoting root growth. In general, the darker the rock, the more heat it absorbs.

Pumice aerates the soil, absorbs excess moisture, and provides plants with micronutrients.

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Debra Lee Baldwin, an award-winning photojournalist, is widely hailed as the “Queen of Succulents.” She helped launched the gardening world’s interest in succulents with her first book, Designing with Succulents (1st Edition), and with her two other books Succulent Container Gardens and Succulents Simplified. Baldwin’s own half-acre garden has been featured in Better Homes and Gardens, Sunset, San Diego Home and Garden, and other publications.

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Click image below for a look inside this book.

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“Many people know about succulents, but using them in the landscape is another matter. Designing with Succulents shows us how; it’s inspiring, practical, and complete—a treasure for any gardener who loves these otherworldly beauties.”—Sunset

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