Drought-Resistant Plants for Pots
In recent years, communities all over the United States have experienced some form of drought, and in response, many have restricted the use of water for gardening. As environmentally conscious gardeners, we need to find ways to create gardens—including container gardens—that require little, if any, supplemental watering.
In 1981, the Association of Landscapers and Contractors of Colorado coined the term "xeriscape." "Xeros" is Greek for dry and "scape" comes from the Anglo-Saxon "schap," meaning view. Xeriscape gardening promotes water conservation through inventive landscaping. It is water-efficient, but by no means restricted to stark collections of rocks and cacti. Drought-resistant container gardens need not sacrifice a variety of form and color. There's an additional benefit in planting a drought-tolerant potted garden—you will spend less time maintaining and more time enjoying it.
There are certain characteristics that indicate drought tolerance, so keep these in mind when choosing xerophytic plants for containers: Silvery foliage and hairy or fuzzy leaves reflect sunlight, thus reducing water loss via transpiration, the normal loss of water vapor from a plant's leaves. Leaf hairs also act as a physical barrier to transpiration by reducing air movement over the surface of the leaf. Succulent plant parts, like the leaves of rose moss (Portulaca species), store water for drier times. A thick cuticle (a waxy coating secreted by the plant's epidermal cells) slows the loss of water through the leaf surface. The leaves of ivy-leaved geranium, Pelargonium peltatum, have just such a cuticle. A taproot is another excellent water storage device. Plants with taproots, like butterfly weed (Asclepias tuberosa), store enough water to get through periods of drought.
There are so many xerophytic plants that it would be impossible to include them all here. A good rule of thumb is to choose plants that are native to your area; a number of the non-native ornamentals recommended as drought-tolerant candidates for the garden have become invasive, threatening North American habitats and their associated plants and animals. Plants known to be invasive should not be used in regions where they have been noted as such or other regions with similar climates and growing conditions.
Plants grown in containers are more exposed to the elements than their peers growing in the ground, and therefore should be treated as less hardy. The hardiness listing provided for each perennial gives the zone to which that plant is reliably hardy in a container setting, which is generally two zones warmer than its USDA listing. For example, sea holly (Eryngium bourgatii) is hardy to Zone 5 when it grows in the ground and container-hardy to Zone 7.
Sea Holly Eryngium bourgatii—This plant has a wonderful structure and is exceedingly tough. Its leaves are stiff and marked by white veins that complement the spiny, silvery white flower bracts. It is container-hardy to Zone 7 and grows to 24 inches tall.
Perennial Flax Linum perenne—The flowers of perennial flax are a deep, clear, true blue. They open in the heat of day and close again by evening. This easy-to-grow plant does best in full sun and well-drained soil. It's container-hardy to Zone 7 and reaches 1 to 2 feet in height.
Coneflower Echinacea purpurea—This drought-tolerant North American native grows best in sandy soil and full sun. The white cultivars are especially attractive and grow to 24 inches tall. This makes them somewhat shorter than their more common pink cousin. All Echinacea bloom from July through August and are container-hardy to Zone 6.
Globe Thistle Echinops bannaticus—This thistle has long-lasting, pale blue, globe-shaped flowers that make excellent cut and dried displays. Foliage and growth habit are also very attractive. Globe thistle is container-hardy to Zone 6 and reaches 2 to 3 feet tall (depending on the cultivar).
Butterfly Weed Asclepias tuberosa—Its taproot makes this North American native an especially drought-tolerant choice, and its flowers attract bees and butterflies to your garden in abundance. Cultivars range from 1 to 3 feet in height, with flowers available in yellow, orange, vermilion, or white. It is container-hardy to Zone 6.
Lantana Lantana species—Available in numerous colors, including yellow, orange, red, white, pink, and lavender, lantana—or shrub verbena, as it is often called—comes in both upright (Lantana camara) and weeping forms (Lantana montevidensis). The leaves have a spicy fragrance, and the plant will flower all summer long if conscientiously dead-headed. Seed heads are also attractive and mature to a shiny, blue-black fruit. (In frost-free areas, Lantana camara is hardy and will grow into a shrub. However, it is known to be invasive in Florida and Hawaii. Gardeners in these states should refrain from growing this plant.)
Sunflower Helianthus annuus—The many varieties range from 2 to 12 feet tall and offer flowers in white, yellow, orange, or red. Some cultivars have huge, single flowerheads, while others have several flowers per stalk. All make excellent accent plants and add height to your containers.
Blue Marguerite Felicia amelloides—This marguerite has lovely blue petals surrounding a yellow center. It ranges from 1 to 3 feet tall and grows best in full sun. This annual flowers best in cool weather, so use it for early spring bloom, then cut it back for another round of flowers in fall.
Zinnia Zinnia angustifolia—Available with white or orange flowers, both with yellow-orange centers, Mexican zinnia grows 8 to 12 inches tall and is quite drought-tolerant. The plant flowers profusely, and its leaves are an attractive gray-green with a linear shape. It is sometimes sold as Zinnia linearis.
Ivy-leaved Geranium Pelargonium peltatum—Dark green, shiny leaves and a trailing growth habit make this plant particularly valuable for container culture. Its blooms are not as large as those on some other geraniums but the color and shape are lovely, and its foliage helps weave together the diverse contents of your container.
Annual and Perennial Vines
Bougainvillea—Nothing beats the brilliance of Bougainvillea. An annual in the North, it's a fast grower, with solid green- or white-variegated leaves and colorful petal-like bracts (not flowers) that can be magenta, white, yellow, orange, or pink. Cut it back and bring it indoors for the winter if you have a sunny window.
Trumpet Creeper Campsis radicans—An excellent choice to cover a trellis or arbor, this North American native vine grows quickly and gives good coverage within two or three years. Flowers can be shades of orange or yellow, depending on the cultivar, and the vine blooms for several months in summer. It is container-hardy to Zone 7.
Morning Glory Ipomoea tricolor—The classic "morning glory blue" is a true symbol of summer, but a rich array of purples, pinks, and stripes are also worth growing. Ipomoea grows quickly and prefers sandy, poor soil. It can easily cover a full-sized tree or two-story house in a single growing season.
Sweet Autumn Clematis Clematis terniflora—This vine delivers a blast of bloom just when you need it: in autumn, when thoughts of winter creep into every gardener's brain. Throughout the summer, its attractive, three-lobed leaves nicely cover an arbor or fence. In early fall, the profusion of white blooms is the finishing touch. The vine, often sold as Clematis paniculata, is container-hardy to Zone 7.
Cape Leadwort Plumbago auriculata—The flowers of cape leadwort are usually a clear pale blue, although a white cultivar is also available. Dead-heading helps guarantee bloom throughout the summer season. This vine is tender north of Zone 9, but just like Bougainvillea, it can be cut back in fall and overwintered indoors.
Snowdrop Galanthus nivalis—It is impossible to overpraise this earliest harbinger of spring. Snowdrop makes a fragrant cut flower, although its scent isn't discernible in the cold winter air. On a warm day, or indoors, its perfume is lovely and delicate. Snowdrops bloom in late winter, and the foliage disappears when the plant goes dormant in mid-spring.
Bearded Iris Iris germanica—The many bearded iris hybrids offer a huge range of color choices, including purples, whites, golds, pinks, and reds. Flowers are intricate and showy, and the upright foliage is an excellent accent for the container garden, even when the plant is not in bloom.
Tulipa Tarda—While some tulips can be temperamental, Tulipa tarda is an outstanding, reliable, hardy, drought-tolerant perennial. It blooms in April, and its brilliant, two-toned flowers are real showstoppers.
Onion Allium species—There are many alliums to choose from, all of them quite drought-tolerant. Heights range from 6 inches to 3 feet, and umbels come in many shades of purple and blue as well as yellow and pink.
Fall-blooming Crocus Crocus speciosus—This crocus blooms without foliage. Its flowers are considerably larger than those of the spring-blooming crocus, and it grows well in sandy, well-drained soils. Full sun is best, but some shade is fine.
Bluemist Spirea Caryopteris x clandonensis—This is an outstanding shrub with blue flowers in August and September. It blooms best in full sun and a well-drained soil, and is container-hardy to Zone 7. Its attractive gray-green foliage has a spicy scent. Treat this shrub, also called bluebeard and false blue spirea, as a perennial and cut it back to the ground in late winter; flowers are borne on new growth.
Cranberry Cotoneaster Cotoneaster apiculatus—This low-growing shrub has an attractive, stiff branching pattern. Its small leaves are shiny and the plant is covered with cranberry-red fruit. It is container-hardy to Zone 7 and its cascading growth habit is especially useful at the front of a large container.
Oregon Grape Mahonia aquifolium—A lovely shrub with blue-green, spiky leaflets, it is container-hardy to Zone 7 and can take some shade. Yellow flowers are borne in spring, followed by grape-shaped (non-edible) fruit. This evergreen shrub grows to approximately 3 feet tall.
Japanese Holly Ilex crenata—A small-leafed evergreen with black berries borne on female plants, this holly is more drought-tolerant than most and grows best in well-drained soils. It grows well in sun or shade and is container-hardy to Zone 7.
Spirea Spiraea thunbergii—One of the earliest spring-flowering shrubs, it has numerous white flowers. The foliage of this bushy plant turns a pretty orange-yellow in fall. Prune it to keep it in shape. It is container-hardy to Zone 6.
Purpleleaf Sand Cherry Prunus x cistena—The purple foliage makes this tree an excellent and valuable accent plant. Grow it as a multi-stemmed shrub or a small tree. It is container-hardy to Zone 4.
Apricot Prunus armeniaca—This attractive small tree has pretty pink flowers in April or May, followed by edible fruit in July and August. This apricot is container-hardy to Zone 6.
Colorado Bristlecone Pine Pinus aristata—The needles of this slow-growing North American native evergreen have an attractive bluish cast. Its picturesque growth habit is reminiscent of a trained bonsai and makes this plant a natural focal point. It is container-hardy to Zone 6.
Downy Serviceberry Amelanchier arborea—This North American native has several things to recommend it. Delicate, white flowers precede foliage in very early spring and its gray bark is lovely year-round. This Amelanchier is the most drought-tolerant of the genus, grows in sun or shade, and is container-hardy to Zone 6.
Black-Haw Viburnum prunifolium—An incredibly tough North American native, black-haw or plum-leaf viburnum, as it is also known, tolerates dry conditions and will grow in partial shade or sun. White, flat-topped flowers in May are followed by black fruit in September. This tree has reddish purple fall color and is container-hardy to Zone 5.
Carpet Bugleweed Ajuga reptans—This is an attractive groundcover all summer long that comes in a wide variety of foliage colors (bronze, purple, white, green). Lovely purple-blue flowers cover the plant in spring. It grows quickly, spreading by stolons, and is container-hardy to Zone 5.
Common Bearberry Arctostaphylos uva-ursi—This North American native is a slow grower but worth waiting for. It's container-hardy to Zone 5, and its evergreen foliage takes on a pretty bronze tint in winter. Long-lasting red berries follow pink, bell-shaped spring flowers.
Creeping Juniper Juniperus horizontalis—A tough North American native whose prostrate growth habit is well suited to draping a container edge. Container-hardy to Zone 5, its numerous cultivars offer varying shades of evergreen foliage, including blue-green, gray-blue, and dark green. Blue berries are an added bonus.
Cliff Green Paxistima canbyi—A North American native evergreen shrub with a low growth habit that makes it a useful groundcover. It's container-hardy to Zone 6 and will grow in sun or shade. Well-drained sandy soil is best. Leaves are small and linear and turn bronze in fall.
Wooly Thyme Thymus pseudolanuginosus—The creeping growth habit of this thyme is particularly useful in containers, allowing it to fill in the gaps between neighboring plants. Its leaves are fuzzy, fragrant, and very tough. This herb is container-hardy to Zone 6.
Feather Reed Grass Calamagrostis x acutiflora 'Karl Foerster' (syn. 'Stricta')—The botanical name is a mouthful, but worth learning to pronounce. This grass has a narrow, upright growth habit, reaches 5 feet in height, and needs full sun. It blooms in summer and its panicles are persistent, adding winter interest to your container. It is container-hardy to Zone 7.
Big Blue Stem Andropogon gerardii—This native North American grass once covered the prairies. It grows to 4 to 6 feet tall in containers, and its silvery blue foliage is truly beautiful. In fall, stems turn a striking coppery color. This grass grows best in full sun and is container-hardy to Zone 6.
Maiden Grass Miscanthus sinensis 'Gracillimus' and zebra grass (M. sinensis 'Zebrinus') are two cultivars of Miscanthus with a clumping habit and a moderate growth rate. 'Gracillimus' reaches 5 to 6 feet tall and is topped by showy flowers in October. 'Zebrinus' has horizontal yellow stripes and reaches 7 feet tall. Both are hardy to Zone 7 and provide excellent winter interest. Maiden grass is invasive in some areas throughout the eastern U.S., from Florida to Texas, north to Massachusetts and New York. People who live in areas where maiden grass has proven problematic should refrain from growing it.
Tufted Fescue Festuca amethystina—A superb accent plant with beautiful gray-blue foliage topped by tan panicles of flowers in late summer. One of our smaller ornamental grasses, it grows to approximately 12 inches and does very well in containers. It is container-hardy to Zone 6, frequently evergreen, and can be cut back to the ground in early spring.
Fountain Grass Pennisetum setaceum—An annual grass in the north and well worth growing for its long-lasting, beautiful, fuzzy flower spikes. Cultivars with coppery red spikes and foliage are particularly useful as accent plants. This grass grows to 24 to 36 inches tall, depending on the cultivar.
Xeriscaping Tips for Container Gardeners
Container gardening presents its own set of challenges, among them more stressful growing conditions: As it holds only a limited amount of soil, a container offers limited room for roots to spread, dries out faster, and has a higher soil temperature. The following tips are based on principles formulated by the National Xeriscape Council, Inc., a non-profit organization, which serves as an informational clearinghouse for people interested in xeriscaping.
Plan Ahead: Consider where you're placing your containers. For example, a spot in the sun can be 20° F. hotter than a nearby spot in the shade, so put your most drought-tolerant plants in the most exposed part of the garden. Trellises and arbors, as well as trees, create useful pockets of shade, so take advantage of them. In addition, group only plants with similar water requirements in the same container. By choosing plants with similar requirements, you can reduce water waste and improve your plants' health, since each will receive what it needs; no more, no less. If you want to include a few water-lovers in your garden, select shade-tolerant varieties, and place the container in the shade.
Select Appropriate Plants: Choose plants suited to your region and microclimate. You've got some leeway here, because xeriscaping can mean different things in different parts of the country, depending on average temperature and rainfall. Start by looking at plants native to the drier habitats in your area; these plants frequently thrive without supplemental water.
Improve the Potting Mix: Use a potting mix that's quick-draining, water-retentive, and nutrient-rich. Consider adding an inorganic soil conditioner to your mix. Water-retaining polymers (hydrogels), for example, hold several hundred times their weight in water and release it gradually to the plants' roots; one teaspoon absorbs one quart of water. Finally, mycorrhizal fungi improve the ability of a plant to take up water and nutrients by working with the plant's root system. Packets of mycorrhizal fungi (combined with hydrogels, soil conditioners, and bio-stimulants) are available commercially and should be added to the soil before planting.
Irrigate efficiently: If you use an irrigation system, minimize water waste by applying the water exactly where it is needed. If possible, use drip emitters to deliver water to each container in your potted garden; drip irrigation systems use about 30 to 50 percent less water than sprinkler systems. They are highly efficient, delivering water directly to the roots of the plants, minimizing evaporation and run-off.
Use Mulch: A two- to three-inch layer of mulch covering the soil surface will cool the soil and help it retain moisture. In fact, soil that's one inch below a layer of mulch can be up to 10° F. cooler than unmulched soil at the same depth. Mulch reduces weed growth and organic mulch improves the fertility of the soil as it decomposes. It also prevents crusting of the soil surface, allowing water to penetrate to the root zone. Finally, the dark color and uneven surface of mulch limits reflectivity. Sand and clay soils can be highly reflective and bounce heat and light up onto plants. The fragmented surface of mulch reduces reflectivity and cools the adjacent area. Shredded or chipped bark, compost, and cocoa hulls make excellent mulches and will help you conserve water.
Maintain the Xeriscape: The initial soil preparation should be adequate for at least the first growing season. Do not overfertilize your xeriscape container garden, since this promotes weak growth that requires extra water. Keep pruning to a minimum as it actually encourages growth. Rather than pruning, research the growth habits of the plants you're interested in and pick only those that are the right size for your space. Be a vigilant weeder. Weeds compete with your plants for water and nutrients, thus increasing the total amount of water the container requires.