Low Water? No Problem.

Andrew Bunting

Conserving water in the garden is increasingly becoming a challenge throughout many parts of the country. Some areas have naturally arid climates, and many others are experiencing extended periods of drought during the growing season. As a result, more gardeners are starting to use drought-tolerant trees, succulents, cacti, sedums and deep-rooted prairie plants in their ornamental plantings to mitigate the impacts of low water conditions and extended periods of drought in the garden.

Schizachyrium scoparium

There are a handful of outstanding drought-tolerant trees. At the Pennsylvania Horticultural Society, we promote two native oaks, including the swamp white oak (Quercus bicolor) and the bur oak (Quercus macrocarpa). Both species have a broad native range, and a picturesque habit as they mature and yellow to golden fall foliage. Both have proven to be “urban tough.”

Additionally, used throughout the Midwest and the east is the Kentucky Coffeetree (Gymnocladus dioicus). In its youth, it can be a bit gangly and awkward, but over time it develops into an upright architectural canopy. The large compound leaves have small leaflets, which create light shade. The female trees can produce a stout pod that can be messy, so a male selection such as Espresso is recommended.

There’s perhaps no tree more urban and drought tolerant than the London planetree (Platanus x acerifolia). Introduced through the Chicagoland Grows Program, Exclamation! is a more fastigiate form that’s pyramidal. Because it’s upright rather than spreading, it can be used in landscapes where space might be an issue.

The deep-rooted flowering perennials and grasses of the Midwestern prairies are outstanding plants for withstanding drought-like conditions. There are many excellent ornamental grass selections that have been made. Garden designer Jeff Epping, who’s often called the “gravel guru,” uses the little bluestem (Schizachyrium scoparium) in his designs. As the name would suggest, the strict upright foliage is blue, but can also have hints of pink and red. Turning orange-red in the fall, it’ll also maintain its form for most of the winter. 

Agave parryi Paloma

Larger in stature is a selection on the big blue stem, Andropogon gerardii Blackhawks. This native grass reaches 4-ft. tall and has attractive upright leaves that are deep purple. Both schizachyrium and andropogon combine well with flowering perennials such as baptisia, amsonia, parthenium and milkweeds.

In many Mediterranean climates around the world, euphorbias are either native or thrive in these low precipitation and well-drained soil conditions. At home in my gravel garden where the granite gravel is 4- to 6-in. deep, I grow several different euphorbias. The burrow-tail euphorbia (Euphorbia myrsinites) has blue-gray leaves on stems that clamber over the ground and striking chartreuse flowers in the early spring. E. myrsinites serendipitously self-sows throughout the gravel garden. If I don’t want it in a particular part of the garden, then I simply pull out the seedlings. Both Miner’s Merlot and Blackbird have tufts of upright foliage with purple leaves. Atop the foliage in the spring are sprays of yellow flowers. 

At the nearby Chanticleer Gardens in Wayne, Pennsylvania, they grow in their gravel garden the very architectural Euphorbia characias subsp. wulfenii. This euphorbia will take on shrub-like proportions in California gardens and in eastern Zone-7 gardens they make a statement once established. This evergreen euphorbia has stout upright stems that have large clusters of striking chartreuse flowers in the early spring. 

Plantings can include some very tough water-wise plants such as native cacti. There are a host of cacti that are native to the western U. S. that are also perfectly hardy in the Philadelphia area. The prickly pear (Opuntia humifusa) is native to the east coast. It’ll clamber and spread, and in late spring, produces an abundance of bright yellow flowers.  At the Pennsylvania Horticultural Society’s public garden, Meadowbrook Farm just north of Philadelphia, we showcase many species of hardy cacti, including opuntia and cylindropuntia. 

Opuntia humifusa

The Adam’s needle (Yucca filamentosa) is evergreen with very spiky foliage. As it grows, it develops a very deep tap root whereby it requires minimal to no supplemental watering.  Tall spikes of flowers arise at the base of the leaves in late spring. The flowers spikes can reach over 6-ft. tall and are covered in pure white, bell-like flowers. Color Guard is a cultivar that has variegated leaves with a yellow center and a green edge. This selection is great for winter interest. 

In USDA Zones 8 or warmer, there are endless species and cultivars of agave that can be grown. Both the Norfolk Botanical Garden in Norfolk, Virginia, and Juniper Level Botanical Garden near Raleigh, North Carolina, showcase the best of the best.  Agave ovatifolia is a large stature agave with striking steely-blue leaves, while Agave parryi is more diminutive and one of the hardiest species.

Aesthetically, gardens can be created to mirror natural ecosystems, such as the deserts of southern California and Arizona; the high elevation mountainous regions; rock gardens of Idaho, Wyoming and Colorado; or the Mediterranean climates of California. 

Additionally, a rising trend in the United States is to install both crevice gardens and gravel gardens. There are great public examples of crevice gardens at Juniper Level Botanical Garden in Raleigh, North Carolina, Cantigny Gardens in Wheaton, Illinois, and at the Sarah P. Duke Gardens in Durham, North Carolina. Excellent gravel gardens are on display at Olbrich Botanical Garden in Madison, Wisconsin, The Scott Arboretum of Swarthmore College, Swarthmore, Pennsylvania, and at Chanticleer. GP

Andrew Bunting is the Vice President of Horticulture for the Pennsylvania Horticultural Society (PHS), which uses horticulture to advance the health and well-being of the Greater Philadelphia region. To learn more about PHS, or to become a member and support greening initiatives in over 250 neighborhoods, visit PHSonline.org.