Designing the Home Garden for Drought Resilience

Summers in Pennsylvania are characterized by a combination of heat and humidity, punctuated by thunderstorm downpours and occasional periods of drought. Although too much rain can be catastrophic to plants, lack of rainfall, combined with summer heat and sun, is a much slower stressor that can extend over a period of weeks. What are a plant and a gardener to do during periods like this when there is no rain?

Drought in Pennsylvania

In Pennsylvania, the average annual rainfall is generally between 38 and 46 inches. That is a lot of rain compared with the western United States, which typically sees an average annual rainfall of 10 to 20 inches, and the Great Plains of the Midwest, with an average annual rainfall of 20 to 30 inches per year. The wettest year on record in Pennsylvania was 2018, with a statewide average of 64 inches of rainfall, followed by 2011 with an average of 61 inches.

Despite this generally abundant rainfall, Pennsylvania is still subject to patchy drought conditions, which usually occur in different areas of the state at various times. The driest year on record in Pennsylvania statewide was 1930, with an average of 28.9 inches of rainfall; the longest dry period on record in Harrisburg, where weather records have been kept since 1888, was 35 days, from September to October in 1947. For more information about Pennsylvania’s climate, see additional resources at the end of this publication.

Planning for Drought

Planning for drought resilience is a good idea when designing a garden because it goes hand in hand with water conservation. During drought conditions, gardeners may face a conflict between the desire to keep plants alive by watering and the need or requirement to conserve water. Proactive gardening practices to conserve water are at the core of xeriscaping, a concept developed in 1981 in Denver, Colorado. These practices include the following:

• Grouping plants with similar water needs
• Adding organic matter to the soil and using mulch to conserve soil moisture
• Capturing, saving, and directing rainfall in the garden with rain barrels, rain gardens, and irrigation systems
• Selecting plants that can tolerate drought conditions

Plants that are drought resilient have evolved or adapted different strategies to survive periods of drought. Two such strategies are drought evasion and water conservation. Drought evaders either lose their leaves or enter dormancy as part of their life cycle to avoid drought stress. Water conservers, on the other hand, possess leaf, root, and plant characteristics that minimize environmental moisture loss. In the next two sections, we will highlight examples of plants that use each of these survival strategies.

Drought Evaders

Plants that are drought evaders enter dormancy when conditions are less than favorable. Familiar spring-flowering bulbs, such as crocuses, daffodils, and tulips, go dormant in the summer. Many spring wildflowers in the woods of the eastern United States, such as Virginia bluebells and dwarf crested iris, become dormant after a brief period of growth and flowering in early spring.

During summer heat and dry spells, cool-season turfgrasses, such as Kentucky bluegrass, go dormant until cooler temperatures and rain arrive at summer's end. Trees may enter dormancy early by starting to drop their leaves to conserve water and nutrients. Many plants have evolved an annual lifecycle and survive difficult environmental conditions such as drought as seeds—the ultimate drought evaders.

Water Conservers

In contrast to drought evaders, which go dormant during periods of drought, water conservers exhibit a variety of traits to retain water under such conditions. These include structures such as deep taproots (e.g., Baptisia spp., sea holly) to access underground water; thick, fleshy roots (daylilies) or succulent leaves (sedums) that store moisture; silvery-gray foliage (lavender, sage) or hairy leaves (coneflower) that reflect intense sunlight and reduce evaporation from the leaf; small, narrow, or waxy leaves (conifers) that minimize moisture loss; and finely divided foliage (artemisia, mimosa) to increase airflow over the leaf surface, cooling the leaf and reducing evaporation. Some groups of plants, including sedums, yuccas, and most grasses and sedges, have evolved adaptations to their photosynthetic processes to lessen water loss through pores in their leaves.

Water conservers are preferred when designing drought-tolerant gardens because they continue to look attractive during periods of drought and do not go dormant, as drought evaders are inclined to. Conifers, ornamental grasses and sedges, yuccas and agaves, succulents, herbs, and many prairie plants are all well-suited to drought-tolerant gardening.

Choosing the Right Plants for a Drought-Tolerant Garden

When researching and selecting drought-tolerant plants, look at their natural habitats, soil preferences, and hardiness, not just to cold winter temperatures but also to high humidity levels. Plants from drier climates, such as the Mediterranean, Eurasian Steppes, or the western United States, are adapted to low levels of precipitation but may struggle with high humidity. Soil moisture preferences can be categorized as dry, mesic (medium), or moist; many plants are adaptable to a range of soil moisture levels, from dry to wet. One final caveat regarding drought-resilient plants is that they are not fully tolerant of drought until their root systems are well established. That is, just because a plant may be labeled as "drought-tolerant" does not mean it can be planted and never watered. As with any plant, it is up to the gardener to plant properly and provide sufficient water for at least the first growing season to establish a strong root system capable of withstanding the next dry spell.

Additional Resources

Cornell Botanic Gardens. "Creating a Climate-Forward Garden."

Gardner HW. 2011. Tallgrass Prairie Restoration in the Midwestern and Eastern United States. Springer Press.

National Drought Integrated Information System.

The Pennsylvania State Climatologist.

Prepared by Andy Faust, Penn State Extension program manager, and Annette MaCoy, Master Gardener, Franklin County