When thinking about designing a drought-tolerant garden, you will be pleased to find that the list of potential candidates for your borders is quite long and colorful. What makes a drought-tolerant plant? Plants have evolved some clever ways of adapting to dry conditions and even extended periods of drought. They are fairly easy to identify if you know what to look for.
Plants such as stonecrop (Sedum) and hens and chicks (Sempervivum) have evolved fleshy leaves to help them retain water during periods of drought. This is the same strategy used by cacti and makes them the camels of the plant world. Other plants have evolved a waxy, whitish coating (glaucous) on the leaves. Still others have leaves that are leathery or finely cut to help prevent water loss. A similar strategy can be seen in bearded irises (Iris). They have fleshy rhizomes that store water.
Other plants have evolved hairy or woody surfaces to help conserve moisture. One of the favorites for children in the garden is lamb's ears (Stachys). It is a common site to see a child stroking the plant. Plants with fine hair are easy to identify in the garden; they have grey or silvery foliage that reflects light and heat. Lavender (Lavandula), wormwood (Artemisia), yarrow (Achillea) and culinary sage (Salvia officinalis) are several examples. These plants need full sun and good drainage to survive.
Many prairie plants have deep tap roots. The advantage of these tap roots are twofold: to help the plant rejuvenate when consumed by grazing animals and to help it weather dry spells. Plants with deep root systems dry out less quickly than those with shallow roots. A grassland species that is notable for a large tap root is false blue indigo (Baptisia).
There are some wonderful cultivars of false blue indigo on the market. Baptisia 'Purple Smoke' has been available for a number of years. It has steel gray stems and robust purple flowers. 'Carolina Moonlight' is a more recent introduction that has creamy yellow flowers. The latest addition, Baptisia TWILITE PRAIRIEBLUESTM has burgundy flowers highlighted with yellow.
Baptisia 'Carolina Moonlight' is a recent introduction; photo by Tom Clark
An example of a coastal plant with the same, deep tap root adaptation is sea holly (Eryngium). Site and space these plants with care so that you do not have to move them once they have settled in.
In addition to conserving water, there are plenty of other reasons why drought tolerant plants are desirable for the garden. Many, such as tickseed (Coreopsis), ornamental sage (Salvia) and calamint (Calamintha), are long-blooming. Others, such as sea holly (Eryngium) and butterfly weed (Asclepias) make excellent, long-lasting, cut flowers.
A host of drought tolerant plants, including many herbs, are wonderfully fragrant. They attract butterflies and bees yet, due to their strong fragrance, are unattractive to deer. Anise-hyssop (Agastache) falls into this category. Two of my favorite cultivars that flower from July until late September are the hot pink 'Tutti Frutti' and the smoky purple 'Black Adder' which has menthol-scented foliage.
Tips for a Successful Drought-Tolerant Garden:
Plan your garden by grouping plants with similar cultural requirements. Place drought-loving plants together to create a low-watering zone in your garden.
Site your plants carefully. Drought-tolerant plants will either flop or die in soils that are too rich, have inadequate drainage or are heavily fertilized. For many Mediterranean plants, it is not the cold but the combination of the wet, water-logged soil with the cold that kills them in the winter. Good drainage is important for drought-tolerant plants.
Amend your soil with good organic matter (compost) before you plant to retain moisture. If you have heavy soil, amend with grit or pea gravel to improve drainage.
Substitute ground cover plants in areas where it is difficult to grow turf; particularly shady areas or narrow sections of your yard.
Space plants properly so that they do not compete with each other for root space, water or nutrients.
Water wisely. Water early in the morning before the heat of the day to minimize evaporation. Allow nature to do her share; you do not need to water your garden after a heavy rain. Watering by hand at the base of plants, with soaker hoses or with drip irrigation, is highly efficient. Oscillating sprinklers tend to be less efficient, but can be used early in the day.
Water deeply and less frequently as opposed to shallow and frequent watering. Deep watering means deeper, more efficient root systems develop on your plants. Do not water your plants unless they need it. To check stick your trowel 4 inches into the ground and see if the soil is moist. The rule of thumb is 1 inch per week (approximately 1/2 gallon per sq.ft.).
Mulch your garden not only to suppress weeds but also to retain moisture. A 2 to 3 inch layer of mulch is more than sufficient for most areas of your garden. Shredded pine bark, shredded leaves and fine gravel are three good options that provide very different looks.
Weed your garden frequently in the spring. Rather than trying to tackle everything at once spend 15 to 30 minutes weeding several times a week. As well as getting the job done, you will be spared of unnecessary back pain and exhaustion. Weeds compete with plants for water and nutrients.
Most plants take 1 to 2 years to establish a good root system. They will need to be watered conscientiously during the first year to establish a healthy roots. Once they are established, you will need to consider your soil conditions (e.g., clay, loam or sandy soil), as well as the temperature and age of the plant when deciding when to water.
Do not fertilize water-stressed plants. The salts in the fertilizer will burn the weakened, water-deprived roots.
Use water-retaining polymers (e.g. Terra-Sorb or Soil MoistTM) in your container plantings to absorb and hold water.
Look for "reduced maintenance" cultivars and blends of turf grasses including Kentucky bluegrass (Poa pratensis) and tall fescue (Festucaarundinacea) cultivars that have been bred for turf. They tend to have deeper root systems than other turf grasses and will require less water.
Have fun designing with drought-tolerant plants. They come in all shapes and sizes and offer a nice selection of textures and colors to experiment with in the garden.