Plants such as stonecrop (Sedum) and hens and chicks (Sempervivum) have evolved fleshy leaves (same strategy as cacti) to help them retain water during periods of drought. They are 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 (modified stems) that store water. In the Home Gardening Center at The New York Botanical Garden we have rich garden soil. We have planted the bearded irises high, so that the rhizomes are clearly visible above ground to ensure that they stay dry and do not rot from excessive moisture. The varieties in the Botanical Garden include remontant, or reblooming irises, that produce a second flush of blooms in early fall.
Other plants have evolved hairy or wooly surfaces to help conserve moisture. One of the favorites for children in the Garden is lamb's ears (Stachys byzantina). It is a common sight to see a child stroking the plant and explaining to their parents that they will be taking it home. Plants with fine hairs are easy to identify in the garden; they have grey or silver foliage that reflects light and heat. Lavender (Lavandula) is one of my personal favorites. Wormwood (Artemisia), yarrow (Achillea), and culinary sage (Salvia officinalis) are several other examples. These plants need full sun and good drainage to survive.
Many prairie plants have deep tap roots. The advantage of these tap roots is twofold: to help the plant rejuvenate when consumed by grazing animals and to help them survive dry spells. Plants with deep roots 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 (cultivated varieties) of false blue indigo on the market. 'Purple Smoke' has been out 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, 'Twilite Prairieblues',has burgundy flowers highlighted with yellow.
An example of a coastal plant with the same adaptation (a deep tap root) 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.
We offer a wonderful new book in our shop, The Green Gardener's Guide, Simple, Significant Actions to protect and preserve our Planet, by Joe Lamp'l, that is an essential resource on this topic. The Green Gardener's Guide offers numerous cause-and-effect scenarios of the environmental consequences of seemingly minor lifestyle changes. For instance, if U.S. gardeners collectively watered early in the morning instead of in the midday sun, the nation would save at least 700 billion gallons of water annually.
Why Use Drought Tolerant Plants in Your Garden?
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, they 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 Fruiti' and the smoky purple 'Black Adder', which has menthol-scented foliage.
Keep reading, for tips for creating your own drought-tolerant garden and a list of plants to include.
For more gardening tips visit us online at http://www.nybg.org. For great garden and garden-inspired product visit NYBG's online shop.