Survival of the Fittest
Drought Strategies For Two Gardens.
By Rachel Foster 4/14/05

My friend Lotte prefers not to water her small garden. Observing it for more than a decade has provided me a valuable opportunity to see what can be done with very little water. Existing shrubs and trees, mostly non-native, have survived for years without any help at all, and it's proved easy to establish new, mostly native shrubs with just one season of light supplemental watering. Many bulbs adore the dry summer routine and return year after year. Finding non-bulbous perennials that survive and bloom is the ongoing challenge. But I have learned that some perennials have far lower summer water needs than others.
At home on my own fifth of an acre, a central, sunny area is watered every one to two weeks in the driest months, for a monthly rainfall equivalent of roughly 2 inches a month. I cut back further on water in September. This regime supports lilies, day lilies, hardy geraniums, kniphofia, salvia, campanula, echinacea, iris, many kinds of grasses and even (to my surprise) dahlias and canna lilies. Included in these beds are many things that would perform well with less water: artemisia (the silver ones), yarrow, mulleins, phlomis, phygelius, sedum, Sisyrinchium striatum, thermopsis, penstemon, oriental poppy, liatris, catnip, rose campion (Lychnis coronaria) and all manner of herby things such as oregano and anise hyssop.
Much of my garden, does, in fact, receive less water. This is partly because some spots are difficult to irrigate efficiently. But thanks to my experience at Lotte's, I also have an interest in making some zones more hospitable to bulbs by deliberately allowing them to dry out in summer. I'm experimenting with an awkward, sloping bed next to the driveway (and outside the deer fence). I watered it only twice last year. Survivors include lavender, comfrey, chartreuse leafed lamb's ears, hellebores and various irises, including some clumps of a wonderful Turkish iris, Iris lazica, that are crammed with hundreds of lavender blue flowers in March. California poppy and biennial money plant add welcome color in early summer.
A narrow border along a boundary fence relies mostly on shrub roses for summer interest. I maintain them with a leaky hose that runs about every three weeks. The roses were originally interplanted with clematis, but some of these have failed. Generally, species clematis have done much better along this fence line than large-flowered hybrids. Kniphofia does quite well in this "dry" border with occasional spot watering, but day lilies and heuchera do not. I am about to replace unhappy plants with gray-leafed grasses and bronze New Zealand sedge. Amsonia, helenium, columbine and certain geraniums seem to like it here, as do native irises. Tulips and ornamental onions love it.
Well-drained soil that encourages strong, deep root systems and doesn't get soggy in winter is a basic requirement for a drought-resistant garden. My own soil is a fairly heavy, moisture-retentive loam amended with compost. Some areas of the garden hold too much water in winter for the most drought-adapted plants to survive. Forget gaura. But most areas drain well enough and, substantial as it is, I consider the soil a blessing. For one thing, shaded areas, quite conventionally planted, go many weeks in summer without water.
My strategy in the perennial garden is to plant early, feed lightly, and mulch if I can get around to it before the soil dries out. I use only organic fertilizers, because I believe they promote good root growth. I also suspect that synthetic fertilizers, which become available to the plants faster and earlier in the year, encourage lush spring top growth that can be difficult for the plants to support as soil moisture declines. For perennials that wouldn't thrive under my watering regime (astilbe, phlox and delphinium, for example) I substitute proven survivors, including shrubs and sub shrubs like lavender, fuchsia, phygelius, and blue beard (caryopteris).
In Lotte's garden, where the goal in summer is simple survival, there will never be much in bloom during the dry months. My own garden is a compromise between reasonable water economy and a desire for a colorful garden. If I were compelled to turn off the spigot in midsummer, I'm confident that most of my plants would pull through and come back to bloom another year. But if dry winters and low snow packs become a regular thing, I'll be planting more shrubs and mulching my beds with a heavy layer of gravel.