McCreary: Low-water plants not good in all microclimates

This spring I’ve noticed an expanded selection of captivating, low-water plants in our local nurseries and garden centers. Although all create an energizing splash, none of these beauties comes with clear, cautionary warnings and could be problematic in most of our microclimates.

Two of them are beguiling enough to entice any gardener, even those who have witnessed their shortcomings and hope to try once again. But when these species begin to struggle, the weekend gardener is likely to be quite perplexed.

Mirror plant (Coprosma) is featured in nearly all local nurseries and for good reason. Its shiny, multi-hued foliage, as eye-catching as any floral spray, promises to add sparkle to gardens and, once established, this easy-care, evergreen shrub needs little summer water.

Hybrids of the large-growing species, Coprosma repens, now include many named cultivars that are more compact, brighter, and more garden friendly. Small, glossy leaves are tinted silver, lime green, creamy yellow, orange, or pink, depending on the selection.

What’s not to like about coprosma? In a word: Tenderness.

Native to New Zealand, its hardiness rating generally claims to suit most of the Bay Area and North Coast. But mirror plants can be seriously damaged by cold and sometimes do not survive in many micro-climates nestled around our homes, in low valleys, and wherever cold air collects in winter.

Unless global warming hurries along, this plant needs winter protection to survive unscathed. Perhaps more sensibly, they should be planted only where cold winter air never accumulates or reliably flows away.

Cold-damaged plants can be severely pruned in spring when buds begin to show on living stems that have lost foliage. If all wood above ground dies, new sprouts can form at the base, but the process is slow. Young plants may not survive.

Another vulnerable beauty

Several different conebush (Leucadendron) cultivars have also appeared for sale in growing numbers this spring. Native to South Africa, it’s long been a popular plant in San Diego’s and Santa Barbara’s coastal climates. And above Monterey Bay, many extraordinary specimens fill the UC Santa Cruz Arboretum.

But in our area, success with leucadendrons can be iffy. Plant tags on some cultivars indicate they are hardy in Sunset zones 16 and 17, which lie in a very narrow coastal strip from the Oregon border southward, as well as in thermal belts on hillside micro-climates slightly inland.

A few cultivars are said to be hardy throughout the more expansive inland micro-climates, Sunset zones 14 and 15, but even here these may need winter protection when temperatures drop below 20 or 25 degrees causing plants to freeze to the ground.

Special care

Besides providing consistent winter protection, leucadendrons need other special care. They require fast-draining, acidic soil and do not tolerate phosphorous, one of the three main ingredients in most bagged fertilizers.

Several selections reach 4 to 5 feet or more in height but can be kept lower with pruning. Pruning, however, must be done carefully, since 3 to 5 branchlets will form at the point of each cut and will result in awkward structure.

But on the upside, leucadendrons are deer and drought tolerant and their highly colored green-red-pink-golden foliage becomes a year-round, cheery mosaic on fluttering, willowy branches that rise from the ground.

Bright colorful bracts similar to leaves surround small cone-like blooms on branch tips over a long period in the cool season to create a dazzling show.

Leucadendrons are pleasant companions for grasses and small conifers, but they are stalwart enough to stand alone as large specimens in dryscapes and are equally effective in large containers.

Tender in the night

More and more types of citrus have also become commonplace in the past year or two, especially in big-box garden centers. Besides oranges and lemons, it’s easy to find kumquats and grapefruits, mandarins and limes, and even the sour Calamondin.

All of these are cold sensitive to some extent, but lemons and limes are most easily damaged in nearly all of our micro-climates, though they rarely freeze completely once established. Still, all can be grown successfully if care is taken to shield them from heavy, cold air in winter.

If you find that your citrus does freeze and re-grow, check to see if the new growth rises above or below the graft. Any shoots below the angled graft line grow out of the root stock and must be removed. If no growth recovers above the graft line, remove the plant.

Rosemary McCreary, a Sonoma County gardener, gardening teacher, and author of Tabletop Gardens, writes the monthly Homegrown column for The Press Democrat. Contact her at rosemarymccreary@gmail.com or write to her at 427 Mendocino Ave., Santa Rosa 95401.