Of course, most plants have ID tags and zone ratings, but David contends that these are simply guidelines, not prohibitions. Further, he maintains that ratings for popular ornamental plants are often incomplete or wrong and that many “tropical” plants are tougher and more adaptable than we might think. In addition, zones give broad regional information, but can’ tell a gardener what his or her yard is like, and hardier cultivars are being created all the time that can survive outside of their designated zones. A few of the plants David highlights in his book are needle palm, windmill palm, dwarf palmetto, temperate bananas, Eucalyptus neglecta, and Rhapidophyllum hystrix.
To grow warm-weather plants in cool areas, you should begin by educating yourself about your garden. Define the microclimates in it, as well as its temperature fluctuations, to determine the right spot for planting; in fact, you can create a zone map unique to your garden. Then, to maintain the plants, be sure to think about four-season care, not just winter care; shelter the plants, especially smaller ones; and mulch heavily to conserve soil moisture availability. To provide winter protection, cover the bases and crowns with leaves in late fall or early winter. Of course, “pushing the zone” doesn’t mean that any warm-weather plant can thrive anywhere, but as David concludes, his book gives cold-weather gardeners “a 64-crayon box of possibilities, rather than the 8-crayon box of plant staples.”
Professor of Botany
Zone map for plant hardiness
“Palms Won’t Grow Here and Other Myths” (Timber, 2002)