Ornamental horticulture uses basic concepts from a variety of disciplines including plant physiology, molecular biology, soil science, entomology, and pathology to answer questions concerning horticulture professionals. Climate changes could alter current USDA hardiness zones (Figure 1) which provide a guide for horticulturists to select plants that survive in cold climates. This would impact the diversity of plant species grown in nurseries and landscapes throughout Maine and provide a market opportunity for professionals to introduce new, less cold hardy plants. However, some plants which require lengthy vernalization periods, such as tulips, may not perform as well as in the past. It is also possible that species with more plastic responses to temperature extremes (i.e. red maple; hardy to zones 3b to 9) may be more adaptable to temperature changes throughout the United States than less plastic species (i.e. paperbark maple; hardy to zones 5-7). Some species, such as lilac, which flower in response accumulated temperature, would flower earlier than in previous years. Climate change predictions indicate an increase in the length of growing seasons. Thus, commercial growers could sell ornamentals earlier, and greenhouse growers would need less fuel for heat. It would be important to balance economic benefits of longer growing seasons with potential environmental impacts of increased agricultural production. For example, commercial growers would fertilize and water plants more frequently which may increase the amount of fertilizer in ground water. Efficient irrigation systems which use moisture sensors to automate irrigation are being researched at the University of Maine in collaboration with researchers from the University of Georgia. These systems may produce no fertilizer runoff and would reduce one environmental impact of longer agricultural growing seasons.
Figure 1- Current plant hardiness zones in Maine range from 3a east of Fort Kent to 6a on the southeast coast. The USDA is currently revising hardiness zone maps, and it is likely that some areas in Maine will be in warmer zones once new maps are released. We gratefully acknowledge Dr. Lois Berg Stack and The University of Maine Cooperative Extension Service for helpful insights and the reproduction of this figure.