Ask a Master Gardener: Selecting Suitable Plants for Coastal Alabama
By: Dr. Judy Stout, Mobile County Master Gardener | www.mobilecountymastergardeners.org
Q: We moved to Fairhope last year from Indiana and are now ready to take on our 1.5-acre yard. We’ve received numerous catalogs of great looking plants to review over the winter. However, we’re not sure how to determine what will grow best here. Your suggestions?
A: Welcome to exciting possibilities on this wonderful Alabama Gulf Coast! Rather than recommending a list of plants, let me provide a little background on plant requirements for our environment and some research tools that may help you. You can then select suitable plants that fit your taste and goals.
We are in a semi-tropical, humid environment with hot summers and abundant rainfall distributed unevenly over the year. Our winters are relatively mild, but we can experience brief low winter temperatures very damaging to plants. Damaging low temperatures can kill a plant immediately, whereas high temperatures stress plants and can cause cumulative damage over time. For any plant you are interested in, first check the 2012 Plant Hardiness Zone Maps of the US Department of Agriculture for the hardiness zone of the plant
( https://planthardiness.ars.usda.gov/). This map is applicable to perennials, shrubs, and trees and assumes that plants are adequately watered.
Coastal Alabama is in zones 8-9, with 30-year average extreme low temperatures of 15-20°F and 20-30°F, respectively. The higher the zone number, the higher the extreme minimum temperature average. Hardiness zone numbers are found in good catalogs, reference books, web sites and on plant labels. On the coast, cold temperatures may be moderated by nearby water bodies or urban development. You can check your zip code for more specific information at the same USDA web site. Microclimates in your yard may also create warmer temperatures. Consider the location of structures providing protection from wind or structures reflecting the sun’s warmth. Slopes and low valleys can trap heavier, cold air.
Of greater concern for plant success here is the level and duration of heat and humidity. Temperatures exceeding 86°F cause the unsuitable plant to be unable to process water fast enough to maintain normal functions, destroying essential enzyme activity. Prolonged heat stress can be expressed by leaf discoloration and drop, flower bud wither, reduced root growth and subsequent death. Effects are not immediate and can accumulate over multiple growing seasons. Although including fewer varieties of plants, the American Horticultural Society Heat Zone Map designations are helpful. These zones are based upon the annual average number of days with temperatures above 86°F. Mobile and Baldwin Counties fall within Heat Zones 8 and 9 with averages of 90-120 and 120-150 days above 86°F (https://www.lawnstarter.com/blog/wp-content/uploads/2019/02/Plant-heat-zone-map.jpg).
Do not be confused. Coincidentally, we are in zones 8-9 on both the Hardiness and Heat Zone maps. Check whether the zone number associated with a plant variety applies to hardiness or heat. For instance, Mobile and Seattle are both in hardiness zone 8, but Seattle is in heat zone 3 with only 7-14 days above the 86°F threshold. Though Seattle plants would survive Mobile winters, they would melt in our heat and humidity!
Local nurseries carry species and types suitable for our area or can order for you. Nationwide “big box” stores may offer plant varieties not suited for the Alabama Gulf Coast. Check plant labels and do your research to avoid wasted investments and disappointment.
If your landscape plans include small fruits or fruit tree crops, you need to also consider the necessary winter chill hours required for flowering, fruit production, and ripening of your desired fruit. Fruits require a period of winter chill-induced dormancy to resume normal spring growth. Winter chill hours accumulate at approximately 29°F to 64°F with the best accumulation at 43°F. You may not have much success with cherries and most apple varieties but should have lots of figs, rabbiteye blueberries, and blackberries! Alabama winter chilling hour maps and lists of specific fruit requirements can be found in Alabama Extension System ANR-0053-D and at https://www.aces.edu/wp-content/uploads/2019/02/ANR-0053-D_WinterChilling_121418Lg.pdf .
Do you also want a vegetable garden? There are, generally, warm season and cool season groups of vegetables based upon their soil temperature requirements for germination, length of growing season, and temperatures at which flowers open or bolt (go to seed, e.g., broccoli, reducing harvest and flavor). Similarly, increased temperatures can cause flowering and fruit production to cease (e.g., tomatoes). There are, however, some wonderful southern vegetables that really flourish in our hot summers – peppers, okra, and eggplant! Vegetable seed catalogs are good at suggesting crop planting seasons and length of time to production maturity. The Alabama Cooperative Extension System offers great guidance on soil temperatures for germination (ACES ANR-1061), planting guidance for numerous vegetable types (ACES ANR-0063) and vegetable seasons (ACES ANR-1165). Extension agents are also available to answer questions and guide you.
The Mobile County Master Gardeners Association maintains a productive “Dream Garden” at the Jon Archer Center on Schillinger Road. The garden demonstrates varieties of perennials, shrubs, fruits, and vegetables you may like. You may also want to visit the Mobile Botanical Gardens to view suitable plants in a garden setting for shape, size, flowering, and other characteristics.
Enjoy your fall/winter catalog shopping and visit the Mobile Botanical Gardens’ March 18-19, 2022 plant sale for hundreds of trees, shrubs, perennials, fruits, herbs, and vegetables selected specifically for success at your new home!