Ready, Set, Adapt! Climate Change – What’s a Gardener to Do?

Part 2: What’s a Gardener to Do? 

By Wendy Mills, Certified Extension Master Gardener

Increasing winter temperatures are expected to result in a northward shift of the zones conducive to growing various types of plants, known as plant hardiness zones. These maps show the mean projected changes in the plant hardiness zones, as defined by the U.S. Department of Agriculture (USDA), by the late 21st century (2070–2099) under a higher scenario (RCP8.5). The USDA plant hardiness zones are based on the average lowest minimum temperature for the year, divided into increments of 5°F. Based on these projected changes, freeze-sensitive plants, like oranges, papayas, and mangoes, would be able to survive in new areas.142 Note that large changes are projected across the region, but especially in Kentucky, Tennessee, and northern Arkansas. Sources: NOAA NCEI and CICS-NC  

Increasing winter temperatures are expected to result in a northward shift of the zones conducive to growing various types of plants, known as plant hardiness zones. These maps show the mean projected changes in the plant hardiness zones, as defined by the U.S. Department of Agriculture (USDA), by the late 21st century (2070–2099) under a higher emissions scenario (RCP8.5). Sources: NOAA NCEI and CICS-NC

While predictions about climate change and its impacts appear nothing short of apocalyptic, adapting to the changes to come will require a return to gardening fundamentals.

Illicium floridanum (Florida anise tree) flowers in April at the National Arboretum. Photo © 2017 Elaine L. Mills

Illicium floridanum (Florida anise tree) flowers in April at the National Arboretum.
Photo © 2017 Elaine L. Mills

  • Select Plants Carefully
    Although Arlington and Alexandria are in USDA Hardiness Zone 7a, plants that thrive in zones 7b and 8 increasingly are doing well here.

“As gardeners we need to be aware that changes in climate will increasingly affect the choice of plants we can grow,” says Kirsten Conrad, Agricultural Resource Extension Agent. “We can expect species migration and the movement out of our growing zone of plants  like sugar maple and rhubarb that prefer cooler, moister summers.”

At the same time, “Gardeners can be delighted by the potential migration northwards of plant species from southern climates, such as Illicium floridanum (Florida Anise Tree), Acer floridanum (Florida Maple), Gordonia lasianthus (Loblolly Bay),  and Persea borbonia  (Red Bay Laurel).”

Conrad recommends selecting Virginia natives, xeriscape (drought-resistant), and heat-tolerant plants. Before making your selection, figure out where you will place the plant in your garden. Microclimates in your landscape could magnify hot, cold, wet, and windy conditions.

    • Worms converting kitchen scraps to compost.

      Worms converting kitchen scraps to compost.
      Flickr: looseends, Creative Commons license 2.0

      Build your soil and keep it cool: Organic matter improves drainage and lightens heavy soils. It provides food for soil microorganisms which enable plants to absorb water and essential nutrients through their roots. Add organic matter and compost to your soil and grow cover crops to further enrich it. Mulch your vegetable and annual flower beds with grass clippings and nitrogen-rich shredded leaves, and use wood mulch for pathways and as a light dressing around shrubs, trees, and in natural areas. Mulch and cover crops reduce erosion and weed growth and moderate soil temperature and moisture levels.

    • Symptoms of water stress: From mild to extreme signs: • Plants are slow growing and stunted. • Grasses show signs of wilt and do not spring upright after being stepped on. • Diminished leaves, flower buds and flowers. • Lack of seed set, surface, and tissue damage to vegetables, and reduced production. • Leaves are discolored, wilting or show signs of burning or scorching on edges. Early fall color. • Bare spots appear in ground covers. • Plantings show the effects of weeds, insect pests, and diseases. • Plants appear dead and/or die. Source: Missouri Botanical GardensWater deeply and regularly to promote root development. Healthy plants are 75- to 90 percent water. Like all living beings, they need water to carry out vital functions. How much water they need depends on the plant, where it is in its lifecycle and its placement in the landscape, as well as soil type and weather conditions.

As a general rule, watering deeply means that water is able to soak six inches below the soil surface. In most soils, according to Virginia Cooperative Extension, this is about one inch of water applied each week in the form of rainwater, irrigation water, or both. (Some vegetables, like tomatoes, may require close to two inches of water per week for optimum production.) After watering use a moisture gauge or dig down into the soil with a trowel to see if it is moist six or so inches below the surface. You can also place several empty tuna fish cans around your garden to measure rainfall and water from sprinklers. Keep in mind that a gentle soak over a longer period of time will allow for better absorption than short, heavy bursts that create puddling and runoff. Deep watering helps protect plants in times of drought as the soil surface will dry out much quicker than it will below ground where the soil is cooler. And remember: Water the soil, not the plant!

    • Get the facts then feed your plants: Testing your soil is the only way to determine if phosphorus, potassium, calcium or magnesium are in short supply or if a pH adjustment is needed. Without a soil test, any application of fertilizer could be detrimental to the landscape. Soil test kits are available through the Virginia Cooperative Extension Office in Fairlington and Master Gardener Plant Clinics. You will need one test kit for each area of your garden, for instance lawn, vegetable garden or acid-loving shrubs. Virginia Tech’s soil lab will analyze the samples and email you the results and treatment recommendations within a week. (A routine test costs $10.)
Example of a soil test report. Separate soil samples should be submitted for different parts of the garden--lawn, vegetable, fruits, flower, perennials. Results are calculated based on the pH level and amount of key nutrients required by different plants.

Sample soil test report. Separate soil samples should be submitted for different parts of the garden. Results are calculated based on the pH level and amount of key nutrients required by different plants.

Gardening in unpredictable times requires a willingness to adapt one’s tried and true strategies to changing facts on the ground. It’s a call to experiment with new tools and strategies, to move plants around, say goodbye to those that no longer thrive, and select others that will.

It’s an invitation to be curious and a reminder to seek out local experts at the Master Gardener Help Desk and plant clinics who can help you identify and manage pests and plant diseases. Now more than ever, gardeners need to pay attention to how their plants are faring through the seasons and take early action to reduce the stresses posed by erratic weather and the pervasive influence of climate change.

Stay tuned for Part 3, April 10, 2019: 2018 Notes from the Field to learn about changes seen in 2018 by Extension Master Gardeners at the Organic Vegetable Garden due to changing weather.

Special thanks to Kirsten Conrad, Mark Habeeb, Joanne Hutton, Joyce Hylton, Judy Johnson, Jessica Kaplan, Elaine Mills, Paul Nuhn, and Judy Salveson for their insights and material contributions to this article.

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