The U.S. Department of Agriculture (USDA) Plant Hardiness Zone map has long served as a foundational tool for gardeners, providing guidance on which perennial plants can survive the coldest winter temperatures in a region. Zone 6b, which includes Greene County, is defined by average annual minimum temperatures ranging from -5°F to 0°F, has traditionally been characterized by cold winters and warm, long summers, making it suitable for a diverse range of plant life, including hardy fruits, vegetables, trees, and perennials. However, the stable definition of this zone is now in a state of flux.

The most definitive evidence of this change is the northward migration of plant hardiness zones, a phenomenon that has been observed and documented across the contiguous United States.

Data from the USDA Plant Hardiness Zone Map, the first update since 2012, explicitly shows this climatic evolution. The updated map, which incorporates data from over 13,000 weather stations, indicates that roughly half of the country has shifted to a warmer hardiness zone. This trend is expected to continue, with projections indicating that 90 percent of locations are likely to shift to even warmer zones by the middle of the century.

The Paradox of an Extended Growing Season

A lengthening growing season is a prominent feature of the new climate. Data from the EPA shows that the average length of the growing season in the contiguous 48 states has increased by more than two weeks since the beginning of the 20th century, with a particularly significant increase occurring since the 1970s. This extension is driven by two key phenomena: The final spring frost is occurring earlier than at any point since 1895, and the first fall frost is arriving later.

While an earlier spring offers the opportunity for earlier planting to avoid later summer heat stress, it can also disrupt the natural dormancy cycles of plants. In response to an unseasonably warm spell in early spring, perennials, shrubs, and fruit trees may break dormancy and begin to bud or leaf out. This early growth is tender and highly susceptible to damage. The risk arises when the early warm spell is followed by a late-season freeze event, which is becoming a more common feature of volatile weather patterns. The very change that appears to be a benefit—a longer growing season—is concurrently creating a new and devastating risk.

The Volatility of Weather Patterns

The climate in Zone 6b is not merely warming; it is becoming more volatile, characterized by an imbalance of extreme weather events. The rise of heavy precipitation events is a significant concern. The EPA reports that a larger percentage of precipitation has come in the form of intense, single-day events, with nine of the top 10 years for extreme one-day precipitation occurring since 1995. This shift from steady rainfall to intense deluges can overwhelm garden beds, leading to soil erosion, nutrient leaching, and the risk of plants developing “wet feet,” a condition that can lead to root rot.

This problem is compounded by longer periods of drought and extreme heat, a contrasting but equally impactful feature of the new weather patterns. The combination of these extremes means that gardeners must now manage for both a super-saturated soil one week and a parched landscape the next.

Furthermore, the character of winter is changing. Winters are warming more rapidly than summers in many regions, and a direct consequence is that more winter precipitation is falling as rain rather than snow. The absence of consistent snow cover, which acts as a natural insulator, leaves the ground vulnerable. This leads to more frequent and drastic freeze/thaw cycles in the soil, which can physically “heave” plants out of the ground, exposing their root balls to the elements and leading to death. The shift from a consistently cold, snow-covered winter to a warmer, wetter one introduces a new, physical stressor on plant root systems that was not historically as prevalent.

The Proliferation of Pests, Diseases, and Invasives

The warming of minimum temperatures is allowing pests and pathogens, previously confined to southern climates, to expand their geographic range northward. This represents a significant new challenge, as gardeners must now prepare for threats that were not historically relevant to their region. For example, the brown marmorated stink bug, a nuisance pest and agricultural menace, is expanding its range into Zone 6b. Furthermore, the Asian needle ant, a species with the potential to disrupt forest ecosystems and pose a health risk, is projected to reach Missouri due to its northward migration. Similarly, Japanese beetles are becoming a greater threat to corn and soybean crops in Missouri and can appear in greater numbers than in previous years.

New plant diseases are also emerging as a threat. The warmer, wetter conditions create a more favorable environment for fungal and bacterial diseases. The drought stress and prolonged heat that are a key feature of the new climate severely affect a plant’s physiological and biochemical attributes, weakening its overall vitality. This is followed by a reduction in the expression of natural immune receptors in the plant. Simultaneously, the new climatic conditions of high humidity and elevated temperatures create ideal conditions for new pathogens to germinate, proliferate, and spread. This means that when a new pathogen arrives, the plant’s capacity to fight it off is already compromised. The combination of a weakened host and a thriving pathogen creates a complex web of interconnected problems that are more difficult to manage than a single threat in isolation.

The shift in climate also enables new invasive species to move into and overwinter in Zone 6b, where they can outcompete native plants. Examples include the fast-growing kudzu vine, various species of honeysuckle, and water hyacinth, which may be newly able to survive winter in these regions. These invasive plants, which have not evolved with the local ecosystem, can form dense thickets and smother native vegetation, severely disrupting the natural balance.

Pollinators, Birds, Insects, and Wildlife

Important connections between pollinators, birds, insects, wildlife, and the plants they depend on can also be disrupted by climate change. Pollinators, such as hummingbirds and bees, may arrive too early or too late to feed on the flowers on which they normally rely. Native bees rely on certain plants for food. If that species of plant emerges and develops earlier than usual, their food sources can be compromised. Studies done by the Center for Pollinator Research at Penn State have shown that wild bees are most affected by temperature and precipitation extremes.

Strategic Planning and Plant Selection

Successfully navigating the challenges of a changing climate requires a shift in mindset from simple hardiness to long-term resilience. A gardener’s response must be proactive, focusing on strategic planning, regenerative practices, and a multi-layered approach to building a healthy, stable ecosystem.

The first step in adaptation is the intentional selection of resilient plants. Rather than simply choosing plants rated for Zone 6b, it is now important to select species and varieties that can withstand both the colder winter extremes and the hotter, drier summer conditions

The most powerful strategy is to prioritize native plants. Native species are already genetically adapted to local climate, soil conditions, and pest and disease pressures. They require less water, fertilizer, and pesticides, which drastically reduces the cost and labor of maintenance while benefiting the local environment. https://mggreene.org/?s=plants

Adaptive Soil and Water Management

Healthy, resilient soil is the first line of defense against the volatility of alternating drought and deluge. The addition of organic matter, such as compost, is crucial for building soil structure. Compost improves drainage during periods of heavy precipitation, preventing root rot and “wet feet,” while also enhancing the soil’s water-holding capacity during drought. (It’sa good idea to have your soil tested periodically. See “Soil Testing.“ https://mggreene.org/2025/09/soil-testing).

Efficient watering methods are also essential. Drip irrigation systems and soaker hoses provide consistent moisture directly to the root zone, which is critical for plant health during prolonged dry periods and minimizes water waste. They also reduce the risk of foliar diseases that can be caused by overhead watering.

Cultivating a Resilient Ecosystem

Successful adaptation requires a shift in horticultural practices. Adjusting planting schedules is a key strategy; gardeners can take advantage of an earlier spring by planting certain crops earlier to avoid the intense heat of late summer. Conversely, a quick transition from frozen ground to near-summer temperatures may make it impractical to plant cool-weather crops in the spring, making a fall planting schedule more reliable for vegetables like lettuce, spinach, and broccoli.

A central principle of a stable, adaptive garden is “functional redundancy”. A volatile climate means that a single plant species, even if well-chosen, may fail due to a specific stressor like a late frost or intense heat. By planting multiple species that perform the same ecological role at the same time—for example, multiple types of flowering plants that all bloom in mid-summer—gardeners can ensure that if one species succumbs to environmental stress, others will still be present to provide nectar and pollen for pollinators. This safeguards the continued health of the garden ecosystem.

Cultivating a Sustainable Future

The effects of climate change are profoundly reshaping ourgardening landscape. The evidence is clear: The traditional boundaries of the hardiness zone are shifting, weather patterns are becoming more imbalanced and volatile, and new pests, diseases, and invasive species are moving northward.

However, these challenges are not insurmountable. By embracing a proactive, adaptive mindset, Greene County gardeners can respond to a problem and become part of the solution by building landscapes that are more resilient, sustainable, and productive.

SOURCES: MU Extension, Penn State Extension, Master Gardeners of Greene County, and Climate Central