The USDA Plant Hardiness Zone system guides gardeners in determining which perennial plants can survive typical winter temperatures in a specific location. Based on the most recent data, Lincoln, Nebraska, now falls primarily within Zone 6a on the official USDA map. While some outlying areas and older maps still place the region in Zone 5b, this 6a designation indicates a slight warming trend over time. The zone number is an indicator of a plant’s ability to survive the coldest part of the year.
How the USDA Plant Hardiness Zone System Works
The USDA system divides North America into 13 zones, each representing a 10-degree Fahrenheit range of the average annual minimum winter temperature. This metric uses thirty years of weather data to determine the coldest temperature a plant must endure to survive the winter. The map focuses solely on cold tolerance and does not account for heat, rainfall, or soil conditions.
To provide greater precision for plant selection, each major zone is further divided into ‘a’ and ‘b’ sub-zones, representing a narrower 5-degree Fahrenheit band. Lincoln’s Zone 6a classification signifies that the average lowest winter temperature falls between -10°F and -5°F. This is a measurable shift from the previous Zone 5b designation, which had a range of -15°F to -10°F. Gardeners should select plants rated for Zone 6 or colder to ensure reliable winter survival.
Beyond Hardiness: Local Growing Factors in Lincoln
While the hardiness zone addresses winter survival, other local climatic and environmental factors in Lincoln dictate overall plant health and growing season success. Timing is crucial for annual crops, as the average last spring frost typically falls between late April and early May. The first fall frost generally occurs in the first half of October, defining an approximately 160-day growing season. These dates inform when to safely transplant frost-sensitive plants outdoors.
The unique soil composition presents a specific challenge for local gardeners. Much of the soil in Lincoln is heavy clay or clay-loam, which compacts easily and drains slowly. This density restricts root growth and can lead to issues with standing water, potentially suffocating plant roots. Incorporating organic matter, such as compost, is necessary to improve soil structure and water infiltration rates.
The Great Plains environment subjects plants to intense summer conditions not measured by the hardiness zone. Summers in Lincoln are often hot, with frequent temperatures reaching into the 90s, causing significant heat stress. Plants cold-hardy for Zone 6a may still struggle with summer heat, strong winds, and the dense local soil. Plant selection must prioritize both winter cold tolerance and summer heat resilience.
The urban environment creates microclimates, contributing to Lincoln being shown as a split zone. The city center and densely developed areas retain more heat, resulting in the warmer 6a designation. Gardeners in the immediate city limits may experience milder minimum temperatures than those in rural, outlying areas, which often align with the colder Zone 5b. Understanding specific yard conditions, such as proximity to a building or paved area, can be as informative as the broad zone map.
Successful Planting Choices for Lincoln’s Climate
Perennial Flowers
For perennial flowers, species known for their hardiness and ability to tolerate heavy soil are recommended. Excellent choices include Daylilies and Peonies, which are robust and reliably return each year. Native options, such as Narrowleaf Coneflower and Dotted Blazing Star, are particularly well-adapted to the seasonal extremes and soil type.
Trees and Shrubs
Trees and shrubs should be selected to withstand both the winter cold and the summer stress. Common Purple Lilac is a reliable, fragrant choice, as is the Eastern Redbud, which provides early spring color. Woody plants like certain varieties of Maple, such as Autumn Blaze, or the Gray Dogwood, handle the region’s winter temperatures and tolerate a range of soil types.
Annuals and Vegetables
The late spring frost date dictates the planting schedule for warm-weather varieties. Tender vegetables like tomatoes, peppers, and squash should not be transplanted outdoors until the danger of frost has fully passed, typically around mid-May. Cool-weather crops, such as lettuce, peas, and spinach, can be planted earlier in the spring and again in the late summer for a fall harvest.