What Plant Zone Is St Louis

If you’re planning a garden in the Gateway City, knowing your plant zone is the first step to success. For gardening success, you need to know what plant zone is St Louis, as this number guides every planting decision you’ll make.

St. Louis sits in a unique climatic crossroad. This means our gardens can grow a wonderful mix of plants, but also face challenges from both hot, humid summers and occasionally harsh winters. Your official plant hardiness zone is the essential tool to navigate these conditions.

According to the latest USDA Plant Hardiness Zone Map, most of the city of St. Louis itself is firmly in Zone 7a. This zone has an average annual extreme minimum temperature of 0 to 5 degrees Fahrenheit. However, this is a general guide. The metro area shows more variety.

Microclimates can cause significant variations. Urban areas, with their concrete and buildings, often create “heat islands” that can mimic a warmer zone. Conversely, low-lying valleys or exposed hilltops might be a half-zone cooler. It’s always smart to talk to neighbors or a local nursery about there specific experience.

Understanding the St. Louis Metro Area Zones

When you look at a broader map, you’ll see a patchwork:

City of St. Louis & Inner Suburbs: Primarily Zone 7a (0°F to 5°F).
Outer Western & Southern Suburbs (e.g., Chesterfield, Fenton): Often Zone 7a, but some parts may be 7b (5°F to 10°F).
Areas Near the Missouri River & Further North: These can dip into Zone 6b (-5°F to 0°F).
Across the River in Illinois: Many areas are Zone 6b, with some pockets of 7a.

To find your exact zone, use the USDA website and enter your zip code. Remember, the map is a starting point, not a absolute rule.

Why Your Zone Matters for Plant Survival

The zone number tells you a plant’s cold hardiness—its ability to survive our coldest winter lows. A plant rated for Zone 5 can handle -20°F, so it will be very confident here. A plant rated for Zone 8 might only handle 15°F, making it a risky perennial that could die in a tough St. Louis winter.

Ignoring the zone often leads to dissapointment and lost money. Planting a zone 8 beauty like a gardenia in the ground might work for a few mild years, but a classic St. Louis cold snap will likely kill it.

St. Louis Gardening Calendar by Zone

Your zone dictates your planting dates. Here’s a seasonal guide for Zone 7a/6b gardeners.

Early Spring (March – April)

Cool-Season Vegetables: Direct sow peas, spinach, radishes, and kale as soon as soil is workable. Plant onion sets and potato eyes.
Perennials & Shrubs: A excellent time to plant bare-root or container-grown trees, shrubs, and hardy perennials.
Pruning: Prune roses and summer-blooming shrubs before new growth gets too far along.

Late Spring (May)

Last Frost Date: The average last frost is around April 15, but wait until early May for true tender plants. Always watch the forecast!
Warm-Season Crops: Transplant tomatoes, peppers, eggplants, and basil after danger of frost has passed. Direct sow beans, corn, and squash.
Annual Flowers: Plant marigolds, zinnias, petunias, and other summer bloomers.

Summer (June – August)

Focus on maintenance: watering deeply, mulching, and pest control. St. Louis heat can be intense.
Harvest summer vegetables regularly to encourage more production. Plant a succesion of beans or cucumbers for a fall harvest.
Late summer (August) is time to start seeds for fall crops like broccoli and Brussels sprouts indoors.

Fall (September – November)

Fall Planting: This is arguably the best time to plant perennials, trees, and shrubs! The warm soil and cool air encourage root growth.
Cool-Season Crops Again: Transplant those broccoli starts and direct sow lettuce, carrots, and beets for a late harvest.
Bulbs: Plant spring-flowering bulbs like tulips and daffodils after the soil cools, usually late October through November.

Winter (December – February)

Plan next year’s garden, order seeds, and protect tender plants with mulch. Winter is also good for pruning many deciduous trees while they are dormant.

Top Plant Picks for St. Louis Gardens

Choosing plants rated for Zones 6 or 7 ensures they are well-suited to thrive here. Here are some reliable winners.

Perennials & Flowers

Coneflower (Echinacea): Tough, drought-tolerant, and loved by pollinators. Many varieties available.
Black-eyed Susan (Rudbeckia): A cheerful, long-blooming staple.
Hostas: Excellent for shade gardens, though you’ll need to watch for slugs.
Daylilies (Hemerocallis): Adaptable and prolific, with thousands of cultivars.
Russian Sage (Perovskia): Loves heat, provides beautiful lavender haze in late summer.

Shrubs & Trees

Oakleaf Hydrangea (Hydrangea quercifolia): Native, stunning foliage and flowers, more forgiving than bigleaf hydrangeas.
Serviceberry (Amelanchier): A small native tree with spring flowers, edible berries, and great fall color.
Witch Hazel (Hamamelis): Unique, spidery flowers in late winter or fall.
Panicle Hydrangea (Hydrangea paniculata): Blooms on new wood, so winter cold doesn’t affect flowering. ‘Limelight’ is a favorite.

Vegetables

Most common vegetables grow well. Focus on timing for heat-lovers (tomatoes, okra, peppers) and cool-lovers (lettuce, broccoli, peas). Heirloom tomatoes are a particular passion for many local gardeners.

Overcoming St. Louis Gardening Challenges

Your zone is about more than just cold. Our humid continental climate brings other factors.

Clay Soil

Much of our native soil is heavy clay. It holds nutrients but drains poorly. The single best thing you can do is add organic matter—compost, leaf mold, or well-rotted manure—every year. Raised beds are also a fantastic solution for improving drainage quickly.

Summer Heat & Humidity

This stresses plants and encourages fungal diseases like powdery mildew. Choose disease-resistant varieties, space plants for good air circulation, and water at the soil level (not overhead) in the morning. Mulch is crucial to keep soil cool and retain moisture.

Variable Winters

We can have mild winters followed by a sudden polar vortex. Use mulch to insulate plant roots. For tender perennials or new plants, consider temporary burlap screens against harsh north winds. Avoid planting broadleaf evergreens in exposed, windy spots where winter burn is likely.

Step-by-Step: Using Your Zone to Plan a Garden

Find Your Exact Zone: Use the USDA website with your zip code. Note if you’re in 7a, 6b, etc.
Make a Plant Wish List: Write down plants you love.
Check Zone Ratings: For each plant, verify its hardiness zone. A reliable nursery tag or catalog will list it (e.g., “Hardy to Zone 5”). Ensure your zone number is equal to or lower than the plant’s rating. (A Zone 5 plant is fine in Zone 7; a Zone 8 plant is risky).
Consider Microclimates: Do you have a sheltered south-facing wall? That’s a warmer spot. A low, frost-prone corner? That’s cooler. Place plants accordingly.
Follow Zone-Based Dates: Use your zone’s average last frost date (early-mid April for 7a) to schedule seed starting and transplanting. Don’t rush spring planting.

FAQ: St. Louis Planting Zones

Has St. Louis’s plant zone changed?

Yes. In the 2012 USDA update, much of the city shifted from Zone 6b to Zone 7a. This reflects a warming trend in average winter low temperatures over recent decades. It’s important to use the current map.

Can I grow plants from a warmer zone?

You can, but treat them as annuals or be prepared to provide winter protection. For example, a fig tree (often Zone 8) can be grown in a container and moved to a garage in winter, or planted in ground with heavy mulch and wrapping. It’s an experiment, not a guarantee.

What is the difference between Zone 7a and 7b?

It’s a 5-degree Fahrenheit difference in the average coldest temperature. Zone 7b (5°F to 10°F) is slightly warmer than 7a (0°F to 5°F). This might mean a borderline plant has a better survival chance in 7b. For most gardening, the principles are the same.

Where does the “heat zone” map fit in?

The AHS Heat Zone Map measures how many days per year exceed 86°F. St. Louis is in Heat Zone 7. This is useful for understanding if a plant can survive our summer heat, which is just as critical as winter cold. Always look for plants that match both your cold and heat zones when possible.

Knowing your St. Louis plant zone takes the guesswork out of gardening. It empowers you to choose plants that will come back year after year, saving you time and money. By combining this knowledge with an understanding of our local soil and climate quirks, you can create a beautiful, resilient garden that thrives through every Missouri season. Start with your zone number, and you’re already on the path to a more succesful garden.