Zone Pushing, Montana Edition
What is Zone Pushing?
Zone pushing is the gardening practice of growing a plant outside its recommended USDA hardiness zone. A "tender perennial" is a plant that is perennial (comes back year after year) in warm climates but is not winter-hardy in your colder zone.
Zone pushing is about creatively helping these plants survive winter so you can enjoy them for multiple seasons.
A Short Guide to Zone Pushing Tender Perennials:
It's part experimentation, part optimism, and all reward!
Step 1: Know Your Zone & Their Zone
· Your Zone: First, know your exact USDA Hardiness Zone. This is based on your average annual extreme minimum temperature.
· Their Zone: Check the plant's label or description. If you are in Zone 4, a plant rated for Zone 5 is a good candidate for pushing. A plant from Zone 8 or 9 is a much bigger, but sometimes possible, challenge.
Step 2: Choose the Right Candidates
Not all tender perennials are equally pushable. Good choices often have these traits:
· Woody Stems: Plants like Lantana, Rosemary, Mexican Bush Sage.
· Dense Crowns: Plants like Canna Lilies, Dahlia (tubers), Agapanthus.
· Strong Will to Live: Some plants just seem determined. Salvia greggii, Pennisetum 'Fireworks', and Chinese Hibiscus can often be pushed.
· Avoid: succulent type plants or those extremely prone to rot (e.g., some Begonias) are trickier.
The Three Main Strategies
You can use one or a combination of these methods.
1. The Cozy Blanket (Heavy Mulching)
· Best for: Plants with a hardy crown or base, slightly borderline (e.g., Zone 7 plant in Zone 6).
· How-To: After the first hard frost kills the foliage, cut the plant back to 4-6 inches. Pile a thick, fluffy, dry mulch (like straw, shredded leaves, or pine boughs) at least 12 inches deep over the crown. The goal is to keep the soil consistently frozen, preventing damaging freeze-thaw cycles.
· Remove the mulch gradually in spring after the danger of hard frost has passed.
2. The "Lift & Store" Method (Overwintering Indoors)
· Best for: Plants with tubers, rhizomes, or bulbs (Dahlias, Cannas, Gladiolus, Elephant Ears).
· How-To: After frost blackens the foliage, carefully dig up the root structure.
· Gently brush off soil, cut stems to an inch, and let them cure (dry out) for a day or two.
· Store them in a cool (40-50°F / 4-10°C), dark, and dry place for winter. Pack them in a box or paper bag filled with slightly moist peat moss, vermiculite, or sawdust.
· Replant outdoors after your last spring frost.
3. The Sunny Window (Bringing Pots Inside)
· Best for: Any tender perennial you've grown in a container.
· How-To: Before your first frost, bring the pot indoors.
· Option A (Dormancy): Place the pot in a cool, dark place like a basement or garage (ideally 35-50°F / 2-10°C). Water just enough every few weeks to keep the roots from completely drying out. The plant will go dormant and drop leaves.
· Option B (Houseplant): Place it in a sunny window and water as needed. It may continue to grow slowly. Be sure to check for pests like aphids or spider mites first.
Pro-Tips for Success:
Patience in Spring
· Don't be too quick to declare failure! Tender perennials are often the last to wake up in spring. Wait until the soil is truly warm before you dig up a spot to check for signs of life.
· For mulched plants, wait until new growth appears from the base before fertilizing.
Location is Key:
Plant tender perennials in a sheltered microclimate—against a warm south-facing wall, near a foundation, or in a courtyard. These spots can be a full zone warmer than the middle of your yard.
· Well-Drained Soil is Non-Negotiable: Wet, cold soil kills roots. Ensure your planting bed has excellent drainage. Raised beds are perfect for zone pushing.
· Let Them Harden Off: In fall, allow the plant to experience a few light frosts. This signals it to go dormant and helps harden off tissues for winter.
· Experiment & Keep Notes: Zone pushing isn't a guarantee. Consider every plant that comes back a victory and every loss a learning experience. Keep a garden journal to track what works and what doesn't in your specific garden.
Remember: The worst that can happen is you have to buy a new plant next year. The best that can happen is you get to enjoy a unique, mature, and thriving plant that none of your neighbors have!
Happy Gardening!
-Tali
