Preparing your outdoor tender perennials for winter is crucial to ensure their survival and vigorous return next spring. This involves a strategic approach of hardening them off, protecting their root systems with insulation like mulch, and sometimes covering their foliage to shield them from freezing temperatures and harsh winds.
Why do I need to winterize my tender perennials?
Winterizing tender perennials is essential because these plants are not naturally adapted to withstand freezing temperatures common in many climates. Unlike hardy perennials that can tolerate frost, tender varieties are susceptible to damage from cold snaps, frost heave, and prolonged freezing, which can kill their root systems or delicate foliage. Proper winterization protects them from these harsh conditions, allowing them to conserve energy and regrow come spring.
How do I prepare my tender perennials for winter?
Proper preparation begins before the first hard frost, allowing your plants to gradually adapt to cooler temperatures. Start by reducing fertilizer application in late summer to discourage new, tender growth that would be easily damaged by cold. Continue watering deeply until the ground freezes, as well-hydrated roots are more resilient to cold damage.
Here are some key steps to get your plants ready for the cold:
Gradual Transition: Allow plants to experience cooler nights as autumn progresses, but bring very sensitive potted plants indoors or to a protected location if temperatures are consistently dropping below 7°C / 45°F.
Deep Watering: Ensure plants receive adequate water until the ground freezes solid. Dry soil provides less insulation than moist soil, leaving roots more vulnerable.
Clean Up: Remove any diseased or pest-infested foliage to prevent overwintering issues. However, don't remove all dead foliage yet, as some can offer natural insulation.
How does mulching protect my plants in winter?
Mulching is a highly effective way to insulate the root systems of your tender perennials from extreme cold and temperature fluctuations. A thick layer of mulch acts like a blanket, keeping the soil temperature more consistent, preventing the damaging freeze-thaw cycles that can cause roots to heave out of the ground. It also helps retain essential soil moisture.
What kind of mulch should I use, and how much?
For winter protection, organic mulches are best as they offer good insulation and slowly break down to enrich the soil. Excellent choices include straw, shredded leaves, pine needles, or wood chips. Apply a generous layer, typically 10 to 15 cm (4 to 6 inches) deep, around the base of your plants, extending slightly beyond the drip line. Apply it after the ground has begun to cool but before it freezes solid, usually late autumn.
Straw: Provides excellent insulation and is lightweight.
Shredded Leaves: Readily available and decomposes well. Avoid whole leaves that can mat down and suffocate plants.
Pine Needles: Acidifies the soil slightly, great for acid-loving plants, and provides good aeration.
Wood Chips: Denser and lasts longer, providing good insulation.
Should I prune my tender perennials before winter?
The decision to prune tender perennials before winter depends on the specific plant and your local climate. For many tender perennials, it's often best to wait until spring to do major pruning. Leaving some foliage on the plant can provide a bit of natural insulation for the crown and roots through the colder months. However, there are exceptions.
What and when to prune:
Dead or Diseased Material: Always remove any clearly dead, damaged, or diseased stems and leaves to prevent disease spread and pest harborage.
Avoid Heavy Pruning: Generally, avoid severe pruning in the fall. New cuts can stimulate new growth that is highly vulnerable to frost damage.
Tall Stems: For very tall, brittle plants like some ornamental grasses, you might trim them back partially to prevent them from snapping in heavy snow or wind, but leave enough to provide some insulation.
Spring Pruning Advantage: Many gardeners, including Planta, recommend waiting until early spring to prune back most tender perennials. This allows the old growth to offer protection through winter and makes it easier to see what truly died back and what is viable for the new growing season.
What are cold weather covers for plants?
Physical covers provide an additional layer of protection for tender perennials, especially in very cold climates or during unexpected deep freezes. They shield plants from frost, harsh winds, and heavy snow, creating a microclimate that is slightly warmer than the ambient air.
Types of plant covers and how to use them:
Row Covers/Floating Remay: These lightweight, breathable fabrics can be draped directly over plants or supported by hoops. They allow light and water to penetrate while raising the temperature by a few degrees. They are excellent for protecting broader areas of planting beds.
Cloches: Individual bell-shaped covers made of glass or plastic can protect single plants from frost. They are best for smaller, isolated plants.
Burlap Wraps: For larger, more sensitive shrubs or small trees (like some containerized tender perennials), wrapping them loosely in burlap can protect foliage from windburn and extreme cold. Ensure good air circulation to prevent fungal issues.
DIY Shelters: You can create temporary structures using stakes and plastic sheeting or old blankets for short-term cold snaps. Remember to remove non-breathable covers during the day if temperatures rise to prevent overheating.
Remember to remove covers once the danger of hard frost has passed in spring to allow plants full access to sunlight and air circulation.
By following these steps, you're not just winterizing your plants, you're investing in their future health and beauty. With a little care and preparation, your beloved tender perennials will happily return to grace your garden next spring, stronger and more vibrant than ever.