How do I overwinter perennials?

Overwintering perennials involves preparing them to survive the cold temperatures of winter, ensuring they return vigorously in spring. This typically includes a combination of pruning spent foliage, applying a protective layer of mulch, ensuring proper drainage, and for tender varieties, digging and storing or bringing indoors. The specific approach depends on the perennial's hardiness zone and type.

What is overwintering and why is it important for perennials?

Overwintering refers to the process of preparing plants to survive the cold, dormant period of winter. For perennials, which are plants that live for more than two years and typically die back to the ground in colder climates, proper overwintering is crucial for their survival and health in subsequent growing seasons. It helps them endure freezing temperatures, heavy snow, and drying winter winds, ensuring they return bigger and stronger each spring. Without adequate winter protection, many perennials, especially those at the colder edge of their hardiness zone, would perish from cold damage, root heave, or dehydration.

Here's why overwintering is so vital:

• Survival in Cold Climates: Many perennials are not naturally adapted to extreme cold. Overwintering provides the necessary insulation and protection to keep their root systems and crowns (the point where stems meet roots) from freezing solid.
• Protection from Root Heave: During winter, repeated freezing and thawing cycles can cause the soil to expand and contract, pushing plants out of the ground. This phenomenon, known as root heave, exposes the roots to freezing air and can dry them out. Proper mulching helps stabilize soil temperature and prevent this.
• Disease and Pest Prevention: Cleaning up dead plant material can remove overwintering sites for diseases and pests, reducing their presence in the next growing season.
• Improved Spring Vigor: A well-overwintered perennial has stored enough energy to emerge strong and healthy in spring, ready to put on a spectacular show of foliage and flowers.
• Long-Term Garden Health: By ensuring the survival of your established perennials, you maintain the structure and beauty of your garden year after year without needing to replant.

When is the best time to start overwintering perennials?

The best time to start overwintering perennials is typically in late fall, after the first few light frosts but before the ground freezes solid. This timing allows the plants to naturally enter their dormant phase and signals to you that it's time to begin preparing them for winter's chill. It's not a single-day event but rather a gradual process that aligns with the changing seasons.

Here’s a general timeline to consider:

• Late Summer/Early Fall (September - early October in many regions):

  • Reduce Fertilization: Start tapering off nitrogen-rich fertilizers. High nitrogen encourages new, soft growth that is very susceptible to frost damage. Switch to a low-nitrogen, high-potassium fertilizer if feeding, or stop feeding altogether.
  • Monitor Moisture: Continue regular watering, especially if the weather is dry. Well-hydrated plants handle cold stress better.
  • Observe Plant Signals: Pay attention to your perennials. Are their leaves starting to yellow, brown, or drop? This is a natural sign of dormancy approaching.

• Mid to Late Fall (October - November, before hard freezes):

  • Clean Up Garden Beds: This is the prime time for most overwintering tasks.
  • Pruning: Decide which perennials to prune and when. Some prefer pruning after a hard freeze, while others benefit from being left standing.
  • Mulching: This is the most critical step for many perennials. Apply mulch after the ground has started to cool but before it freezes deeply.
  • Digging Tender Perennials: If you live in a colder zone than your perennial's hardiness, this is when you'd dig up tender bulbs or roots for indoor storage.

• Early Winter (December - January in colder regions):

  • Monitor Protected Plants: Check on overwintered container plants or those in storage to ensure conditions remain stable.
  • Add More Mulch (if needed): In extremely cold zones, additional layers of mulch might be considered after the ground freezes hard.

Key Timing Considerations:

• Your USDA Hardiness Zone: This is the most important factor. If you're in a warmer zone (e.g., Zone 8 or higher), many perennials might not need extensive overwintering steps. In colder zones (e.g., Zone 5 or below), proactive measures are essential.
• Local Weather Patterns: Watch your local forecast. The first hard frost (temperatures consistently below 28°F or -2°C) is a strong indicator that dormancy is setting in and serious overwintering should commence.
• Plant Type: Different perennials have different needs. For example, some benefit from standing stems through winter, while others should be cut back.

The goal is to prepare your plants gradually, allowing them to acclimate to colder temperatures naturally, and then provide targeted protection when the true cold sets in.

How do I prepare perennials in the garden for winter?

Preparing perennials in the garden for winter involves several key steps to ensure their survival and health for the next growing season. The main goals are to protect the plant's crown and root system from extreme cold and root heave, and to minimize disease and pest issues.

Here's a detailed guide:

1. Stop Fertilizing:

   • When: Late summer to early fall.
   • Why: Cease applying nitrogen-rich fertilizers by late summer. Nitrogen promotes lush, new growth, which is soft and highly susceptible to frost damage. Instead, allow the plant to naturally harden off and direct its energy into root development for dormancy. If you must fertilize, use a low-nitrogen, high-potassium formula like Jobe's Organics Bone Meal Fertilizer in early fall to help strengthen roots.

2. Water Deeply:

   • When: Throughout fall, until the ground freezes.
   • Why: Adequate moisture in the soil helps insulate roots. A dry soil freezes faster and more deeply than moist soil, and plants can suffer from winter desiccation (drying out from cold winds) if they don't have enough moisture. Give your perennials a good, deep watering before the ground solidifies.

3. To Prune or Not to Prune?

   • When: Depends on the plant and your preference, generally after a hard frost.
   • Why: This is one of the most debated topics in perennial care.
     • Prune Back: Many perennials like hostas, daylilies, and irises benefit from being cut back to within a few inches of the ground after their foliage dies back and turns brown (usually after a hard frost). This removes dead or diseased material, which can harbor pests and diseases, and creates a tidy look. Use sharp, clean pruning shears like Fiskars Pruning Shears.
     • Leave Standing: Some perennials, particularly those with attractive seed heads (e.g., coneflowers, sedum, ornamental grasses), provide winter interest and food for birds. Their hollow stems can also catch snow, providing additional insulation. Many pollinators also overwinter in hollow stems. You can cut these back in early spring instead.
     • Avoid Early Pruning: Do not prune green, healthy foliage in early fall, as the plant still uses these leaves to photosynthesize and store energy for winter. Wait until they are fully dormant.

4. Clean Up Debris:

   • When: After pruning, or whenever plants start dying back.
   • Why: Remove any diseased leaves, spent flowers, or general plant debris from around the base of your perennials. This reduces the hiding places for overwintering pests and disease spores, minimizing potential problems next spring.

5. Apply Mulch (The Most Important Step):

   • When: After the ground has frozen solid or at least after consistent cold temperatures have set in, usually late fall to early winter. Do not apply mulch too early on unfrozen ground, as it can trap warmth and encourage pest activity or rot.
   • Why: A layer of organic mulch insulates the soil, helping to maintain a more consistent soil temperature. This prevents the damaging freeze-thaw cycles that cause root heave. It also protects the crown of the plant from extreme cold.
   • How: Apply a 2-4 inch layer of material like shredded leaves, straw, pine needles, or wood chips around the base of your perennials. Don't pile it directly against the stem or crown, as this can encourage rot; leave a small gap. Gardener's Best Organic Mulch is a good option.
   • Rose Specifics: For roses, particularly tender varieties, you might create a mulch mound of 8-12 inches around the base of the plant after a few hard frosts.

6. Protect from Winter Winds and Sun (for evergreens/broadleaf evergreens):

   • When: Late fall/early winter.
   • Why: Broadleaf evergreen perennials (like some Heucheras or certain ferns) can suffer from winter burn (desiccation) from strong, dry winter winds and intense sun reflection off snow.
   • How: Consider erecting a burlap screen or applying an anti-desiccant spray to protect them. Ensure they are well-watered before the ground freezes.

By following these steps, you give your in-ground perennials the best possible chance to survive the winter and return with vigor in the spring.

How do I overwinter container perennials?

Overwintering container perennials requires different strategies than in-ground plants because their roots are much more exposed to cold temperatures. The soil in pots freezes much faster and deeper than garden soil, making container plants highly vulnerable to root damage and desiccation.

Here are several effective methods for overwintering perennials in containers, depending on your hardiness zone and the plant's specific needs:

Option 1: Bringing Indoors (for tender perennials or very cold zones)

This is the safest method for perennials that are not hardy in your zone or if you live in a very cold climate.

1. Prepare the Plant:

   • Clean Up: Before bringing indoors, inspect the plant thoroughly for any signs of pests (e.g., aphids, spider mites, mealybugs) or diseases. Treat any infestations using insecticidal soap or neem oil solutions. Remove any dead or yellowing foliage.
   • Prune (Optional): Lightly prune back leggy growth or overly large plants to make them more manageable indoors.
   • Acclimatize: Gradually introduce the plant to indoor conditions over a week or two, if possible. Move it to a shadier spot outdoors before bringing it inside to a cooler, less bright room.

2. Choose an Indoor Location:

   • Cool and Bright: Ideally, find a cool, unheated room that stays between 40-50°F (4-10°C), like an unheated garage, basement, or cool spare bedroom.
   • Light: Provide some light, ideally bright, indirect light. A south-facing window is great for light-loving plants, but be mindful of direct sun that could cause overheating. For very cool, dormant storage, minimal light might suffice.
   • Humidity: Indoor air can be very dry. If possible, increase humidity around the plants using a humidifier or pebble trays.

3. Watering During Dormancy:

   • Reduce Dramatically: Once indoors, significantly reduce watering. The goal is to keep the soil barely moist, not wet. Overwatering indoors is a leading cause of rot.
   • Check Soil: Check the soil every 2-4 weeks. Water only when the top few inches are dry to the touch.

4. Monitoring:

   • Pest Watch: Continue to inspect for pests, as the stress of moving indoors can sometimes trigger outbreaks.
   • Air Circulation: Ensure good air circulation to prevent fungal issues.

Option 2: Insulating Outdoors (for hardy perennials in borderline zones)

This method is suitable for perennials that are hardy in your zone, but whose roots need extra protection in containers.

1. Group Containers:

   • When: Late fall, before hard freezes.
   • How: Gather all your container perennials and group them closely together in a sheltered location, such as against a south-facing wall of your house, under an overhang, or in an unheated garage/shed. This grouping helps them share warmth.

2. Elevate and Insulate from Ground:

   • Why: Cold concrete or direct ground contact can draw heat away from pots.
   • How: Place pots on bricks, wooden blocks, or a layer of insulating material like styrofoam to lift them off the cold ground.

3. Insulate the Pots:

   • Materials: Surround the grouped pots with insulating materials. Options include:
     • Burlap and Straw: Wrap the entire cluster of pots with multiple layers of burlap, filling the gaps between pots with straw or shredded leaves. You can secure it with twine or chicken wire.
     • Bubble Wrap: Layers of bubble wrap can provide good insulation.
     • Leaves/Straw in Boxes: Place individual pots into larger plastic or wooden containers and fill the void with insulating materials.
   • Purpose: This creates a protective barrier around the pot, preventing the soil from freezing solid.

4. Mulch the Top:

   • How: Apply a 2-3 inch layer of mulch (shredded leaves, straw, wood chips) on top of the soil in each pot. This insulates the soil surface.

5. Watering:

   • Reduce, but Don't Dry Out: While drastically reducing frequency, container perennials still need some moisture during winter, especially on warmer days. Check the soil every few weeks. If it's dry and the temperature is above freezing, give a light watering. Avoid overwatering.

Option 3: Burying Pots (for hardy perennials in garden beds)

This method effectively mimics in-ground conditions for container plants.

1. Dig a Trench:

   • When: Late fall, before the ground freezes.
   • How: Dig a trench or individual holes in a well-drained spot in your garden, deep enough so that the rim of the pot is level with the surrounding garden soil.

2. Place Pots:

   • How: Place the entire container into the hole.

3. Backfill and Mulch:

   • How: Backfill around the pot with soil, and then apply a 4-6 inch layer of mulch over the entire area (including the top of the pot and surrounding soil) after the ground has frozen. This provides superior insulation.

Option 4: Emptying Pots and Storing Roots (for specific perennials like Cannas, Dahlias)

This method applies to very tender perennials that form tubers, rhizomes, or corms.

1. Dig Up:

   • When: After the first light frost kills the foliage, but before a hard freeze.
   • How: Carefully dig up the plant, trying to keep as much of the root ball intact as possible.

2. Clean and Cure:

   • How: Gently remove excess soil. For tubers/corms (like dahlias, cannas), allow them to cure in a cool, dry, dark place for 1-2 weeks. This helps toughen the skin and prevents rot.

3. Store:

   • Materials: Store the cleaned and cured roots in a cool, dark, dry, and frost-free location (e.g., basement, unheated closet) in containers filled with a slightly moist medium like peat moss, vermiculite, or wood shavings.
   • Temperature: Ideal storage temperatures are usually between 40-50°F (4-10°C).
   • Monitor: Check periodically throughout winter for signs of desiccation (shriveling) or rot. If shriveling, mist lightly. If rotting, discard affected parts.

By selecting the appropriate overwintering method for your container perennials, you can significantly increase their chances of thriving year after year.

How do I overwinter specific perennial types?

Overwintering specific perennial types often requires tailored approaches, as different plants have evolved unique strategies to survive cold temperatures. While general principles like mulching and proper watering apply to most, some perennials, especially tender ones or those with particular growth habits, benefit from specialized care.

Here’s a breakdown of common perennial types and their overwintering needs:

1. Herbaceous Perennials (e.g., Hostas, Daylilies, Peonies, Coneflowers, Salvia, Astilbe, Bleeding Hearts)

• Characteristics: These perennials die back completely to the ground each winter, with their energy stored in their root systems or crowns.
• Overwintering Steps:
  1. Pruning: After a hard frost causes the foliage to die back and turn yellow or brown, prune the stems down to 2-3 inches above the ground. This removes diseased or pest-infested material and tidies the garden. For plants like coneflowers or sedum, you can leave their attractive seed heads standing for winter interest and bird food, cutting them back in early spring.
  2. Cleanup: Rake away all the dead foliage and debris from around the plant's base to reduce hiding spots for slugs, pests, and disease spores.
  3. Mulching: Once the ground has frozen or consistently cold temperatures have set in, apply a 2-4 inch layer of organic mulch (shredded leaves, straw, pine needles, or wood chips) over the crown of the plant. This insulates the roots and prevents root heave. Do not apply too early, as it can trap warmth and cause rot.
  4. Watering: Ensure the plants are well-watered throughout the fall until the ground freezes.

2. Ornamental Grasses (e.g., Miscanthus, Switchgrass, Fountain Grass)

• Characteristics: Most ornamental grasses offer beautiful winter interest with their dried foliage and seed heads.
• Overwintering Steps:
  1. Leave Standing: Do not cut back ornamental grasses in the fall. Their upright stems and foliage provide natural insulation for their crowns and look beautiful catching snow and frost. They also provide shelter and food for wildlife.
  2. Cut Back in Spring: Wait until late winter or early spring (just before new growth emerges) to cut them back. Use sharp bypass pruners or a hedge trimmer for larger clumps, cutting them down to 4-6 inches from the ground.
  3. Mulch (Optional for New Plantings): Established grasses usually don't need additional mulch. For newly planted ornamental grasses or those at the edge of their hardiness zone, a light layer of mulch around the base in late fall can offer extra protection.

3. Broadleaf Evergreen Perennials (e.g., Heuchera/Coral Bells, Hellebores, some hardy Geraniums)

• Characteristics: These perennials retain their foliage through winter.
• Overwintering Steps:
  1. Minimal Pruning: Remove only any damaged, diseased, or yellowing leaves. Do not cut back healthy foliage.
  2. Watering: Ensure they are thoroughly watered throughout the fall until the ground freezes. This helps them stay hydrated and prevents winter desiccation (drying out from cold winds and sun when water is unavailable).
  3. Protection from Winter Burn: In areas with harsh winter winds or strong sun reflecting off snow, consider providing a burlap screen or applying an anti-desiccant spray to the foliage to prevent winter burn.
  4. Mulching: Apply a light layer of mulch around the base to insulate the root zone.

4. Tender Perennials/Bulbs (e.g., Dahlias, Cannas, Gladiolus, Elephant Ears, Begonia Tubers)

• Characteristics: These are perennials that are not hardy in cold climates (typically USDA Zone 7 or below) and their underground storage organs will freeze and rot if left in the ground.
• Overwintering Steps (Digging and Storing):
  1. Dig Up: After the first light frost kills the foliage, carefully dig up the tubers, rhizomes, or corms. Be gentle to avoid damaging them.
  2. Clean and Cure: Gently remove excess soil. For tubers/corms, allow them to cure in a cool, dry, dark place (e.g., garage floor, covered porch) for 1-2 weeks. This dries and toughens their outer skin, preventing rot.
  3. Store: Store the cleaned and cured roots in a cool, dark, dry, and frost-free location (ideal 40-50°F or 4-10°C) in containers filled with a slightly moist medium like peat moss, vermiculite, sawdust, or sand. This medium helps maintain humidity and prevents desiccation.
  4. Monitor: Check periodically throughout winter for signs of shriveling (too dry) or rot (too wet). If shriveling, mist the medium lightly. If rotting, discard the affected parts immediately.

5. Roses (Shrub Roses, Hybrid Teas, Floribundas)

• Characteristics: Roses are technically shrubs, but often treated like herbaceous perennials in colder climates due to their dieback.
• Overwintering Steps:
  1. Stop Fertilizing: Cease feeding by late summer.
  2. Water Well: Provide deep watering into fall.
  3. Pruning: Do minimal pruning in the fall, mainly removing dead, diseased, or damaged canes. Wait until spring for major shaping.
  4. Mounding: After a few hard frosts (when the plant is dormant), create a mound of 10-12 inches of compost, garden soil, or shredded leaves around the base of the rose bush to protect the graft union and basal canes.
  5. Protection: For very tender varieties or in extremely cold zones, you might use rose cones or wrap the entire bush with burlap and fill with straw, but ensure good air circulation to prevent fungal issues.

By understanding the specific needs of your perennials and implementing these tailored overwintering strategies, you can ensure a beautiful and thriving garden year after year.