Can I overwinter perennials in the indoor?

Yes, you can absolutely overwinter perennials indoors, especially those that are not cold-hardy in your specific USDA planting zone. This common practice involves bringing plants or their dormant root structures inside to protect them from freezing temperatures, allowing them to survive the winter and return to your garden the following spring. Success depends on understanding each perennial's specific winter needs, whether it requires active growth, dormancy, or storage as bare roots or bulbs.

Why consider overwintering perennials indoors?

Overwintering perennials indoors is a highly beneficial practice for several reasons, offering a way to save beloved plants, extend growing seasons, and even cultivate varieties that wouldn't normally survive your climate. It's an act of plant preservation and a smart gardening strategy.

Here’s why you should consider it:

• Protecting Tender Perennials from Cold: The most common reason to overwinter perennials indoors is to save those that are not cold-hardy in your local USDA planting zone. Many beautiful perennials (like geraniums, fuchsias, cannas, dahlias, or even some rosemary varieties) are hardy only in warmer climates. Bringing them inside shields them from freezing temperatures and harsh winter conditions that would otherwise kill them. This allows gardeners in colder regions to enjoy these plants year after after.

• Saving Money on Replacements: Instead of buying new plants every spring, overwintering allows you to keep existing plants alive. This can lead to significant cost savings, especially if you have many non-hardy perennials or expensive specimen plants. A mature, overwintered plant also often performs better and blooms earlier than a new transplant.

• Preserving Favorite or Sentimental Plants: You might have a specific variety of fuchsia that you adore, a geranium passed down through generations, or a dahlia that performed exceptionally well. Overwintering ensures these unique or sentimental plants survive, allowing you to enjoy them for many more seasons.

• Early Start to the Growing Season: Overwintered plants often have a head start compared to new plants purchased in spring. If kept actively growing, they can continue to mature and even bloom earlier. If dormant, they are already established and ready to burst forth with vigor once replanted outdoors, resulting in earlier and more robust displays.

• Cultivating Rarer or Unusual Varieties: Some perennial varieties might be difficult to find or expensive to purchase each year. Overwintering allows you to grow and propagate these less common plants, expanding the diversity of your garden.

• Experimentation and Learning: Overwintering encourages gardeners to learn more about their plants' specific needs for dormancy, light, and temperature. It's a rewarding process that deepens your understanding of plant physiology.

• Control Over Growing Conditions: Indoor environments often allow for more control over temperature, humidity, and light compared to unpredictable outdoor conditions. This control can be vital for successful overwintering, especially for sensitive plants.

• Avoiding Crowding Outdoor Beds: For gardeners with limited perennial bed space, bringing some plants indoors can free up valuable real estate for winter annuals or other cold-hardy plantings.

In summary, overwintering perennials indoors is a practical, economical, and rewarding way to extend your gardening season, protect valuable plants, and ensure your favorite blooms return year after year, regardless of your winter climate.

Which perennials can be overwintered indoors?

Many types of perennials can be overwintered indoors, but the method of overwintering depends heavily on the plant's natural dormant cycle and cold tolerance. Generally, the candidates are those perennials that are tender (not hardy) in your climate zone.

Here’s a breakdown of common perennials suitable for indoor overwintering and their typical methods:

1. Perennials Overwintered as Dormant Plants or Root Structures:

These plants naturally go dormant in winter, storing energy in their roots or specialized structures. They require cool, dark conditions and minimal watering.

• Dahlias:
  • Method: Dig up the tubers after the first light frost kills the foliage. Clean off excess soil, allow them to air dry for a few days, then store them in a cool (40-50°F or 4-10°C), dark, frost-free place in boxes filled with peat moss, sawdust, or vermiculite to prevent drying out. Check periodically for rot or shriveling.
• Cannas:
  • Method: Similar to dahlias. Dig up rhizomes after frost, clean, dry, and store in a cool, dark place in slightly moist peat moss or sawdust.
• Gladiolus (Corms):
  • Method: Dig up corms after foliage dies back. Clean, dry thoroughly, and store in mesh bags or open trays in a cool, dry, dark place.
• Caladiums (Tubers):
  • Method: Dig tubers when foliage declines. Dry and store in peat moss in a warm, dry place (warmer than dahlia tubers, around 60-70°F or 15-21°C).
• Elephant Ears (Colocasia/Alocasia tubers):
  • Method: Dig tubers before hard frost. Clean, dry, and store in peat moss or sawdust in a cool, dark, frost-free location.
• Begonias (Tuberous):
  • Method: Dig tubers when foliage yellows. Clean, dry, and store in peat moss or vermiculite in a cool, dry place.

2. Perennials Overwintered as Actively Growing Houseplants:

These plants don't typically go dormant and prefer to continue growing, albeit at a slower pace due to reduced light and temperatures indoors.

• Geraniums (Pelargoniums):
  • Method: Bring potted plants indoors before the first frost. Place them in a bright, sunny window. Water sparingly through winter, allowing the soil to dry out between waterings. You can also take cuttings in late summer to root indoors.
• Fuchsias:
  • Method: Bring potted plants indoors. Many varieties will continue to bloom if given enough light. Provide bright, indirect light and reduce watering somewhat. Alternatively, some gardeners trim them back and keep them barely dormant in a cool, bright spot.
• Coleus:
  • Method: Can be brought indoors as potted plants or rooted from cuttings taken in late summer. Provide bright light. They tend to get leggy indoors but can be pruned.
• Tropical Hibiscus:
  • Method: Bring indoors before frost. Provide bright light (south-facing window if possible). Keep temperatures warm and maintain moderate humidity. They may drop leaves initially due to shock.
• Some Herbs (Rosemary, Lemon Verbena, Bay Laurel):
  • Method: Bring potted plants indoors to a cool, bright spot. Water sparingly. Rosemary particularly likes cool conditions to prevent fungal issues.
• Lantana:
  • Method: Can be brought indoors as a potted plant. Give it bright light and reduce water slightly. May lose some leaves.
• Impatiens (New Guinea and Walleriana):
  • Method: Can be brought indoors to continue growing in bright, indirect light. Or, take cuttings in late summer to root for next season.

3. Perennials Overwintered in a Cool, Semi-Dormant State:

These plants require a cool, often darker, environment to rest, but aren't fully dormant like tubers.

• Ornamental Grasses (tender varieties like Fountain Grass):
  • Method: If in pots, bring into a cool, unheated garage or basement (40-50°F or 4-10°C) with some ambient light. Water very sparingly, just enough to keep the roots from completely drying out.
• Hydrangeas (Potted/Tender Varieties):
  • Method: Bring potted hydrangeas into a cool, dark, frost-free location like a garage or basement once dormancy sets in. Water just enough to keep the soil from completely drying out once a month.

General Considerations for All Overwintered Perennials:

• Pest Check: Always inspect plants thoroughly for pests (aphids, spider mites, mealybugs) before bringing them indoors. Treat any infestations.
• Acclimatization: Gradually acclimate plants to indoor conditions by bringing them in for increasing periods over a week or two.
• Light Needs: Match the indoor light to the plant's specific needs (bright for active growth, darker for dormancy).
• Watering: Always reduce watering in winter, especially for dormant plants.
• Temperature: Match the indoor temperature to the plant's dormant or active requirements.

By selecting the right perennials and applying the appropriate overwintering method, you can successfully bridge the winter gap and enjoy your favorite plants again come spring.

What steps should I take to prepare perennials for indoor overwintering?

Proper preparation of perennials for indoor overwintering is crucial for their survival and successful reintroduction to the garden next spring. It involves a series of steps to minimize stress, prevent pests, and encourage a healthy dormant or semi-dormant state.

Here are the essential steps to take:

1. Timing is Key:

   • Bring Indoors Before First Hard Frost: The ideal time to bring tender perennials indoors is before the first hard frost (temperatures consistently below 32°F or 0°C). A light frost (above 32°F but below 40°F) might just nip foliage, but a hard frost can damage roots and crowns. Check your local forecast.
   • Gradual Acclimatization: If possible, transition plants gradually. Bring them indoors for a few hours each day over a week or two, increasing the time indoors until they are fully inside. This helps them adjust to lower light and humidity.

2. Thorough Pest Inspection and Treatment:

   • This is one of the most critical steps to avoid bringing unwanted guests into your home.
   • Inspect Every Inch: Carefully examine all parts of the plant – top and bottom of leaves, stems, soil surface, and pot rim – for any signs of pests (aphids, spider mites, mealybugs, scale).
   • Treat Immediately:
     • Hose Down: For light infestations, blast plants with a strong stream of water (especially undersides of leaves) to dislodge pests.
     • Insecticidal Soap/Neem Oil: For more stubborn pests, spray thoroughly with an insecticidal soap (Safer Brand Insect Killing Soap) or neem oil (Garden Safe Brand Neem Oil Extract Concentrate). Repeat as directed.
     • Manual Removal: For larger pests or scale, use a cotton swab dipped in rubbing alcohol to wipe them off.
   • Isolation: After treatment, keep the plant isolated from other houseplants for a week or two to ensure no pests resurface.

3. Pruning and Cleaning:

   • Remove Dead/Damaged Foliage: Prune off any yellowed, diseased, or damaged leaves and stems. This improves air circulation and reduces potential hiding spots for pests.
   • Cut Back (for Dormant Plants): For plants that will go fully dormant (e.g., dahlias, cannas), cut back the foliage significantly before digging or after bringing indoors. Leave a few inches of stem for easy handling.
   • Clean Potting Medium: Remove any debris from the soil surface (leaves, spent flowers). This also helps reduce potential pest habitats.

4. Repotting or Root Preparation (as needed):

   • Potted Plants: If your perennial is in a pot that has good drainage and isn't rootbound, you can often bring the entire pot indoors. Ensure the soil is well-draining.
   • Digging Up Tubers/Rhizomes: For plants like dahlias, cannas, gladiolus, and tuberous begonias:
     • Wait until a light frost has blackened the foliage.
     • Carefully dig them up, being mindful not to damage the tubers/rhizomes.
     • Gently brush off excess soil. Do not wash unless absolutely necessary, and then allow them to air dry thoroughly in a cool, protected spot for several days to a week. This "curing" process is vital to prevent rot.
     • Once dry, store in a cool, dark, frost-free location (40-50°F or 4-10°C is ideal for most, but check specific plant needs) in materials like peat moss, vermiculite, sawdust, or shredded newspaper to keep them from drying out completely. Check periodically for rot or shriveling.

5. Watering Before Bringing Indoors (and adjusting after):

   • Potted Plants: Water the plant well a few days before bringing it indoors. This ensures it's well-hydrated for the transition.
   • Adjusting Indoor Watering: Once indoors, significantly reduce watering, especially for plants entering dormancy. For actively growing plants, water sparingly, allowing the top inch or two of soil to dry out completely between waterings. Overwatering is the biggest killer of overwintered plants.

By diligently following these preparation steps, you set your perennials up for a successful journey through indoor overwintering, ensuring they return vibrant and ready to grow when spring arrives.

What are the ideal indoor conditions for overwintering perennials?

Providing the ideal indoor conditions for overwintering perennials is paramount to their survival, whether they are actively growing or in a dormant state. The specific requirements vary by plant, but generally revolve around light, temperature, humidity, and airflow. Ignoring these can lead to weak plants, pest infestations, or even death.

Here’s a breakdown of ideal indoor conditions:

1. Light Requirements:

• For Actively Growing Perennials (e.g., Geraniums, Fuchsias, Tropical Hibiscus):
  • Bright Light: These plants need bright, indirect light to continue photosynthesizing, albeit at a slower rate. A south-facing window is often ideal, or a bright east or west-facing window.
  • Supplemental Lighting: If natural light is insufficient (which is common in winter in many regions), consider using grow lights (GE Grow Light LED Bulb for Plants or a full grow light fixture). Place lights 6-12 inches above the plant and run them for 12-14 hours a day.
• For Semi-Dormant Perennials (e.g., Some Tender Grasses, Potted Hydrangeas):
  • Cool, Ambient Light: These plants don't need intense light. A cool, relatively dim area like an unheated garage, basement, or cool spare room with a small window or some ambient light is usually sufficient. They don't need grow lights.
• For Fully Dormant Tubers/Rhizomes (e.g., Dahlias, Cannas, Gladiolus):
  • Darkness: These stored root structures require complete darkness or very minimal ambient light. Light exposure can encourage premature sprouting.

2. Temperature Requirements:

• For Actively Growing Perennials:
  • Cool to Moderate Room Temperature: Aim for cooler room temperatures, typically between 60-70°F (15-21°C). Avoid very warm rooms, as this encourages leggy growth that won't strengthen in low winter light.
  • Avoid Fluctuations: Keep plants away from cold drafts (windows, doors, vents) and heat sources (radiators, fireplaces) that cause rapid temperature swings.
• For Semi-Dormant and Fully Dormant Perennials:
  • Cool and Stable: The ideal range is often 40-50°F (4-10°C). This is crucial for maintaining true dormancy and preventing premature sprouting or chilling damage. Unheated basements, garages, or cool cellars are perfect.
  • Above Freezing: Ensure temperatures remain consistently above freezing.

3. Humidity Requirements:

• For Actively Growing Perennials:
  • Moderate Humidity: Indoor heating systems often create very dry air. Many houseplants and actively growing perennials prefer moderate humidity (around 40-60%).
  • Increase Humidity: Use a room humidifier (LEVOIT Humidifiers for Home), place pebble trays filled with water beneath pots (ensure pots don't sit in water), or group plants together to create a microclimate.
• For Dormant Perennials/Tubers:
  • Slightly Moist Environment: Stored tubers/rhizomes need some moisture in their storage medium (peat moss, vermiculite) to prevent desiccation. They don't need high ambient humidity, but ensure the storage area isn't bone dry.

4. Air Circulation:

• For All Overwintered Perennials (Especially Actively Growing):
  • Good Airflow: Ensure adequate air circulation around plants, especially in humid conditions. Stagnant air can encourage fungal diseases (like powdery mildew) and pest infestations.
  • Spacing: Don't crowd plants together.
  • Gentle Fan (Optional): A small, oscillating fan can provide gentle air movement in a confined overwintering space.

5. Watering (General Rule):

• Reduce Watering: Regardless of the state, all perennials require significantly less water indoors during winter than they do outdoors in summer.
• Actively Growing: Allow the top 1-2 inches of soil to dry out between waterings.
• Semi-Dormant/Dormant Potted Plants: Water very sparingly, just enough to prevent the soil from becoming completely bone dry. Perhaps once a month or every few weeks.
• Stored Tubers/Rhizomes: The storage medium should be barely moist, never wet.

By carefully managing these indoor conditions, you can successfully overwinter your perennials, whether they are enjoying a winter growth period or a well-deserved dormancy, ensuring their return to your garden in the spring.

What common mistakes should I avoid when overwintering perennials indoors?

Even with the best intentions, several common mistakes can derail your efforts when overwintering perennials indoors. Avoiding these pitfalls is as crucial as following the correct preparation and care steps, as they often lead to plant stress, disease, or even death.

Here are the common mistakes to avoid:

1. Overwatering (The Biggest Killer):

   • Mistake: Treating indoor, overwintering perennials (especially dormant or semi-dormant ones) like actively growing summer plants. Indoor light is typically lower, temperatures are cooler, and plants use far less water.
   • Consequence: Leads to root rot, fungal diseases, wilting, yellowing, and ultimately plant death. The soil stays soggy, roots suffocate and decay.
   • Solution: Drastically reduce watering frequency. Always check soil moisture (top 1-2 inches dry for active, top 3-4 inches or more for semi-dormant/dormant) before watering. For dormant tubers, ensure the storage medium is barely moist, not wet.

2. Not Checking for Pests Before Bringing Indoors:

   • Mistake: Neglecting a thorough inspection for insects before bringing plants inside.
   • Consequence: You inadvertently introduce pests (aphids, spider mites, mealybugs, whiteflies) into your home, where they can rapidly multiply in the warm, stable indoor environment and infest your other houseplants.
   • Solution: Isolate new plants (even if they appear clean) for a few weeks. Inspect all surfaces, including undersides of leaves and stems. Treat any infestations before bringing plants indoors.

3. Providing Insufficient Light (for actively growing plants):

   • Mistake: Placing actively growing perennials (like geraniums or fuchsias) in a dark corner or a window that doesn't provide enough bright, indirect light.
   • Consequence: Plants become leggy, weak, and pale, with sparse foliage. They may drop leaves and struggle to survive or thrive, producing poor growth in spring.
   • Solution: Place them in the brightest available indirect light, such as a south-facing window. Supplement with grow lights if natural light is inadequate.

4. Not Providing a True Dormancy Period (for dormant-requiring plants):

   • Mistake: Keeping plants that require a dormant chilling period (like dahlias, cannas) in warm, active growing conditions indoors all winter.
   • Consequence: The plant becomes stressed, weak, or may not flower properly the following season as it hasn't had its necessary rest period. Tubers/rhizomes may rot if kept too warm and moist, or sprout prematurely and become weak.
   • Solution: Store dormant root structures in cool, dark, frost-free conditions (40-50°F or 4-10°C).

5. Exposing Plants to Harsh Temperature Fluctuations:

   • Mistake: Placing plants near drafty windows or doors, active heating/AC vents, or open fireplaces.
   • Consequence: Sudden temperature swings stress plants, causing leaf drop, wilting, or weakened growth.
   • Solution: Choose a stable location with consistent temperatures.

6. Forgetting About Humidity (for actively growing tropicals):

   • Mistake: Placing tropical perennials in dry indoor air, especially when heating systems are running.
   • Consequence: Leads to crispy leaf edges, leaf drop, and makes plants more susceptible to spider mites.
   • Solution: Use a humidifier, pebble trays, or group plants to increase ambient humidity.

7. Over-Fertilizing:

   • Mistake: Continuing to fertilize plants as if they are in their outdoor growing season.
   • Consequence: Excess fertilizer can burn roots, especially in plants that are semi-dormant or growing slowly, leading to brown leaf tips/edges and overall plant decline.
   • Solution: Do not fertilize dormant plants at all. For actively growing plants, fertilize very sparingly, perhaps at half or quarter strength, no more than once a month, only if they show signs of active growth.

8. Not Providing Good Air Circulation:

   • Mistake: Cramming too many plants into a small space without airflow.
   • Consequence: Stagnant, humid air creates a breeding ground for fungal diseases like powdery mildew and can worsen pest issues.
   • Solution: Space plants adequately. A small, oscillating fan can help circulate air.

By consciously avoiding these common mistakes, you can greatly increase your chances of successfully overwintering perennials indoors, ensuring they thrive and return to your garden rejuvenated in the spring.