Can I overwinter perennials in the in hot summers? - Plant Care Guide

Overwintering perennials in hot summers is certainly possible, though it requires a different approach than cold-weather overwintering. Instead of protecting plants from freezing temperatures, the goal is to shield them from intense heat, drought, and excessive sun. This process often involves strategies to help plants survive dormancy or a period of reduced activity during the most extreme summer conditions.

What is summer dormancy in perennials?

Summer dormancy in perennials is a natural survival strategy where plants enter a period of reduced metabolic activity during hot, dry periods. Unlike winter dormancy, which protects against cold, summer dormancy (also called estivation) protects plants from extreme heat and drought. During this time, plants may slow or stop growth, shed leaves, or even die back completely to their underground roots or bulbs, only to re-emerge when cooler, wetter conditions return.

Understanding Summer Dormancy:

• Survival Mechanism: It's an evolutionary adaptation for plants native to regions with hot, dry summers and mild, wet winters, like the Mediterranean or parts of California.
• Reduced Activity: Plants conserve energy and water by minimizing growth, flowering, and even leaf production.
• Visible Changes: You might notice leaves yellowing, browning, or dropping, and flowers fading or failing to appear. The plant may look "dead" above ground.
• Underground Survival: The plant's root system, rhizomes, or bulbs remain alive underground, storing energy for future growth.
• Trigger Factors: The primary triggers are usually a combination of high temperatures and lack of moisture. Extended periods of both will signal the plant to go dormant.

Examples of Perennials Prone to Summer Dormancy:

Many geophytes (plants with underground storage organs like bulbs or corms) and certain Mediterranean herbs exhibit summer dormancy.

• Bulbs/Corms:
  • Spring-flowering bulbs like daffodils, tulips, and hyacinths often go dormant after flowering as summer heat arrives.
  • Cyclamen species from Mediterranean climates.
  • Some ornamental alliums.
• Rhizomatous Plants:
  • Certain Irises (especially bearded irises, which prefer a dry rest).
• Herbaceous Perennials:
  • Many California native plants are adapted to summer dormancy, such as California Poppies (though often grown as annuals, they can reseed or act as short-lived perennials) and some native salvias.
  • Oriental Poppies often go completely dormant in summer.
  • Some lavenders might appear stressed and reduce activity.

Differentiating Dormancy from Death:

It's easy to mistake a dormant plant for a dead one. Key indicators that a plant is dormant, not dead:

• No new growth but the plant doesn't feel brittle or completely shriveled.
• The stems or crown still have some give or are firm, not mushy.
• If you gently dig around the base, you might find firm, healthy roots or bulbs.
• The plant's historical behavior – does it usually "disappear" in summer?

Understanding summer dormancy helps gardeners provide the right care (often less water) during these periods and avoid accidentally killing a resting plant.

How do I prepare perennials for hot summers?

Preparing perennials for hot summers involves a series of steps focused on strengthening the plant and providing protection from intense conditions. This isn't just about survival; it's about helping them thrive or at least endure the stress without succumbing.

Key Preparation Steps:

1. Select Heat-Tolerant Varieties:

   • The most crucial step. Choose perennials that are naturally suited to your USDA Plant Hardiness Zone and specifically, your summer heat and humidity levels.
   • Look for plants labeled "heat tolerant" or those native to hot climates. For example, Agastache and many Sedum varieties thrive in heat.

2. Improve Soil Health and Drainage:

   • Well-draining soil is vital. Roots sitting in soggy soil in heat can quickly rot. Amend heavy clay soils with organic matter like compost to improve structure and drainage.
   • Healthy soil also holds moisture better and provides a steady supply of nutrients, buffering plants against stress. A soil testing kit can help assess your soil.

3. Strategic Planting Location:

   • Consider the sun exposure of your planting site. Even full-sun plants might benefit from some afternoon shade in extremely hot climates. Planting on the east side of a building or under a taller, deciduous tree can provide this relief.
   • Avoid south-facing walls that radiate intense heat.

4. Mulching:

   • Apply a 2-4 inch layer of organic mulch (like straw, shredded bark, or wood chips) around the base of plants.
   • Benefits of Mulch:
     • Retains soil moisture: Reduces evaporation, meaning less frequent watering.
     • Moderates soil temperature: Keeps roots cooler in summer and warmer in winter.
     • Suppresses weeds: Reduces competition for water and nutrients.
     • Adds organic matter: As it breaks down, it improves soil structure.
   • Ensure the mulch doesn't directly touch the plant stems or crowns to prevent rot. You can find various garden mulch options.

5. Proper Watering Techniques:

   • Deep and infrequent watering is generally better than shallow, frequent watering. This encourages roots to grow deeper, making them more resilient to drought.
   • Water in the early morning to minimize evaporation and allow foliage to dry before nightfall, reducing fungal disease risk.
   • Consider a drip irrigation system or soaker hoses for efficient water delivery directly to the root zone. A soil moisture meter can help gauge when to water.

6. Pruning and Deadheading (Pre-Summer):

   • Remove spent flowers (deadhead) to prevent seed formation and redirect the plant's energy into root development or future blooms.
   • For some perennials, a light prune before the hottest weather can encourage a bushier, more resilient form. Avoid heavy pruning which stimulates new, tender growth that is vulnerable to heat.

7. Fertilization (Spring/Early Summer):

   • Apply a balanced slow-release fertilizer in spring or early summer. This provides a steady supply of nutrients, helping the plant build strength.
   • Avoid excessive nitrogen in late spring/early summer, as it promotes lush, tender growth that is more susceptible to heat stress.

By implementing these preparation steps, you give your perennials the best chance to endure the summer heat and continue thriving for years to come.

What are the best watering practices for perennials during hot summers?

Watering practices for perennials during hot summers are critical for their survival and health. The goal is to provide sufficient moisture without overwatering, which can lead to root rot, especially in warm soil. It's about efficiency and understanding the plant's needs.

Best Watering Practices:

1. Water Deeply and Infrequently:

   • Instead of light daily sprinkles, water for a longer duration, allowing the water to penetrate 6-12 inches into the soil. This encourages roots to grow deeper, making the plant more drought-tolerant.
   • Allow the top few inches of soil to dry out between waterings. Continuously wet soil, especially in heat, can lead to root diseases. Use your finger or a soil moisture meter to check.

2. Water in the Early Morning:

   • The best time to water is before 10 AM.
   • This minimizes water loss due to evaporation from the sun and wind.
   • It allows the foliage to dry completely before nightfall, which is crucial for preventing fungal diseases that thrive in damp, warm conditions.

3. Target the Root Zone:

   • Apply water directly to the base of the plant and around its root zone.
   • Avoid overhead watering, which wets the leaves and can promote disease, especially in humid climates.
   • Drip irrigation systems or soaker hoses are highly efficient, delivering water precisely where it's needed with minimal waste. You can find various drip irrigation kits.

4. Monitor Plant and Soil Moisture Closely:

   • Observe your plants: Wilting leaves that perk up after watering are a clear sign of thirst. However, wilting can also indicate overwatering (root rot) or heat stress, so check the soil.
   • Feel the soil: Stick your finger about 2-3 inches deep. If it feels dry, it's likely time to water.
   • Consider plant type: Some perennials (e.g., sedums, lavender) prefer drier conditions, while others (e.g., astilbe, hosta) need more consistent moisture.

5. Adjust for Environmental Factors:

   • Temperature: Plants need more water during heatwaves.
   • Humidity: In humid climates, plants transpire less, so they might need less frequent watering. In arid climates, they'll need more.
   • Wind: Windy conditions increase evaporation and transpiration, requiring more frequent watering.
   • Soil type: Sandy soils drain quickly and need more frequent watering than clay soils.

6. Mulch (Reiterate Importance):

   • A good layer of mulch significantly reduces evaporation from the soil surface, allowing you to water less often. This is one of the most effective water conservation strategies.

By adopting these practices, you can ensure your perennials receive the right amount of water to survive and even flourish during the challenges of a hot summer.

Should I fertilize perennials during hot summers?

Generally, you should avoid heavy fertilization of perennials during hot summers. While plants need nutrients to grow, applying a lot of fertilizer during periods of extreme heat can stress the plant. Most perennials benefit from fertilization in spring or early summer, allowing them to build up reserves before the peak of summer heat.

Why to Limit Fertilization in Hot Summers:

• Promotes Tender New Growth: Many fertilizers, especially those high in nitrogen, encourage lush, soft new growth. This type of growth is very vulnerable to heat stress, sunburn, and pest damage. The plant's energy is better spent on root development and heat resilience during summer.
• Increases Water Needs: Rapid growth stimulated by fertilizer demands more water, which can be difficult to provide consistently during drought conditions.
• Root Burn Risk: Concentrated fertilizers can "burn" roots, especially in dry soil or when temperatures are high, further stressing the plant.
• Reduced Absorption: Plants may be less efficient at absorbing nutrients during heat stress or summer dormancy, making fertilization less effective and potentially wasteful.

When and How to Fertilize:

• Spring or Early Summer: The best time to fertilize most perennials is in early spring as new growth begins, or early summer after the first flush of blooms. Use a balanced, slow-release granular fertilizer. This provides nutrients over an extended period without a sudden surge.
• Organic Amendments: Instead of synthetic fertilizers, consider top-dressing with a layer of compost or worm castings in early spring. These organic materials improve soil structure, slowly release nutrients, and enhance microbial activity, which helps plants absorb nutrients more efficiently and build natural resilience. You can find organic compost readily.
• Foliar Feeds (Use with Caution): If a plant shows specific nutrient deficiencies (e.g., iron chlorosis leading to yellowing leaves) during summer, a diluted liquid foliar feed applied in the early morning or late evening might be an option. However, avoid spraying during direct sunlight as it can scorch leaves. Always dilute according to product instructions.
• Dormancy Period: If your perennial goes into summer dormancy, do not fertilize it during this period. The plant is resting, and nutrients won't be effectively used. Resume fertilization when it breaks dormancy in cooler weather.

Signs a Plant Might Need Nutrients (Even in Summer):

• Persistent yellowing (not related to dormancy).
• Stunted growth despite adequate water and light.
• Lack of flowering in a normally free-blooming perennial.

If you must fertilize due to clear signs of deficiency, use a highly diluted liquid fertilizer and water thoroughly before and after application to minimize stress. Prioritize watering and mulching over heavy feeding during the hottest months.

How can I provide shade for my perennials during hot summers?

Providing shade for perennials during hot summers is an excellent strategy to protect them from scorching sun, reduce water stress, and prevent heat-induced dormancy or death. Even plants labeled "full sun" can benefit from some afternoon relief in regions with intense summer heat.

Methods to Provide Shade:

1. Strategic Planting:

   • Plant on the East Side: Locate heat-sensitive perennials on the east side of a house, fence, or taller evergreen shrubs. This allows them to receive gentle morning sun but shields them from the most intense afternoon rays.
   • Under Deciduous Trees: Plant beneath a deciduous tree (one that loses its leaves in winter). In summer, the tree provides valuable shade. In winter, when the tree sheds its leaves, the perennials get full sun, which is often beneficial during cooler months.

2. Temporary Shade Structures:

   • Shade Cloth: This is one of the most effective and versatile solutions.
     • How to Use: Drape a piece of shade cloth (typically 30-50% shade rating for general garden use) over a simple frame of stakes, PVC pipes, or hoops. Secure it to prevent wind damage.
     • Benefits: Reduces direct sunlight, lowers air temperature around the plants, and decreases water evaporation.
     • Placement: Position it to block the afternoon sun (typically from west to southwest).
   • Umbrellas or Parasols: For container plants or small garden areas, a large patio umbrella or garden parasol can be temporarily positioned to block the sun during peak heat hours.
   • Movable Screens/Panels: Lightweight lattice panels or even old screens can be propped up to cast a shadow on specific plants.

3. Companion Planting/Living Shade:

   • Taller Plants: Plant taller, heat-tolerant annuals or perennials (like sunflowers, ornamental grasses, or heat-loving shrubs) on the south or west side of more delicate perennials. These "nurse plants" will cast natural shade as they grow.
   • Consider Timing: Ensure the companion plant grows large enough to provide shade when needed, and doesn't outcompete the perennial for water or nutrients.

4. Container Gardening Flexibility:

   • If your perennials are in pots, you have the ultimate flexibility. Simply move the containers to a shadier location (under a patio, a tree, or even indoors if necessary for extreme heat waves) during the hottest parts of the day or season.
   • Use light-colored pots to reflect heat, and consider self-watering planters to maintain consistent moisture.

Important Considerations:

• Monitor Plants: Even with shade, watch your plants for signs of stress. Too much shade can lead to leggy growth and reduced flowering.
• Air Circulation: Ensure that any shade structure or companion planting doesn't restrict air circulation too much, as this can increase humidity and disease risk.
• Balance: The goal is to provide relief from intense direct sun, not to plunge sun-loving plants into deep shade. A balance is key.

By thoughtfully implementing these shading strategies, you can help your perennials stay healthier, reduce their water demands, and continue to look their best even when the summer sun is at its fiercest.

What are the best perennials for hot summers?

Choosing the best perennials for hot summers involves selecting varieties that naturally thrive in high temperatures, intense sun, and often, drought conditions once established. These plants are adapted to withstand the rigors of summer without excessive fuss, making them ideal for gardens in warmer climates or those experiencing increasingly hot summers.

Top Perennials for Hot Summers (and Often Drought-Tolerant):

• Agastache (Hyssop):
  • Why they're great: Extremely heat and drought tolerant, attracts hummingbirds and butterflies, long-lasting blooms. Many varieties offer wonderful fragrance.
  • Popular varieties: 'Blue Boa', 'Rosie Posie', 'Kudos Mandarin'.
• Salvia (Sage):
  • Why they're great: A vast genus with many species that excel in heat and drought. Most are magnets for pollinators and offer extended bloom times.
  • Popular varieties: Salvia greggii (Autumn Sage), Salvia nemorosa (Meadow Sage), Salvia leucantha (Mexican Bush Sage). You can find various salvia plants.
• Sedum (Stonecrop):
  • Why they're great: Succulent foliage allows them to store water, making them incredibly drought-tolerant. They thrive in full sun and poor soils. Upright varieties provide late-season interest.
  • Popular varieties: 'Autumn Joy', 'Firecracker', 'Angelina'.
• Echinacea (Coneflower):
  • Why they're great: Iconic summer bloomers, very tolerant of heat and dry spells once established. Attracts butterflies and birds (for seeds).
  • Popular varieties: 'PowWow Wild Berry', 'Magnus', 'Cheyenne Spirit'. Find echinacea seeds for a wide selection.
• Lavender (Lavandula):
  • Why they're great: Mediterranean native, loves full sun, heat, and well-drained, even poor, soil. Drought tolerant once established, fragrant foliage and flowers.
  • Popular varieties: English Lavender (Lavandula angustifolia), French Lavender (Lavandula stoechas).
• Yarrow (Achillea):
  • Why they're great: Tough, adaptable plants with fern-like foliage and flat-topped flower clusters. Excellent for hot, dry sites and attract beneficial insects.
  • Popular varieties: 'Paprika', 'Moonshine', 'Terra Cotta'.
• Gaillardia (Blanket Flower):
  • Why they're great: Bright, daisy-like flowers bloom tirelessly through the summer, even in heat and drought. Very low maintenance.
  • Popular varieties: 'Arizona Sun', 'Goblin'.
• Coreopsis (Tickseed):
  • Why they're great: Cheerful, long-blooming flowers. Many varieties are very heat and drought tolerant, especially the threadleaf types.
  • Popular varieties: 'Moonbeam', 'Zagreb', 'Red Shift'.
• Perovskia (Russian Sage):
  • Why they're great: Airy, silvery foliage and spikes of lavender-blue flowers. Extremely tough, thriving in hot, dry, sunny conditions.
  • Popular varieties: 'Blue Spire', 'Little Spire'.
• Daylilies (Hemerocallis):
  • Why they're great: While individual blooms last only a day, the plant itself is incredibly tough, adapting to a wide range of conditions, including heat. Many reblooming varieties extend the show.
  • Popular varieties: 'Stella de Oro', 'Happy Returns'.

Tips for Success with Heat-Tolerant Perennials:

• Proper Establishment: Even heat-tolerant plants need regular water during their first growing season to establish a strong root system.
• Well-Drained Soil: This is a recurring theme because it's so vital for plants in hot climates. Root rot is a common issue when soil stays wet in heat.
• Mulch: Always use a good layer of organic mulch to conserve moisture and regulate soil temperature.
• Choose Wisely: Match the plant to your specific microclimate. Even within "hot summer" regions, there are variations in humidity, nighttime temperatures, and soil types.

By incorporating these resilient perennials, you can create a beautiful, low-maintenance garden that looks vibrant even during the most sweltering months.