Herbaceous Plant Care: Perennials and Groundcovers

Herbaceous Plant Care: Perennials and Groundcovers

Learning Objectives

  • Describe and demonstrate the process of splitting and transplanting perennials and groundcovers.

Perennial Beds Overview

Maintenance of Perennial Beds
Watering
  • General Characteristics
    • Most perennial plants possess deeper root systems compared to annuals or turf, enhancing their drought resistance.
    • Perennials can endure drought conditions but dry out faster than anticipated under windy, low-humidity circumstances.
    • Ensuring soil moisture is crucial for the health and vitality of perennials.
Soil Moisture Assessment
  • Check soil moisture by digging into the soil; if top 4 to 5 inches are dry, deep watering is necessary.
Watering Guidelines
  • Irrigation Schedule
    • Avoid fixed watering schedules; water only when required.
    • Allow plants to dry out between watering without letting them wilt.
    • Early morning is the optimal time for watering.
    • Overhead irrigation at night may encourage fungal diseases like powdery mildew, as well as slug infestations.
  • Recommended Practices
    • Employ a small sprinkler or drip hose at the plant base, allowing it to run for 3 to 4 hours until the next rain.
General Watering Rule of Thumb
  • Summer Watering
    • Aim for a total depth of 1 to 2 inches of water per week (combining rainfall and irrigation).
  • Fall and Spring Watering
    • For plants established over two years, apply 1 to 2 inches of water every two weeks.
  • Rain Gauge Use
    • Utilize a rain gauge to monitor applied water levels.

Fertilization of Perennials

Guidelines for Fertilization
  • Most perennial flowers, ground covers, and grasses require minimal fertilization.
  • Risks of Over-Fertilization
    • Excessive fertilizer leads to:
    • Leggy growth and flop-over due to excessive foliage.
    • Increased foliar growth without corresponding root development.
    • Root burn from high nutrient concentrations.
When to Fertilize
  • Optimal conditions often negate the need for fertilization if planted in healthy garden soil or rich compost.
    • Light fertilization may benefit plants in sandy soils lacking organic material.
  • Fertilization can include:
    • Liquid fertilizers every two weeks if necessary – high phosphorus or balanced options are recommended.
Fertilization Recommendations
  • Apply slow-release granular fertilizers before or during the emergence of new spring growth. Options for application:
    • Broadcasting: Even distribution across plant zones to meet nutrient needs throughout the season.
    • Side Dressing: Applying several teaspoons/tablespoons of fertilizer close to the root zones, adhering to manufacturers' guidelines.
Balanced Fertilizer Options
  • Use balanced fertilizers such as 20-20-20. If phosphorus levels are sufficient, consider a 10-0-20 option.
  • Natural supplements, such as manure or compost, can serve as effective alternatives to synthetic fertilizers.
Fertilizer Application Tips
  • Avoid clustering fertilizers at the plant's crown to prevent burning.
  • Cool spring soil can affect nutrient uptake, sometimes leading to foliage discoloration.
  • Important Note: Never fertilize in late summer or early fall with high nitrogen levels, as this can incentivize growth that fails to harden off before winter freezes.

Deadheading Perennials

  • Purpose of Deadheading
    • Improves the aesthetic appeal of plants, gardens, and containers, while promoting further blooms.
    • Redirects plant energy towards robust growth and additional flowering.
    • Prevents seed formation post-pollination, which can hinder overall growth and blooming cycles.

Division of Perennials

  • Perennials have an extensive lifespan and occasionally need dividing due to excessive growth, typically every 2 to 5 years depending on the species.
    • Division not only rejuvenates plants but also allows propagation for additional planting/spacing needs.
  • Indicators for Division:
    • Plants show reduced flowering, smaller leaves, or sparse growth in the center.
    • Crowded plants competing for nutrients, water, and light exhibit weak growth.
    • Conduct division while plants remain healthy to minimize stress.
Timing for Division
  • Iris Division
    • Irises (that grow from rhizomes) should be divided as the roots become dense.
  • Ideal Division Seasons:
    • Spring: Best for fall-blooming perennials and ornamental grasses.
    • Fall: Optimal for spring-blooming perennials; six weeks growth recommended for root establishment before frost.
  • Example of Timing:
    • Iris can be divided shortly after their peak blooming period (Ideal by August).
Division Timing Considerations
  • For spring division, the plant should settle in before hot weather arrives.
  • Spring-divided plants may bloom later than usual post-transplanting.
  • It is recommended to wait for cloudy days or after precipitation for division to minimize heat stress.
    • If necessary, materials should be covered with moist burlap and moved to shade.
Preparation for Division
  • Thoroughly water plants one or two days prior to division.
  • Prepare the planting area before lifting parent plants and prune stems to about 3 inches from ground level to reduce moisture loss during division.
Extraction Method
  • Use a sharp shovel and fork around the base of the plant, digging about four to six inches away in a circle.
  • Lift the entire clump for division, cutting heavy plants as needed.
Separation of Divisions
  • Shake or wash off excess soil, removing dead leaves to reveal tangled roots.

Dividing Perennials by Growth Habit

  • Clumping Perennials (e.g., daylilies, asters):

    • Grow from a central crown that expands over time.
    • Best divided when lifted entirely; maintain several new offsets if present.

  • Spreading Perennials (e.g., bee balm, phlox):

    • Characterized by slender roots spreading out, requiring careful excavation of desired sections.

  • Tap Rooted Perennials (e.g., Asclepias, Euphorbia):

    • Division presents challenges; better to avoid unless necessary by cutting through tap roots with attached foliage. Older plants may allow division of multiple tap roots without harming the parent.
Examples of Perennials by Root Systems
  • Clumping Examples:
    • Daylilies and Siberian Iris have thick intertwined roots; ensure divisions comprise vigorous shoots.
Dividing Hostas
  • Extraction involves careful lifting from the ground to preserve roots, cleaned thoroughly.
  • To detach stems from crowns, pull gently until a break occurs.
Dividing Peonies
  • Peonies should be divided in September, ensuring buds (‘eyes’) are planted just below the soil’s surface with a focus on rich soil and ample light exposure for optimal blooming.
General Instructions for Planting Divisions
  1. Ensure divisions stay moist until replanting.
  2. Trim all broken roots before replanting them at the same depth as originally found.
  3. Firm surrounding soil and water thoroughly after planting.
  4. Apply mulch for fall-divided perennials to avoid soil heaving throughout winter.

Conclusion and Implications

  • Proper maintenance, irrigation, fertilization, and division of perennial plants are essential for maximizing flower production, overall plant health, and garden aesthetics. Timeliness, correct seasonal practices, and environmental considerations foster strong plant growth and flowering through responsible gardening practices.