Companion planting beneath large shrubs like hydrangeas requires selecting smaller plants that thrive in the specific conditions created by the hydrangea’s canopy and root system. The goal is to create a cohesive, layered garden design. Success depends on choosing plants that complement the large, bold blooms above. This approach results in a lush, finished look for the garden bed.
Defining the Ideal Underplanting Environment
The specific conditions directly beneath a mature hydrangea are the primary factor dictating successful underplanting. Hydrangeas prefer a location that receives morning sun and is protected from the intense heat of the afternoon, meaning companion plants must also be tolerant of partial to full shade. The soil must be consistently moist but possess excellent drainage, as hydrangeas are thirsty plants that suffer quickly in dry conditions but will not tolerate soggy roots.
A major challenge is the extensive, shallow root system of the hydrangea, which spreads widely near the soil surface to absorb water and nutrients. Any underplanting selection must be non-aggressive to avoid competing directly with these feeder roots for moisture and nutrition.
Selecting plants with a compact, clumping habit or a delicate, fibrous root structure is necessary to minimize disturbance to the established shrub. The soil should also be rich in organic matter.
Low-Maintenance Foliage and Groundcovers
The foundation of a successful underplanting relies on plants chosen for their texture and leaf color, providing year-round structure. Hostas are a classic choice, but selecting smaller to medium-sized varieties is prudent to prevent them from becoming too competitive or visually overwhelming. Look for compact cultivars like ‘Blue Mouse Ears’ or ‘Mighty Mouse’ which feature attractive blue or variegated foliage and maintain a manageable height of under 14 inches.
Ferns introduce a fine, airy texture that contrasts beautifully with the large, coarse leaves of the hydrangea. The Japanese Painted Fern (Athyrium niponicum ‘Pictum’) offers striking silver, green, and maroon fronds, providing color without relying on flowers. The Autumn Fern (Dryopteris erythrosora) is another option, unfurling with a warm, bronzy-coral color in spring before maturing to a lustrous green.
Heuchera, or Coral Bells, are invaluable for their vibrant, semi-evergreen foliage that provides continuous color interest. Cultivars like ‘Citronelle’ offer bright chartreuse to lime-green leaves, which visually lift dark, shady areas. For contrast, consider deep purple or nearly black varieties such as ‘Primo Black Pearl’ or ‘Obsidian’ planted near blue-flowering hydrangeas. These low-mounding plants require minimal maintenance and help cover the often-bare stems at the base of the shrub.
Adding Seasonal Color and Contrast
Adding flowering perennials and annuals introduces bursts of color and variety timed to complement the hydrangea’s bloom cycle. Astilbe is an ideal perennial companion because it shares the same requirements for moist soil and dappled light. Its delicate, feathery plumes contrast sharply with the hydrangea’s large, mophead or lacecap flowers. These plants offer upright spikes of red, pink, white, or purple in early to mid-summer.
For early spring interest, Bleeding Heart (Dicentra spectabilis) offers whimsical, heart-shaped flowers before the hydrangeas fully leaf out. Its foliage often fades and goes dormant by mid-summer, conveniently creating space for the hydrangea and other later-season plants to dominate. Shade-tolerant annuals are useful to ensure color throughout the hydrangea’s long blooming season.
Impatiens (Impatiens walleriana) are highly floriferous and establish quickly, providing a carpet of continuous color. Alternatively, Begonias, such as the Wax or Tuberous types, offer glossy foliage and long-lasting blossoms that thrive in the same consistently moist, shady environment. Using white or pale yellow annuals creates a visual pop and high contrast when planted beneath hydrangeas with deep blue or pink blooms.
Essential Planting Techniques for Success
Installing companion plants beneath an established hydrangea requires a delicate touch to avoid damaging the shrub’s shallow feeder roots. Instead of digging large holes, use small plants, known as plugs, or quart-sized containers, which require minimal soil disturbance. When preparing a spot for a new plant, gently push aside the mulch and use a trowel to make a pocket just large enough for the root ball.
Avoid amending the soil in a single planting hole, as this can create a “bathtub effect” of poor drainage. Instead, incorporate a thin layer of compost or leaf mold over the entire planting area and gently scratch it into the surface. After planting the new additions, water them immediately and deeply to settle the soil and eliminate air pockets.
A final layer of two to three inches of mulch will help retain moisture and keep the root zone cool. Ensure the mulch is kept away from the hydrangea’s main crown to prevent rot.