• A number of plants serve as ideal companion plants with winterberry. Winterberry (Ilex verticillata) is a deciduous, dense holly that grows to a mature height of 5 to 15 feet. The shrub has slender stems and simple, ovate, double toothed foliage. Winterberry blooms with white flowers from April to July followed by red to orange fruit in late summer. The fruit persists until the middle of winter and is an important food source for small mammals and more than 48 species of birds.
  
  

Nellie Stevens (Ilex x 'Nellie R. Stevens')

• The "Georgia Gardener's Guide" by Erica Glasener and Walter Reeves suggests using an evergreen holly such as Nellie Stevens as a backdrop and companion planting with winterberry. The evergreen foliage of Nellie Stevens makes the bright fruit of winterberry stand out in the garden. Nellie Stevens (Ilex x 'Nellie R. Stevens') grows in a pyramidal shape to a full height of 15 to 25 feet. The shrub was developed in Maryland and introduced to nurseries in 1954. Nellie Stevens grows best in an acidic soil but adapts to most soil types. The shrub thrives in areas of full sun to partial shade and is hardy in United States Department of Agriculture Plant Hardiness Zones 6 to 9. Propagate it with cuttings at any time during the year.
  
  

Yellow Flag Iris (Iris pseudacorus)

• Winterberry is well adapted to growing in wet or dry soils and Glasener and Walter in "Georgia Gardener's Guide" suggest using perennials such as yellow flag iris (Iris pseudacorus) that also thrive in wet soil as a good companion plant with the shrub. Yellow flag iris is a hardy variety with 3- to 5-foot long, sword-shaped foliage and 3- to 4-inch wide, yellow flowers in the typical six-petaled iris form. Plant it in full sun when growing in wet soils and in some shade when the soil is on the dry side. The flowers are hardy in USDA Plant Hardiness Zones 4 to 9 and the yellow contrasts well with the red fruit of winterberry.
  
  

Cardinal Flower (Lobelia cardinalis)

• Cardinal flower (Lobelia cardinalis), a perennial for wet soil, is suggested as a possible companion planting with winterberry in the "Georgia Gardener's Guide" by Glasener and Reeves. The cardinal flower is a herbaceous perennial that grows to a mature height of 1 to 3 feet. The plant has purplish-green stems and foliage, and blooms with 1-foot long racemes of bright-red 1- to 2-inch long flowers in the middle of summer. The flowers contrast well with the white flowers of winterberry that bloom around the same time. Cardinal flowers continue blooming well into the first frost. Plant in areas of full sun to partial shade and moist soil. The plant is hardy in USDA Plant Hardiness Zones 3 to 10 and self sows freely.