Foster holly (Ilex × attenuata 'Fosteri')

Overview

Foster holly, scientifically known as Ilex × attenuata ‘Fosteri’, is a highly valued hybrid holly prized for its dense, pyramidal habit and reliable winter interest. As a broadleaf evergreen, it provides essential structure and deep green color to the landscape throughout all four seasons. This cultivar originates from a natural cross between I. cassine (dahoon) and I. opaca (American holly).

A distinctive feature of the Foster holly is its ability to produce a showy crop of bright red drupes in the fall that persist well into winter, offering excellent visual appeal when deciduous plants are bare. Furthermore, female Ilex × attenuata ‘Fosteri’ plants are parthenocarpic, meaning they can set fruit successfully without needing a separate male pollinator nearby.

While generally hardy, gardeners should site Ilex × attenuata ‘Fosteri’ where it is protected from harsh winter winds, especially in cooler zones. This medium-maintenance evergreen excels when used for screening or as a formal upright specimen tree.

Fast Facts

• Plant Family: Aquifoliaceae
• Plant Type: Broadleaf evergreen
• Hardiness Zones: USDA Zones 6-9
• Size at Maturity:
  • Height: 20-30 ft
  • Spread: 10-20 ft
• Bloom Time: April to May
• Bloom Description: White
• Sun Exposure: Full sun to part shade
• Water Needs: Medium
• Maintenance Level: Medium

How to Grow

Planting Ilex × attenuata ‘Fosteri’ is best accomplished in the dormant season, typically early spring or fall, ensuring the establishment period is not stressed by excessive heat. This species thrives in acidic, well-drained soils with medium moisture levels. While they tolerate full sun, providing some relief from intense afternoon shade is beneficial, particularly in hotter summer climates.

Consistent watering is crucial until the Foster holly is well established. After the first year, this plant requires medium water input; mulching heavily around the base helps conserve soil moisture and suppresses competing weeds. Avoid poorly drained locations, as damp roots can lead to stress or potential disease issues.

Pruning, if necessary, should be scheduled for the winter months to shape the dense, pyramidal form. Because female Foster hollies do not require male cultivars for fruit set, planning your planting is simplified. Always site this variety in locations shielded from freezing winter winds to minimize the risk of foliage scorch or drop.

Landscape Uses

The strong, upright architecture of the Ilex × attenuata ‘Fosteri’ makes it an excellent choice for formal plantings. It performs beautifully when utilized as a dense hedge or screen, providing immediate privacy and excellent winter screening capacity. Many gardeners train the Foster holly into a small tree form, capitalizing on its columnar habit.

Use this striking evergreen as a strong vertical accent near entryways or to anchor larger mixed shrub borders. The combination of glossy, dark green foliage and persistent red berries ensures that this plant contributes color and texture year-round. For effective winter interest, pair mature Foster hollies with broadleaf deciduous shrubs that feature colorful bark or fine branching structure.

Standout Features

Flower Qualities

• Insignificant

Fruit Qualities

• Showy

Noteworthy Characteristics

Ilex × attenuata ‘Fosteri’ is a natural hybrid, combining traits from Dahoon and American holly. It forms a conical evergreen structure, usually growing 20-30’ tall unless heavily pruned. Its leaves are glossy, dark olive green, and elliptic with sparse, tiny marginal teeth. The abundant, pea-sized red fruits persist throughout the winter, offering dependable seasonal color.

Tolerances

• Air Pollution

Potential Problems

Gardeners should remain vigilant for common holly pests, including scale insects, whitefly, and spider mites, alongside the larval damage caused by the holly leaf miner. Fungal difficulties, such as leaf spot and tar spot, can arise, often exacerbated by poor air circulation or overly wet conditions. To mitigate issues, ensure proper spacing for air flow and promptly remove any fallen, diseased foliage. Chlorosis, or yellowing of the leaves, may indicate that the soil pH is too high, necessitating soil amendment to maintain the required acidity for optimal health of the Foster holly.

Frequently Asked Questions

What hardiness zones is Foster holly suitable for?

Ilex × attenuata ‘Fosteri’ is reliably hardy in USDA Zones 6 through 9.

How large does Ilex × attenuata ‘Fosteri’ grow?

This cultivar typically reaches a mature height between 20 and 30 feet tall, with a spread ranging between 10 and 20 feet wide.

What sun exposure does Foster holly need?

For best performance and fruit production, the Foster holly prefers full sun, though it can successfully tolerate partial shade, especially during the hottest parts of the afternoon.

When does Ilex × attenuata ‘Fosteri’ bloom?

The inconspicuous white flowers of the Foster holly appear relatively late in the season, generally blooming from April into May.

Conclusion

The Ilex × attenuata ‘Fosteri’ remains a cornerstone specimen for landscapes requiring reliable evergreen screening and vibrant winter decoration due to its dense form and abundant red fruit. Its unique self-pollinating nature makes managing the planting scheme considerably easier for the home gardener. Before incorporating this popular variety, always confirm that your site falls within USDA Zones 6-9 and plan for soil conditions rich in acid.

Wildlife Benefits

The abundant red fruits displayed by the female Ilex × attenuata ‘Fosteri’ are an excellent food source for numerous bird species during the lean winter months. Providing persistent berries ensures vital caloric intake for local wildlife when other food sources are scarce, making this holly beneficial beyond its ornamental value. Ensure the variety you plant is female to maximize this wildlife benefit, keeping in mind that fruit production will be plentiful.

Companion Planting

Companion plants for Foster holly should share similar cultural needs, thriving in acidic, well-drained soil and appreciating medium moisture levels. Consider pairing I. × attenuata ‘Fosteri’ with acidic-loving shrubs like Azaleas or Rhododendrons, which offer contrasting spring flower colors against the holly’s heavy foliage. Groundcovers that enjoy dappled or partial shade, such as various ferns or English Ivy (used cautiously), can help moderate soil temperature and moisture near the base of the maturing tree.