Westringia ‘Zena’ (Coastal Rosemary Hybrid)
Westringia ‘Zena’ is a cultivated form of the Australian native genus Westringia, commonly referred to as coastal rosemary due to its fine, needle-like foliage that superficially resembles that of true rosemary (Rosmarinus officinalis). Despite this resemblance, it belongs to a completely different botanical family, the Lamiaceae, which it shares with many aromatic herbs. ‘Zena’ has gained popularity in landscape design due to its compact growth habit, soft grey-green foliage, and strong tolerance to drought, wind, and coastal exposure.
This plant is widely used in Australian landscaping, particularly in urban, coastal, and low-maintenance garden schemes. Its durability, neat form, and year-round visual appeal make it suitable for both residential and commercial applications, including mass planting, borders, hedging, and container use.
General Characteristics
Westringia ‘Zena’ is an evergreen shrub that maintains a dense and rounded structure throughout its life. It is considered a medium-sized shrub, though it can be kept smaller through pruning.
Typical dimensions are as follows:
Height: approximately 1.5 to 2 metres at maturity
Width: approximately 1.5 to 2 metres
Under ideal growing conditions, the plant forms a naturally symmetrical mound, making it particularly desirable for structured landscapes or formal plantings. Compared to other Westringia varieties, ‘Zena’ is moderately vigorous but still controlled enough to maintain a tidy appearance without excessive pruning.
The foliage consists of narrow, linear leaves arranged in whorls along the stems. The leaves are typically grey-green to silvery, giving the plant a soft, muted tone that contrasts well with darker green plants. The underside of the leaves is often lighter, enhancing the overall silvery effect when moved by wind.
Growth Rate and Establishment
Westringia ‘Zena’ is considered a moderate-growing shrub. Its growth rate depends heavily on environmental conditions such as soil quality, sunlight, and water availability.
In general:
Establishment phase (first 6–12 months):
During this period, the plant focuses on root development. Top growth may appear slow, but this stage is critical for long-term performance.
Early growth phase (1–3 years):
The plant begins to increase in size more noticeably, often reaching around 1 metre in height and width within 2–3 years under favourable conditions.
Mature size (3–5 years):
Full size is typically achieved within 3 to 5 years. Growth may continue slowly beyond this point, but the plant will largely maintain its form.
In poorer soils or low-water conditions, growth will be slower but often results in a more compact and hardy plant.
Flowering
Westringia ‘Zena’ produces small, tubular flowers that are typically pale mauve, light purple, or white depending on conditions. The flowers are borne along the stems and are not large individually, but they appear in abundance.
Flowering characteristics:
Main flowering period: spring and early summer
Secondary flowering: intermittent throughout the year in mild climates
The flowers attract pollinators such as bees and small insects, contributing to biodiversity in garden environments. While not grown primarily for its flowers, the subtle blooms add seasonal interest and soften the plant’s appearance.
Light Requirements
Westringia ‘Zena’ performs best in full sun but is adaptable to partial shade.
Full sun (recommended):
At least 6 hours of direct sunlight per day promotes dense growth, compact form, and optimal flowering.
Partial shade:
The plant will still grow, but may become slightly more open or leggy, with reduced flowering.
Heavy shade:
Not recommended, as the plant may lose density and overall health.
In coastal or high-heat environments, full sun is typically not an issue due to the plant’s natural adaptation to Australian conditions.
Watering Requirements
One of the key advantages of Westringia ‘Zena’ is its drought tolerance once established.
During establishment (first 3–6 months):
Water regularly to encourage root development. Typically, watering 2–3 times per week depending on soil type and weather is sufficient. The soil should be kept slightly moist but not waterlogged.
After establishment:
Watering frequency can be significantly reduced. In most cases, watering once every 1–2 weeks is adequate, particularly in well-drained soils.
In dry or hot conditions:
Occasional deep watering is beneficial, especially during prolonged drought periods.
Overwatering considerations:
Westringia does not tolerate poorly drained soils. Excess moisture can lead to root rot and reduced plant health. It is preferable to underwater slightly than to overwater.
Soil Requirements
Westringia ‘Zena’ is highly adaptable to different soil types, provided drainage is adequate.
Ideal soil conditions:
Well-drained sandy or loamy soil
Neutral to slightly alkaline pH
It can tolerate:
Sandy coastal soils
Poor or low-nutrient soils
Light clay soils (if drainage is improved)
In heavy clay soils, it is recommended to improve drainage by incorporating organic matter or planting on a raised mound.
Pruning and Maintenance
Westringia ‘Zena’ responds very well to pruning, which helps maintain its compact shape and encourages denser growth.
Pruning guidelines:
Light pruning:
Can be done regularly throughout the year to maintain shape.
Hard pruning:
Can be carried out if the plant becomes woody or overgrown. It tolerates rejuvenation pruning well.
Best timing:
After the main flowering period in spring or early summer.
Regular trimming makes this plant ideal for low hedging or formal shapes. Without pruning, it will naturally maintain a rounded form but may become slightly looser over time.
Fertilising
Westringia ‘Zena’ is not a heavy feeder and generally performs well without excessive fertilisation.
Recommended approach:
Apply a slow-release fertiliser once or twice a year
Use a native plant fertiliser that is low in phosphorus
Over-fertilising can lead to excessive soft growth, which may reduce the plant’s natural resilience.
Tolerance and Hardiness
Westringia ‘Zena’ is valued for its ability to withstand challenging conditions.
Key tolerances include:
Drought tolerance: high once established
Wind tolerance: excellent
Salt tolerance: suitable for coastal environments
Frost tolerance: moderate (light frosts are generally tolerated)
These characteristics make it particularly suitable for exposed sites where other shrubs may struggle.
Uses in Landscaping
Westringia ‘Zena’ is highly versatile and used in a variety of landscaping applications.
Common uses include:
Low to medium hedging
Mass planting for ground coverage
Feature shrubs in garden beds
Coastal plantings
Container planting
Its consistent form and muted foliage colour make it a useful structural plant that pairs well with both native and exotic species.
Spacing Recommendations
When planting as a hedge or mass planting, spacing is important to achieve the desired density.
For hedging:
Plant approximately 1 to 1.5 metres apart depending on how quickly coverage is desired.
For mass planting:
Spacing can range from 1 to 2 metres depending on the scale of the project.
Closer spacing results in faster coverage but may require more pruning over time.
Longevity
Westringia ‘Zena’ is a long-lived shrub when grown in suitable conditions.
With proper care, it can thrive for 10–20 years or more. Regular pruning and good drainage are key factors in maintaining plant health over time.
Pests and Diseases
This plant is generally low-maintenance and resistant to most pests and diseases.
Occasional issues may include:
Root rot in poorly drained soils
Minor insect activity such as aphids or scale (rare and usually not severe)
Overall, it is considered a very hardy and reliable plant.
Summary
Westringia ‘Zena’ is a robust, adaptable, and visually appealing shrub suited to a wide range of landscaping applications. It typically grows to around 1.5 to 2 metres in both height and width, reaching maturity within 3 to 5 years. It requires minimal watering once established, thrives in full sun, and tolerates challenging conditions such as drought, wind, and coastal exposure.
Its low maintenance requirements, combined with its neat form and year-round foliage, make it a practical choice for both residential and commercial landscapes.
