Carissa tetramera (Sand Numnum): Complete Shrub Growing Guide
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Carissa tetramera
1. Introduction & Taxonomy
The Forest Num-Num is an elegant South African shrub bearing sweetly fragrant flowers and edible purple-black fruits. This shade-tolerant species grows naturally in coastal forests, producing white star-shaped blooms and plum-like berries with superior flavor to many Carissa relatives. Less thorny than desert species, it brings edible ornamental value to subtropical shade gardens where few fruiting shrubs thrive.
Carissa tetramera, the sand num-num, is a plant in the dogbane family Apocynaceae. The specific epithet tetramera means 'four parts', referring to the flower.
Taxonomic Classification
Habitat and Distribution
Carissa tetramera is native to tropical and subtropical regions. This species inhabits environments typical of the Apocynaceae.
Botanical Note: A large family of flowering plants including many ornamental and medicinal species. Notable for often producing milky latex and frequently showy, tubular flowers. Includes desert succulents (Adenium, Pachypodium), tropical flowering shrubs, and important medicinal plants.
Native Range & Distribution Map
The map below shows the native range and notable cultivation regions for Carissa tetramera.
2. Biology & Morphology
Growth Form & Architecture
Carissa tetramera is an evergreen broadleaf shrub maintaining dense, lustrous foliage year-round. This dependable greenery provides consistent structure and privacy in the landscape.
Flowers & Reproductive Structures
Shrub flowers vary enormously across families, from tiny wind-pollinated catkins to large, showy insect-pollinated blooms.
Key Characteristics
- Height: 1-3m
- Growth Habit: Erect Shrub
- Growth Rate: Moderate under optimal conditions
- Life Cycle: Perennial
3. Reproduction & Propagation
Primary propagation methods for Carissa tetramera: Cuttings, seed, or layering (varies by species).
Propagation Methods
Semi-hardwood cuttings taken in late summer. Layering for difficult-to-root species. Seeds may need stratification.
Propagation Tip: Wound the base of cuttings and use rooting hormone for best results.
4. Cultivation Requirements
Soil / Substrate
Rich, well-draining soil with organic matter. Many prefer slightly acidic conditions (pH 5.5-6.5).
Watering
Consistent moisture during growing season. Mulch to retain soil moisture.
Light Requirements
Full sun to partial shade. Most ornamental shrubs perform best with at least 4-6 hours of direct light daily.
Temperature
- Optimal Growth: 18-30°C (65-86°F)
- Minimum Tolerance: -12°C (10°F)
- USDA Hardiness: Zones 8-11
Pruning
Light pruning after flowering. Can be formally clipped for hedging. Remove dead or diseased wood anytime.
Fertilization
Apply a balanced slow-release fertilizer in spring. Most shrubs are moderate feeders.
Common Cultivation Mistake: Over-watering is the most common cause of shrub failure. Ensure good drainage and match watering to the species' natural habitat.
Seasonal Care Calendar
Follow this season-by-season guide for optimal care timing throughout the year.
🌱 Spring (March–May)
Primary flowering period begins with fragrant white blooms. Apply balanced fertilizer to encourage flowering and fruiting. Prune lightly to shape if needed. Monitor for pest activity.
☀️ Summer (June–August)
Fruits develop and ripen to purple-black. Harvest regularly for best flavor. Water consistently during dry spells, especially in containers. Mulch to conserve moisture in shade gardens.
🍂 Fall (September–November)
Late fruits ripen. Reduce watering frequency as growth slows. Good time for planting new specimens in mild climates. Light pruning to remove wayward growth if desired.
❄️ Winter (December–February)
Protect from frost below 28-30°F; more cold-sensitive than desert Carissa species. Minimal watering needed. Avoid pruning during dormancy. In frost-free areas, sporadic flowering may continue.
5. Diseases & Pests
Carissa tetramera is generally robust and pest-resistant when cultural conditions are optimal.
Major Diseases
Root Rot (Phytophthora, Pythium)
Caused by overwatering or poor drainage. Ensure good drainage and avoid waterlogging. Improve soil aeration.
Powdery Mildew
White powdery coating on leaves. Improve air circulation, avoid overhead watering, and apply fungicide if severe.
Leaf Spot (various fungi)
Brown or black spots on foliage. Remove affected leaves, improve airflow, and avoid wetting foliage.
Common Pests
- Scale Insects — Hard or soft scales on stems and leaves; treat with horticultural oil
- Spider Mites — Fine webbing on undersides of leaves in dry conditions; increase humidity
- Mealybugs — White cottony masses at leaf axils; spray with soapy water or neem oil
- Aphids — Cluster on new growth; spray with soapy water or introduce ladybirds
- Whiteflies — Tiny white insects on leaf undersides; use yellow sticky traps
IPM: (1) Choose the right species for your conditions. (2) Maintain good air circulation and hygiene. (3) Monitor regularly and act early. (4) Use chemical controls only as a last resort.
6. Indoor & Container Growing
Carissa tetramera can be grown in containers and brought indoors during winter in cold climates.
Container Selection
Use containers with adequate drainage holes. Choose pots at least 5 cm larger than the root ball. Plastic retains moisture longer; terra cotta dries faster.
Indoor Light
Place in the brightest available location. Most shrubs need at least 4-6 hours of direct or bright indirect light.
Container Success Key: Match your container medium to the species needs: free-draining for xerophytes, moisture-retentive for tropical species.
7. Landscape Use & Design
Carissa tetramera is a versatile landscape plant offering structure, colour, and seasonal interest.
Design Applications
- Hedging & Screening: Dense shrubs for privacy, windbreaks, and boundary definition
- Foundation Planting: Soften building lines and define entrances
- Specimen / Accent: Showcase plants as focal points in the garden
- Mixed Border: Combine with perennials, grasses, and bulbs for year-round interest
- Topiary & Formal: Shape dense evergreens into geometric or sculptural forms
Companion Planting
- Perennials — Echinacea, Salvia, Lavandula for mixed borders
- Other Shrubs — Layer heights and textures for depth
- Grasses — Ornamental grasses add movement and contrast
- Ground Covers — Underplant with low-growing species for a finished look
Design Principle: Plant shrubs in groups of odd numbers (3, 5, 7) for natural-looking compositions. Repeat key species throughout the garden for cohesion.
8. Cold Climate Strategies
Carissa tetramera tolerates cold to USDA Zone 8. Winter protection or container culture may be needed in colder areas.
Hardiness Thresholds
- USDA Zones: 8-11
- Minimum Survival Temperature: -12°C (10°F)
Overwintering Options
- In-Ground Protection: Apply 10-15 cm of mulch over the root zone before first frost. Wrap trunks of borderline-hardy species with fleece.
- Container Culture: Move potted plants to a frost-free garage, conservatory, or cold greenhouse for winter.
- Microclimate Selection: Plant against south-facing walls or in sheltered spots to gain 1-2 zones of extra warmth.
Winter Survival Rule: Most shrub losses occur from late frost after spring growth has started. Avoid premature uncovering.
Frequently Asked Questions
Can I grow this in shade?
Yes, unlike desert Carissa species, C. tetramera tolerates and even prefers partial to light shade, making it ideal for woodland gardens and shaded courtyards. It will flower and fruit in conditions where C. macrocarpa would fail.
How does the fruit compare to Natal Plum?
Many consider Forest Num-Num fruits superior in flavor, sweeter and less tart than C. macrocarpa. Fruits are similar in size but ripen to darker purple-black. Both are edible when fully ripe.
Is it as thorny as other Carissa?
No, C. tetramera has fewer and smaller thorns than desert species like C. macrocarpa, making it more user-friendly for gardens. Still has some thorns, but generally easier to manage and harvest from.
Will it tolerate coastal conditions?
Moderately salt-tolerant for protected coastal gardens, though not as tolerant as C. macrocarpa. Prefers sheltered locations rather than direct salt spray exposure. Coastal forest edges are its natural habitat.
Explore More Species
Discover related species in our Shrub Encyclopedia:
Summary & Key Takeaways
Carissa tetramera, is a erect member of the genus Carissa (Apocynaceae), native to Worldwide.
Key Points to Remember:
- Propagation: Cuttings or seed
- Light: Full sun to partial shade for most species
- Substrate: Well-draining, moderately fertile
- Watering: Moderate — match to species needs
- Hardiness: USDA Zones 8-11, minimum -12°C (10°F)