How to Grow and Care for Kohuhu (Pittosporum tenuifolium)

Kohuhu (Pittosporum tenuifolium), also known as Tawhiwhi, is a broadleaf evergreen shrub or tree that can grow to over 30 feet and 15 feet wide. It is densely branched, with slender stems which on young shoots are gray to nearly black. Favored for hedges, it thrives in full sun and frost-free temperatures like Pacific Northwest coastal gardens.

Native to New Zealand, Kohuhu has naturalized in Australia as well as California. There are more than 25 cultivars offered in the nursery trade with several compact versions suitable for container gardening.

Kohuhu Care

If you choose a Pittosporum tenuifolium  that is not compact, pruning will be necessary to maintain a hedge, however, the plants are low maintenance. Plant kohuhu in a full sun location for optimum growth. It can tolerate partial shade but should be in a sheltered site to protect it from strong winds, especially if planted in a container.

Kohuhu prefers moist, well-draining soils and can tolerate some maritime salt spray. Planting should be done in spring or fall and the new shrub watered deeply for the first year. Until the plant is established, protect roots from frost by adding mulch around the base of the plant.

Light

Kohuhu prefers full sun but can tolerate partial shade. If used as a container plant, it should receive at least six hours of sun each day.

Soil

The shrubs or small trees will thrive in fertile, well-draining soil. If planting in an area with clay soils, add compost to improve drainage.

Water

Newly planted kohuhu should be watered deeply and frequently until the plant becomes established. Mature shrubs require additional watering only during periods of drought. Container shrubs require frequent watering, especially during periods of higher temperatures.

Temperature and Humidity

Kohuhu prefers the warmer temperatures of Hardiness zones 8 - 11. They will tolerate light frost but not sustained periods of freezing temperatures. High levels of humidity are well-tolerated.

Fertilizer

When planting new shrubs, add some bone meal to the soil to help the plant become established. Once established, if the soil is fertile, additional fertilization is not needed. However, if growth slows, add a well-balanced (8-8-8 NPK) slow-release granular fertilizer around the drip line of the shrub in the early spring.

Types of Kohuhu (Pittosporum tenuifolium)

Within the nursery trade, you can find more than 25 cultivars of kohuhu ranging from tall-growing shrubs suitable for privacy hedges to compact, rounded forms for shrubbery beds and containers.

• Pittosporum tenuifolium 'Marjorie Channon': A slow-growing shrub with light green variegated leaves with cream-colored margins and dark purple to black stems. Grows in a rounded pyramidal habit reaching 8-12 ft. tall and 6-8 ft. wide.
• Pittosporum tenuifolium 'Silver Sheen': Densely branched with dark, very thin stems, small silvery-green leaves, and fragrant red flowers in the spring.
• Pittosporum tenuifolium ‘Gold Star’: Tall and compact, the leaves are variegated light green with a yellow center. Grows to around 6 feet and 36 inches wide.
• Pittosporum tenuifolium ‘Golf Ball’: With a natural round growth habit, 'Golf Ball' can be easily pruned into a perfect round topiary in the garden or a container. It has dark stems and light green foliage and can grow to a height and equal spread of around 4 feet.
• Pittosporum tenuifolium ‘Tom Thumb’: New growth leaves emerge as green and later turn dark purple in the winter. The shrub has a rounded growth habit and remains small reaching only 3 feet and is a good choice for garden beds or foundation plantings.

Pruning

The amount of pruning needed for kohuhu is dependent on the look you desire. Kohuhu doesn't require pruning to keep it healthy but if you want to keep a shrub compact or maintain a sculpted hedge or topiary, then pruning is necessary.

The best time to prune kohuhu is in the spring. In early spring, check for any winter damage and remove broken stems. After new growth has emerged in late spring, prune stray branches to maintain the shape and size you desire. Do not prune in the fall because new growth stimulated by the pruning may be more easily damaged during the winter.

Propagating Kohuhu

Kohuhu can be propagated easily by taking cuttings or layering.

Cuttings

1. Select young, healthy, vigorous, non-flowering shoots in mid to late summer.
2. Remove the lower leaves, then coat the cut end with a rooting hormone.
3. Place the cutting in a mixture of perlite and coarse sand, and keep the cutting moist and warm until roots develop.
4. After 8 to 10 weeks, you can transplant the cutting into a large pot filled with a loam and sand mix.
5. Transplant to a permanent location in the spring.

Layering

• Layering is done directly under the shrub by rooting stems while they are still attached to the parent plant.
• Select healthy young shoots growing near the ground
• Bend the branch down to touch the soil.
• Use a sharp knife to remove a sliver of bark at the contact point.
• Use a landscape pin to keep the branch firmly in place in the soil.
• Allow up to 12 months for strong roots to form.
• Carefully dig up the rooted plant and transplant it to the new location.

How to Grow Kohuhu From Seed

While kohuhu can be propagated from seed, it is a long process and not always successful. The seeds take at least two months to germinate, often as long as four months. It is not the recommended way to grow new plants. However, if you'd like to give it a try, here's how:

• Select fully-ripened fruit (wrinkly black) in the fall and store them in a cool, dry place.
• In the spring sow seeds individually in small pots filled with a good seed-starting mix.
• Place the pots in a sunny, sheltered spot and keep the soil moist.
• Once the plants reach 3 to 4 inches, transplant into a larger pot.
• Transplant into the garden in the spring and keep the plant well-watered.

Overwintering

Container-grown kohuhu should be placed in a sheltered location away from strong winds. If growing in a rainy winter environment, make sure the container does not become water-logged. Overwintering requires no special care unless extremely cold temperatures or heavy snows are expected. Use a plant cover during extreme weather to prevent damage to limbs and foliage.

Common Pests and Plant Diseases

Kohuhu is usually problem-free; however, it can be affected by plant diseases especially if over-watered or stressed by growing conditions.

Leaf spot can occur if the plant is overwatered. The affected leaves develop dark spots and eventually fall off. If the water level is not corrected, the plant may die. To combat leaf spot, remove the leaves and dispose of them. If the disease is extensive, prune the plant severely in late spring and remove all of the debris. There should be new growth within a month.

Powdery mildew may appear in the spring mainly on new shoots. The mildew appears because of poor air circulation and high humidity. Remove the mildewed leaves, prune the plant to improve air circulation, and use a fungicide if the mildew spreads.

While unusual, aphids can affect kohuhu. Follow recommended steps to remove aphids from shrubs.

Common Problems with Kohuhu

Kohuhu varieties are easy-to-grow and maintain shrubs. The most common problems are overwatering and planting in an area with too much shade.