PITTOSPORUM TENUIFOLIUM (KOHUHU)

Article by David Marks
There are over 200 species of Pittosporum with differing heights, hardiness and general features. This article is aimed at the most popular in the UK, Pittosporum tenuifolium, sometimes called the New Zealand Pittosporum. They originate from coastal regions of New Zealand (where they are called Kohuhu) and vary in height from dwarf forms up to small tree size. Pick your variety carefully!

Use the checklist below to decide if a Pittosporum Tenuifolium is suited to your preferences and garden conditions:

• An evergreen shrub with attractive slender leaves. Many are multi-coloured.
   
• They have flowers but in reality these are very insignificant. The flowers are scented but many forget to mention that they are only scented at night.
   
• Height varies from 1m / 3ft up to 3m / 10ft. Most are upright plants, the larger ones can be considered as small trees when left unpruned.
   
• They are frost hardy down to -8°C / 17°F. Below these temperatures the plants are damaged but not necessarily killed. They are not well suited to areas where they are exposed to a combination of high winds and freezing temperatures.
   
• Pittosporum tenuifolium do best in well drained soil. They will suffer if the ground becomes water-logged.
   
• They show their best foliage colour when grown in full sun but will also do well in partial shade.
   
• They require minimal care, pruning is only required to keep them to shape or increase the density of the foliage.
   
• Some varieties are very well suited to growing in containers.
   
• Disease resistance is good. See our section below on pests and diseases of this shrub for top tips about avoiding this problem.

WHERE TO BUY PITTOSPORUM TENUIFOLIUM

Pittosporum are widely sold as potted plants in garden centres and from online plant companies. Online companies hold the largest choice of varieties. The National Collection of Pittosporum is held at Bicton College in Budleigh Salterton but is not open to individuals. 

Online stockists which we recommend include Crocus (low prices and quality combined with a year's guarantee) and Burncoose.

HOW AND WHEN TO PLANT A NEW PITTOSPORUM

Follow the steps below to ensure your Pittosporum Tenuifolium is planted correctly and in the best position:

• Choose a full sun to partial shade position. The plant needs some air circulation so although it will thrive against a wall or fence, avoid planting it in the corner of two walls fences. See the section on varieties below for planting distances.
   
• If the soil is heavy or is not free draining add lots of well rotted compost to the area and dig it in well.
   
• It can be planted all year long if the soil is not frozen and you can water well when conditions are dry. Mid March to April and mid September to October are the best times to plant this shrub.
   
• Dig a hole twice the width of the rootball. Sprinkle in a handful of blood, fish and bone and work into the ground.
   
  
• Place the plant into the hole, filling in with soil so that it is at the same depth as was in the pot. Fill around the rootball and firm the soil down gently but firmly. Water well to settle the surrounding ground around the rootball.

Pittosporum tenuifolium are at their most vulnerable to freezing conditions in their first year after planting. As they age they become more frost-hardy.

DIFFERENT VARIETIES OF PITTOSPORUM TENUIFOLIUM

We list below some of readily available varieties which we recommend.

Pittosporum Tenuifolium Tom Thumb

The most popular of all because of its relatively small size, compact habit, attractive foliage and stems. A slow growing variety which requires almost no maintenance. It makes an excellent low level dense, hedge / border when planted 80cm / 30in apart.

In our view it is an ideal alternative to a low box hedge - far more attractive and definitely better pest and disease resistance. This is not a rockery plant but it is ideal for smaller gardens.

Pittosporum tenuifolium Tom Thumb
Multi-coloured foliage

Height and spread	1.2m / 4ft high and 80cm / 30in spread
Leaf colour	Bronze / purple topped with bright golden green new growth. Very striking undulating leaves which provide year round interest.
Flowers?	Yes in May to June but very insignificant. Only slightly scented at night
Growth Habit	Bushy, rounded and compact. Well suited to even small gardens and excellent for growing in containers. Easy to prune to that ideal rounded, mound shape.
Frost Hardy?	Hardy in most areas of the UK but needs a position protected from strong winds in cooler regions.
Awards	RHS Award of Garden Merit.

Pittosporum Tenuifolium Golf Ball

This is our favourite variety because it requires no maintenance, tolerates a wide variety of conditions and keeps a dense rounded shape. The name "golf ball" was given because it it is an ideal alternative to the traditional Box plant, trimmed to a round shape. A Pittosporum Golf Ball will achieve a 1.2 m / 4ft height and spread in as little as three years - a Box plant would take eight years or so.

It's ideal for smaller or medium sized gardens, normally grown as a single specimen. The lime-green foliage looks good all year long. It can loose some of its shape if the winter brings a heavy snow fall which tends to sit on top of the plant but a quick brush of the snow will sort out that problem.

We have seen several growing quite happily in heavy clay although a lighter soil is likely to make it more frost hardy. As long as they are not water-logged, they will grow well and they tolerate drought conditions better than most shrubs.

Height and spread	1.2m / 4ft high and spread
Leaf colour	Lime green providing year round interest.
Flowers?	Insignificant
Growth Habit	Dome shaped by nature, it forms a dense cover of leaves. For those who want the perfect rounded shape they can be pruned very easily to perfection.
Frost Hardy?	Hardy in most areas of the UK but needs a position protected from strong winds in cooler regions.
Awards	None, but it can only be a matter of time before the RHS give it an AGM

Pittosporum Tenuifolium Irene Patterson

This variety is included here because it seems to be a favourite of garden designers and horticulturalists. We have to admit that it's not amongst our favourites but each to their own.

This variety is grown for its white streaked green foliage which looks very attractive. It grows to a more open shape compared to the two varieties above but pruning twice a year can result in dense foliage. Another shrub for small and medium sized gardens, it is unlikely to grow taller than 1.6m / 5ft in the UK. In warmer climates it can reach 2.4m / 8ft.

As with other Pittosporum it is tolerant of most soil conditions and withstands drought conditions for short periods of time.

Height and spread	1.6m / 5ft high and spread
Leaf colour	Green with white streaks and spots providing year round interest.
Flowers?	Insignificant
Growth Habit	Slightly more open than some Pittosporum but regular pruning can shape it to a neat and tidy column shape
Frost Hardy?	Hardy in most areas of the UK but needs a position protected from strong winds in cooler regions.
Awards	RHS AGM

CARE OF PITTOSPORUM TENUIFOLIUM

These really are very low maintenance shrubs and can be left entirely to their own devices in most garden situations. We recommend a twice yearly feed with Blood, Fish and Bone in March and September to ensure they don't suffer mineral deficiencies on poor soils. They are drought tolerant so only water in the very driest conditions.

Frost tolerant down to -8°C / 17°F, they are at their most vulnerable to frost damage when young. Damaging conditions only occur in most of the UK every ten years or so and in this case a temporary fleece over young plants will go a long way to getting them through the first two winters. In warmer parts of the UK they will be fine.

The dome shaped varieties such as Tom Thumb and Golf Ball can collect snow on the top in some winters. It's best to go out and brush this off if you want to maintain that perfect dome shape the next growing season.

HOW AND WHEN TO PRUNE PITTOSPORUM TENUIFOLIUM

Pittosporum don't need pruning to keep them healthy, they can be left to grow to their natural shape. However some gardeners do prune them once or twice a year top maintain a good shape. They respond to pruning very well and their narrow leaves don't brown at the edges when cut. Simply prune to the shape and size you require.

If you do want to prune your Pittosporum the best times are between April and July. If you prune them later in year the new foliage which grows as a response to pruning may be damaged more easily during the winter.

GROWING PITTOSPORUM TENUIFOLIUM IN CONTAINERS

The main need for growing Pittosporum in containers is to water them so that the compost is kept moist but not water-logged. Rainwater collected from a water butt is the best source of water for this shrub in containers. Pittosporum are generally more drought tolerant compared to most other shrubs so they will survive the odd time you forget to water them.

They have no particular soil requirements, ordinary multi-purpose compost will do fine as will John Innes type composts. Make sure the container has holes in the base to allow drainage and add a few small stones at the bottom to reduce the risk of water-logging.

From April to September a feed once every two months with a small handful of blood, fish and bone worked into the surface of the compost. In winter place the plants where they out of the wind and have some frost protection - against the wall of a heated house will do fine or in an unheated greenhouse.

The most recommended variety for container growing is Tom Thumb and it's easy to see why. The plant is naturally compact, small and keeps its shape well. It provides year round interest and can be pruned to a variety of shapes and sizes. Another good variety with similar qualities is Golf Ball, slightly larger but container growing will naturally limit its size. Both of these varieties can be bought online at Crocus.

PESTS AND DISEASES OF PITTOSPORUM

Pittosporum are generally healthy plants with the problems noted below being caused by cooler than average conditions or water-logging.

LEAF SPOT

The symptoms of this problem are dark spots on the leaves. Affected leaves eventually fall off and in bad cases the plant can be severely affected. The latest research indicates that in most cases the damage is caused by damp, humid and / or cold conditions rather than disease. 

Where the plant is only partially affected the solution is to remove spotted leaves and burn them as soon as they are noticed.  Where the damage is more severe you have two choices:

• prune back hard in mid May, remove all the prunings and in all likelihood the plant will bounce back with new red growth in a month or so.
   
• accept the fact that the position of the plant is the cause, dig it up and plant something there which can cope better. You may want to take cuttings before you do this, read our section below on propagation.

POWDERY MILDEW

The classic symptoms appear in mid Spring and are a white powdery coating mainly on new shoots. If left unchecked older shoots and stems can also be affected. This is caused by environmental conditions, mainly irregular watering and lack of air circulation. See our page devoted to identifying, understanding and treating Powdery mildew by clicking here.

HOW AND WHEN TO PROPAGATE PITTOSPORUM

There are two common methods for propagating Pittosporum, cuttings and from seed, neither is guaranteed success! The seeds take at least two months to germinate, often as long as four months so we don't recommend this as a method of propagation.

Taking cuttings is likely to be more successful but the plants grow very slowly and some varieties may take three years or more before they contribute to your garden. Semi-ripe cuttings have the best chance of success and the method is the same as described for Photinias which can be found by clicking here.

Other similar shrubs in this series include Ceanothus, Choisya, Hebe, Skimmia, Magnolia, Mahonia, Mock Orange, Lilacs, Potentilla and Rose of Sharon (hibiscus syriacus). For the full list, click the Shrub Index link at the end of this article..

PITTOSPORUM TENUIFOLIUM SUMMARY

Below we list the key strengths and weaknesses of Pittosporum Tenuifolium.
 

HARDY	(to -8°C)
CLAY SOIL	Yes
SANDY SOIL	Yes
DRY SOIL	Yes
SHADE	No, partial, full sun
EVERGREEN	Yes
EASY CARE
SMALL GARDENS	Yes
POT / CONTAINER	Yes
FLOWERING
FLOWER TIME	Not relevant