The genus Pittosporum is some 200 species strong but most are only suitable for growth in warm climates or under glass. This genus' range is very wide and species can be found through out Australia, Asia, and some parts of Africa. Pittosporum is named after the Greek phrase "pitch seed", this is because the seeds are very resinous and will stick to most surfaces. Many herbivores dislike the resinous seeds but the seeds of P. resinferum can be used to produce bio fuel. Only seven species seem to be appropriate for the UK climate; the most notable are P. tenuifolium and P. ralphi, of which there are many cultivars. As well as having attractive leaves and honey scented flowers, P. tentuifolium has interesting cultivars such as the pale cream variegated 'Variegatum' and the silvery green leaved 'Silver Queen'
Culture for Pittosporum
Most species naturally form medium sized trees (8 to 20m in height). However if pruned correctly, they can be used as hedges and screens since they are frost hardy to negative 5 C, evergreen, densely bushy, and recover well if pruned hard in mid spring. Pittosporum grows best in fertile and moist (but well drained) soil in full sun or partial shade. Soil should be acidic to neutral with a pH between 5 and 7.
Concerns about Pittosporum
It is advisable to plant Pittosporum in partial shelter in the colder parts of the UK since it is vulnerable to harsh winter wind chill. Plants of the Pittosporum genus are resistant to Armillaria root rot but can be sensitive to Phytophthora root rot. Pests and diseases such as red spider mite, aphids, cushion scale, Pittosporum sucker, powdery mildew, and fungal leaf spots are risks due to densely packed foliage and the low air flow.
Management Practices for Pittosporum
Treat foliar pest and diseases in early mid April to late May using sprays of insecticides and/or fungicides in a scheduled PHC programme. Follow with winter washes to prevent infection and reduce overwintering populations. Phytophthora infection can be treated with a soil management programme (RCX, biochar, phosphites, and mulch) and prescription fertilisers.