New Zealand Rimu (Dacrydium cupressinum)

Dacrydium cupressinum or the New Zealand Rimu is a slow-growing evergreen coniferous tree in the Podocarpaceae family. The Rimu is native throughout New Zealand, on the North Island, South Island and Stewart Island/Rakiura. Once found throughout New Zealand, it was extensively logged for its timber. The largest remaining concentration of trees is now found on the west coast of the South Island, the biggest trees tend to be in mixed podocarp forests near Taupo (the Pureora, Waihaha, and Whirinaki Forests).

The Rimu is a slow-growing tree, eventually attaining a height of up to 50 m, although most surviving large trees are 20 to 35 m tall. It typically appears as emergent from the mixed broadleaf temperate rainforest, although there are almost pure stands (especially on the west coast of the South Island). There are historical accounts of exceptionally tall trees of 61 m, from the central North Island, which are now all but destroyed. Its lifespan is approximately 800 to 900 years, and it is dioecious, with male and female cones found on separate trees. The straight trunk of the rimu is generally 1.5 m in diameter but may be larger in old or very tall specimens.

In garden settings, expect heights of 1.5 to 2 metres in 10 years, with eventual heights under optimal conditions of at least 20 metres tall, with a spread of 6 to 8 metres. The Rimu has a very interesting leaf structure, with leaves spirally arranged and awl-shaped, up to 7 mm long on juvenile plants, and 1 mm wide; and 2 to 3 mm long on mature trees. Both male and female trees are required to produce seeds; the seeds take 15 months to mature after pollination and occur irregularly, sometimes with 10 to 15 years between masts. The mature cones comprise a swollen red fleshy scale bearing one (rarely two) apical seeds. The seeds are dispersed by birds which eat the fleshy scale and pass the seed on in their droppings; the cones are an important food resource for some species, particularly the kakapo, whose breeding cycle has been linked to the fruiting cycle of the tree.

Although slow to establish, with a long juvenile period and fairly high moisture requirements, rimu is widely grown as an ornamental tree in New Zealand. It is attractive at all growth stages, usually quite narrow when young, then developing into a broader tree with weeping branches before finally progressing to its more upright adult form. It does well in most soil types and will tolerate mild poorly drained sites. It will do best in moist but well-drained soils that are lightly acidic.