Farm Forestry New Zealand

Planting

Container-grown and bare-rooted stock is available from some commercial nurseries; Price per tree should range from $0.80 - $2.50 for 1-2 year-old contract-grown forestry stock (2020 prices). Clonal redwood stock should be ordered well in advance so supplies can be available for planting.

To get optimal growth in the first year, plant well before spring on sites that are not prone to frost. On colder sites plant in late winter; in warmer areas with few frosts, plant in autumn.

Redwood thrives best in sheltered inland sites such as valley floors, gully bottoms and river flats with deep, fertile, moist but reasonably well-drained soils. It prefers relatively high humidity and a reasonably high, well-distributed rainfall. If you are planting in an unreliable rainfall area use wetted water-absorbing gel in the planting holes to ensure they don’t dry out before they establish roots. Young trees are shade tolerant, but for vigorous early growth need good weed control. Spray releasing for the first year or two is recommended and depending on natural fertility of the site may benefit from fertiliser. Young redwoods may be killed by out-of-season frosts.

Redwood may be planted with a nurse crop. Italian alder is suggested as being an excellent companion species that is faster growing at first but slows later. This the redwoods to grow upward with fine branching, but the redwoods eventually overtake the alders and dominate the site, killing the alders.

Spacing

The natural form of redwood is narrow and conical, thus high initial stockings are not necessary. If planting at 833 stems per ha, plant at 4m x 3m spacings or use alternating rows of seedlings and clones 6 metres apart with trees planted every 2 metres in the rows. This will allow thinning out of either row in the future. A more sparse planting of 625 stems per ha at 4m x 4m spacings using elite, fine branching clones will reduce the need for later thinning.

Releasing

Redwood is shade tolerant but establishes much faster with good weed control. Release spray after planting once weeds begin to regrow, then check the trees annually and release spray weeds until the trees are 2 metres high.

See Successful establishment of tree seedlings »

Grazing/Browsing

Young redwood seedlings are palatable to hares and rabbits. They will slice off trees near ground level at a 45 degree angle, killing them.

Possums can cause damage to leaders in some locations and if establishing a redwood plantation it is prudent to poison, trap or shoot them.

Pests and diseases

Cicadas can damage leaders and dead branches can offer entry points to borers, which can attack the heartwood.

See Pests and diseases of redwood »

Redwood seed has low viability and falls close to the tree, preventing unwanted spread.

Suitability for steep slopes: Redwoods resprout from the stump (coppice) making them suitable for erosion control. However, because redwood likes a reasonable soil depth and shelter, it is not usually suitable for steeper eroding slopes, but is well suited to lower slopes.

Being shade tolerant, redwood can be harvested under a mixed-age continuous canopy system (i.e. where individual trees are harvested on reaching a particular size rather than a particular age). When grown for timber the target is to achieve large pruned buttlogs and upper unpruned logs with green or moribund branches less than 50 mm diameter. Because of its narrow conical form and shade tolerance this species is one of the easiest to grow for timber production.

Redwood is good at withstanding flood events and sedimentation below sites where gully erosion is likely, and it can be planted in flood zones to filter debris flows.

Grown for timber, the target is to achieve large pruned butt logs and upper unpruned logs with green or moribund branches less than 50 mm diameter. If regenerating the trees from coppiced stumps, reduce the stems to three per stump and later thin again to one.

Pruning

Redwood has good form with few malformations or double leaders. However, when multiple leaders occur resulting from wind or possum damage, these should be reduced to a single leader if it is a crop tree. Malformed trees are usually thinned in favour of well formed crop trees.

To develop quality clearwood redwood requires pruning.

Prune the stem in 3 to 4 lifts (depending on site productivity) to a stem diameter of 12 cm, and to at least 6 metres height. Annual pruning from 4 years old is suggested to minimise knotty core. Epicormic shoots (i.e. budding from thin bark on the stem in response to sunlight) can be a problem in low-stocked stands and need to be removed.

Thinning

Target diameter needs to be fairly large because market demand is for heartwood. This means final crop stocking should not be more than 350 stems per hectare for a rotation length of 35 years.

Redwood is shade tolerant and will survive in very low light but grows faster with space and sunlight. Thin to final crop stocking a year or two after pruning is completed, or when the crowns begin to compete. Care should be taken to thin trees before lower branches die, to prevent bark-encased ("black") knots from forming, which allow borer entry into the tree and devalue the timber. Stumps will coppice and shoots will survive in the shade of the crop trees until these are harvested. Managing the coppice growth removes the need to replant. If regenerating the trees from coppiced stumps, reduce the stems to three per stump and later thin again to one.

When to harvest

On sheltered fertile sites in New Zealand redwoods can easily reach heights of over 35 m with diameters of over 65 cm at 50 years. They will continue growing vigorously far longer. Yields can be equal to radiata pine, and for practical purposes a rotation length of around 35 years is suggested, or when the trees reach a target diameter of 60 cm at breast height.

Redwood is valued for its beauty, light weight, and resistance to decay. The wood is soft and straight-grained, easy to work, odour free, non-resinous and free of oily materials. Its lack of resin makes it absorb water and resist fire. It can be readily air-dried with little shrinkage and degrade, and once dry it is brittle, but very stable. The sapwood is almost white and is perishable, but can be treated with LOSP or boron. The deep reddish brown heartwood is moderately durable, and changes to nut brown when exposed to light.

Redwood’s strength and stiffness values are about 70% of those for radiata of equivalent grade. In New Zealand it complies with the building code as an acceptable solution for exterior cladding but not decking or framing. It may be used as weatherboards and as decorative interior panelling, but its low density, low strength and low hardness restrict its applications. End uses are illustrated in the specialty timber group’s page on redwood.

Markets and demand

Most redwood logs exported from New Zealand have been marketed to Asian countries, such as Korea and Taiwan, where they have fetched good prices. Locally they sell at similar prices to radiata pine. A handful of mills around the country have developed a small marketplace for redwood timber.

A redwood growth model and volume and taper equations have been developed for redwood. The model predicts basal area and mean top height for a variety of sites around the country. It is described in the Tree Grower article Performance of coast redwood in New Zealand and may be downloaded as an Excel spreadsheet, the Redwood calculator.

On good quality sites growth rates for redwood can equal or better those of radiata pine, with mean annual increments in excess of 30 m³/ha/year.

Practical hints for measuring trees offers some advice on monitoring growth.

As redwood is an exotic softwood, tables A2.2 and A2.4 apply, suggesting that over its first 30 years it stores carbon roughly half as fast as radiata pine. However the Field Measurement Approach of the Emissions Trading Scheme (applicable for forests of 100 ha or more) might well give higher figures for redwood grown on productive sites.

Timber return on investment

Studies of the economics of redwood are few and variable. To date very little is understood about the timber grade and hence value recovery from various log types arising from different management regimes. Log quality is a critical factor in returns. For good sites with regular rainfall such as Taranaki and Bay of Plenty, IRRs may be of the order of 9% pa, assuming Californian prices converted back to NZ$ and including direct costs, overheads and management fees (at 15% of costs), but ignoring land costs.

• The Sequoia action group may put you in touch with growers in your area.
• Redwood - Information resources
• The NZ Redwood Company operates redwood plantations and offers good information.