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No. 26 Growing Paulownia

NZFFA Information leaflet No. 26 (2005).

Based on a Waikato Farm Forestry Association April 2010 fielday and Forest Research Institute Bulletin No. 231, Paulownia Handbook (2007). This leaflet Summarises 15 years of experience and limited research in New Zealand.

Timber Market – the first place to start!

Paulownia timber is becoming revered by boat builders, surf board builders, as a sound absorbing finish in buildings, and as a balsa wood substitute By far demand is strongest for use as a light, strong component of integrated fibreglass/wood constructions!  (See Tree Grower November 2007)

Demand is for 3m or 6m lengths of timber without any knots. At the end of each growing season Paulownia stops its height growth and forms a growth knot across the diameter of the tree which leaves a scar “timber defect”, once new height growth starts next season!  Hence growers have developed the following:-

Nursery Preparation – Aim to produce 6m high poles

In August, take root cuttings from mature trees (grows slow) or from plants in the nursery. Cuttings with a diameter of 0.75 – 2cm and 10 – 12cm length usually give consistent results. (make a straight cut closest to the tree trunk for the upper end of the cutting and slanting cut for the lower end)

Treatment of Cuttings

Wash them, soak for 30mm in Captain or Thiram fungicide solution, then lay them on open trays to dry for at least 3 days in a ventilated glasshouse. Then they can be coolstored and planted by 2 – 3 weeks.

Root cuttings should be buried in mounded-up rows in nursery beds protected from strong winds. Spacing should be 1m x 1m to achieve maximum height growth of up to 6m and diameter of 7cm. Well drained, water, fertile, and weed free are basic!! Prune off any side shoots like tomatoes! Undercut in autumn and/or dig up in winter and transplant into the fields with the roots and pole intact!! Very labour intensive!

Silviculture

Plant out using 6.5m x 6.5m to 8m x 8m (gets more wind damage) final spacing or in single rows at least 5m apart, keep all side shoots off your top first nursery years pole growth! Protection from grazing animals must be absolute! Any little nick of damage to the stem will produce a distortion in timber growth and rot which quickly spreads and totally wastes long lengths of timber. And any stock (including sheep) love them – leaf and bark! Young trees are also easily weed spray damaged! Any organic or fertiliser matter applied is well rewarded with tree growth!

Do not worry about the form and growth of the tree above 6m! It is too costly to maintain, and every breath of wind will result in branch breakages! Be prepared to do big cleanups after a good strong wind, although young branches are quite flexible in the wind. If the main pole is damaged, you can cut it off at ground level (in winter) to try to get another one year 6m growth in the next season!! (You will need to select vigorously your best coppice!) Wind may blow poles over, so you may have to repack the pole root systems in again! You can reach 50cm dbh in 12 years.

Final Planting Site Features

Best Paulownia tree growth is obtained in places where kiwifruit is grown commercially, but where natural rainfall averages 50 – 100mm/month. (see paragraph P40 FRI bulletin 231, 2007). Hot summers are great, but after 3-4 weeks of dry weather, the trees suffer. The first year planted out is rewarded by being irrigated over summer. Well drained soils with low clay content are favoured – water table lower than 1.5m. No heavy frosts between September and April. Slopes with a northerly aspect. Wind force less than 30km/hr – other specie shelter belts are probably wise but some do not worry!

Species – who knows!

Paulownia elongata seems a good all rounder. Paulownia fortunei seems to have good apical dominance. Paulownia fargesii does fine!! Look at specimens in the locality where you want to grow them! FRI Bulletin No. 231, Paulownia Handbook has pictures of flowers to help identify the different species.

Timber Marketing

There is no organised regular market at the moment. Growers are cutting and drying timber and then individually marketing limited quantities. The key to current superior value is the 5 – 6m clear wood first year stem! Then it will depend how many people are successful in applying these growing skills and trying to co-ordinate a very immature and irregular market that can reach prices of $1000/18yr old tree!! The key advantage is light but strong wood!

John Mortimer stands by 15yr old Paulownia elongata 53cm DBH April 2010

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