Farm Forestry New Zealand

Willows are commonly sold as bare stakes and poles, and sometimes as rooted cuttings. Stakes and rooted cuttings are much cheaper than poles. Rooted cuttings have the most reliable strike rate in areas with dry summers or on exposed hillsides.

Planting

Most regional councils operate nurseries. The Hawkes Bay Regional Council offered willow stakes and poles in 2019 at prices of: 1 metre, $2.20; 2 metre $5.40; 3 metre $10.00. Protectors were 1.1m Netlon $3.40; 1.7m Netlon $4.60; 1.7m Dynex pole protector $7.20. Delivery was extra.

The best time to plant willows is from late June to early August. Plant across the lower half of exposed windy slopes, and plant only the sheltered, moist sites on the upper part of slopes. Irrigation may be needed during establishment, especially on lighter, free-draining soils. For shelter planting use trickle irrigation.

Stakes and rooted cuttings may require some vegetation control so that grasses and weeds are not competing with the willow for soil nutrients and moisture.

All poles, stakes and cuttings planted in paddocks must be protected from stock. Cattle should be kept out for at least one and preferably two or three years. Do not plant poles where there are goats or deer, they will ringbark the poles.

Willow poles are generally planted into pasture which requires no site preparation. For better establishment and growth, poles are best placed in moist hollows on drier hillsides, or south facing slopes and gullies. Avoid planting on ridge tops exposed to prevailing winds. When planting on very steep slopes plant the poles away from steep banks with thin soils, and angle them out from the vertical. This will prevent stock on the uphill side from eating the growing tips.

On arrival, willow stakes and poles should either be planted immediately, or soaked in fresh water until planting time. Do not leave them soaking for more than 21 days before planting and do not soak in stagnant water. Poles may also be stored in moist shade for a few days, for example under trees sheltered from wind.

Planting techniques are shown in the following short videos:

• Planting Poplars & Willows: Choosing the Best Poles
• Planting Poplars & Willows: Successful Planting
• Managing Poplars & Willows: Re-Ramming Recently Planted Poles

For good survival after planting, check poles regularly and make sure that as the soil dries out the poles remain firm in the ground. Loose poles can be firmed up by carefully ramming around the base, taking care not to damage the lower bark. Poles that are in good condition when planted are more likely to survive a drought in their first year.

Spacing

When planting poles for soil conservation, space poles at between 25 and 100 stems per hectare (spha). Steep slopes require closer planting as described in this short video: Planting Poplars & Willows: Successful Planting.

The closer willows are spaced the sooner the root systems of separate trees can start overlapping. The intermeshing of adjoining root systems greatly enhances soil stabilisation.

Remember:

• Willow is most vulnerable to drought in the first season after planting
• Willow prefers sites with good soil moisture levels

Releasing

Spray or clear weeds around stakes and rooted cuttings during the first summer, if necessary more than once. Be careful not to spray the willows themselves. Glyphosate is the safest, and can be sprayed on wet sites, but must not come into contact with green stems. As they grow willows are unlikely to shade out weeds, so problem weeds such as gorse and blackberry should be sprayed out before planting.

Form pruning

After two or three years young willow trees should be form pruned to a single leader. A single leader will resist strong winds and be less likely to split down the middle when older.

Grazing/Browsing

All poles, stakes and cuttings planted in paddocks must be protected from stock, usually with sleeves to prevent rubbing and bark stripping. Cattle should be kept out until the willow develops its rough bark, after 4-5 years.

Tangoio willow is favoured by possums and these should be controlled so they do not break out leaders and branches.

Pests and diseases

Giant willow aphid may reduce the growth rate of tree willows. This sap sucking insect produces honeydew which leads to a black mould on leaves and stems. Willow sawfly can also cause defoliation. Less important are the lemon tree borer, which does not cause much damage; and late spring flights of grass grub and manuka beetle that can defoliate isolated trees, which usually recover.

See Willow pests and diseases »

Willows are enormously versatile and no special management is required. They readily coppice (i.e. the stumps resprout after harvesting), and so may be regularly harvested for biofuels or for taking up nutrients in riparian strips. Their leaves and small branches are palatable, so the trees may be pollarded for fodder. 

Pollarding

Grown for supplementary feed, pollarded trees may be cropped on a 3-4 year cycle from age 8 or once they reach around 10 cm in diameter at breast height. Pollarding is described in this poplar fodder trial. Another study, Poplar and willow as supplementary fodder sources suggests that the nutritional value of intact willow leaves in summer and autumn is similar to that of pasture during the same period, particularly during drought, and the leaves are rich in trace elements such as zinc. Tangoio has the highest leaf protein of the willows.

Pollarding may involve the use of a chainsaw and the operator needs to be mindful of their safety at all times.

Pruning

Willow leaves are palatable to both sheep and cattle and prunings may be a useful feed source during drought, so pruning should be scheduled for summer. Form prune tree willows late in summer at age 3 to encourage one dominant leader. 

Suitable pruning tools include loppers and a pruning hand-saw, a battery-operated reciprocating saw, or battery-operated loppers.

Thinning

To maintain grass growth, as trees mature it is generally safe to fell every second tree between years 10 and 15, to a final spacing of 20 to 24 metres on gentle slopes, and 10 to 12 metres on stream banks. On more unstable slopes a higher stocking of trees is required and thinning should aim for a stocking of 10 metres apart.

Mature tree management

Regularly pollarded for supplementary feed, willows will remain productive and manageable.

Willows grown for erosion control will live for 30-40 years. Older unmanaged trees will likely become a liability as they come to the end of their lifetime. It may also be useful to have a programme of planned replacement of one tree in three every 10 years. Because willows are not grown for timber, removing older trees tends to come at a cost, unless there is demand for firewood or fuelwood.

In riparian margins, old willows can break out and block watercourses. Over-mature trees may require removal or a regular management programme of removing limbs.

Tangoio willow will produce firewood, fuelwood and chipwood, but does not produce useful timber.

Markets and demand

Tangoio willow is not grown for timber.

Tangoio grows rapidly reaching heights of 20-30 metres at rates of 1 to 2.5 m a year depending on rainfall and soil fertility. After age 20 the trees keep growing but may be regarded as mature.

This paper offers some advice on monitoring growth.

Timber return on investment

Tangoio willow is grown to enhance farm productivity through shelter, fodder and erosion control. The financial benefits are discussed in this report.

As tree willow is an exotic hardwood tables A2.2 and A2.4 apply, suggesting that over its first 30 years it stores carbon at a similar rate to radiata pine.

See Emissions trading »

• The authoritative source of information on poplars and who grows them is the Poplar and Willow Research Trust.