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Classic boron deficiency
Photo by Scion

Terminal dieback in sequoia

Hydroboracite chip

Resin pockets

Boron - an essential element

It is important that tree growers are aware of the benefits of applying boron to trees.
Many New Zealand soils are very deficient in boron, which is an important trace element to all plants, especially where summer droughts cause apical bud dieback and resin pockets in the timber.

Foliage testing of trees in March is the only reliable method of establishing accurately your trees boron status.


After three years with FRI based mainly at Milton, planting and maintaining provenance trials, Eric joined H. Baigent & Sons Ltd, a plantation owning timber firm in Nelson. Selecting superior Pinus radiata, grafting for a seed orchard, led to management and expansion of the company nursery, and a realisation that low fertility was limiting growth in second rotation stands. Resultant pine regeneration was yellow and slower growing than the first rotation. Trials with various agricultural superphosphate blends failed to bring any improvement on gorse free sites. Later nitrogen applications brought a marked greening, with long needles, increased height and diameter growth.

A different problem was occurring in young first rotation Pinus radiata stands on ridges in the Waiwhero area on weathered clays, where the leader died back annually forming an inverted ‘J’. Eight-year-old trees were squat bushes in stunted gorse. Superphosphate application resulted in a strong leader, which then died forming an inverted ’J’ when the summer drought occurred.

About 1963 Eric Chittenden from the Cawthron Institute with a background in nutrition of Nelson fruit crops visited the Waiwhero trials with other foresters and suggested trying boron. Timbor (used to treat pine timber) was applied as a spray on the pine foliage and borated superphosphate spread by hand along cut lines in the gorse and pines. Both treatments brought dramatic improvement with 2m leaders within six months and no die back for three years.
The Forest service then established boron and phosphate trials on deeply weathered granites at Kaiteriteri and on clays at Waiwhero with similar dramatic improvement in form and growth.

Eric subsequently saw similar growth deformity on West Coast dredge tailings and in shelter belts on flat terraces near Tarras, Otago.

A Perspective on Boron

by Andy McCord

It is very important that tree growers are well aware of the benefits of applying Boron to their conifer species. New Zealand soils are very deficient in boron which is critical to all dicotyledon plants

In the early 70s, especially after a dry summer, tip die back in Autumn was thought to be frost, research proved otherwise. The problem was a boron deficiency accentuated by drought conditions.

Our first attempt to correct this deficiency back in 1976 was a bit of a disaster.

A combination of using a quick release granular borate, combined with uneven application, resulted in toxicity, especially on trees growing in alluvial soils.


Our first source of a positive product came from Turkey. It was called Ulexite (double release) in the form of a chip (mined rock). This product had three advantages for forestry use. The first was that within its chemical make up one part was a quick release, namely sodium borate. While the other was two parts slow release, namely calcium borate. The third and most important was its physical state, namely chip. Being a type of rock it weathered slowly allowing higher rates to be applied without the threat of toxicity or leaching. Thus being able to apply only one application for the whole crop rotation. This product was available from the late 70’s through to1991, at which time the product became unavailable as a fertiliser.


Before we could find another chip source we opted for a granular ulexite. There are several dry salt lakes in northern Chile and southern Peru which consist primarily of sodium borate and small areas of calcium borate. So to compensate for the unavailability of the chip we blended the salts into one part sodium borate and two parts calcium borate, then granulated the salts into hard balls so they could be evenly spread from a spinner bucket. Even application was therefore achieved but on contact with wet soil or after a rain the granules broke down back into salt crystals and were therefore prone to leaching. After only a few short years we were forced to reduce the ratio to one part sodium and one part calcium simply because the latter was running out. At this stage we found we could not apply the full rate of boron to our stands as we were inducing toxicity especially in the lighter soils. To solve this problem we planned to reduce our rates and treat our crops possibly two or three times during its rotation.


However our problem was solved in 1999 when we discovered a boron mine in northern Argentina which mined a borate rock called hydroboracite. This product had the added advantage of a triple release. Not only did it have the quick release of the sodium borate and the slow release of the calcium borate, but also a medium release of magnesium borate. Therefore for the past seven years we have been able to apply the correct amount of product, and only need one application for the whole crop rotation, without the threat of toxicity or leaching, especially near streams and waterways.


Therefore it is critical that the health of your stand is maintained, and for this to be assured regular foliar sampling should be undertaken in March/April, to ascertain if your trees have the correct amount of nutrients as well as the correct balance.

After three decades of treating our conifers with boron we can now see the advantages of not only improved tree growth but also improved wood quality. We are well aware that if we got tip die back in young trees, the eventual butt log of that tree would be significantly down graded if left to mature.


What we are now finding, after decades of boron applications, is that other improvements are being found within these treated trees. Namely;

  • Treated trees grow taller and produce smaller branches. This not only increases volume , but also improves the timber grade because of the smaller knots.
  • Boron deficient trees are renowned for their resin pockets, and in many cases the argument is , “why prune, when we get down grade of our clearwood because of resin pockets.” Boron drastically reduces this problem.
  • We have also known for sometime that fibre (tracheid) length and thickness is also increased. This not only strengthens the timber properties, (increased stiffness) it also has a marked affect on the out turn of timber per log. Checking and warping of the sawn timber after seasoning is also significantly reduced.
  • Boron treated trees not only increase terminal growth, but also root growth. This has a multitude of advantages. Not only has the trees stability increased, but nutrient levels of both macro and micronutrients also increase. At the moment we are speculating about the reason, however, recent studies suggest that an increased root system can scavenge more nutrients and moisture. There also appears to be a dramatic increase in mycorrhizae associated within the feeding roots. Nurserymen are also finding this. Seedlings treated with boron, significantly increase their root fibre levels, as well as their mycorrhizal levels.
  • Tree health is also improved. Since applying boron to our plains forests the incidence of Diplodea has been significantly reduced.
  • Another serious concern is that higher genetic stock appears to be more prone to boron deficiency. It has been argued that it is because the higher genetic stock has been established as a second or third rotation and that they are already planted into a boron deficient site. Alternatively it is argued that since these higher genetic stock grow faster their demand for nutrients is higher. Whatever the reason, it is imperative that stock continually grow in boron rich soils and that is why we advocate that all woodlots should be boron treated at the start of the second growing season.

A boron treatment is one of the cheapest forest operations, and is the second most critical behind good weed control. However, since each forest site is different, (soil type, climate etc.) it is critical that the appropriate borate is applied to each specific site, and the aircraft applying the product is suitably calibrated.


Application rates are important and if correct product is applied, only one application is required for the whole crop rotation. The minimum amount required for a pine plantation is 8kg/ha elemental boron. This equates to approximately 60kg/ha of product which has a boron content of around 12%. Redwoods, on the other hand, require a higher rate of between 10-12kg/ha elemental boron. It is recommended that boron chip (mined rock) is used as toxicity will occur if a more soluble product is used. Other factors to consider with regard to finding the correct applied rate, is slope and weed content of the site.

For further information on the above, especially regarding foliar analysis or boron supply please give me a call.

Andy McCord - Technical Forest Services Ltd.
Field 027 224 3271. Office 027 282 7580
A/H (03) 313 4153. Fx 03 313 4953.