What should a healthy Paulownia look like?
The following photos were taken in the middle of the growing season (summer).
The planting site needs to be well cultivated; usually by first breaking up the entire field using discs, rotary cultivator or chisel plough (depending on soil type) then by raising the planting rows into high mounds preferably using a grader so as to achieve a 'V' drain between the rows for drainage and flat edges on the mounds for easy slashing and plantation maintenance work. The optimum planting grid is 4m apart between trees within the mounded rows with the rows at 6.25 metres apart. This gives 400 stems per hectare and requires no thinning before harvest at 8 to 15 years. After harvest the stump regrows, negating the need to replant .
The first aim in the management of Paulownia is to grow a sapling with 4 metres or more trunk height free of branches in one season. This will become the butt log - the most valuable part of the tree, producing clear timber - free from knots and flaws. The reason it is worth aiming for such spectacular height growth in one season is it is normal for the tip of the trunk to die back during winter and regrow with a kink the following spring, resulting in a slight wave in the centre grain of the timber. TGG have developed a plantation establishment method which has proved effective in most circumstances. In an ideal climate Headstarters™ may reach 4 metres tall in their first season, but often this is not possible so any trees less than 3 or 4 metres tall should be regenerated by cutting the trunk off at ground level in the winter after its first growing season. Drastic as this may sound, the Paulownia will regrow from the stump in spring and develop a new trunk, stronger, straighter and larger both in height and girth by the end of the second season than that which would have grown had the original trunk not been removed. From this point the trunk is usually allowed to grow on to a harvest age of eight or more years. No branches are allowed to grow on the first year trunk - any that sprout from the trunk just above a large leaf stalk are pinched out or cut, but with great care not to remove the large leaves directly attached to the trunk. The large leaves on young Paulownia are the trees' solar panels - catching the sunlight and, in combination with water and nutrients, converting it into rapid growth. Removing these leaves will slow the growth of the tree. The plantation is usually further pruned until about 4 or 5 years of age to ensure a clear trunk to five or six metres. From the second year of the trunk onwards (when the leaves become smaller) lift pruning should be gradual, leaving at least one third of the height of the trunk covered with leaved branches. Excessive pruning will inhibit the normal formation of a canopy and prevent the natural establishment of the tree, resulting in slow diameter growth of the trunk.
Paulownia have high nutrient requirements to reach their full potential. Usually 200 - 250 grams (one standard cup is about 250g) per tree of a N.P.K.S. 8-11-10-7 granular fertiliser (such as Incitec Pivot Croplift 800) is applied as a manual top dressing at spring planting. Later in the season a further 300g - 500g (depending on soil) per tree is applied using a fertiliser spreader with a side shoot that directs the granules down the centre of the planting row. This is repeated in the following seasons as needed to maintain rapid green growth during the warm weather (usually 2 or 3 applications per season until year 4 or 5 when one broadly spread application of 500-600g per tree at the start of each season should be adequate). The best type and rate of fertiliser will vary from site to site, depending on climate and soil type. In a very dry climate liquid fertiliser (fertigation) may be the only way to adequately supply enough nutrition as granulated fertiliser requires rain to properly wash it into the root zone. After a number of seasons something of a self supporting nutrient cycle develops from the now deep roots and the normal falling of the leaves in autumn (assuming the leaves are not collected). Frequent plantation inspection and timely action are the keys to success in a Paulownia plantation and it is important to be able to recognise when the trees are suffering nutrient deficiency.
Unless in a zone which receives reliable summer rainfall, watering is critical for fast growth. It's generally best to use a multiseasonal integrated dripper line (with emitters with a labyrinth and vortex structure which create a turbulent water flow which results in clearing of residues and resistance to clogging). The lower the litres per hour rating of the emitters the more can be run at the same time (2Lph is adequate but up to 4Lph is suitable in soil types where the water does not pool). The emitters should be spaced at 50cm so that a drip emitter will never be further than 25cm from the stem of the plantlet - this is critically important in the early weeks after planting, especially in sandy soil. Close emitter spacing also result in more even delivery to the root system of more mature trees. The dripper line should be run straight down the centre of the planting row mounds, placed on alternate sides of each tree to keep them in place on the middle of the row when they move due to varying temperature causing expansion and contraction. A good deep soaking every 7 to 21 days during their first summer is usually sufficient and generally better than light frequent sprinklings in encouraging a good root system. (The exception to this is if you have shallow soils with a hard clay pan and high water table - in this case more frequent shallower watering may help to encourage the roots to stay within their most viable zone - any that go too deep will only rot in the wet season.) If a drip irrigation system is used it should be left on long enough to thoroughly soak the depth of the root area. Observation and common sense are the keys to correct watering. Obviously sandy soils will need more than heavy loams, but overwatering in sand will result in wastage and leaching of nutrients out of the root zone. It is also important to note it is normal for Paulownia to wilt during a hot day - this is a mechanism for avoiding excessive transpiration. If the trees are wilting because it is hot, but the soil is moist don't water them or you risk causing root or collar rot. If they have enough moisture the leaves will stand up again when it cools in the evening.
Weed control is crucial in the early years. Make sure the ground is completely free of weeds prior to planting. If you have a lot of weed seeds in the topsoil it may be best to plant the trees within a small square of biodegradable weed mat (such as Jutemat). Protect the young plants with a plastic tree guard sleeve supported by 3 stakes or a reusable wire frame. This allows spraying of glyphosate weed killer using a stripper dome sprayer which is mounted on an ATV (farm bike - causes less soil compaction than a tractor). Stripper domes are generally 60cm wide so a run up each side of the tree line results in a 120cm bare centre strip. The inter-row can simply be slashed - maintaining some green cover on this zone is advantageous in terms of beneficial biology, erosion control and avoiding nutrient run-off and excessive evaporation. A side throw mower is ideal as throwing the grass and weed trimmings up onto the bare strip in the centre of the mound will act as a mulch - conserving moisture and inhibiting weed seed germination.
Protection from severe wind is advantageous and can be provided by a windbreak of fast growing trees such as Virgilia, Tagasaste or Willow (which are all useful fodder trees) or maybe some other fast growing timber tree such as an Acacia or Eucalyptus - just make sure you leave at least a 12 metre gap between Eucalyptus trees and Paulownias or the Eucalyptus will inhibit the Paulownias' growth.
© 2000 - 2010 James S. Lawrence
You will find more detailed "How to" information in the Data Sheets, Technical Bulletins and Sales Support PDFs available on the main Paulownia Information page. In particular, for commercial plantation establishment information see Techincal Bulletin # 1 (PDF).
Paulownia are planted primarily for timber production. The decoratively grained timber is soft and easy to work, but strong for its weight and does not easily warp or split. Paulownia timber air dries well, thus eliminating or reducing the expense of kiln drying. As it is a pale timber, plantation grown Paulownia can be stained to imitate a wide range of other timber types and can be used to replace tropical rainforest timbers. Uses include doors, window frames and other interior fittings as well as furniture and anywhere light but relatively strong and visually attractive timber panels are required, such as boats and aircraft.
Paulownia trees are also useful for various biomass applications, fodder, shade, protection for crops, prevention of land degradation through erosion or salinity, honey production during the spring and their outstanding value as a fast growing landscape and feature tree. They are also very effective as a sink for waste water with the ability to rapidly convert nutrient rich effluent into useful wood and biomass. Their fast growth and large leaf area also make Paulownia highly efficient in the sequestration of carbon, thus helping to combat global warming.
Paulownia have a natural distribution ranging from latitude 22° to 40° in China (tropical to cool temperate) with P. fortunei also extending into Vietnam and Laos. Paulownia tomentosa also grows in Korea and Japan. Paulownia taiwaniana, P. kawakamii and P. fortunei are indigenous to Taiwan.
The most important requirements to consider when choosing a site for Paulownia are very well draining soil, summer rainfall or availability of irrigation water, sunny aspect, ease of access for planting and harvesting and proximity to the target market or a port. The latter is not quite as important with Paulownia as with most timber trees as the light weight and high value of the timber makes longer distance transportation more viable.
The soil must be well drained because any more than three or four days of waterlogging is enough to cause fatal root rot - especially in winter when the trees are dormant. They perform best in deep soils with a water table at least 1.5m deep. Paulownia are tolerant of a wide range of pH from 5 to 8 and research comparing soil and foliage analysis on various soils indicate Paulownia can selectively absorb calcium and magnesium from the soil. Paulownia are indigenous to zones that receive summer rainfall, therefore in drier areas artificial irrigation is required.
TGG Headstarters™ can be planted almost all year round in tropical zones, avoiding the driest and wettest periods (although if irrigation is provided they can be planted during the dry). In other climates they can be planted from spring (after the last frost) to mid autumn, although it is usually best to avoid planting out in the hottest part of the year - if you must plant in hot weather the results are usually very good as long as you avoid planting during extremely hot or windy days, make sure the soil is moist before planting and water them in immediately after planting.