As professional horticulturists we are often asked specific questions regarding tree and plant biology. Below we have some of the most frequently asked questions (FAQ) about our trees and how our growing techniques affect their growth.

  • When and how often to prune semi–mature trees after planting
  • tree acclimation to local conditions
  • From a success standpoint, when should we plant?

When and how often to prune semi–mature trees after planting.

Due to the busy schedules for tree managers through the winter period with public consultation, selection, purchasing and installation of streetscapes, previous year plantings are often not pruned as they should be. Many trees will require repeated formative pruning, normally one to two years after planting. Winter and early spring is often the best period as many trees will be deciduous and structure is more easily assessed, while providing opportunity to direct branch growth before spring flush.
Ensure that the trees you purchase have been well structurally pruned for streetscape requirements. Often trees will not have branches removed to an appropriate level or bifircations and apical dominance maintained for a streetscape situation. Significant cross branching should have also been removed by the grower prior to shipping. Do not be frightened by a light branch structure in the trees you purchase, as the grower has most likely begun pruning for the appropriate branch configuration for your intended streetscape.

When you go to prune the trees in-ground, look carefully at the form. You should find a tree that has problems with new growth only, and not in the canopy that you bought. Pruning a tree after one or two years should take a few minutes: you should look for crossing branches, and remove them; then look to make sure that a second leader is not growing, and if it is the secondary leader should be reduced to 1/3 of its length; finally, check for suckers at the tree’s base and remove any present (this can be a problem with some grafted trees like pears). This kind of pruning is easy, should take less then 5 minutes for each tree, and will save hours of corrective pruning in the future.

After the tree has been in the ground for three to five years, the tree should have a last formative prune. At this time, the tree should be 5m+ tall, and the canopy can be lifted to its final height. If next to the footpath, this height should be about 2m. Again, crossing branches and co-dominant leaders should be removed at this time. This formative pruning requires care and skill, but will give the tree appropriate form for the rest of its life.

Tree acclimation to local conditions

Acclimation of stock moving from a hills climate or from a tropical/semi – tropical environment is necessary for successful establishment in south-eastern Australia. Many brokers and growers sourcing stock from further north fail to understand this need for the tree to adapt to its new destination. A four to six week period is required involving slow cuticle development by reduced watering in a climatic region similar to its final planting location. Without appropriately timed acclimation, stock will go through defoliation, yellowing and burning. Careful watering regimes may help in reducing these symptoms but in many streetscape and project developments the level of care is often unachievable (Gilman, 1997).
The best ways to ensure the best desired outcomes for your projects is to ensure the grower/broker has allowed for this period of acclimation, otherwise greater costs will incur for maintenance and/or replacement. Normally, acclimation will take at least 6 weeks in the nursery, if temperature/humidity acclimation is the only issue. If you are planning on using trees like Ficus spp. where light levels are low, the trees will also have to undergo a period of light acclimation. After temperature acclimation, the trees are moved into an intermediately-lighted area (normally under shadecloth) for 4-6 weeks. After this intermediate acclimation, the shadecloth density should be increased to the same light levels as the final planting area. After a final 4-6 weeks, the tree is ready for planting with little leaf drop or damage.
Acclimated trees normally cost about twice the price of their non-acclimated Queensland cousins. Acclimation is expensive, but will assure greater success in the final location.

From a success standpoint, when should we plant?

Most tree planting happens in winter, regardless of the kind of tree that’s being planted. We understand that tradition, water availability and staff timing all contribute to this planting frenzy. Metropolitan Tree Growers believes that by extending the planting window from April through October, better results can be gained.
Most deciduous trees will have finished all canopy growth by mid-February, and from February until April, these trees are growing roots, and hardening off. With most deciduous trees, by mid-April, these trees are ready to plant and will not harden off further. Any manager can be assured that planting in late April or early May will not be detrimental to the tree’s survival.
Evergreens, and especially Australian trees, require more careful timing for selecting the best planting date. This date has to be determined by the condition of the tree, not a calendar date. Australian trees are normally grown from seed, and especially in smaller sizes, growing these trees to a specific date is impossible. These trees are very dependent on the weather; from seed to 1.5m, 16 litre tree, the timing can be off by up to 3 months if the weather is cool. We are committed to growing a tree that is not over-grown in its container; it is virtually impossible to grow a tree to order without some allowances for weather.

We have found that many of the Australian trees grow canopies when the weather is warm and as night temperatures drop, these trees expand their root systems and develop stem caliper. Our production system requires that the fastest growing taxa, such as E. scoparia, will have started to harden-off by late April. The trees with average growth speed, like the casuarinas and many eucalypts, will be hardened-off and ready to plant in June or July. Our most popular eucalypts, like E. leucoxylon selections, will normally require the full winter to harden-off, and normally should be planted in September or October.
It can be very difficult for tree managers to organise planting these trees, but it is impossible for a tree grower to change the weather. If you are going to plant a significant number of 16 litre Australian trees, you need to order early, and then check the progress in January, March and early winter. At each progress check we will be able to give you a better idea of timing for these trees.

 

References:

  • Gilman, E.F. 1997. Trees for Urban and Suburban Landscapes. Delmar Publishing, Albany, New York USA.
  • May, P.B. 2000. pers. comm. Head of Campus, University of Melbourne, Burnley Campus, Richmond, Vic.