Post-planting – Maintenance for Best Establishment

James Will
Senior Lecturer, University of Melbourne, Burnley Campus

Recommendations

 

  • Differentiate between those trees that will establish quickly (in 1 year) and those that will require 2 years’ maintenance to establish correctly
  • Budget for as much irrigation as possible each week
  • Make certain that water is appropriately applied to wet the rootball and surrounding soil.
  • Re-mulch when necessary to improve water-holding capacity and weed suppression of the site
  • Control weed competition

The Establishment Period

The commonly-held wisdom dictates that trees are planted in late winter or early spring, and then will establish over the first summer post-planting. For this reason, most establishment maintenance is contracted for 6 to 9 months. With fast-growing trees, this one-summer maintenance will establish the tree, but with slow-root-growth varieties, such as Ginkgo, Magnolia and others, it may take 2 spring/summer periods for the tree to become established. Trees that fail in the second year after planting may be failing because they require an additional year of establishment watering and care. Further, many large, super-advanced trees will require at least 2 years’ maintenance.

Water: the Essential Factor

Dr. Peter May is famous for saying, “Identify the irrigation that you believe will be adequate, and then double the figure.” Water is the most important factor in establishing plants in the landscape. North American authors suggest rates of at least 4 litres water/week/25mm trunk diameter. In south-eastern Australia, rains occur only sporadically in summer, and you must expect that added irrigation is the only way for watering trees.

Using the 4 litres/week/25mm trunk diameter (at 100mm above ground level) as a starting point, these trees will need:

Container size Tree height Ave. trunk diameter Litres of water/week
15-20 litres 1.5-2.0m 30mm 5
40-50 litres 2.1-3.0m 50mm 8
75-100 litres 3.1-4.0m 75mm 12

There are few instances where this water requirement is met.

Irrigation is most important in late spring through early autumn. Deciduous trees may have shut down growth earlier in the season, and irrigation after 1 March may not be necessary, but Australian trees and other evergreen trees will require irrigation at the rates indicated above until 1 April.

With homeowners, you frequently find that over-watering is a major reason for tree death, but with urban trees this is less likely. Seemingly the only times when trees die from too much water is when the site is originally waterlogged and not corrected by pre-planting preparation.

Fertilisation in the establishment phase is not critical unless the trees are in a luxuriant state. As noted in the previous article, fertilisers will not aid in root growth during the establishment phase unless irrigation and soil conditions are ideal.

Note that weekly irrigation is best to keep soil moisture at the critical level for best root growth; irrigating twice as much each fortnight will not give the same benefit to the root system. Further, be concerned with low-infiltration-rate soils; trees planted in these soils will require careful irrigation to assure that water ends up in the rootball.

Reducing Competition

If trees have been planted properly, a mulch layer of between 75 to 100mm will have been installed at planting. This mulch layer, preferably of a moderately-coarse composted bark, woodchips or prunings, will help insulate the root zone, and reduce evaporation from the planting hole. This mulch will also reduce weed competition around the root zone of the newly-planted tree.

If the mulch layer is too thin, top this mulch up to at least 75mm during the establishment period to assure that the benefits possible from mulching can be realised.

Weed competition will severely limit the root growth of newly-planted trees. Weeds will use available water and compete for nutrients that should be available to the tree. Newly-turned soil will expose the soil-seed-bank that exists in most soils, and after planting a tree these weed seeds will grow. A layer of mulch will restrict weed growth, but clean-up with a herbicide or by hand-weeding when weeds are visible.