Time and place

The best time for planting native trees and shrubs in Adelaide (and Hills) is late April, May and the first two weeks of June or all of September if wet. This gives them time to get established with the help of natural rainfall. Check that your soil type is acceptable for the plant. For example, banksias prefer freely draining sandy soil, and not clay. Most plants require full sun so select a spot that is open in the tree canopy for lots of light throughout the day. If shade is recommended, select a spot that is shaded (or semi-shaded) in the afternoon as most plants require some light in the morning for growth. Next look for a shallow depression of say 50mm in a dish of 500mm diameter so rainwater can collect in the immediate vicinity of the plant. Ideally plant into a drain-way to feed more water onto the plant. Often when the ground slopes 5°to 20°, the supply of rainwater can be increased to the tree by digging an arrowhead into the ground with a garden trowel. Dig the two shallow arms of the arrowhead about 40mm deep and 50mm wide, the same profile as the trowel, 90° apart and 300mm long with the point leading to the tree.

Digging the hole

The ideal hole is twice as deep and twice the diameter (or width) as the plant container. Do not scatter the dugout soil.  Keep it close to the hole, as you will need to fill it back in again. If the soil is hard or has lots of clay, avoid making a hole with smooth polished sides. Such a hole restricts the growth of the roots in the same way as a pot does. The plant could become root-bound, preventing the roots from spreading into the adjacent soil. Any smooth edges can be removed by looseni ng the sides and bottom with a small fork. You want the hole to look “rough”. A jemmy bar is the ideal tool (borrow one from your local burglar) to open the ground and remove any small rocks. If the ground appears too rocky and/or has heavy clay, select another site.

Water and nutrients

Back fill the hole with some of the removed soil and temporarily put the pot into the hole. The soil in the pot should be at the same level as the external ground. Remove the pot and add a teaspoon of slow release NPK fertiliser or some old manure or seaweed extract into the hole. Use low phosphorus fertiliser for plants that are sensitive to phosphorus such as banksias and grevilleas. Mix up this bottom layer of soil.  Give the plant a good watering while it is still in the pot. This will also make it easier to get it out of the pot. It is a good idea to place the whole container into a bucket of water but do not submerge the whole plant. Wait until the water stops bubbling and then remove it from the water. For sandy soils, including a wetting agent in the soaking water enables rain (after planting) to easily rewet the root-ball.

Removal of the plant from the pot

Hold the plant with say the left hand and place two fingers from the right hand, one either side of the stem at the soil surface and tip the pot upside down. Then gently squeeze the pot with the left hand and the soil and root ball should fall out. If it doesn’t come out easily, tap the edges of the pot vertically up with a trowel. Turn the plant and root ball over and hold it upright in your left hand. If the roots are tightly coiled, gently tease them out. If they are very tight, cut them by running a sharp knife vertically down the root-ball on two sides. Try not to disturb the roots any more than necessary.

The planting!

Using both hands, hold the roots and soil together as you place it into the hole. Check again how far the soil goes up the stem. The aim is to plant the seedling so the same amount of the plant stem that was covered by the soil in the pot is also covered when the plant is in the ground. Hold the seedling in place with one hand and scoop the soil back into the hole. Fill it evenly around the sides and then press it firmly with your hands or the heel of your shoe. It’s desirable to leave a small depression around the plant to act as a water bowl to help keep the plant moist.

Immediately after planting

Always water new plants straight away. This reduces the chance of the plant going into transplant shock. Freshly planted seedlings need a good soaking – not just a light sprinkle. It takes a lot of water to reach the roots under the soil and the neighbouring soil also soaks up the water. Slowly add about 2 to 5 L from a dripping container over 5 to 10 minutes to allow it to soak into the soil.

To reduce water evaporation and suppress weeds, add a layer of mulch such as wood chips. Keep the mulch about 25 mm away from the stem so it does not rot the stem. Over time, the mulch will break down and improve the soil. Add a semi-circle mixture of soil with 25mm to 100mm diameter rocks around the lower side of the plant to dam rainfall and reduce loss of topsoil. Finally, add a green “corflute” guard and stake it. If there is any possibility of animals such as horses or kangaroos damaging the new plant, install a circular ring-lock fence (with100 x 100mm “holes”) of 1.5m diameter and 900mm high held in place with three-star droppers at angles of 120°.

Long term — the first summer

Deep watering reduces water evaporation and encourages the roots to become stronger by growing deeper when they are looking for moisture. Most native plants need to be watered at least twice during their first summer. Consider using a 20L (ex-chemical) container with a valve cracked open to allow just one drop of water every second to seep slowly into the earth over a week.

References and further reading

  1. Australian Trees, their Care and Repair, by P Hadlington and J Johnston. Second edition published in 1988 by New South Wales University Press.  Highly recommended book: a tree lover’s first aid manual with colour photographs. Two special appendices: the first lists trees with special requirements and any problems and the second lists trees for particular situations (colour, shade, beach front, suburbs, schools, industrial areas, wind breaks etc.).
  2. Trees for Rural Australia, by KW Cremer. Published in 1990 by CSIRO Division of Forestry. A comprehensive book with colour photographs. How to grow trees from seed, germination, planting etc. Discusses trees for control of salinity, soil erosion, and soil acidity. Ideal for large scale tree planting on farms rather than bush blocks.
  3. Economic Trees and Shrubs for South Australia by Neville Bonney. Published in 1997 by Greening Australia (SA) Inc. 167 pages with one page devoted to each plant with colour photographs. Each page details the districts where it grows well, plant uses, soil and rainfall required and management details.
  4. Farm Trees for the Mount Lofty Ranges by Peter Bulman. Published in 1995 by Primary Industries SA. A comprehensive book with colour photographs, mainly for agroforestry