With more than 800 known types of trees and shrubs, acacia is one of the largest genera of plants. Acacias belong to the legume family as their seeds are contained in pods just like beans and peas. The pods will turn brown as they ripen and eventually split open to let the seeds fall to the ground. Gathering the acacia pods just before they open will give you good seeds that have the best chance of germination, according to the Australian Native Plants Society.
Apply pressure to the sides of the pods to force them open. Acacia seeds come in various colors but they all have the same hard coating. The key to germination is to soften or abrade the coating so that air and water can get through. In their natural habitat, the dormancy of acacia seeds is normally broken by the heat of brush and grass fires. This effect can be imitated by the application of boiling water.
Put the seeds in a bowl and pour a few inches of boiling water. Because there are so many different species of acacia, the challenge in germination is to determine how much heat to apply. Varieties that grow natively in areas of grassland and scrub usually need less heat since grass fires burn very quickly. If you have this type of seed, add cool water to the bowl after a few minutes to reduce the temperature. Acacia seeds originating from forest species will need much more time and may be left in the bowl for about 12 hours.
Remove the seeds from the bowl and check to see which ones are swollen. The seeds will swell if water has penetrated the coating which means they are ready for planting. There will probably be at least a few seeds that have not responded to the boiling water method. You can try rubbing the coatings of these seeds gently with some fine grit sandpaper. This method is known as scarifying and the objective is to nick or scratch the surface enough to allow water through coating.
Prepare the potting mix by blending two parts sterile potting soil and one part of either perlite or vermiculite. Fill your planting tray with soil and plant the seeds about 1/2 inch apart. The seeds need to be shallow, about 1/4 inch below the surface. Press down gently to ensure good seed to soil contact and add a little water. Place the tray in a warm location out of direct sunlight and keep the soil moist. Seedlings can be transplanted to individual pots when they are an inch or two high. The young trees can be planted outside during warm weather in a well drained location.