Frequently Asked Questions

16. What is the best potting mix to use for plant propagation and potting on?

There are probably as many different potting mixes as there are propagators. With experience, most propagators develop their own variations to suit the conditions that they have available.

For seed raising and for striking cuttings it's hard to go past the often recommended sand-peat moss mix in the ratio of about 7:3 as a starting point. These days many growers are turning to the artificial peat mosses which are becoming available and which are made from such waste products as coconut fibre. Experience so far indicates that the artificial products are capable of excellent results. The sand used should be clean and should have a high proportion of grains in the 1 to 3 mm range.

Once the seeds have germinated and the cuttings struck, the time will come for transplanting the small seedlings or cuttings into larger pots. For potting on, the mix should be of open texture so that it will drain freely. Potting mixes that have been used successfully include a coarse river sand/coco peat moss mix in the ratio of 3:2 and a mix of coarse river sand/coco peat moss/sandy loam in the ratio of 5:4:3.

If you make up your own mix, add some slow release ferilizer at the rate recommended on the pack. Most native plants don't require any special fertilizer, however, some are sensitive to excess phosphorus and should be fertilized with special "native plant" fertilizers.

You can also purchase bagged "native plant mixes" from nurseries and garden centres. These usually come with fertilizer and trace elements already mixed through so there is no need to add additional fertilizer. Look for quality mixes manufactured to the specifications of Standards Australia.

A good reference on potting mixes generally is the CSIRO's booklet simply titled Potting Mixes (No.9 in the "Discovering Soils" series). The principle in the CSIRO's approach is to have a balance between water holding properties and air in the root zone of the plant. You can increase the amount of air in the mix by adding coarse material such as gravel (5-10 mm particles) or pine bark chips which have been stored and watered frequently for about six weeks to remove potentially toxic compounds.

A more thorough treatment of potting mixes can be found in Kevin Handreck's book Gardening Down Under, also published by the CSIRO.

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