Down to Earth - Episode 5: Potting mixes (1990)

[Music plays while Gardening Australia logo appears on screen with the number 5 and the words Potting Mixes.  Image changes to show Kevin Handreck at a garden nursery]

Kevin Handreck:  Most of us have had the experience of coming to a nursery store and seeing all of the different brands of potting mix available and wondering well which one of these is going to be the best for the plants that we want to grow? 

[Images pans in to close up of Kevin Handreck standing next to bags of potting mix]

Is it the one with the word premium on it or is it one of the ones with some other type of information on?

[Image shows close up of bags of potting mix.  Image pans back out to show Kevin Handreck speaking]

In the past buying potting mix has been a bit like taking out a ticket in a lottery, sometimes we get something that’s been pretty good, other times we find that the mix, even though it might be from the same brand, from the same company, isn’t quite as good.

[Image shows close up of bags of potting mix]

How do we tell which is going to be a good potting mix?

[Image shows close up of Kevin Handreck speaking]

Well I have good news for Australian home gardeners, we now have in place an Australian Standard for potting mixes.  

[Image shows close up of label on bag of potting mix]

What that means is that when you see a label like this on a potting mix bag you can be sure that the contents of that bag have been manufactured according to quite stringent conditions. 

[Image shows close up of Kevin Handreck speaking]

And in effect what it means is that you are guaranteed that plants will grow well in that potting mix.

[Image shows loader emptying load of potting mix.  Image changes to show machines processing wood waste]

Most potting mixes are based on wood wastes such as pine bark.  The raw bark is ground in a hammer mill.  In the best manufacturing plants it is then screened into various particle sizes. 

[Image shows machine screening processed wood waste.  Image changes to show man bucketing product into machine]

Nutrients and water are added but the bark can’t be used immediately because it contains naturally occurring toxins.

[Image shows machine turning bark particles]

To remove these toxins the bark has to be composted. 

Part of the composting process involves regular turning of the heaps so that they always contain plenty of oxygen.

[Image shows piles of composted bark]

After several weeks the composted bark is ready to use.

[Image shows Kevin Handreck handling various potting mixes]

The various size gradings are combined in proportions that give the potting mix just the right amount of openness.

[Image shows close up of Kevin Handreck holding two different potting mixes.  Image changes to Kevin Handreck walking through garden beds]

You can use the same potting mix for just about all of the plants you might want to grow, both indoor and outdoor. 

The Australian Standard specifies two grades of potting mix, one is the regular grade and the other one is premium grade.  With the regular grade you need to use fertiliser right from potting because there’s very little soluble nitrogen in those sorts of mixes.  With the premium grade you don’t need to use any fertiliser until about a month after you’ve put your plants in the pot because there’s plenty of fertiliser there for at least that long.

[Image shows close up of seedlings]

The potting mix standard also specifies the properties of a number of specialist mixes.  There’s one for seedlings, a very fine mix. 

[Image pans out to show Kevin Handreck pointing to various plants]

There’s one for orchids, very free draining mix.  There’s another one for banksias and proteas and other proteaceous plants, very low phosphorous.  And there’s another one for azaleas and camellias and other similar plants, an acid mix.

[Image shows close up of bags of potting mix]

These mixes are good because they’re based on several years of research by the CSIRO Division of Soils in conjunction with leading potting mix manufacturers. 

[Image pans out to show Kevin Handreck speaking]

This research has given the manufacturers a number of simple tests that they’re now using in their standard quality control programs.

Of course there are still a number of other mixes on the market.  They generally don’t conform with the Standard so why bother with them when you can give your plants the very best.

[Screen fades out]