Tuesday, May 17, 2005

Potting Mixes

Interesting item on Gardening Australia at the weekend. John Patrick and Dr Peter May conducted an experiment over a number of weeks to see whether there was any real difference between potting mixes of various prices. They tried 3 mixes in 25 litre bags - cheap, containing no additives, about $5; medium priced, contained some fertilizer and watering agent, about $8; and expensive, containing fertilizer, watering agent and water retaining crystals, about $14. The mixes were used in large plastic pots, each planted with petunias. One set of pots had the PM straight from the bag, but in another set of pots they added 40gm of slow-release fertilizer. The end result was that, of the untreated pots, the cheap one did fairly poorly whilst the other two did well and there was little difference between them. However, with fertilizer, even the flowers in the cheap mix did very well, and the other two were magnificent.

The conclusion was that had they used terracotta pots, which dry out more, then the dearer mix would have been clearly ahead, but in the plastic pots there wasn't so much need for the water crystals, and therefore, the medium priced mix would have been quite sufficient. However, no matter which mix was used, the addition of slow-release fertilizer greatly improved the display.

We have been buying 25 litre bags from one of the Supermarket chains (beginning with C)for $2.99. Whilst it doesn't have the additives, it seems to be of a good consistency and it is easy enough, and much cheaper, to add the other things to the mix if you empty it into a big container, like a Trug or wheelbarrow.

So today I hope to contine the pruning and repotting that I started on Sunday. By tonight I should have lots of happy pot-plants. Do they really feel the pain of being pruned? I just won't think about that.


Chloe said...

However ....

The most scary thing is where do they source the actual soil from. From my knowledge of soil remediation from places like service stations, the potting mix trade is where they onsell what they believe is "remediated" soil.

Scary. :(

Alice said...

I've never really looked into what potting mix actually contain, although I understood that it didn't contain any soil. One hopes that whatever it is, that it has been sterilised, making it fairly inoccuous and something just to support the plants. Guess that's why we need to add fertilizer. However, I guess it can't be all that harmless either if we are told that we should wear masks and gloves when handling it. In my mind it's now almost on a par with surgical operations - I don't want to watch them or know anything about them! Just when I was having fun, too !!!