Thursday, February 17, 2011

Dirt, Soil or Potting Mix?

I didn't grow up in and around Scotsburn Nurseries, but my mother did so I was taught "It's not dirt, it's soil" from a young age.
Soil/potting media was such a critical element of the nurseryman's craft.  My Grandfather, Uncle Dave would collect Elephant poo (manure) from Wirth's Circus which had a permanent site on StKilda Road (Wirth's 'Olympia' Circus building burnt down in 1953, the site is now the Arts Centre). The elephant manure was mixed with local South Oakleigh sand to produce potting mix. Now that's recycling.

Wirth's Circus Elephants 1932
Wirth's Circus Elephants crossing the Sydney Harbour Bridge, 1932.

In 1957 Kenneth F Baker published the UC System for Producing Healthy Container Grown Plants. Baker's system turned plant production in pots on it's head. Out with soil and animal manures, in with sterile, measurable, manageable materials that minimized the risks of disease. The UC system was introduced to Australia primarily by bedding plant growers: Peter Wood (Woodlyn), Dick Wall (Floriana), Fred Wood (FG Wood Nurseryman) and young Dave Wood (my uncle Robert) amongst others were heavily involved.  I think it was all a bit technical for Uncle Dave but each grower developed his own blend that made their plants special. As much as the blend was important the attention to detail in preparation was critical. A key element was steaming the blended soil to kill the disease organisms, steaming at the right temperature for the correct time pasteurized the soil leaving good organisms healthy. The growers all invested in boilers and steam chambers (Bakerizers, I'm still embarrassed at sniggering at the name before I put Baker in his place... under a withering stare).

Australia had it's own potting mix pioneer in David Nichols who developed soil less potting mixes at CSIRO before moving to Debco. In my 20 plus years as a nurseryman I have never mixed a potting media from scratch, the attempt we made in recycling old mix is another story altogether. Scotsburn started purchasing mixes from Decbo shortly before I started here and despite many trials of other mixes we use Debco potting mixes almost exclusively. What was once a major competitive advantage to good nurserymen has vanished it is now just so easy to buy consistently premium quality mix. Potting mix, please note. Not dirt or soil. Our pot mix is essentially Terra Cotta and Tub mix with a little extra controlled release fertiliser. We use a finer blend for punnets and a really fine mix for seed raising.

What prompted writing this item? We have had a bad batch of mix. We have had 3 or 4 batches like this over 20 years, always in January. I believe it has something to do with composting bark in hot weather, it may also be that slight imperfections are amplified when growing in hot weather. The variation in technical specifications is so slight that our measurment of pH, salt level and ammonia can't pick up a problem so I have given up regular testing of new batches of mix. We rely on observation of our plants. The symptoms are plants that just won't grow, they don't die, they just get very hard and refuse to move. Except of course for the odd plant that finds a prill of mini Osmocote and bolts away from the rest. Observation is of course a very reactive way to deal with this type of problem and forcing extra liquid feed into these plants can end up with all of them racing away from us.

So what's the point? Not poor me. I am a loyal Debco customer because I'm confident they supply the most consistent potting mix minimizing the possibility of problems like the one we currently face. This is why I beg and plead with garden clubs and anyone else who'll listen to use quality potting mix. Inexperienced gardeners won't try to fix problems caused by planting into raw plant litter (cheap potting mix), they'll just give up thinking they just aren't cut out for gardening.

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