As I mentioned a little earlier, my backyard patch has been aseasonal this winter. Rather than the bleak harvest of cabbage from the previous year, this season promises a voluminous crop.

My tactic has to plant whatever worked last year alongside heirloom vegetables that are nigh on impossible to buy at a reasonable price. This somehow breaks a golden rule of backyard vegetable gardening: if you’re not doing this for survival, only plant what you like to eat.

To be sure, I have planted a full court press of brassicas but in a wider range of varieties than last year: frilly leaves of red Russian kale, purple cabbage, Chinese cabbage (wong bok), Calabrese broccoli, a commercial looking variety of cauliflower that was on sale at my local supermarket and ruby brussel sprouts.

I planted twice as much beetroot as the previous year and am being repaid handsomely. I’ve planted 'chioggia' that grows with alternating white and pink concentric rings, 'golden' that promises yellow flesh that does not bleed, and 'blankoma' that grows roots that are a shade of bright white. A few messy rows of the higher yielding 'globe' beetroot take up the rest of the patch, destined for more bottling.

Filled with an uncharacteristic bout of wintertime hubris, I’ve also decided to renovate the whole patch and build the sort of garden beds that grace the screens of many a garden show: four beds constructed from the old redgum stumps from beneath my house and thick slabs of redgum to replace the CCA-treated pine slabs that currently holds the dirt in place.

While there is much talk on the dangers of treated pine use in garden beds, my decision was based on price: each redgum sleeper was $2 a piece more than the equivalent pine, so I thought why not?

“CCA” stands for “copper chrome arsenate” and is shorthand to say that the pine planks were treated with the chemicals to retard fungal growth and deter termites. An untreated pine sleeper might last a few years in the ground; a treated one a few decades.

The research into the effects of CCA treated pine on garden beds shows that it is safe. In a review of the research, the CSIRO states:

A number of studies have shown that CCA is not absorbed into above-ground food crops such as grapes, tomatoes and cucumbers. There are, however, some reports of a slight increase in arsenic content in root crops such as carrots and beets grown against treated timber, although the arsenic is in a safe organic form and most of it is removed with peeling.

Any concern can be eliminated by growing these vegetables more than 100 mm from treated timber garden edgings or by lining the edgings with plastic. This has the additional useful effect of reducing soil contact with the wood, which could further extend the wood's life.

Further, if the arsenic is released from the timber, it is in a relatively safe form. At least for beagles and sheep:

Ingestion studies with animals have shown that this greatly reduces its mammalian toxicity. For example, no evidence of toxicity was found after beagle dogs were fed 10 grams of CCA-treated sawdust per day for five days in food. Seventy percent of the arsenic passed with wood through the faeces. The rest was expelled in urine, having been extracted from wood in the stomach. The bulk (85 per cent) of the urinary arsenic was detoxified to dimethylarsinic acid.

In another experiment, researchers in New Zealand found no abnormalities after sheep and calves were fed 454 grams of CCA-treated pine on one occasion, or 113 grams per day for 25 days.