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This year has seen gardeners dealing with something they haven't had to worry about for a long time - drainage. It seems most of my gardening life has revolved around strategies to hang onto water as much as possible. Not this year. Gumboot sales are up, kids are playing in these weird things called 'puddles' and after a few good years of good soaking rain we now have sub-soil moisture. All the ingredients that maybe giving your veggies wet feet.
So during the last decade-plus of well below average rainfall, we've stopped using a lot of the techniques that assist drainage. The most effective one is what we're going to explore today, the raised garden bed.
It's not just the height of the raised bed that helps with drainage it's your ability to modify the growing medium (soil) to ensure the right balance of drainage and nutrient holding. This is of course the holy grail of gardeners all over the world and one that deserves a separate post all of its own. Of course even without the benefits of improved drainage and soil, not breaking your back is a good enough reason alone to look at raised beds.
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Materials for raised beds
Over the years, raised beds have become far more sophisticated. Perhaps they started with off-cuts of fascia or other plank like timber, held in place by tent pegs, rocks or those very handy star-pickets. Many of Australia's European migrants build very sturdy brick edged gardens in the 50's and filled them with as much cow, sheep and chook manure as they could get their hands on. Brick and stone are of course very durable and can help maintain more even soil temperatures. The main downside is they are expensive and labour and skill intensive. Additionally you'd better be sure you don't want to move the bed in the future and pretty much forget it if you're renting.
The Aussie equivalent of the Mediterranean masonry edging is perhaps the old galvanised water tank which was too rusty to hold water but fine to angle-grind down to a round garden bed edging.
This 'recycling an old tank' idea has now evolved to see tank manufacturers designing raised garden beds with new materials. Of course the edges need to be folded down or covered with protective stripping to make them safe. The corrugated looks look good in old and new houses alike, and seems synonymous with Australian homes.
We then move onto timber. Now I have to confess right from the start that I'm not a big fan of chemically treated timbers. Everything I know about organic gardening involves increasing your soil biology and diversity to open up the best possible nutrition to your plants. It makes sense if the soil biology is prevented from rotting the wood over time then your soil must be compromised. Recently there's been the introduction of 'Eco' type treatments on plantation pine which although seem to be an improvement on the old 'treated pine' (which was Copper Chrome Arsenic - CCA )they still can't be composted or burnt…the real tests as to whether or not a material can be harmlessly reintroduced back into your garden. Proceed with caution and read more here if you're interested.
So what are some other timber options? Well you can look at untreated plantation pine, such as these boxes which were used for the Grow It! project last year.
They're cost effective and a great height to work with. Red gum and rough sawn native hardwood are both excellent, long lasting timbers although knowing how sustainably they were harvested can be challenging. Hardwood is also a little tricky to work with - heavy and particularly hard on drill bits and saw blades. Which leads me onto what I think is the champion of raised bed timber - cypress macrocarpa. Now this isn't the same cypress you're starting to see available at hardware stores. Macrocarpa is an introduced species - a true cypress from North America. It was used in Australia on farms as wind breaks, but as the trees reach over-maturity they're being pulled down and often piled up and burned. A couple of local millers have seen this opportunity and have started producing small quantities of this marvellous stuff. I love the stuff.
There's also vintage (or recycled, reclaimed) beds. I'm a big fan of old apple/potato/onion crates which are about 1.200m square and 0.6m high. They originate from the fruit and vegetable packing industry and despite being made from untreated pine, have quite a long life. The first ones of these I saw was at the Barwon Heads Community and Arts garden - a fantastic example of small scale organic agriculture mixing with a wonderful community space. You'll even see a garden growing in the back of an old truck! Recently OH&S regulations have seen the move away from timber bins to plastic ones. Apparently the risk of splinters for supermarket contract staff is too high…
Anyhow, be sure to grab hold of these vintage timber bins before they all disappear. I know I'm having to look further to source them.