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Vegetable gardening with raised beds

You'll find the information in this feature is the flip side to our no-dig garden feature.

What are raised beds?

Raised beds give your vegetables extra root growing room and are vital for good drainage. Free draining soil is extremely important to growing vegetables so raised beds are definately the way to go.

Do you want raised beds or just hilled soil?

Some gardeners will suggest that when setting up your vegetable beds you should start shovelling the soil to make paths, building up the beds. Then you can start adding manures and other goodies to each bed in appropriate amounts depending on what you're growing. Or you can think ahead, planning where each particular bed will be and pouring old manures, blood and bone and compost in appropriate amounts to where each bed will be. This way if you do have a rotary hoe you can automatically till the good stuff into the soil. Then hill up the beds by shovelling your paths.

These types of raised beds are really just hilling the soil up above the existing soil level. You can also make things tidy by pouring saw dust or pebbles over your paths.

Nothing appears to be wrong with this method at the start. Sounds enticing but we wouldn't recommend it. We did this twice in former vegetable gardens. The problem starts around six months after your garden has been going when you start noticing that your 'raised' beds don't look very raised any more. Rain and watering causes soil erosion, losing extra height in your beds. This means a lot of back breaking movement of soil in an established garden. Get it right from the start. Go with raised beds with a bit of support.

Think ahead about timber raised beds

Railway sleepers as raised beds

By Kathy Reed

A Queensland organic gardener's research shows railway sleepers can be okay if you do your research.

We recently purchased sleepers for a raised bed garden and only afterwards thought about the fact that they would have been chemically treated.
We had difficulty finding out what they were treated with and so did a heap of research into CCA and creosote on the Internet. We aslo made heaps of phone calls to all sorts of places including the National Testing Authority, CSIRO, the Biological Farmers Association etc etc. We had just decided to get rid of the sleepers (and had in fact made an order for untreated timber at our local mill) when the guy we bought the timbers off returned our call and told us that our timbers were not treated. Apparently railway sleepers were only treated for one year in Queensland and the treated railway sleepers are marked in 2 ways - they have a metal plate on one end (which could, of course, come off) and they also have "pockmarks" in them which were made to help the creosote soak in. We rang Queensland Rail and they confirmed this.
Apparently they only treated the sleepers for one year about 15 years ago. They had so many workers getting skin irritations and having time off work and/or claiming compensation that they decided to stop treating the timbers. Rather than treating the timbers, they use durable hardwood.
I'm not sure whether sleepers in other states and countries have been/are treated, but according to Queensland Rail the sleepers have not been should be safe to use if there is no evidence of the "pockmarking" on the timbers and so should be safe to use.

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You've got a couple of options when it comes to raised beds that give a bit of support. But it pays to do a little research especially if you're thinking about building wooden frames around the beds.

The American magazine 'Organic Gardening' has been leading the fight against using pressure treated timber in the garden for the last few years. They often refer to scientific research showing that CCA treated timber leaches arsenic and chromium into the soil. And from the soil it goes into your homegrown vegetables and then according to OG into you. For some more info on this check out their web site. Even the American Consumer Product Safety Commission and the Australian Pesticides & Veterinary Medicines Authority (a Commonwealth Government body) are now looking at banning the use of CCA treated timber in playground equipment.

For more info visit the Australian Pesticides & Veterinary Medicines Authority web site.

Think about it, if CCA treated timber is not safe enough for kids to play on, it's hardly safe enough to build your vegetable garden in. Me, I think I'd prefer not to be digesting arsenic and chromium thankyou very much!

Until recently I used to also consider old timber railway sleepers, but recent studies have also shown problems with these and their chemical treatment from years ago. For more information about researching whether your local old timber railway sleepers were treated chemically, read Kathy Reed's research in the right hand column.

Of course you could find some recycled timber. Not only is it good for you (versus the arsenic tainted pressure treated wood) and the environment (no trees to cut down), its old weathered look is more aesthetically appealing!

Just remember that recycled timber is a product of nature. This means it will break down over time, so you might have to replace the beds in 5, 10 or maybe 15 years time.

Raised beds
Our old vegetable patch used besser blocks to form raised beds 5 inches above the soil level

Strong blocks, strong character

But here in sub-tropical Queensland old recycled wood isn't the answer. Non treated wood encourages our local termites to start a march on the house. One of our solutions? Besser blocks, like what is used in landscaping retaining walls. They look great, are hardy and get around the arsenic and termite problems.

Non treated timber

In our new vegetable patch, we've gone back to timber, but unlike CCA treated timber, what we've done is 100% safe. Well tell you how to do this below.

Getting down to business

Now that you've decided to invest in raised beds with some decent support it's time to plan the bed placement and put down some thick layers of newspaper to kill off the grass underneath. To stop it blowing away we wet it deeply. Then we built our raised bed. We dug deep into our pockets and trucked in some wonderful organic soil. We also poured heaps of old manures into the appropriate beds. Confused about what manures, the quantity and what beds you should plan? Don't be. It's all in our crop rotation article.

Why should you put all of this animal manure, compost and organic matter into the beds you might ask. Well its all about organic gardening and feeding the soil. Organic matter improves the condition and structure of the soil. According to James Stephens on the University of Florida, it boosts your soil's ability to hold water and nutrients which are slowly released. It also helps support the soil's microbiological activity and helps your vegetables survive stress periods. James says organic matter really helps boost your vegetables' ability to grow. Micro-organisms, like fungi, algae, bacteria, moulds and earthworms decompose organic matter, gradually converting insoluble and unavailable nutrients into simple useable nutrients for your vegies. For more information about organic fertilisers click here.

One thing to always remember when handling manures, soil or any organic matter is to always wear tough gloves to protect you from bacteria getting into any cuts.

So how much organic matter should you add to the soil? I think as much as you can get your hands on! Here's a few reasons. Dig a foot deep hole in one of the beds you've just created and pour into it a bucket of water. Walk away for half and hour. After this time if there's any water still in the hole you've got poor drainage and vegetables hate wet feet. The answer, dig in more organic matter. This will mix with your clay soil, improving its texture over time and its ability to drain properly. The same rules apply if you've got sandy soil. Sandy soils don't retain water or nutrients for that matter. Answer, dig in more organic matter. Over time, with the help our friend the earthworm, organic materials will help improve your soil's texture and composition, until you've got a healthy loam soil. So overall, organic matter improves the quality and health of your soil. Remember as J.I.Rodale said, healthy soil means healthy vegetables and healthy people.

Throw a good fistful of blood and bone into each square metre of your beds. Don't forget to mix in one part potash to ten parts blood and bone. This way you'll get healthy leaf, stem, root and flower growth… perfect! You can use most aged manures in your vegetable patch, like sheep, cow, horse and poultry manure. The secret though is to only use matured manure (sounds like a good bottle of red). If you use anything reasonably fresh it'll "burn" your vegetables, either killing them or making them very sick. So compost the fresh stuff instead. And don't use cow pats (or similar) which have been sitting out in the open for a while. Any nutrients in them would've been leeched out a long time ago. Mix your aged manure into the soil at the rate of half a bucket per square metre and put as much homemade compost or mushroom compost into the beds as you can. Peat moss is good too but tends to be expensive and isn't too good for the environment (afterall they have to dig up old peat bogs).

Another important indicator of your soil's health is its acidity or alkalinity level. Different vegetables prefer different levels of acidity or alkalinity. Tomatoes, capsicum and eggplant like an acidic soil while onions prefer a sweet alkaline soil. High acidity or alkalinity will "lock-up" essential nutrients so its important to get your soil's pH balance right. Invest in a pH soil testing kit from your local nursery and test the pH in each bed. Australian gardeners are likely to find that their soil is slightly acidic with a pH around 5.0 to 6.5 (1 is highly acidic, 7 is neutral and 14 is highly alkaline). This has a lot to do with the Australian continent's old age and will make it generally easier for you to grow your vegetables. That's because it's a lot easier to boost the alkalinity of soil compared to increasing the soil's acidity. Adding calcium in the form of lime, limestone or dolomite will increase your pH level. I'm not too sure about what organic materials to use to boost a soil's acidity. I've heard pine needles, saw dust and tea leaves, but don't hold me to that!

One way or the other raised beds do have their benefits; improved drainage, less stooping over and they tend to warm up quicker in spring (which means earlier crops!) When this is all finished water the beds deeply and leave it for at least two weeks. This helps reduce the volatility of the beds, lets unhealthy gases escape and lets the beds settle. Your vegetable beds will stink to high heaven for at least a week. And I mean stink. I'd personally prefer to describe it as a "wonderful earthy aroma" but your neighbours may not refer to it in such flattering terms, so a word of advice. If you're going to locate your vegetable patch anywhere vaguely near your neighbours talk to them first. They should be accommodating if you give them a warning (and the promise of future harvests). You mightn't want to start your vegie patch though in summer when their windows are open… try late winter or early spring instead! (This is from personal experience).

Sheet composting involves a thick layer, or sheet, of compostable materials being applied over the soil. This can include straw, sea weed, sugar cane trash and grass clippings. This organic material acts as a mulch. Natural fertilizers (like blood and bone and aged manures) are sprinkled in, hastening its decomposition and improving the soil below. As this rots down it becomes a feeding mulch. In much the same manner as the no-dig garden the sheet compost conserves moisture, reduces the soil temperature, smothers weeds and feeds the soil. The big advantage of this method compared to the no-dig garden is its ability to warm the soil. You shouldn't mulch vegetables until its starting to get hot and stressful. This way your soil warms earlier in spring and doesn't stay as cold in winter compared to the no-dig garden. The only other time you should mulch is when a particular vegetable, like sweet corn, tomatoes or leeks, prefers to be mulched. The only vegetable which hates being mulched is onions. Their bulbs go mouldy and rot.

Our latest secret to a healthy and cheap raised bed garden!

As I mentioned before, in our new vegetable patch, we've gone back to timber, but unlike CCA treated timber, what we've done is 100% safe.

It involves using a rotary hoe (you can hire one or get a guy in) to churn up your soil, and any goodies like trucked-in organic soil and manures, etc. Then you dig paths around your beds with a shovel. We then 'reinforced' the walls of the beds with sugar cane mulch. It's worked great and has prevented soil erosion. To stop grass growing into the vegetable patch we've put a two inch deep border of untreated pine timber around the whole bed. Covering around 20 metres (about 60 feet) cost us a whole $14. At that price almost anyone can afford for all the timber to be eaten by termites and replaced every few years, knowing full well that you won't be polluting your body with arsenic and chromium leaching from CCA treated timber raised beds. 

So which method is better? The no-dig garden or raised beds? I think it really depends on what you're growing and your lifestyle, but generally I prefer raised beds. I haven't even touched on the square foot method of gardening or container gardening. But they're articles in themselves!


Last updated 23 October, 2008

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