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Raised Beds

Raised beds for gardening is a great way to make gardening easy and at the same time produce a good range of vegetables or flowers.

The advantages as I see them are; less bending, tidy gardens, attractive gardens, less weeding, no digging, superior produce or plants, ease of watering, great drainage, ease of harvesting and a pleasure to garden even if you are not really into gardening.
I have viewed some excellent raised gardens over the years and have always been very impressed with the lay out and thought that the owners have put into their work.
To obtain really good crops you need about 30cm of good humus based soil to allow plants to root deep.
Deep rooting plants will produce greater amounts of foliage when compared to shallow rooting ones.
When this is applied to brassicas, lettuce, silverbeet and similar foliage crops the more tops the better harvest. Plants that can root deep require less spacing giving you greater production on each square metre. With root crops such as potatoes, carrots, parsnips, beetroot etc they fair better and bigger when they can easily penetrate deeper into the soil.
A raised garden can be of any height over 30cm tall built on top of the ground in a fairly sunny situation. An ideal height would likely be 70cm tall and at that height a person in a wheel chair is able to garden still. The width of the raised garden should not be too wide with one metre being ideal as long as you have access from both sides. A metre wide allows three rows of potatoes or brassicas, two of which are planted near the sides with one in the middle.
The length of the raised garden will depend on your needs and the amount of room available.
As with anything new it is better to start in a small way and extend over time as your enthusiasm for this way of gardening increases.
A starting raised garden would likely be a metre wide, 70cm tall and between 1 metre to 2 metres long.
Timber is likely to be the best material to use for the structure but a combination of timber and corrugated iron for the sides is another alternative and one that has the advantage of collecting heat from the sun to warm the growing medium. The added heat will greatly reduce maturity times.
For this structure you simply need 2 sheets of corrugated iron 1.8 metres long and another sheet cut into two, 1 metre lengths for the ends and 6 lengths of wood 100x100mm 70cm long.
The wood used should be ground treated tanalised to ensure the structure has a long life.
We do not want the chemicals from the tanalising process leaching into our garden so the first step is to paint them all over with a couple of coats of acrylic paint. If you prefer not even to use tanalised timber then obtain non treated wood and treat it yourself with a solution of borax to preserve the wood.
The formula is 150 grams of borax dissolved in 1 litre of water and painted on the wood including the ends. Allow to dry and then give it another coat or two. The borax would soon wash off if you did not seal the wood so once again a couple of coats of acrylic paint.
You will note that I have suggested that the wood is only 70mm long which is the same width of the corrugated iron, this will make the raised garden free standing and a structure that could be dis-assembled if need be in the future. This also avoids the need to dig holes and cement posts into the ground. The structure will be very stable once it is filled with our growing medium.
Rather than nail the iron to the wooden uprights (posts) drill holes through the iron and screw it to the posts. How to construct: Lay the posts on the ground and place a sheet of iron over them so that there is a post at each end flush with the iron and one dead centre in the middle. Now drill your holes for the screws and screw it up. There should be one screw at every place where the iron touches the post.
Repeat the same with the other 3 posts and the one remaining 1.8 metre length of iron.
Now move these two sheets and their posts to the spot where you are going to have your raised garden.
The spot should be in a sunny area with either the end or one side facing towards the north. One side facing north will be best for maximum heat to the growing medium.
Now on the remaining sheet of iron mark off one metre and cut the iron with tin snips. Repeat for a second one metre length being the two ends.
Lay one of the sides on the ground with the iron on the ground and the posts exposed, drill and screw the two ends to the outside of the exposed posts. Once done stand this side where you want the structure to be and raise the other side to match keeping it squarely in shape. Drill and screw the remaining side to the iron ends. We now have an oblong box 1.8 metres long and a metre wide with two posts in the middle. If we were to leave it at that, when filled the iron would likely bend outwards so a central support is needed. This is done simply by taking a couple of one metre lengths of 50×100 timber (painted as described previously) and screwing these half way up the centre posts on either side of the posts. Now we have a stable structure that has been very easy to build.
To fill this structure firstly place a layer of twigs and thin branches over the bottom. This will aid in initial drainage and provide carbon. Next cover this with a inch or two of untreated saw dust or wood shavings to further increase the carbon content. Next a couple of inches of top soil.
From this point up wards a number of materials maybe used in layers such as straw, animal manures, kitchen scraps, wet newspaper, grass clippings, green waste, top soil and compost. You need not fill the raised garden to the top at this stage in fact with the materials just mentioned take it to about 40cm deep and the finish off with5 to 10 cm of compost with a little top soil added.
Now sprinkle Ocean Solids and Simalith, for the extra minerals they provide, at the recommended rates on the jars.
Then make a mix of one part Rapid lime, one part Gypsum and one part Dolomite and also sprinkle this over the area at the rate of 100 grams per square metre. Lightly water and you are ready to start planting or sowing seeds. If you have a worm farm or worms in the garden collect some and add them to the raised garden as you are putting the initial layers, in but do not put them directly onto lawn clippings or green waste.
When you harvest crops, disturb the growing medium as little as possible and with foliage crops and weeds just cut them off with a sharp knife just below soil level. Root crops should be carefully lifted with disturbance. To plant seed potatoes take a round pole 100mm wide with a sharped point and press this into the mix to a depth of about 20 to 30 cm. Drop the seed potato into this hole and push some mix in to just cover the potato. When the new shoots appear in the bottom of the hole sprinkle a little compost to just cover. Repeat till the foliage breaks free of the top of the mix. A little mounding maybe done as required after this. When you harvest use your hands, so once again the medium has minimum disturbance. The reason for non disturbance of the soil is to not upset the soil life and beneficial fungi.
When a crop is harvested you simply cover the area with some fresh compost and plant up again.
If you do not want to plant vegetables straight away, plant a cover crop such as lupin, oats, wheat, peas, mustard etc. (A mix of several is great) If you wish to grow tall crops such as corn or tomatoes place them on the southern side of the raised garden so the lower crops are closer to the north for sun and do not get shaded by the taller plants. You can grow runner beans up the stalks of the corn, once the corn is up 20cm tall plant the bean seeds. To keep the area around the raised garden tidy lay a strip of weedmat and cover with pebbles or bark chips or lay some paving slabs. Later on you may wish to construct more raised gardens after you have so much success with the first one.
A nice project this time of the year so that it is ready for spring planting.

8 comments on “Raised Beds

  1. phil on said:

    Hi
    I have been told that raw mined coal is good to use instead of rock to start to build up the first layers of the garden as it carries the trace elements often found missing in our soils today. We would be looking at laying in coal to a depth of approx 400mm before we start the build up of dry matter.
    Has this got any merit ?? or are we barking mad?

  2. Give it a go Phil, I cant see what the harm would be and would be interested to hear progress.

  3. Wally Richards on said:

    Hi Phil
    I do know that a old drivitive of coal called Coke was used in base material layer of glasshouses for drainage and their properties.
    400mm would appear to be too greater layer in my thinking and likely a layer of about 150mm would be adequate.
    We also have a product called Magic Botanic Liquid which is derived from low grade coal which works a treat as a soil drench and foliar spray.
    This would be more readily available when compaired to lumps of coal. Coal dust would likely be even better.

  4. My husband has taken your advice and has built numerous raised vegetable beds using treated timber. Where there is no paint, he has used black polythene. (And unfortunately, along one edge there is no protection at all, where we have a beautiful row of garlic growing – may have to throw this out).

    All my life I have invested heavily in keeping myself toxic free as much as possible, and to be honest, I feel nervous about the practice of using treated timber near my food. This I have expressed to my husband who has said . . . well, remove it then. (I have to bear in mind the financial cost he’s invested and his good intentions – there’s a relationship here to maintain. Hence I won’t be ripping it up until I’ve done my research – meanwhile trusting he’s made a healthy/safe decision for us).

    To support your’s (and my husband’s) argument for using treated timber, are you able to provide evidence that paint does in fact prevent leaching and how long does this have an affect? Have you done soil tests, and how far from the timber, and at what time intervals?

    Also please, when will I/we know it’s time to pull the retaining timber up, as the paint will have it’s own life span and won’t be able to protect us from these heavy metal toxins forever. (I’m relying on paint to prevent potential future ill health?)

    Whenever I read about building raised beds, I find it very difficult to find any reference to using treated timber, most people advise against this, and to use hardwoods, stones or nothing. Interestingly, food growers can’t get BioGro certification using this practice. Do you know why?

    I look forward to your reply. Thank you very much.

    Kind regards, Diane.

    p.s. we own your books – Gardening Guide and Green Tips for Gardeners and appreciate you are very mindful of poisons and health etc, hence I am a bit perplexed about your stance regarding the use of treated timber.

  5. Hi
    The only reason I say treated timber is because it is more readily available than untreated.
    A couple of coats of arcylic paint should logically keep the chemicals from leaching into the soil.
    I only use treated posts for the corners of my raised gardens and long run roofing iron between the posts, so not a lot of wood is used.
    Yes untreated mac would be a better option and you would not need to paint it and it would last a number of years.
    Regards
    Wally Richards

  6. RAY JONES on said:

    JUST A THOUGHT REGARDING TANALISED TIMBER LEACHING OUT WHEN USED TO CONSTRUCT A RAISED BED. WHY NOT HAVE THE TIMBER FRAME ON THE OUTSIDE & THE TIN INSIDE.

  7. Wendy Wood on said:

    I have just read with interest how to make a raised garden, by Wally Richards. I would like to make 1 700mm high as my elderly father, who lives with us, always enjoyed gardening but unless it’s a raised garden, he wouldn’t be able to manage.
    To fill the garden, would I just repeat the fillings or is there something else to ‘bulk’ it up. 700mm is quite a depth to fill.
    Thanks
    Regards
    Wendy

  8. Hi Wendy,

    You can fill the bottom up with Polystyrene of all things – larger pieces that would normally be landfill – this makes the bed lighter should you want to move it anywhere – the other option is pumice or pea metal or a bail of peat. With the polystyrene – make sure there are holes and easy drainage of the bed and not small pieces – you need to be conscious that they are in there and not fork them up so just down at the bottom. You can cover the polystyrene planks with weed matt to stop it mixing in with the soil and compost.

    A really cheap and easy raised bed is an apple bin from an orchard. I am not sure where you are in the country – but these are really great and about 700 mm high.

    kind regards

    Tim Durrant

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