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.