There are many advantages in growing your vegetables and herbs in raised gardens.
But raised gardens should be really raised and not just a few centimetres or even 30cm above soil level; in fact, a good raised garden is about 80cm tall.
This means you are not doing a lot of bending and if used correctly, are fairly free of weeds.
In my third book, Wallys Gardening & Health, I wrote about building a perfect raised garden. Here is an extract:
A few years back I came up with an idea to build a raised garden using corrugated roofing iron and 100 x 100 posts to secure the iron to. The structure would not be set into the ground, instead it would sit on top of existing soil. It could be sitting on gravel or concrete if need be.
I selected new roofing iron 1.8 metres long and thus needed 3 sheets to make up the raised garden with one sheet cut in half for the two ends. (900cm wide). Sheets of galvanised iron are 85cm wide so this would be the height of the raised garden.
I obtained some treated 100 x 100 fence posts and cut them to 4 lengths of 85cm. As the wood was treated and I did not want any chemicals leaching into the garden I gave each post two coats of acrylic paint to seal in the chemicals.
Once they had been left for a few days to dry completely I laid two of the posts on the ground 1.8 metres apart and placed one full length sheet of iron over the posts so that it was all square and the iron completely covered the posts.
Next a drill was used to drill suitable sized holes in the iron to take the roof type screws (the ones with washers). The holes were drilled into the iron on most of the corrugations that were touching the posts.
This is opposite to how you would affix iron for a roof as on a roof you want the water flow to go down the corrugated channels with no holes to allow the water to enter the building.
Then it was a simple matter of screwing the iron to the two posts. The same was then repeated for the other two posts and the long sheet of iron. Now I had two long sides and only need to stand them up and drill and screw the two ends made by cutting one sheet in half.
It is best to do this final operation in the spot where you want your raised garden to be.
Ideally one long side should be facing as near as possible to the north so that side will be in full sun for most of the day to warm up the mix used. To fill the raised garden I started by laying a few sheets of cardboard over the soil at the base. This can go over existing grass if in a lawn area or over existing weeds in a garden area. If there are any tall weeds these should have been cut down prior to assembly.
The cardboard creates a temporary barrier and is loved by earth worms to encourage them into our raised garden.
Next I used a lot of organic rubbish to cover the cardboard which included trimmings of shrubs, leaves, grass clippings, food scraps, animal manure, saw dust or shavings of non-treated wood, weeds and straw. You can use any of these in layers to build the height up to over half the height of the structure. Trample this down and add the organic rubbish until the garden is a bit over half filled after the final tramping. Then a good dose of garden lime can be sprinkled over. Next I placed a couple of thicknesses of cardboard over the rubbish.
Having a good amount of my own compost and spent mix from containers, I applied it over the last lot of cardboard. I also spread more animal manure into this layer along with vermicast and worms from a worm farm. If you do not have a worm farm then use a little top soil instead. If you do not have your own compost and old mix from containers then I would suggest you purchase mushroom compost or purchased compost.
As this layer may contain weed seeds I then covered it with a few thickness of wet newspaper.
Over the newspaper I applied Rok Solid, Ocean Solids, Gypsum, Lime, BioPhos, Bio Boost, dry chook manure, Neem Tree Granules and dolomite. If the area is to be used to grow potatoes or tomatoes leave out the Lime. Sheep manure pellets and Blood & Bone can also be used.
The final layer will be purchased compost and would recommend Daltons or Oderings for this.
So what should the layers be in depth? Seen we start of with a structure that is 85cm tall I would recommend the following;
- First layer of organic material about 35cm deep compressed.
- Second layer of homemade compost and spent mix about 15cm deep.
- Third layer of purchased compost about 10cm deep.
This leaves about 25cm between the height of the last layer and the top of the iron.
You are now ready to either sow seeds or plant seedlings.
Because of the 25cm gap between the last layer of mix and the top of the garden we have created a natural wind barrier which is great protection for the establishment of the vegetables.
If you notice a problem with either birds or cats getting into the raised garden then simply place a sheet of small gauge wire netting over the whole structure. This can be stretched into place and held secure at each of the 4 corner posts with a nail in each post. Later on, when the plants have matured, to the point where they are touching the netting, then remove it.
Now all you need to do is keep the top layer of mix moist by watering with non chlorinated water. This can simply be achieved by placing a 5 to 10 micron filter and housing onto your outdoor tap. A two weekly spray of MBL and Mycorrcin will help keep your vegetables healthy and produce better crops faster.
If planting different types of vegetables in the raised garden then ensure that the tallest ones go to the rear or southern aspect and the shorter ones to the front or northern aspect so they all gain their share of sun light without shading each other.
When harvesting a crop do not pull the plants out, instead cut them off with a sharp knife just below the mix’s surface. This of course does not apply to root crops where you have to disturb the soil to lift. Leaving roots intact is additional food for the raised garden and does not disturb the beneficial fungi in the soil.To replant all you need to do is apply the products mention above prior to the last layer of mix and about 40mm of fresh purchased compost. As the organic material in the bottom layer breaks down over time the level of your mix will drop. The fresh compost applied will make up for the drop at re-planting time.
The system is like growing on a compost heap which many will have noticed that pumpkin seeds and potato peelings grow into great plants from a compost heap. Another advantage of this type of raised garden is if you move house you can unscrew the iron sheets and take the posts and iron to your new home. The materials used should give you many years of satisfactory gardening.
The walkway area around the raised garden can be kept clear of weeds by laying a strip of black plastic film and covering with stones or bark.