Plan your plot and get growing
Before you start
If you’re thinking about building a raised vege garden, the first step is deciding where it’s going to go. Veges like a nice balance. A bit of shelter, a bit of shade and decent amount of sun so try to find a spot where they’ll get at least 5 hours of sun a day.
A reasonably level site is a good idea as well, and since it’s a fresh food garden try not to have it too far from the kitchen.
Site preparation
This is pretty simple. Once you’ve decided where your raised garden will go and what size it’s going to be, mark it out, grab your spade, and skim off any grass and vegetation.
You don’t need to take a lot, 20mm should get you down to bare dirt but you might find you’ll need to take a little more off in places to get your planks sitting even and level.
Standard build
200x50 planks Going with the 200x50 planks will cost less plus it’s quicker and easier because it’s nailed together rather than screwed. Otherwise the process is just the same.
Get your bottom four planks in place, line them up and nail them together using 100mm galvanized nails.
Measure corner to corner diagonally to make sure everything’s square, use a spade to trim any high spots on the ground to make everything’s sitting down level and you’re ready to put the top planks on.
Nail them together then simply skew-nail top and bottom planks together in each corner.
For extra stability you can drive a wooden peg into each inside corner and nail it in place.
What size timber?
Once you know where the garden’s going, work out what size you’d like it to be.
You can go any size and shape but 2.1 x 1.8 metres is pretty common, partly because you’re dealing with standard lengths of timber but also because anything wider than 1.8 metres makes it a bit of a stretch to reach the plants in the middle of the garden.
On a garden this size, good, solid, 200x50mm planks will ensure the garden holds it shape and two planks each side will give you a comfortable 400mm working height. A popular alternative to the 200x50mm planks are the big, 200x100mm macrocarpa timbers.
At 200x100mm ‘‘sleeper’’ is probably a more accurate description than plank, and while they cost more and
don’t make a better raised garden, they do create a great look.
Like the smaller planks, they’re also available in the 2.1m and 1.8m lengths.
A general rule-of-thumb is that two, well-managed, 2.1 x 1.8 metre gardens is just about right for a family of four.
What kind of timber?
There’s ongoing debate about what timber you should use to build a raised garden. An untreated hardwood like macrocarpa is rot resistant and looks great, but you pay a premium for it. H4 treated pine is popular because it’s economical and you can buy it anywhere.
And because it’s treated, it won’t rot either.
The debate is around whether the timber treatment chemicals will leach into the soil you’re growing your veges in.
If you’re not comfortable with treated timber you can staple polythene sheet around the inside of the planks as a barrier between the timber and soil.
Just remember that good drainage is important for a raised garden so don’t run the polythene sheet over the bottom of the garden.
Get growing
You’ve got the ‘‘raised’’ part of your raised garden sorted, now it’s time for the garden.
Spread about six layers of old newspaper over the ground to help prevent weed growth then wet down with a little water to hold the paper in place while you add soil.
The first layer should be green material such as green waste and the sod you removed when you were preparing the garden.
This green material will rot down and provide great worm food, attracting worms to your garden and creating nice rich soil.
Then cover your green waste with layers of potting mix and compost, or make it even easier by simply filling with vege mix (a garden mix and potting mix combo).
Aim to fill your raised garden up to about 50mm from the top, rake it level then and decide what veges you want to grow.