When the best place you have to grow vegetables and herbs is a sloping hillside, you can terrace your way to a garden that’s beautiful, productive, and reasonably easy to maintain. I have been gardening on a slope for more than 10 years, and every season I learn a little more about the hillside and its potential.
Planning a Terraced Vegetable Garden
Because water always runs downhill, it is always best to stabilise a slope with reinforced beds that run across the slope. An ideal design is comprised of beds sized to fit the hillside in ways that make them easy to plant and maintain.
Start by making a side view drawing of your slope as shown below. Then use a measuring tape to estimate the site’s rise (elevation gain) and run (distance from front to back). You can now play with various bed designs and materials, using your drawing as a planning tool. Very steep slopes that require steps to navigate need beds that sit atop one another and must be maintained from the sides, while more moderate slopes can include pathways between shallower tiered beds. Level places from which to work are invaluable when gardening on a slope, because gravity pulls people downhill, too.
Don’t take on too much at first, because most terraced vegetable gardens are tended by hand, which requires slogging up and down a slope in addition to the usual stooping, lifting and bending. It’s like being on a stair-step machine sometimes but you get used to it, which may be one of the reasons why living in the mountains is associated with longer life.
Raised Beds for a Sloping Vegetable Garden
Building a terraced vegetable garden is basically making raised beds on a slope, and it’s important to start at the bottom and work your way up. Some sites may need only a low stone wall to transform them into good gardening space, while others will require compact beds stacked up like boxes.
The frames or low walls used to stabilise a terraced vegetable garden can be made from many different materials, including those discussed below. All can be reinforced with iron rebar stakes, which are far superior to wood stakes because they never rot.
Natural stone is often free if you live in a mountainous area, and as long as you stack a low wall so that it tilts slightly backward, into the slope, it should need only minor restacking at the beginning of each season. Plants and stone always look great together, so it is often a top choice for hillside beds less than 18 inches (45cm) high.
Retaining wall blocks that mimic stone are easy to work with, and their uniform size simplifies bed construction. Extra reinforcement is not needed for block retaining walls less than 18 inches (45cm) high. Concrete blocks are less costly, though heavy to handle.
Logs and untreated boards need replacing every few years, but this is part of their value in a terraced vegetable garden. As the wood decays, mycelium from the wood-feeding fungi also infiltrate adjoining soil. In this way, retaining logs or boards have what you might call a hugelkultur effect. In hugelkultur, logs or other wood are buried beneath a hilled garden which slowly benefits from the wood’s decomposition. A terraced vegetable garden stabilised by raw wood follows similar processes, only from the side.
Steel panels are trendy now, and they can last forever, as can some types of plastic lumber. There are no rules on the materials you choose provided they don’t leach nasty chemicals into the soil, as can happen with treated lumber or landscape timbers.
By midsummer, the structure that underpins a terraced vegetable garden disappears as it is overrun by exuberant plants. I love the way plants stack up in a hillside garden, layer upon layer, so that it looks even more lush than it really is. Drainage is never an issue, though I’ve noticed that some soil moves downhill along with rainwater. Over time, the lowest tiers of a sloped site gain organic matter as it trickles down from the higher beds, so adding organic matter to the higher beds benefits the lower ones, too. This is one of the little quirks you learn from gardening on a slope.