Raised-bed gardening provides multiple benefits for home gardeners. It facilitates a no-till approach, lets one focus amendments and nutrients instead of broadcasting them, makes weeding easier, and — depending on the height of the beds — can even eliminate much of the back bending demanded by field crops. On the downside, it pretty much eliminates power tools from the equation, a definite drawback for those who have developed hot monkey love for their rotary tillers or who must use mechanized tools to make their market gardens pay.
The definition of “raised bed” is broad. It can simply mean a section of garden that remains higher than the surrounding path by dint of not being walked on. It can also refer to a waist-high, walled enclosure with complicated drip-irrigation and drainage systems. The key point is that the soil in the growing space isn’t compacted by foot traffic or machine wheels and therefore remains more porous. This enhances absorption of water, permits more aeration of the soil, and offers fewer impediments to root growth. It also makes it easier to yank weeds.
On hilly terrain, raised beds can serve as terraces, with high downhill walls creating a flat growing surface to catch rain and impede erosion. In two gardens I built on fairly steep slopes, I enjoyed being able to work the beds from below without much bending — though the uphill edge of each bed was flush with the upper path, which meant that working from that side required deep knee bends. I learned to do most of my tending chores from the bottom.
Enclosing beds raises a number of intertwined issues: appearance, availability, cost, durability and practicality.
Most gardeners like the appearance of stone, and in many gardens it’s all too available, with new material showing up wherever a shovel blade is pushed into the ground. Absent native rocks, good building stone is easy to purchase and hard to haul (though a stone-yard proprietor can offer useful advice or delivery). Hard stone is far and away the most durable material, easily outpacing brick or concrete in the long run. In most cases it is best to lay the stone dry, without mortar or cement. If you want your structure to last for years, take the time to dig a trench the length of the prospective wall and fill it with washed gravel to a depth of 4-6 inches. Lay the stone on the gravel so that upper stones bridge the joint or gap between lower ones: long vertical joints weaken the wall. If individual rocks are wedge-shaped, lay them so the wedge aims left or right down the length of the wall instead of front to back. That makes them less likely to pop out over time.
Brick or concrete-block walls are much easier and a lot less fun to build. These too will last longer with a gravel footer beneath them, and they’re likely to be more satisfactory if laid dry. Any kind of masonry laid without mortar will shift but can be shifted back into line. Masonry laid with mortar tends to shift and then be impossible to realign.
Wooden enclosures are quick and easy to build but less durable than masonry. Used railroad ties can be readily stacked and are often moderately priced. Both a benefit and a drawback of these is the fact that they’ve been treated with creosote, which acts as a preservative but is a known carcinogen. My advice would be to use them around ornamental beds but not where you plan to grow food crops. The same warning applies to pressure-treated wood.
Untreated lumber or logs have the wonderful advantage of turning into soil over time. While this does demand rebuilding the beds every few years, it gives you a fine source of organic matter to mix into your dirt. A useful strategy is to first build your beds with wood and then replace it with stone as the wood rots. This gets your garden up and running quickly and lets you space out the more labor-intensive masonry construction, since wood seems to rot at differential rates.
In my latest garden-building scheme, I am going with the simplest approach of all — designating bed areas with paths between and building no walls whatever. For the time being, at least, I’ll put up with the requisite bending but spare myself the construction effort. And because I’ve flattened most of the area, I have no need of terraces. Along one side of the garden with a 2-foot drop-off, I am piling garden debris, roots, leaves, pine needles, weeds and kitchen scraps. This will act as an informal compost pile while preventing erosion and eventually providing new loam for the beds.
A word of warning for others who may be tempted to use the no-bed approach: I have often yielded to the temptation to install a single row of stones or bricks around the edge of such designated beds. But these masonry markers neither raise the soil level nor prevent erosion.
Last week I was reminded of the major pitfall of such outlining while helping a friend mow an overgrown garden space. Most people’s gardening efforts ebb and flow. Over the past 30 years, my own projects have ranged from a one-acre field with up to 80 caged tomato plants down to a few pots on a windowsill. One season you may have lots of time and energy for planting, and another year you may spend every spare hour bowling or running for elective office. There will be times when your garden grows unattended and weeds form a forest, and you’ll need to abandon all hope (or else mow).
At that point, the single row of stones won’t be your friend. You won’t be able to discern it through the underbrush, and whatever mechanical aid you are using — be it a scythe, a machete, a reel-type push mower or an electric- or gas-powered rotary mower — the tool will scream with pain. If you’re using a Weedeater, you’ll go through miles of string as it repeatedly breaks on the rocks.
So do yourself a huge favor and resist that fatal impulse. Someday you’ll thank me.