How to Start a Square Foot Garden

March 22, 2023 steven

Even if you’ve never held a shovel or picked a ripe tomato, you’ve probably heard the term “square foot gardening.” It’s part of our modern lexicon and an example of how efficiency can improve just about anything, including the alchemy of growing a radish.

Grab a ruler and let’s take a closer look at how thinking outside the row, and inside the grid, can help you construct a better plot in a smaller space with less work. Oh, if you happen to be a traditionalist when it comes to plants, leave your doubts at the gate. This isn’t your granny’s garden.

Mel Bartholomew, construction engineer and efficiency expert, is considered the father of square foot gardening. His reinvention of the backyard garden began in 1975 when he retired, moved to a new home, and started devoting his spare time to his own plot of land.

Dissatisfied with the traditional row planting method used in agriculture and backyard “victory” style vegetable gardens, he began experimenting with other growing methods.

Through trial and error, he discovered he could grow more plants in a smaller footprint while reducing his labor and efficiently using resources like water. To provide adequate nutrition to his crops, he developed a recipe for a lightweight, compost-rich, water-retentive growing medium made up of ingredients that could be sourced at any local garden center.

This foray into organic, smarter gardening resulted in a best-selling book on the subject in 1981 and an equally popular public television series later.

square foot garden bed full of plants

The Frame

A square food garden is pretty distinctive. It’s made up of an elevated box frame filled with a nutrient-rich media and outfitted with a gridded overlay. This frame can be made of wood, vinyl, cinder block, or stone. Basic units are available prefabricated, or they can be cobbled together in an afternoon from 1×6-inch untreated wood, deck screws, and lath strips.

The most popular overall size is 4×4 feet, with a height of six inches, but that can vary. Since an adult has an arm’s reach of about two feet, a 4×4-foot frame would allow for access from all four sides. For a frame with limited access, such as one positioned against a wall or fence, the width would max out at two feet. You get the idea. Although the width is limited, the potential length of a square food garden isn’t. Frames of 4×8 feet and 4×12 feet are also popular. Many square foot gardeners use multiple box frames.

The basic principle is to create a frame that can be separated into 12×12-inch squares using lath strips, rope, or other materials. Each square defines the growing space for an individual plant variety. A classic 4×4-foot square food garden frame contains 16 growing squares.

You’ll notice the height of a normal box frame is only six inches. That’s not a typo. Since the media provides all the nutrition plants need, hungry roots don’t have to dig deep to find sustenance. The exceptions are root crops, like potatoes and carrots, which will need a box height of eight to 10 inches. This height factor is one of the most controversial aspects of square foot gardening.

A Grid for Success

Nothing distinguishes the square food garden as vividly as its grid. You know each box frame is divided into equal 12×12-inch squares, but don’t put your ruler down yet. Every square is then further divided, without an additional grid, based on the estimated size and plant variety it will contain.

For example, one square can accommodate a single tomato plant, or it can house four strawberry, lettuce, or potato plants that only require six inches of space between them. That same square can be home to nine bush beans or 16 evenly spaced carrot, bunching onion, or radish plants.

Here’s a quick cheat when determining strategic square food garden plant spacing:

Six inches apart: four plants per square (two rows of two)
Four inches apart: nine plants per square (three rows of three)
Three inches apart: 16 plants per square (four rows of four)

You can typically place plants closer together than the recommendations on seed packets or seedling labels because they won’t be competing for resources. Overall height and bushiness at maturity do matter, though. We’ll discuss this in more detail in a moment.

This idea isn’t as revolutionary as it may seem. Gardeners have been making tight quarters more plant friendly for centuries with the creation of window boxes and container gardens. This idea may also resonate with indoor gardening enthusiasts who employ hydroponics and other modern cultivation technologies to grow more plants in smaller spaces.

Once assembled, a square food garden can be positioned on any surface that drains well. This includes lawn and unwelcoming soil. Because the media provides all the nutrients plants need to thrive, the composition of the underlayment isn’t very important.

It is a good idea to put down weed cloth as needed, though, and to avoid placing a box frame where its freight of plants will be in competition with tree roots. Other good gardening principles apply as well, including choosing a spot with eight to 12 hours of light a day that’s out of the wind and doesn’t become boggy after a rain.

Frame spacing is also a consideration. Even though one of the big promises of square foot gardening is its ability to produce comparable yields in only 20 percent of the space of a conventional garden, maintenance and harvesting still require access, which means creating space around one or more box frames.

What’s the best width for an access path? That would be about 36 inches. If you’re tempted to go narrower, remember plants will often extend somewhat beyond the borders of their frames as they mature.

If you don’t want to wrestle with greenery all summer, give yourself enough space. Remember, you won’t be stepping into the boxes. That’s a good thing because you won’t be compacting the media, but it also makes planning efficient access more important.

The medium is arguably the most important component of a square food garden, and over time, Mel Bartholomew changed his thinking about how to manage this element of his growing plan. In his first book, he recommended excavating a six-inch depression for the frame box and fortifying the excavated soil with amendments that would contain great nutrition, good moisture retention, and adequate drainage.

When added back into the box, the treated soil would produce a 12-inch deep bed ready for planting. He eventually changed this approach to eliminate the garden soil requirement completely and reduce the bed’s overall depth to six inches.

This change not only reduces labor, but it makes it possible to install an square food garden almost anywhere there is good drainage. It also allows the gardener to create a consistently reliable, lightweight, pH-neutral mixture regardless of soil shortfalls and challenges, as well as reduces problems with weeds and soil-borne pests and diseases.

The mixture itself is designed to be straightforward. It contains three ingredients measured by volume:

1/3 peat moss
1/3 vermiculite (coarse grade)
1/3 blended compost

This is a general purpose, no fuss blend that provides good nutrition for most plants. Let’s take a closer look at these three ingredients.

Peat Moss – The use of peat moss may raise eyebrows. It is not a renewable resource, and you may have a philosophical prejudice against using it. Once an square food garden is established, though, it can be replanted season after season with little or no peat moss replenishment.

Vermiculite – Vermiculite has gotten some bad press in the last few years. It is mined in areas that may also contain asbestos, and there have been reports of asbestos contaminated vermiculite in the past. All processing is now regulated, so vermiculite supplies are widely considered safe to use. If you still have reservations, perlite is an acceptable alternative. Both retain moisture well and are sterile and inert.

Compost – The recipe calls for “blended” compost. This simply means compost from a variety of sources to maximize the number of nutrients in the final blend. Some options are worm castings, chicken manure, and mushroom compost. Check labels to make sure you’re getting a broad selection.

Of the three ingredients above, vermiculite is likely to be the hardest of the three ingredients to source, especially the coarse, agricultural-grade form that has the best water retentive properties. If you can’t find it at your garden center, it’s probably available through special order. When all else fails, you can purchase it online.

How much of the mixture will you need? A standard, 4×4-foot, six-inch high box frame will require eight cubic feet of the soilless blend.

If making this recipe yourself seems like too much work, special pre-blended square food garden soil products are available.

grower planting seeds in a square foot garden

Growing plants in a tight space has advantages, but it also presents some unexpected challenges. For sprawling specimens, regular pruning will be necessary. It’s also a good idea to add a trellis or other support to your box and choose at least a few vining plants or other varieties you can train to grow up instead of out. (See: How to Trellis Plants Properly). This makes general maintenance and harvesting easier. Placing taller plants in the northern-most section of the grid will also give shorter plants better access to sunlight.

To further maximize space, consider staggering planting times. This way, some plants will always be immature, so the frame will be less crowded. A side benefit is that you’ll be able to enjoy lettuce and other fast-maturing produce and flowers all season.

Although the soil blend used in square foot gardening is moisture retentive, the mixture is still porous and lightweight, which can cause it to dry out more quickly than amended garden soil, especially during hot weather. A drip irrigation system works very well with an square food garden set-up, but almost any watering strategy will do as long as it can adapt to weather changes and the increasing water needs of maturing plants.

It’s important to keep an square food garden uniformly moist at all times. Once it becomes dry, the porous mixture requires more water dwell time to rehydrate, making daily short duration watering less effective. During high summer, daily or even twice daily watering may be necessary in some locations.

To reduce watering requirements and better accommodate plants with large root systems, some gardeners have modified the basic square food garden model by electing to build deeper box frames. Popular options are 10 inches and 12 inches.

One of the benefits of square foot gardening is that fertilizing isn’t necessary. Adequate nutrition for the growth cycle of most plants is incorporated into the initial set-up. Further augmentation isn’t necessary for the course of a growing season. Before starting a new crop, or while preparing for a new season in a perennial garden, just add more compost.

Because the special media blend in an square food garden is free of unwanted seeds, a new set-up requires little or no weeding, although second and subsequent seasons may see more weed problems. At the seedling stage, it’s easy to spot uninvited plants and eliminate them. Later, plants grow so closely together they tend to discourage weed growth.

Pests can be a problem in any garden. Because a square food garden gets crowded, it can be harder to detect pests early. Companion planting is a popular option, but it’s also important to take the time to inspect plants regularly and deal with outbreaks using organic or chemical treatments sooner rather than later. Because this type of garden takes up such a small area, it can be easier to add cover fabric or protective mesh framing, deterrents that would be unrealistic in a larger garden.

In conclusion, if you don’t think a melon can flourish in six-inch deep soil or a squash plant can reign supreme in cramped quarters, Mel Bartholomew spent decades before his death in 2016 proving those very things were possible. He showed gardeners around the world what one square foot of growing area can yield with the right strategy, and that thinking small with big intentions can be one of the most best ways to garden.

Have you tried square foot gardening yet? If not, what are you waiting for?

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