How To Fertilize My Square Foot Garden

Popularized by retired engineer-efficiency expert Mel Bartholomew, square-foot gardening allows you to get a high yield from a small area—a win-win situation for beginning gardeners and experienced ones alike. It's especially beneficial to gardeners who don't have much time or yard space. Square-foot gardening typically starts with a 4x4-foot raised garden bed filled with amended soil then subdivided into 1-foot squares with markers like lattice strips. You then plant the appropriate number of plants in each square. (This is determined by plant size.) This method optimizes your space and reduces the amount of effort needed to go from planting to harvest. Follow the steps below to start your own square-foot garden.

1. Pick the Correct Location

As with most vegetable gardens, a square-foot garden needs to be where the ground is relatively flat and gets at least 6 to 8 hours of full sun a day. Avoid low areas that may turn into puddles after a hard rain. You may want to choose a spot near your house to make watering, weeding, harvesting, and other garden chores more convenient—as well as harder to overlook.

Sungold cherry tomato with Shishito peppers

2. Build a Raised Garden Bed

The most common configuration for square-foot raised garden beds is 4x4 feet. At this size, most gardeners can reach the middle from any side. Plus, this size divides easily into a grid of sixteen 1x1-foot squares. Make your sides at least 6 inches deep. Growing root vegetables such as carrots call for sides that are 12 inches deep.

To make a 6-inch-tall raised bed for square-foot gardening in a flash, buy four planter wall blocks (which have 2-inch slots on four sides) and four 4-foot-long 2x6s at your local home center. Set the blocks approximately 4 feet apart on level ground to form a square. Connect two blocks by sliding a 2x6 board into the respective 2-inch slots. Repeat with remaining boards and blocks to create a 4x4-foot frame in about 15 minutes.

For a long-lasting frame, use a more durable material such as pressure-treated lumber or cedar. Avoid using pressure-treated lumber from 2004 or earlier; it may have been treated with arsenic that will leach into the soil.

3. Fill the Raised Garden Bed

You've built the frame for a raised garden bed; now you need to fill it with soil. You may be wondering if you need special soil for square-foot gardening. Actually, you can use what you have as long as you amend it (which is a good idea for any garden). First, loosen and aerate the ground soil. Then mix in enough compost (and extra topsoil if needed) to fill the frame. Editor's Tip: Work compost into the soil at the rate of one-third by volume—a 2-inch layer of compost into 6 inches of soil.

If you want to be more scientific about it, you should test your soil to determine its composition. Once you have that information, add the right amendments in the right proportions to achieve the best growing medium for a vegetable garden.

Another option: Prepare the soilless mix advocated by Mel Bartholomew rather than amending your ground soil. Follow this formula: one-third compost, one-third peat moss, and one-third vermiculite. You'll need 8 cubic feet of it to fill a bed with 6-inch sides, and 16 cubic feet to fill a bed with 12-inch sides. This mix is pricey, but it creates a weed-free bed that is high in nutrients and retains moisture.

Whether you amend existing soil or create a new soilless mix, make sure you blend the ingredients well. Some gardeners use a portable concrete mixer plugged into a household outlet to get a uniform texture and distribution of particle sizes. No mixer? No problem. Blend all the ingredients on top of a tarp, then shovel the mixture into the frame.

To get a speedier start on planting, skip the mixing and fill the frame with high-quality bagged garden soil from a nursery or gardening center.

Once the bed is filled and you've raked the soil or soilless mix smooth, create a grid on top using lattice strips, PVC pipes, or even string. (Use nails or screws to attach the grid to the sides of the frame.) Being able to see each square-foot section clearly simplifies planting. If you like, cover the prepared garden with a thin layer of fine mulch to conserve soil moisture and slow down the growth of weeds.

Planting seeds in raised beds

4. Plant Your Favorite Veggies

If you're building more than one raised garden bed, leave enough space between them to roll a wheelbarrow. When it comes to planting, the formula is simple: one extra-large plant per 1x1-foot square; four large plants per square; nine medium plants per square; and 16 small plants per square.

Here's an idea of what you can fit in each square: one vine tomato, pepper plant, or eggplant; four bush tomatoes, heads of cabbage, or heads of lettuce; nine onions or beets; or 16 radishes. Zucchini needs nine of the 16 squares for just one specimen, but you can plant other vegetables in the remaining seven squares. Vegetables or fruits that spread (such as watermelons) require a separate bed.

About Planting Tomatoes

If you're particularly interested in growing tomatoes while square-foot gardening, compare the different varieties. Bush tomatoes (e.g. cherry or roma) produce fruit all at once. Each plant requires four squares but will not need to be staked. Semi-determinate varieties stop producing fruit when they reach a particular size. These tomato plants require a tomato cage for support, which means they'll take up four squares. Vining tomatoes (aka indeterminate) such as Early Girl and most heirlooms take up to nine squares if unsupported. Or you can stake this type of tomato and only use one square as long as you prune the plant religiously.

Planting Seeds

If you're planting seeds, plant one seed per hole spaced appropriately for the mature plant. (Look on the back of the packet for instructions.) Poke a finger through the mulch into the soil, drop in a small amount of vermiculite, then the seed, and cover it with more vermiculite—a material that will help keep the seed moist while it's sprouting. Mist the newly planted seeds every day so the soil doesn't dry out. Once plants are established, water them approximately once a week.

Transplanting Vegetables

If you're transplanting vegetables from a nursery or gardening center, use the same spacing method mentioned earlier. Place plants in the dirt, leaving a shallow depression around each one to help hold water. You may want to shade newly planted vegetables to protect them from wilting. Water daily for a few days, then remove the shade and water weekly.

woman in rubber boots watering newly planted herbs

5. Maintain Your Garden

Yes, square-foot gardening may take a little less work than traditional gardening, but you still have to pay attention to your produce.

Watering Schedule

You need to water when the soil feels dry, but you won't waste water on any exposed soil between traditional rows. Don't water from overhead. Instead, use a small container to water each plant one by one—pouring the water into the depressions you made when you planted them. Don't panic; it will still take less than 10 minutes to water a 4x4-foot garden this way. If your schedule permits, water in the morning. Editor's Tip: You'll need to water more often on days that are hot or windy because the soil will dry out faster.

Weeding Your Garden

Plan on weeding every week, but either pull weeds when they're small or use scissors to cut weeds off at the base instead of pulling them up by the roots or using a hoe. (You don't want to disturb the roots of vegetables growing nearby.) Make it easy on yourself by weeding every time you walk by the bed or by weeding only one square at a time. Because weeds won't be competing with your vegetables for nutrients, you probably won't need to fertilize.

Pest Control

Inspect your garden daily to spot insect trouble early. Either hand-pick and destroy insects or spray the soft-bodied ones with insecticidal soap. Knock aphids off of plants by spraying them with a hose.

Harvesting Square-Foot Garden Vegetables

Harvest vegetables when they're young, tender, and at their flavor peak. The only difference between harvesting veggies from a square-foot garden instead of a traditional garden is that there is less territory to cover.