Over time, gardeners realize their plants are very similar to people. They need to be fed, cared for, protected, and given space to grow. Plants need ‘personal space’ so they aren’t fighting for nutrients and can stretch out as far and deep as they need. If crowded or in a shallow garden bed, then they won’t grow to full potential…or grow at all.
Each plant has unique spacing and depth requirements, which may sound daunting to new gardeners. Fortunately, online spacing charts, certain planting styles – like square foot gardening, and a general rule of raised garden bed depth, makes growing simple.
Square Foot Gardening & Garden Area Sizing
Traditional row-style gardening isn’t space effective for a typical backyard garden. The purpose of a row is to allow for ease of navigation between plants (e.g. walking); this walking row then of course can not be utilized for growing. Square foot gardening, on the other hand, maximizes space utilization, easily segments your plants and more efficiently utilizes water and nutrients in the garden when coupled with a grid irrigation system. Basically, with square foot gardening you plant by area instead of rows.
Separating a gardening space into roughly square foot sections, gardeners then place the appropriate amount of plants within each square based just on the seed spacing needs (not the row spacing needs). This method, explained in greater detail in the spacing chart link at the end of this paragraph, allows for higher density of growth when compared to rows. However! A pivotal component of this planting method is the dimensions of your garden area/garden bed. To utilize square foot gardening to its best potential, your garden should always have a dimension of 4 feet or less (e.g. 4x12, 4x8, U Shaped with 4 ft ends, etc.) this sizing then allows you to reach the middle of your garden area from one side or another, without needing to walk into it (hence, why we don’t need rows!). Professionals have created square foot garden spacing charts like this one, The Comprehensive Plant Spacing Chart, so anyone can grow a diverse, healthy garden and plant with ease.
How Deep Your Soil Needs to Be
Depending on the vegetables you want to grow, you will need anywhere between 8 and 36 inches of usable soil depth. If you are using a raised garden bed, then use one that is at least 8 inches tall. That way plants can still grow even if it’s placed on concrete. However, garden beds need to be taller or placed on top of earth if you want to plant anything that needs more than 8 inches of soil. Seasoned gardeners will advise the you double-dig the soil beneath your raised bed as well, to ensure loose soil. Roots don’t like packed dirt, so digging two feet into the ground and loosing the soil guarantees roots can grow through.
Gardeners should also slightly overfill their garden beds. Over the course of the first few days of filling a new garden, the soil will compact as it gets weighed down from water and tiny air pockets in the soil collapse. A good rule of thumb is to add about 2 inches of soil above the top of your garden bed, wet the soil to see how much it compresses then add more to bring the level to the top of the bed if needed. There’s a good video explanation overfilling your garden bed with soil here.
Generally, the bulk of plant’s roots will need 6-8 inches of soil depth for healthy growth, with some larger root vegetables such as imperator carrot varieties needing a bit more. So, if you intend to grow deep rooting vegetables remember you can place your garden bed on top of soil or simply grow in a taller bed.
Quality Soil = A Quality Garden
Finally, moist and nutrient-rich soil is a key element to a bountiful garden. Using soil from a gardening center is better than using foreign soil: soil with unknown elements from a yard or field. Soil needs to be cared for and a quality food source for your plants, without it all the spacing and depth won’t matter much.
So remember, when growing a backyard garden follow these tips to ensure your plants have the space they need and to produce the most in your garden area:
1. Plant By Area, Not By Rows
2. Ensure You Can Reach At Least Half Way Across Your Garden
3. Give Your Plants 8 Inches or More of Accessible Soil Depth (Garden Bed Depth, or Garden Bed Depth + Soil Beneath)
4. Overfill Your Garden Bed With Soil When Starting
5. Use Quality Soil For A Quality Garden