Determining the Space Between Plants

Look at practically any plant label, and you'll find a reference to the plant's ideal spacing requirement, ranging anywhere from a few inches to several feet depending on the plant. But just how important is that information, and what is it based on?

Generally speaking, the information is worth paying attention to because it's based on the distance required between plants for optimum growth. After all, there's only so much water and nutrients available to plants, and competition for both can be intense. So if plants are grown too close together, all of them may suffer.

But recommended spacing requirements are merely guidelines and depend on a variety of factors. For example, if your soil is rich with nutrients, you can group plants closer together.

French intensive or biodynamic gardening, for example, which involves techniques such as double digging and routine applications of compost, yields soils so rich that plants can be grown twice, maybe even three times as close together as the standard recommendation. A major benefit of that approach – beyond the bountiful harvest – is that the closely packed plants create a living mulch, shielding the soil from sunlight and thereby preventing weeds from germinating.

Conversely, in poor soils your plants may grow better if they're spaced even farther apart than the standard recommendation. In other words, if the recommendation is eight inches between plants, you might want to consider a spacing of 12 or even 15 inches. Then mulching the areas between the plants helps to prevent weed growth.

Spacing vegetables

In the case of vegetables, the information regarding spacing makes sense only if you intend to run a tiller between the rows. A packet of spinach says that the space between plants should be six inches, and the space between the rows should be 12 inches. Why do the plants need six inches between each other in one direction but 12 in the other? They don't.

This bed measures 4' x 4'. If you sow spinach seeds six inches apart within the rows and spacing the rows 12 inches apart, you wind up with 28 heads of spinach with a six-inch border around the edge of the bed.

However, in a same-sized bed, the spinach is spaced six inches apart in every direction, and the result is 56 heads of spinach, which is double the harvest of the first bed. This is called equidistant spacing.

Then, if you shrink the borders by half, so there are three rather than six inches in every other row, there's a way to increase the harvest even more. By making use of some of the wasted border space, you can squeeze in four more plants for a total of 60 heads of spinach, all spaced six inches apart.

Spacing groundcovers
When planting groundcovers on a budget, you could buy five flats rather than 10, and space the plants twice as far apart. Or, buy one flat, space the plants 10 times farther apart, and be prepared to wait longer for them to grow and fill in the space. Because they're groundcovers, they will cover the ground in time.

Don't worry about spacing plants in an orderly fashion. Random spacing can actually be a lot more interesting, especially if you're looking for a more natural rather than formal look.

Spacing requirements that make sense
Of course, there are some spacing requirements that do make sense. For example, potentially large trees like most oaks and maples should be planted at least 25 feet from the house. This is important for two reasons: Their branches can extend up and over the house and cause serious damage should they fall, and also large roots can cause foundation problems. However, smaller trees such as dogwoods and Japanese maples can be planted closer to the house to soften exposed walls.

Potentially large trees should also be planted at least 15 feet away from paved surfaces such as sidewalks and driveways. In time, their roots may damage those surfaces.

Even small trees should never be planted beneath power lines, as anyone who has lost power on a stormy night or experienced the poor pruning jobs done by utility contractors can attest. If you have a septic system, avoid planting trees within approximately 20 feet of the lateral lines because the roots can clog the lines faster.