Many homeowners like the look of mass plantings on the landscape. But, how many plants will it take to achieve the look you want?
Some simple math can help you figure out how many plants you need to cover a specific area. As long as you know how far apart the plants should be planted, you can easily figure what it will take to fill the allotted space. This will help you from under- or over-buying when planting groundcovers or annual flower beds.
First, you will need to calculate the square footage of the area. This is easy if it is a simple shape such as a square or rectangle, but if it is irregular it will take a little more calculating. Dividing up the irregular shape into several smaller, simple shapes will make it a little easier. After determining the total area, you will need to determine what plants you will plant and what the recommended spacing is. Use the following to determine how many plants per square foot will be needed. The first number is the recommended spacing in inches and the second number is the number of plants per square foot, 6 = 4, 8 = 2.25, 10 = 1.44, 12 = 1, 18 = .44, and 24 = .25.
This is where your math skills will come in handy. For example, if you’ve chosen a plant with a recommended spacing of 6 inches, you’ll need four plants per square foot. If your garden space is 50 square feet, you’ll need 200 plants for the area. For a groundcover that needs spacing of 18 inches, you’ll need only .44 plants per square foot. Multiply .44 by the number of square feet you have. Using the example of a 50-square-feet garden bed, you’ll need about 22 plants.
When there is a range of spacing, as in the case of the vinca, you have options. Going with a closer spacing can help fill in the area faster, which can help prevent weeds because the full canopy will shade them out. However, you’ll obviously need more plants for this scenario.
This might also help compensate for the chance of some plant loss. If your budget is a little tight you can go with the greater spacing to save a little money. Going with the maximum spacing may be wise if you are dealing with a plant that could develop foliar diseases. This allows more air circulation among the plants keeping their foliage drier, which in turn reduces the potential for disease.
David Hillock is a consumer horticulturalist with Oklahoma State University Cooperative Extension.