Understanding numbers usually applies to the high finance world of Wall Street or maybe just our checkbook. We seldom think of numbers in relationship to landscape. The numbers may be the eye appeal that is worthy of second glances from passersby.

The standard rule of thumb has always been planting in threes and fives. Maybe there are ways to successfully incorporate other numbers. Understanding the numbers and how to use them can give you confidence. It gives you the freedom to fudge that long-standing rule and satisfy your own taste in design.

• One plant can be either a specimen plant or a unifying plant. I planted blue lyme grass in front of a giant boulder and close to a blue spruce. The grass has a bluish tint that echoes the blue of the blue spruce. In this case it acts as a specimen plant and a unifier.

Two plants signal formality, and are usually used to mark both sides of an entrance or passageway. Formality is not my style. I would feel like I am being watched, checking I always walk a straight line.

• Three plants are a charm as long as they aren’t used in a straight row like soldiers at attention. That would be dull. If you have enough space, group them in an equilateral triangle. This arrangement looks particularly good with mounding or vertical plants. Be sure to leave space between plants, especially if there are three different kinds. Another arrangement could use two plants with a garden ornament or a birdbath to count as the third item in the set of three.

• Four plants can be divided in various ways. Avoid planting two and two on the sides of an entry. That planting often feels off-kilter, always calling for more, making it three and three.

You could plant one plant in each quadrant of a circle or square, either planting four distinct specimens or repeating the same plant. A planting that also works well would be dividing the four plants into three plants plus one. Position three plants on one side of a path and one on the other. This planting could be especially effective if an evergreen is used as the one plant because of its strong visual weight.

• Five is the number most often used. A classic example of 5 is to set up two parallel rows with three in one row and two in the other. This works best in a rectangular bed. Positioning two plants on one side of a path and three on the other does not work but having four plants balanced with the fifth plant separate feels right.

• Six is two sets of three. This works best when broken into two groups. Either duplicate the arrangement of threes in a staggered row or in a triangle or position them to fill a corner. Dividing into groups of two, or a line of six, doesn’t command much attention.

Now, let the fun begin by drawing out the six possibilities. Roughly sketch out either a straight or meandering path, whichever best suits your landscape. Just use circles to indicate your plantings and let your eyes lead you to a planting what best suits your personality.

When you are working on a plan near an entryway, avoid the following five plant traits:

• Plants that have thorns that can snag clothes and skin.

• Plants that attract bees. Many plants attract a few bees, but try to keep bee magnet plants several feet away from your walkway or patio where you won’t brush against them.

• Plants that sprawl. Plants that spread and sprawl should be planted far enough from a sidewalk that they don’t fall into your path and present a tripping hazard.

• Plants that have branches at face height. Either prune branches high enough to be out of the way, or keep these plants far enough back that at their mature size they won’t hang out over the path. I had to do some pruning on an apple tree after I observed the lawn service man having to duck under the branches to mow.

• Plants that outgrow their space too quickly. If you need to prune a shrub severely every year to keep it within bounds, take it out and replant with a different variety.