Gardening Terms Demystified: “On Center”

Some gardening writers have a frustrating habit of using jargon in their articles and books. I understand how easy it is to fall back on words commonly used among professionals, but when a writer is attempting to explain something to a layperson, she should keep the audience in the forefront of her mind. Sadly, not all do.

New gardeners email me now and then, looking for definitions to words or concepts they’ve read in a gardening book or online article.

For instance, how many “How to Plant” something instructions have you read that include this caveat: “spaced 6 inches on center?” My most recent email, from an exasperated new gardener, pleaded with me to please explain what “on center” means.

What Does “On Center”Mean?

On center, sometimes abbreviated as “o.c,” is a term used to describe plant spacing — how far apart to dig your planting holes for a specific type of plant. For instance, daylilies are typically planted 12 to 18 inches on center.

To plant several daylilies, determine where you want to place the center plant. Measure from the middle of that planting hole 12 to 18 inches on both sides. This is where the middle of the next holes should be.

I like to map out my planting before digging the holes, and flour from the pantry makes a great marker. I drop a spoonful of flour where I want to place the plants and then try to imagine the arrangement in my mind. You can change your mind as many times as you like just by mixing the flour into the soil and starting all over.

How about you? Is there a term that is frustrating the heck out of you? Drop me an email and I’ll clear it up for you.


Image courtesty: Dan4th/