Christina Wells: Planting Trees Properly

Interview with Christina Wells, PhD, Associate Professor of Horticulture

Whenever my family would move to a new house, we planted a tree. You know it’s that whole ‘roots’ thing. Often the tree did better than we did. We moved on and the tree stayed and thrived. Today we’re going to talk with Christina Wells, a plant physiologist who specializes in researching tree roots.

This is a Carolina Allspice tree. This is a wonderful perennial for southern borders.

Well, I guess we would like to plant it and I imagine the best way to do that is with a good deep hole.

That is where you’re wrong and that is the most common misconception about planting trees. Trees’ roots are very shallowly distributed. So, if you imagine this to be a mature tree, the roots are in a plate maybe about a foot deep extending 2 – 4 times the width of the canopy. So, in fact, you want to make a shallow hole; and this is why a lot of people end up killing their trees. Now the things to look for when you’re planting a tree are the structural roots. When they’re young, those structural roots are quite tiny. So your job when you bring a tree home from the nursery is to find those roots. And you’re looking for the first root that emerges from the trunk. And here – can you see it?

Yes, I can.

Right there, it’s about 2 millimeters thick and it’s directly attached to the trunk . So that’s about 2” down in the soil volume. You want to remove all the soil that’s higher than 2” and place this first little structural root right at the soil surface when you plant.

Let’s see if we can go outside and find some trees that are either well planted or poorly planted.

Oh, I think we can find some examples. This is a good example of a properly planted middle-aged tree; and one of the reasons I say it’s properly planted is that you can see all those woody structural roots emerging and 6 – 8” above the surface of the soil; and they’re actually continuing not to grow down but to grow out in a vast plate that probably extends 2 – 3 times the canopy drip line.

Let’s talk about this poor old soul. I wasn’t around when this guy was planted so I don’t know what happened to cause this but this is what we call a girdling root; and this tends to develop in trees that have been planted too deeply. What’s happened is that one of those thin roots that was going to become a woody structural root has grown around and encircled the base of the tree. Now as it expands in diameter, it actually begins to be like a tourniquet cutting off the circulation in the trunk and can with time kill the tree. So planting depth really is an issue in preventing this from happening.

I’ll probably spend, from now on, more time looking at the roots then looking at the tree canopy. Christina, thanks for your time today. I really appreciate it.

Thanks Peter.

Talking with Christina today was really an eye opener. Who knew that you weren’t supposed to plant trees so deep? Keep those roots at ground level. I’m going to do that in the future when I plant trees. On a day like this you realize just how wonderful it is to have a tree in your life. This is Peter Kent for Science and Society.