Buried Root Crown

See this tree over here on the left. It’s a baby Incense Cedar that was planted on a gorgeous estate in San Rafael. But there’s a big problem with this picture. The tree has been planted too low. I can tell just by looking at the way the trunk goes straight into the ground. There should be a flair at the bottom of the trunk where the trunk becomes the roots.

This part of the tree is called the root flair, or the root crown. It should never be buried by soil or even mulch. Otherwise the tree can have all sorts of problems. The bottom of the tree trunk can actually rot.

Here on the right I have started to dig down and expose the root crown. It is buried about 8 inches under mulch and soil. Left unchanged, this tree will become weakened and very susceptible to pests and disease.
Here on the left I have exposed two adventitious roots. Sometimes when a tree is planted too low it get’s confused and sends out roots from the trunk. These adventitious roots are rather large. One should not confuse an adventitious root with the root flair.
In the photo on the left you can see the root flair, well below these two adventitious roots. Sometimes it is okay to remove the adventitious roots. In this case, since they are so large, I’ve decided to leave them.
In San Francisco the number one reason for tree pest and disease problems is a buried root crown. I see it all the time. One reason is that trees grown in pots are frequently sold with buried root crowns. Before you plant you should always excavate the trunk, locate the crown, and place the tree in the ground to that the root flair is just above grade. I’ve had to remove the top 8 inches of soil in a nursery pot just to expose the root crown.
Another reason I see trees failing because of buried root crowns is a raised garden planted around a tree. Gardeners and designers often aren’t aware of the importance of the root crown. They think it would be nice to build a raised bed around a tree. This can look very nice, but not so nice when the tree gets sick. It may take several years for a large tree to react. But by the time the tree has an obvious reaction, like dieback or fungus or discoloration, it may be too late.
Last thing ya’ll should know. Never plant low. Especially in soil that has a heavy clay content.