This is a classic "buried tree" with no visible root flare at all.
How do you uncover your own root flares?
The simple answer is that it needs to be done VERY carefully.
Trees too deep in the ground, an all to common problem, have two basic problems. When the trunk flare in under ground, it stays moist and doesn't breathe properly as bark is supposed to do. The soil too high on the trunk also often hides circling and girdling roots, which choke the tree and drastically slow down growth. Trees grown in containers are highly subject to this damaging condition.
If you do the soil removal yourself, use hand tools and gloved hands being extremely careful not to damage the wet bark tissue. Water can be used but only with a soft flowing stream. Strong water blasts can severely damage the soft bark on the base of the trees.
By far the best route is to hire an Arborist that uses the air spade. It is a fancy sandblasting type tool that blows air (no sand) at a high velocity and removes the soil without damaging even the smallest roots. Once exposed, the small roots trying to grow up to get air should be removed and the depression caused by the trunk/root flare exposure should be left open. As the flare expands from the growth of a more vigorous tree, the open dish will fill in. All I would put in the depression is a thin layer of shredded cedar mulch.
Above is an interesting group of pictures that show a recent Magnolia that we uncovered. It is one of the more dramatic examples of severe girdling roots. I was showing the tree to Sandy Rose and he actually took the pictures. Thanks Sandy! At our office, we are referring to this tree as the “poster child” for problem root flares. The work on the tree was done about a month or so ago. We will continue to monitor how it responds. I predict that we will be surprised at how quickly the depressed sections will fill in or rebound. This tree is sighing with relief and is saying “thank you”.
FM: This burr oak was not too deep compared to the others. Should I go deeper, what about the sucker root?
HG: This flare looks good now. If you are talking about the small root that appears to be crossing, remove it.
FM: All these fruit trees were bare root and are in their 4th year. Peach tree #1 had some roots crossing over and choking at the trunk. The tree leans, should I expose the root flare on the covered side?
HG: Yes, this tree is still too deep in the ground.
FM: Peach tree #2 appears to have several sucker roots above where the flare starts. Do I cut them off and go deeper?
HG: Those are adventitious roots (false roots above the true flare). I would probably wait till fall to remove them.
FM: Plum trees - I cannot find a flare on either. There are sucker roots and swelling, but no roots that are choking the trunk. Do I go deeper and cut off the sucker roots?
HG: Yes, and Yes.
FM: Thanks. I listen to both shows, and I could not believe how deep these trees were planted.
HG: Good work Frank. I wish all gardeners would do this. Next, maybe we can get the growers to put the trees at the correct height in the containers.
QUESTION: I recently purchased a 5-gallon forest pansy redbud tree. I knew from listening to your radio show that the tree could possibly be planted too deeply in the pot, but I found that it was planted a good 5 or 6 inches above the crook in the stem where the graft was, and the root flare was a few inches below that. I went ahead and planted it at the root flare, leaving the graft and a good portion of the "wet" trunk exposed. But I was wondering if the root flare rules are the same when dealing with a grafted tree, or does the original trunk below the graft need to be in the ground? D.P., Savoy
ANSWER: You did the right thing. The root flare should always be exposed. The graft union being up in the air is no problem at all. Good job!