It could be a number of things going on, and you have collected some great information already. This year trees have been very stressed by the severe April freeze.

So first, check to see if there is live tissue under the bark on the trees. Just scrape a small spot on the bark of the twigs to see if there is green underneath. Also if there are leaf buds at the tips of the twigs, cut into a few to see if they are green inside. Then watch the trees for awhile to see if they are going to leaf out.

Next, pull back the mulch and gently pull the dirt away from the base of the tree and feel the tree. If it is slimy and corky, that would be an indication of root rot.

You did the right thing by withholding further water. If the trees have mulch at the base, you should take it off temporarily to let more moisture escape from the soil. 

I have not been able to find information about pumping compressed air into the ground. I think the best thing to do is watch and wait.

 I hope this information helps. If you have further questions, please let us know.

Thanks, MGGPA!

Here's the latest:  the pear tree is dead and the Chinkapin Oak, while alive, has black spots on the few leaves that sprouted.  The oak has been removed from the soil and set aside in my yard.

On the pear tree, I did scrape back some bark...no green.  I did so in several places.  Definitely dead.

On the oak tree, it did leaf out, but extremities appear to be dead (could be 'dieback').  Yesterday, the largest leaves showed black spots on them (please see pics).  Today, I dug the tree out, and carefully hosed down the roots until all clay soil was removed, and it was CAKED on the roots.  

The oak tree's roots appear to show black areas.  Is this root rot?  If so, should I cut the roots back and spray on copper fungicide?  or diluted bleach in water?  followed with powdered root stimulator?  Also, should I cut back the dead branches to, perhaps, encourage growth?  I'm considering removing all clay soil in the hole and replanting with store-bought garden soil, and at a shallower depth.  It appears that water does drain out of the hole, but the roots just don't survive in the clay soil.

If I do replant the oak in mostly garden soil, do you think the roots will eventually grow into the clay soil or will they just circle around the hole, remaining in the garden soil?

I really appreciated your advice!

Regards,

Craig

We are seeing  a lot of damage to  trees this year because of an event last Autumn and another in mid-April, where we encountered sudden and dramatic drop in temperature. The low temperature in early morning of April 12th in Boulder fell to 12 degrees, with subsequent nights near that temperature. This was after a period of warm weather where our trees "woke up", too early as it turns out. The damage to trees on the Front Range has been extensive. It is unlikely that a new tree planted in March could have survived this sudden temperature drop in April.

Regarding the oak, the tree may not have been planted properly. See https://static.colostate.edu/client-files/csfs/pdfs/TreePlanting_636.pdf for step-by-step instructions on how to properly plant a tree. The most common mistakes made when planting a new tree are to a) plant the tree too deeply; b) fail to remove burlap or twine from the root ball or trunk; c) failure to untangle and break up roots in the root ball before planting. Each of these mistakes may cause root girdling, where roots wrap around the stem of the tree (rather than growing outward), which impairs the ability of the tree to move water and nutrients through its tissues.

Do not use potting soil, garden soil, fertilizer or other amendments when planting a new tree. Nearly all soils on the Front Range are heavy clay, and trees grow in this soil. If you amend the soil where you plant a new tree, the tree may do well until its roots start reaching out to the native soil. At this point, they will tend to curl back into the softer soil in the planting hole rather than attempt to grow through the harder clay, resulting in root girdling. It’s highly unlikely that there are adverse organisms or chemicals in your soil. In the case of the oak tree, the issues you’re seeing may have to do either with improper planting, with the extreme temperature drops we encountered in April and last Autumn, or by lack of winter watering.

The lack of winter watering is very likely an issue. We had many dry period last Fall and Winter that required winter watering to keep our trees and shrubs healthy. See https://extension.colostate.edu/topic-areas/yard-garden/fall-and-winter-watering-7-211/ for details. From October through March winter watering is required during any long period (three to four weeks) in which we do not have snow cover. Be sure to winter water this coming Fall and Winter. Summer watering is normally not required once a tree is established. When first planted, if we have not had much rain (which is typical here), you should deep water newly-planted trees about once a week. Use a common lawn sprinkler on the end of a hose to do so.

It will likely be a lost cause to try to replant the oak tree if it is has been out of the ground for any length of time. From the photo, the tree appears to be fairly large. You will have better luck planting the smallest tree you can find. It’s easier to dig a small planting hole (with sloped sides, as discussed in the tree planting guide) than for a larger tree. A smaller tree acclimates to its environment more readily. For every inch diameter of a tree, a year’s worth of root development is required for the tree to be viable and to start growing again. In other words, a tree with a ½” trunk will have established roots in six months. A three with a three-inch trunk will require three years to have well-established roots. In these three years, the smaller tree will likely overtake the size of the larger tree. You’ll also save money by planting a smaller tree. See also Understanding Tree Roots, GardenNotes #659: https://cmg.extension.colostate.edu/Gardennotes/659.pdf

Thank you for responding!  Your comments about finding the smallest tree when planting in heavy clay soil is really helpful (and the time it takes to acclimated based on trunk diameter).

If a younger tree can acclimate to the heavy clay soil faster than a mature tree, it leads one to wonder why even consider a 3+ year old tree from a nursery, especially when that nursery tree has been grown in ideal soil - it would be 'shocked' at being transplanted into heavy clay soil!  What I need is to either grow my oak from acorn (or seedling), or purchase a tree from a nursery that was grown in heavy clay soil (because it will acclimate quickly when transplanted to heavy clay soil)...right?

Hello,

It sounds like you are on the right track with picking out a new tree. You don't need to start from an acorn, but beginning with a new seedling is a good option. Do you have any other questions for us at this time? You are always welcome to write again later.