Red oak tree problem

Can anyone help? Three weeks ago I planted a 5-gallon size red oak tree. The tree stands about 8 ft tall and had wonderful new-season leaves. I dug a wide-enough hole and added mulch to the hole before I planted the root ball into the hole. I water it regularly. Then about 4 or 5 days after it was planted, we had an early-season heat wave of 90+ temps, accompanied by a late-season high wind event (I live in SoCal, where we get those Santa Ana winds). After the wind event was over and after the heat wave ended, the leaves of the red oak went limp and are now turning brown. I did the "thumbnail test" by scratching the bark of a branch with my thumb, and it is still green inside. What has happened to the tree? Did it go into shock because of the extreme heat and/or high winds? What needs to be done to resore its beauty?

Hey, analyst01. Ken here with The Home Depot in the Chicago area. I’m sorry to hear about
your oak tree. From your description, it sounds like the combination of not enough water and
the Santa Ana winds beat it up. Let me ask you a few questions.
What kind of mulch did you add to the hole and did you mix it with existing soil?
Did the tree get regular water? It should be watered every other day in the beginning, every day
during Santa Ana winds. You should thoroughly wet the root ball when you water. The root ball
is tiny and needs to supply water to an eight foot tree.
One last question: Where are you located in SoCal? If you live near the coast, that is out of the
Red Oak’s (Quercus rubra) comfort (plant) zone. It needs some winter chill to really thrive. Its
comfort zone would be in towns like Thousand Oaks (no pun intended), Van Nuys, Burbank,
Pasadena, Covina, Pomona, etc. If you live in the San Diego area, the zone would be in towns
like San Marcos, Escondido, Poway, Lakeside, etc.
Since you did the thumb test and found green, keep up the watering. New leaves should show up.
I hope this helps. Good luck and take care.

Hello, Ken. Thanks so much for your reply. Your information is helpful. Here are the answers to your questions, hopefully they will provide further insight into my situation.

1. The mulch I used in the hole was Kellogg's Gromulch...and yes, I mixed it with the soil that accompanied the root ball.
2. The tree gets regular water, though I do not flood the tree's area, as it is near a vegetable garden.
3. Admittedly I did not add water to the hole before I inserted the root ball, nor did I wet the root ball before insertion.
4. My locaton is further inland than the cities you listed. I am in Riverside, which is somewhat near Pomona, so I believe the climate zone here is appropriate for the red oak, where we do get a (relatively) chilly winter season.

I also wanted to add that I purchased a soil moisture wand, and I regularly test the soil around the oak tree and all plants in my garden. But even if the tree's soil registers "wet" on the wand, should I still water the tree every other day?

Finally, most of the brown leaves have fallen off the tree, but again, the bark is green and it appears the tree is still alive. Would it be realistic to expect new leaves this season? or will I have to wait until next spring?

Thanks again for all your help.

Hello analyst01. Ken here again. Thanks for getting back to me. It sounds like your
doing everything right. You should expect to see new leaves this season. Just keep up
your watering schedule and make sure that the water drains well. Be patient. The tree
needs to produce energy for itself, so it will definitely come out with new leaves. Good
luck and keep me posted on its health.