Post oaks and blackjack oaks don't like irrigation or fertilizer as St Augustine grass does. Cut back on both and apply the Sick Tree Treatment, the first step of which is to remove the excess soil up on the trunk/root flare.
Q: I have 2 live oaks that were planted by the builder when my house was built. Neither tree has done very well. The trees are about 3" in diameter, with one tree currently at about 15' tall and the other about 12'. Both trees (and one in particular) have pale leaves. Leaf coverage is good, and neither tree seems to be losing any foliage, but both look pretty pale. A local nursery here in Frisco recommended "Bio S.I." (liquid concentrated plant food) as a method to help the trees. I've used it periodically but it hasn't had the desired effect. I've been watering the tree deeply periodically as well, and my sprinkler system is set to water 3 times a week at intervals of 15 minutes a zone and again 2 hours later at 15 minutes a zone to avoid runoff. R.B., Frisco.
A: Those trees are lucky to be alive. You are drowning them. That is far too much water, especially for the cool and wet summer we have had. Now that itís fall, no watering is needed at all. Compost tea or the entire Garrett Juice mixture (compost tea, seaweed, molasses and vinegar) are much better root stimulators than the one you have mentioned.