I've read several posts on this forum, and it seems many people use this on citrus. Can it be used on in-ground trees? The instructions on the bag say basically one tablespoon per gallon of water. Just not sure if this is correct for citrus, and how often to use it, or how many gallons per tree. Any suggestions on how you use it are appreciated. I have 5 trees in-ground. One tree is 10' tall, two are 7' tall and 2 are 5' tall. Thanks, Ed