Jacksonville's Worst Lawn Invaders
Three invasive species cause more problems in Jacksonville lawns than everything else combined: torpedo grass, nut sedge, and wild Bermuda. Each one requires a different approach, and if you do not handle them before installing new sod, you are wasting your money.
Torpedo grass is the worst. We have seen its root structure grow all the way underneath a sidewalk and pop up in the lawn on the other side. It has been known to send runners across an entire driveway underground. You cannot kill torpedo grass without killing St. Augustine — there is no selective herbicide that targets one and spares the other. The only option is to nuke everything with a broad-spectrum herbicide and wait until it is completely dead before planting. If even a small piece of root survives underground, it will come back through your new lawn.
Nut sedge is just a given in Northeast Florida. If you have it, it is coming back — period. There is a product called Sedge Hammer that works to slow it down and suppress the growth, but it does not kill it completely. You have to accept that nut sedge is managed, not eliminated. Regular treatments keep it under control, but anyone who tells you they can permanently get rid of nut sedge is not being honest with you.
Wild Bermuda is the ironic one — the same traits that make it an incredible lawn grass (nearly unkillable, deep roots, aggressive growth) make it a nightmare when it invades a St. Augustine yard. It creeps in through runners and takes over sections of the lawn with a different color and texture. Two rounds of herbicide in the hottest weather you can find, two weeks apart, and you might kill it. Might.
The bottom line: every one of these must be completely dead before new sod goes down. That takes a month of prep time. Rushing this step is the single most common reason sod installations fail within the first year.