Question
QUESTION: my lawn is 15 yrs. old -the root system is very shallow and kicks up easily. i use starter fert. only, 2 apps. in fall. help

ANSWER:  The lawn is fifteen years old. It could be due for resodding.
The root system is very shallow. Could be compacted ground.
Kicks up easily. Could be due to grubs which chew roots.
Dig a few random holes 1ft. deep. Examine the excavated soil for grubs. If you find 4 or more grubs per square foot apply a control product.
While you are digging, try to estimate how compact the ground is. Do the grass roots go downward for about a foot? If not the ground may require some sort of tillage down to that foot depth.
Starter fertilizers have a comparatively mild formula. They are applied to grass that is not yet fully rooted and functioning. They are not high enough in nutrients to maintain fully rooted and functioning turf.
So there you have it. Depending upon what you find you might have to address any or all of the above.
If you need some more input do not hesitate to come back

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QUESTION: I lime in spring- feed in fall. What do you recommend for fert? thank you

Answer
Why do you lime as a routine practice? Is there a pH problem? Do you monitor the pH on a regular basis to ascertain that you are achieving your objective?
I would apply a "Turf Builder" type of fertilizer (not a W&F)when the temperature settles down to 70<superscript>degrees around the clock
Avoid using sulfate of Ammonia  type of fertilizer; they react with limestone and release their ammonia to the atmosghere.