Why do you want to do it out of season? If you dethatch now, you will
undoubtedly spread around weed seeds of all types.. Especially Crab and Wire
grasses. If you plug aerate now, you will plant those weed seeds better than
Ma Nature does.
Spring and early summer are for maintenance of existing lawn and existing
weeds. If you have a compaction problem, spread gypsum now and plug aerate
heavy in the fall or late summer in Mich., let the "wounds" heal over then
overseed.

"daniel99mp" wrote in message
oups.com...
I've been reading books on lawn care and they all recommend that I
aerate and dethatch my lawn in the fall because I live in Michigan and
have cool season grass. I would like to do these things this coming
spring. By doing so would I be gaining any true benefit or even
possibly harming my grass? Any advice would be greatly appreciated.