I have several SFH. One home in particular has bald spots in the lawn. Some of the houses have weeds and brown areas. How far do most of you go to have nice lawns? I require tenants to mow the lawn, but I doubt they would go for paying for a spray company to fertilize. You can have houses with perfectly green lush lawns like on a golf course, but that would be very costly. What do you all do if anything?

The basics,, you yourself can do a weed / feed in fall and will help for next year.. a handful of grass seed now and then fine. Otherwise understand it's just gonna be a average lawn if its being done by a tenant.. be glad it's cut.. and maybe have a lawn company do a spring and fall clean up weed / feed treatment so it can perk back up .. 

My concern is that the lawn companies charge a lot for their services. Two of my lawns are just under an acre.

Yes they do charge.. so if you actually have tenants that are mowing a acre size lot you are lucky beyond lucky,, it's hard enough to get a regular city lot done by a tenant..

I have a 1.25 acre property always did my own lawn mowing but last year hired a weed/ feed guy spent 785 for the season for spraying.. and OMG my lawn never looked so nice in 10 years.. I didn't have them back this year, because I figured they killed all the dandy lions and did a great job and my lawn was beautify again this year..so I'm thinking every other or maybe every 3 years.. for a service to do it.. all the bald spots filled in with grass on their own and not a single dandy lion this year.. 

It's a maintenance cost,, I just added to yearly expense report..I