For instance, Giants Stadium has Astroturf, but it’s just a normal stadium. It looks like it could have grass if they wanted it. Since everyone feels grass is so much better (and safer), what’s the rationale here?
Part of the reason they use artificial turf is it allows them to use the field more. Up here the Saskatchewan Roughriders use Taylor field which used to have natural grass, but they went to artificial turf because they could also have Junior football and high school games here, as well as concerts and other events without worrying about the health of the field.
We had the same thing at Legion Field in Birmingham, which switched to Astroturf back in the late 60’s/early 70’s. Lots of folks did it because it’s cheaper to maintain a carpet than having to water, fertilize, mow, and replace sod on a natural grass field; players stayed clean; it was easier to play in bad weather; and of course, there was the lure of the new. Then, theyy pulled up the artificial turf for the soccer regionals during the Atlanta Olympics and put down a verrrry nice grass surface, which is still down. Of course, it has been replaced a couple of times now due to the intense wear (drought+high school games+UAB+Alabama+(ulp…the XFL 'Bolts). Grass is much nicer to play on, but it does have a pretty high overhead to keep it nice.
At Busch Stadium in St. Louis there’s a strip of right field which is pretty much in perpetual shadow. They’ve tried pretty much every type of grass, but it’s difficult to keep anything thriving there. That was not a concern when the field was Astroturf.
I know that the reason Royals (now Kauffman) Stadium was originally designed with aftificial turf was so that the field would drain quickly if it rained shortly before the game. The Royals being the closest major league team (until 1993) to baseball fans as far away as Denver, they didn’t want these faraway fans, apparently a significant part of their attendance base, to go home unsatisfied due to a game canceled from a too-muddy field.
The availability of more modern drainage systems for grass fields made the switch to grass in 1995 viable.
Exhibition Stadium in Toronto, hone of the Blue Jays until 1988, wasn’t domed, but had artificial turf presumably due to weather conditions at the extreme beginning and end of the season.
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Giants Stadium is an unfortunate choice for an example, as it has grass now. 
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The 2000 season was the first year for grass there, and they really had some trouble keeping the stuff alive come December. I’ve heard that the “grass” was little more than green-painted mud by late season.
It’s worth noting that the Astrodome, when first opened in 1965 as the Eigth Wonder of the World, had real grass. Unfortunately, the numerous skylights made it difficult to see fly balls. The skylights were painted white, but afterwards there was no longer enough light to keep the grass alive. It was replaced with Astroturf only in 1966.
AstroTurf ™ and other types of artificial surfaces became popular in the 1970s with the advent of multipurpose stadiums. It was a lot easier to maintain the playing surface when the most you would have to do to it was vacuum it, instead of mowing it and watering it.
Now multipurpose outdoor stadiums are going the way of the dinosaur. You either have a baseball stadium or a football stadium. Veterans’ Stadium is the last, outdoor artificial surface MLB/NFL combo. San Diego and Oakland also do double duty, but use grass. And Oakland’s grass is usually in terrible shape. The Vikings play indoors so they don’t have many options.
When I went to grad school in Berkeley, the intramural fields even had AstroTurf ™.
St. Louis uses grass, but the groundskeepers would prefer an artificial surface. Apparently, the climate in St. Louis makes it very difficult to grow grass that will thrive year all-year round as the area has a combination of relatively cold winters and very hot summers that makes for a short growing season. Hence, the grass just doesn’t have enough time to take root.
For a few seasons in the early '70s, old Comiskey Park in Chicago had an artificial infield and a natural outfield. Or maybe it was the other way around.
Doesn’t seem to be working out very well there either: Game canceled because of turf problem
Many outdoor stadiums are returning to grass fields. Especially college fields. THe football players union is actively pursuing a natural turf policy, since artificial turf causes more injuries, especially to the knees.
… and the problem there was a new-and-improved AstroTurf (called NexTurf) was installed earlier this year, and this week was the first time a baseball-to-football conversion was needed.
And it rained hard the day before, so the drainage was all screwed up, and didn’t allow the covering of the infield dirt areas, causing the seams that the players complained about.
There’s no reason you couldn’t have grass in Toronto. It isn’t any colder or snowier here than it is in Boston or Detroit.
Exhibition Stadium was built long before the Blue Jays played there (and they played there until mid-1989) so it had nothing to do with weather. The Ex was a multipurpose stadium, often used for non-sporting purposes, and it’s just cheaper and easier to use turf in stadia like that.
Similarly, the Skydome, which is a dome but you could obviously leave the roof open to get sun, has turf not because they can’t grow grass there but because the stadium was intended for use for things other than baseball, especially conventions and trade shows. Astroturf is much more cost effective for such a facility. That said, when the Dome was built it was a matter of great controversy; the fans wanted grass, but the builders (including the government) insisted on turf for the sake of cost and revenue potential.
Exhibition Stadium was also unique in major league history for having its outfield fence across the football field. Homers hit to right would clear the fence and keep rolling into the darkness, all the way to the end-zone scoreboard. If the field had been grass, installing and removing the fence for Argonauts game would have torn up the field something awful - with the plastic stuff, it only took a few patches over the post holes.
The allegedly low maintenance cost has been mentioned. My understanding was that the cost of pulling up the rug to replace the foam, which would deteriorate rapidly, and periodically replace the rug itself, made the cost almost a wash. If that didn’t get done, the players might as well have been performing on painted concrete. Even as it is, one can point to any number of career-shortening or career-ending injuries caused by the stuff. The pro players’ unions have made that a strong issue. As a result, there are not many facilities left that could have gone to natural grass but haven’t. Even many of those already have their natural-grass replacements under construction.
Oh, and Comiskey had a plastic infield (for truer bounces) and a grass outfield (for unknown reasons) in the 70’s.
Another reason stadium operators gave for using artificial turf was that it decreased the chances of a game being rained out because the ground got too saturated.
Cincinnati used to go to great extremes to avoid rainouts and would wait for hours for rain to stop. Then a Zamboni™ like machine would come by and suck up the excess water on the field.
Cincinnati, Kansas City, and St. Louis tend to draw fans who have come a long way to see the game.
Improved drainage systems on field and the use of PAT (Prescription Athletic Turf) has made artificial turf less necessary. PAT uses a system where there is a layer of sand below the grass and topsoil to help drainage.
During the World Cup in 1998, the organizers brought in specially grown grass into the Pontiac Silverdome since under FIFA regulations, the World Cup has to be played on grass. However, the grass system was very expensive and it had to be trucked in and out as needed and was pieced together before each match.
The Dallas Cowboys have contemplated such a setup for Texas Stadium, but I’m sure that Jerry Jones would rather just have a whole new stadium.
What we’ve always found funny here in my state is Michigan State University’s Spartan Stadium.
MSU is renowned nation- and worldwide for its agricultural and turf (such as golf course grass) programs. And their football stadium has artificial turf.
I guess they are in the process now of finally converting it to grass.
Yeah, just ask any Seahawk Fan: Springs To Miss Opener
The Answer: Field Turf!