Well, first of all, it's about time you got used to the "non-english speaking labor" as you put it. Hispanic imigrants are here to stay and their numbers will only increase in the coming years. That's a fact. They do god quality work, work harder, are more reliable, and have better character than most of their American counterparts. So it's only natural that they are taking over certain industries and becoming fierce competition for you.
But let's forget about that for a minute and just address the issue of why you lost these jobs people said they'd hire you for.
Like others have said above, you should do the aerating ASAP as soon as the client says, "Go." If you can do it on the spot - DO IT! If not, do it the following day!
I must also agree that it may have been wiser to rent an aerator first until you had mastered the aerating business enough that you were constantly busy doing aerating and could warrant buying one. But I suppse it's too late for that. So I regress....
There are several successful aerating businesses in my area. All they do is just core aeration and de-thatching. And some of them make a pretty good living at it. I have a friend who owns one such company. Here's how they do it;
They have a guy who puts out a few hundred flyers (bright, neon color door hangers) every day with, "Neighborhood Aeration Tomorrow!" in big bold print at the top of the flyer. Then, below, the flyer says, "We'll be in the neighborhood aerating lawns tomorrow. The cost to aerate your front lawn only is $______. The cost for front AND back lawn is $______. If you'd like us to aerate your lawn, please leave this flyer, along with a check made out to AAA Aeration on your garage door tomorrow. We will come by and do the work before 5:00 p.m. tomorrow."
And that's it!
They typically aerate 20+ lawns per day with that method. Their prices are pretty cheap (half of what I charge for aerating). But when you line up 20 or more in one day, all in the same neighborhood, that's good, instant money!
So that's how the pros do it. Take it for what it's worth.