Quote -
"it is supposed to make juice that tastes like cherries"

Well, many wine snobs like to think that they "get cherries in the nose" (and I more or less agree with them), but they're talking about the wine. You'll have to decide for yourself concerning the juice. Since I must have picked Foch some time in the past 25 years, I must have tasted it (I'm an irrepressible taster). However, I have no recollection of having ever tasted a grape that really made me think 'cherry'. I guess I'll just have to make a point of tasting some this fall. Maybe you'd like to remind me around the first of Sept.?
Anyway, a 3 year old plant in OK (even if neglected) has probably established at least a modest amount of roots. Keep as big an area around the vine as weed free as you can (minimun 4' dia., point of diminishing returns probably reached at 8' to 10'dia.). By 'weed free' I mean
no other plants, including grass. Keep it adequately watered (1" to 1.5" of
deep watering per week, natural and/or artificial), and, if you don't have 12" to 18" of new growth by mid June, give it a moderate shot of N.
If you have even a half dozen or so buds that were exposed to sunlight last summer, you're likely to have some fruit to taste this fall.
How big is your vine?