Answer: If your hydrangea has not flowered in 15 years, there's not much hope of it ever flowering. Not because you're not keeping it healthy but because it is probably a big leaf hydrangea (hydrangea macrophylla) and big leaf hydrangeas flower on new shoots which develop on old wood. So, if your hydrangea always freezes down to ground level (which I suspect it does in Rhode Island), all the the old wood will die out so there won't be any old wood for which new flowering shoots can develop. There's nothing you can do to get your hydrangea to flower - it's just the wrong type for your climate. There are several hydrangeas that bloom on both old and new wood so it doesn't matter if they freeze down to ground level every winter. If you want to replace your hydrangea, look for 'Endless Summer'.
Best wishes with your landscape!
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