It's not unusual for rhododendrons to spend their first year in the ground developing a root system and adding to the framework instead of flowering...the buds that were on your plants last year and bloomed were produced in nursery conditions the previous year.

So, be patient...if the foliage looks healthy there is nothing you need to do. They will of course appreciate an organic mulch over their root zones to slowly feed and condition the soil, and regular water.

If later you find you have a problem with flowering, the most common reasons are too much shade, overfertilization (produces foliage not flower buds), drought in summer when they would be setting their buds for the following year, or...it's sounds like you already knew that failure to deadhead can produce sparse flowering every other year.