There are hundreds of Rhododendron varieties on the market, so we can't include an exhaustive list, but can share a few ideas for those that mature short that might be locally available. For example, cultivars of the species Rhododendron degronianum ssp. yakushimanum, usually just referred to as "yak" types/hybrids for short, tend to stay compact.

No plant ever stops growing at a given size, but cultivars that are supposed to mature in the 3-foot range (at least in the next 10 years or so) include those below. Bear in mind, however, that they will almost always grow wider than tall, since that's the natural shape for low-growing rhododendron.

• 'Amity'
• 'April Snow'
• 'Baden Baden'
• 'Barmstedt'
• 'Black Satin'
• 'Bubblegum'
• 'Capistrano'
• 'Chionoides'
• 'Crete'
• 'Doc'
• 'Dora Amateis'
• 'Elmer's Orphan'
• 'Fantastica'
• 'Firestorm'
• 'Fred Peste'
• 'Ginny Gee' (looks almost like an azalea due to smaller leaves and blooms); 'Mary Fleming' is similar
• 'Hachmann's Polaris'
• 'Holden'
• 'Hoppy'
• 'Ingrid Mehlquist'
• 'Landmark'
• 'Lemon Dream'
• 'Mardi Gras'
• 'Midnight Ruby'
• 'Minnetonka'
• 'Northern Starburst'
• 'Olga Mezitt'
• 'Percy Wiseman'
• 'PJM Compact'
• 'Pohjola's Daughter'
• 'Skookum'
• 'Sugar Puff' (also looks a bit like an azalea)
• 'Teddy Bear'
• 'Yaku Prince'
• 'Yaku Princess'

Drainage can vary in fairly short distances, so even if other rhododendron are growing well nearby, there still could be conditions in a nearby spot that don't suit the plants. Foundation plantings often don't suit rhododendron for the long term, but that will depend in drainage (they do not tolerate consistent wetness or poor drainage, so watch out for roof downspout outlets) and if the soil becomes alkaline due to any leaching from the foundation, since acidic conditions are necessary for rhodos to thrive.

If you aren't familiar with this trait, be aware that "yak" type Rhododendrons normally have a fuzzy coating on the young leaves emerging each spring, which wears off as the leaf reaches full size and matures. (Some retain a fuzz coating on the leaf underside, some don't.) This might look like a gray or bronze-colored fungal/moldy layer to gardeners if they're not accustomed to it, but rest assured it's normal and supposed to be there. (And it can be a lovely seasonal trait to serve as aesthetic interest, since the flowers emerge late in the rhododendron flowering season.)

Miri