It would be very helpful to know the specific varieties of rhododendrons involved. Equally important would be their size when planted. Some general observations:

Rhododendron flowering is increased, not decreased by sun exposure. In Z9 especially, that does not mean full all day exposure. Morning sun with afternoon shade would be ideal.

Small young rhododendron plants do, in my experience, benefit from a suitable fertilizer such as Hollytone. If well mulched, larger established rhododendrons do not usually require fertilizer unless a need is indicated by a soil test. The fact that your plants are not growing much may indicate a nutritional deficiency.

Compost can vary so much in compostion, pH, etc. , it's very difficult to generalize. Best mulches for rhododendrons are conifer bark, conifer needles, wood chips - any material that breaks down slowly and contributes to soil acidity. Many composts are too high in nitrogen and too alkaline for rhododendrons. The first seems unlikely in your case since growth is slow.

Most rhododendrons are relatively slow growers. A single flush of growth per year is typical so yours may be doing as well as you could expect.

I live in Southern California and purchased a Rhodie last April. It seems to be doing fine, it's in a pot and is approximately 2 or 3 ft tall. It does not get any sun at all, but very bright light in the afternoon. so here are my questions: 1) how much water so they like, 2) how do they survive in winter? I am from the Pacific Northwest and our neighbors had a beautiful Rhodie, and it seemed to thrive during the winter months when it snowed. Do they like a cold winter and if so, should I put ice around the base during the winter time?

Thanks

Barbra

As with the original post, it's very hard to help without knowing the specific variety of rhododendron you have. So...

In general, rhododendrons want/need an evenly moist but not wet planting medium. In a hot climate like yours, it is much better to err on the side of dryness because wet soil and high temperatures encourage root rot infections.

There are rhododendrons which can withstand winter tempatures of 25 or 30 degrees below zero and others which cannot cope with anything below freezing. If you purchased your rhododendron locally, it's possible that it is one of the latter. There's no way of telling without a name, though.

Barbara,

You don't need ice in the winter but may in the summer. The roots don't like hot wet conditions. Only a few varieties will withstand hot conditions and none like wet conditions. Actually ice in the summer would be a bad idea because it would make the soil too moist. The most important thing is that the container is well drained, It must have holes in the bottom. Second, only water when the soil begins to get on the dry side. Then water thoroughly, assuming you have a well drained planting material and a container with drain holes. Placing in the shade is a good thing, but depending upon the variety, it may not bloom. In the Pacific Northwest, the plants bloomed in the spring and then formed the next year's buds during the summer. In Southern California, your plant may behave like a house plant and loose track of the seasons. Good Luck!

In California it could even be a Vireya or other epiphytic type that needs to be managed almost like an orchid, with the potting medium being kept very well aerated a critical point. As well as being careful about watering with hard water or subjecting the plant to high temperatures in combination with direct sun exposure, low humidity.