I have two Nerium Oleanders that are growing in containers. The leaves are yellow and there has been pretty much no growth for the last two years. In 2008-2009 the plant was damaged by heavy snowfalls and blizzards that occured almost daily for 2 months. A few branches were snapped off and since then the plants haven't really recovered. In summer most of the flowers are brown and many buds fall off.
They might be really rootbound if they haven't been repotted in years.
They have only been in those containers for three years. I will replant them in a few days since the pots are very, very old. I also fertilized them today with a NPK 10-7-14 fertilizer. Perhaps my Oleanders don't receive enough sun (in summer they recieve no more than 3-4 hours of sun and no sun in winter because of the mountains)
They would be happier in full sun, but I don't think that's the only thing going on. Three years is plenty of time for something to get really rootbound so I still suspect that could be a problem. At the very least some fresh potting mix would be good for them--salts from fertilizers and hard water tend to build up over time and that could also cause some of the problems you're seeing.
