It's most likely not getting enough sun. Rhododendrons need partial sun to bloom and I don't think it's getting enough sun. It's sun is blocked by the tree, the other taller plants and that wall behind it. Pruning it will just make it worse. You can, transplant it to a more sunny location. Not full on sun all day, but morning/evening sun or dappled sun - like under a tree; move that azalea in front of it; prune the surrounding plants/shrubs to give it more access to better light.

Also, the ground should be kept evenly moist and that tall tree is sucking up all the water. Rhodies need lots of water to support the flowers or they will abort.

Hello,

Thanks for the reply.

I don't think that lack of sun is the issue. The tree in question is/was a hawthorn, and when I moved in 10 years ago it was quite large and shaded the whole bed. A few years back it got some kind of disease and died. I cut most of the dead branches off, so now there's just a trunk and a a couple of main branches with ivy on them. There's far more light now than there used to be.

[edit: I've replaced one of the photos with a wider view so that you can see what I mean]

Also, the ones I'm thinking of pruning are the biggest plants that are blocking some of the light from the ones below that do flower!

Being dead, the tree you can see in the photo is not sucking up any water at all! On which note, there also used to be a lime tree the other side of the fence that's been cut down, so overall they must be getting more water than previously.

Piers.

Wow, so it gets sufficient light & water yet it doesn't bloom?
Do you know what kind it is? Not all varieties will bloom every year. It looks like a healthy bush, but if you don't like it, replace it with something else. I'm curious now. Did you give it fertilizer? That would kill the blooms too.

You could try watering it with a high potash fertilizer to encourage flower formation. Don't use a high nitrogen one of you'll get leaves at the expense of flowers.. Or you could try one specifically designed for ericaceous lovers, though judging by the colour of the leavers acidity doesn't look like a problem..
I think hard pruning would be a mistake and further prolong your flowerless period. Most mature rhododendrons grow considerably bigger than yours eventually so you could consider replacing it with a variety you know is a smaller one or with an azalea.

I have 3 rhododendrens, each blooms at a different time, but they all give quite a show. I don't do anything special with them - partial sun & give them a drink during a dry spell, but we get plenty of rain, no fertilizer. They don't need it and are quite happy.

Hello,

I don't know what any of the varieties are, as they were planted by the previous occupants of my flat (before 2007). There were originally 6 rhododendrons and (I think) 3 azaleas. One of the azaleas died a while back, and one of the rhododendrons about 3 years ago.

I've been taking photos throughout the year of my garden, but only regularly since 2014. The rhododendron nearest my windows certainly hasn't flowered in that period, and I suspect another hasn't either. The difficulty I have is that the plants have grown through each other, so short of getting right into the bed at ground level (a mass of ivy) it's hard to see which flowers come off which plant.

I could wait till May when the ones that flower will be out, but I'm pretty sure one, if not two, of the plants won't, and in the mean time they're completely blocking my view of the camelia at the rear of the bed.

Steragram, you say hard pruning could prolong the flowerless period. Do some rhododendrons not flower until they've reach full size? That is, does it need to be left to do its own thing for some unspecified number of years before it'll flower at all?

If that's the case, then it's clearly the wrong plant for a small garden, by the time it starts earning its keep it would be way too big. If it should have been flowering all along, then there's something wrong. I can try your suggestion of high potash fertiliser, but either way I think it needs cutting back.

That is, if it'll only flower when huge, it needs to go, and if it'll flower at any size it won't be a problem (in the long run) being cut down to size...?

Thanks for the continuing advice,

Piers.

P.S. What's the right time of year to apply the high potash fertiliser to get more flowers?

Well if you want to try it spring is the best time, but its a last resort as they don't usually need it.
Size shouldn't be an issue, its quite big enough. Its hard to see the buds close up but they don't really look fat enough to be flower buds - I'd love to be wrong...

Hello again,

Just to confirm, when you say 'spring is the best time' I'm assuming you're referring to pruning, rather than when to apply high potash fertiliser?

If so, is there a right time of year to do the latter?

Piers.

No I meant spring for the potash. Pruning would normally be done straight after flowering (or when it should have been...) Even if the rhodie you're asking about does flower it will still be blocking the view of the Camellia won't it? Sounds as those this border was planted by somebody who didn't allow for size at maturity - very common mistake and very easy to do. I think I'd get rid and plant something that won't get too big so you can still see the Camellia.

I just wanted to point out that rhododendrons will set their buds in June for the following Spring. So if you have pruned them anytime after June, you've cut off the flower buds for the following Spring.

OK, so would I be right in thinking that if I added the fertiliser now, it would be to encourage bud formation over the summer for next year, and that it's too late to influence this spring's show?

It's too late to influence this Spring as you said. I would skip the fertilizer altogether. Except for the occasional wayward branch, they don't need pruning at all.