My old Rhodie has less blooms

seattlelisaApril 18, 2011

I have an old Rhodie, 50-60 years old I'd guess, which has bloomed spectacularly for the last 10 years (when we bought the house), but this year has only a scattering of flowers, mostly in a band running across the top from North to South, and on the South facing side. The East side, which faces the house is just empty. The leaves seem to be fewer also. The plant is a great big ball shape naturally, well over 8X8 feet, and I think that that is why it escaped much pruning by the former owners. They seem to have loved shrubs trimmed into ball shapes, even forsythia and ribes.

I've never done much for it, though the lawn it used to be next to has been replaced by vegetable beds. I don't fertilize. I've mulched the veggies quite heavily with compost and chips, but not under the rhodie. I leave the fallen leaves where they are.

We are in Seattle, which generally has mild winters and fine summers. Last summer was very chilly though, even in August really. This winter had an unseasonable cold snap fairly late also. However, I don't see any dead buds, just a lack of buds.

Was it just the weather? Or have I been cultivating too close to it? I've really tried to avail the area under the branches.

Thanks for your help!

Lisa

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rhodyman(SE PA, USDA Z6)

Hi Lisa,

Sounds like a great plant.

Rhododendrons need sunny days in the summer, usually the early summer, to set flower buds. I am on the East Coast and in 2009 we had very cloudy, gloomy weather most of the summer. In 2010 many of our rhododendrons had poor bud set because of this. Hopefully that is what it is and most future seasons will be much better.

However, if that is not what it is, then here are some ideas:

If you had seen buds that didn't open:

If there were, then if they looked sort of hairy on the outside, it would be a disease problem and they should be picked off and destroyed so it doesn't spread.

If there were, and they were not hairy but had some flower pedals coming out that died, then it would be partial bloom that was frozen back.

If there were and they were still closed and dead, then it would be frost damage.

Since there aren't any flower buds, dead for alive, then it most likely is one of 3
things:

1) too much shade, 2) too much fertilizer, or lawn fertilizer, or fertilizing
too late in the year, or 3) pruning to long after they bloom.

Fertilizer, if used at all, should only be used around bloom time and then it should be a good azalea food like HollyTone and applied once at half the rate on the package. Since you don't fertilize, fertilizing may help.

Pruning should be done soon after blooming. The new flower buds form in mid summer.

Most azaleas need some sun to form new flower buds.

One more thing, never cultivate under the rhododendron. They have shallow roots which extend out to the drip line and even beyond. The drip line is the area where a shadow would be if the sun was directly overhead. Cultivating will damage these shallow roots.

Make sure the soil is acidic. Usually if the leaves are nice and green, the soil is OK. If the leaves are yellowish with green veins, then you probably need to acidify the soil. Test to make sure. If you do, then use powdered sulfur to increase the acidity, never use Aluminum Sulfate. It kills rhododendrons.

Steve Henning, Reading, PA USA 6

Here is a link that might be useful: How to care for rhododendrons and azaleas.

    Bookmark   April 18, 2011 at 3:00PM
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seattlelisa

Thanks.

The plant looks fine, and I don't see any evidence or damage or disease. I think I'm just going to assume the problem was that lousy cold summer last year. Seattle is really rhododendron country. There are a lot here, and no one seems to need to do much for them. Our soil suits them, and I've never heard of one getting diseased. Once they are established, they'll survive real neglect. I know of many which are never watered, fed, or pruned, and they just go on. That's why I've been so baffled by the lack of blooms. I think your idea about lack of sun must be right. Last spring and summer were just dark and cold. This spring has been cold too, for us, but not so dark --thank goodness.

Thanks again,

Lisa

    Bookmark   April 19, 2011 at 5:30PM
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Embothrium(USDA 8 Sunset 5 WA)

The default mode for soil here is acidic, if anything often too acidic. The common problem causing reduction in leaf coverage etc. is powdery mildew. This varies in severity from one kind of rhododendron to the next, even within the same planting. After the killer 1990 winter many here assumed the gauntness they were seeing in their rhododendrons was cold damage, when in fact it was powdery mildew - new to the general landscape in this area at that time.

Now it is ubiquitous. Look at the undersides of the leaves, I would be surprised if this is not all or at least part of the problem. Infested plants have reddish spots and blotches, badly infested plants have a dustiness to the leaf undersides and drop many leaves prematurely.

Upon close inspection, as with magnifying lens in hand the dustiness can be seen to be a fungal coating.

The most susceptible varieties may be killed in time. I am currently losing two 'Vulcan' planted here in the 1960s. A 'Unique' that was well above head height went to pot some years ago. Three 'Virginia Richards', that had been producing flower trusses the size of basketballs were turned to sticks within a few years of becoming infested. 'Cynthia' was also spoiled.

    Bookmark   April 20, 2011 at 12:03PM
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