Rhododendron- failure to bloom

Asked April 6, 2019, 3:18 PM EDT

I have Rhodedendrons that are on the south side of the house. They get buds but never bloom. I have attached a copy of a bud that I’ve opened to determine if the buds are already frozen and won’t in fact bloom. Can you tell or help me with this question of Rhodedendron care and blooming. Thank you.

Ramsey County Minnesota

3 Responses

Thanks for the inquiry. It is not clear from your question whether or not your rhododendrons have ever bloomed or if this is a recent occurrence. Additionally, the picture you sent shows a rather mature bud together with well-formed leaves. Is this a picture from last year or is your rhododendron really that fully developed already this year?

The first thing to ascertain is if you have a rhododendron suited for your growing zone which is zone 4. The following describe different varieties of rhododendrons that should be planted in Minnesota:

https://www.gardenguides.com/104765-rhododendrons-minnesota.html

https://www.treestodaynursery.com/wp-content/uploads/2014/04/Azalea-Handout.pdf

The fact that you have observed buds suggests that something might be impeding their development to flowering. If by chance the picture you sent was of a bud from last year when we had some very cold temperatures in April, I suspect that full development of the bud was arrested by those cold temperatures. This would especially be the case if your rhododendron variety was an early bloomer.

There are various types of blight (fungal) diseases that can diminish the blooming abilities of rhododendrons. The following will describe these together with some remedial actions:

https://www.gardenguides.com/108135-rhododendron-blight.html

Finally, this will provide you some general information about rhododendrons and blooming:

https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/rhododendron-not-blooming.htm

Bottom line: if your picture showed a bud from last season, then flower development was probably halted by cold temperatures and frost. Again if this picture was from last year, I would just wait and see what develops on your Rhodie this year.

Good luck!!

Thanks Steve. Sorry for my less than clear question. My Rhodadendrons are about 5 years old. They have never bloomed with the exception of last year I get a very fragile 1 day bloom- 1 flower from 3 plants!

the picture I sent you is of the bud that is showing right now. These buds were formed last fall. The picture of the inside of the bud suggests to me that the bud is dead. Is this correct?

So this is the second year that I have well defined buds (formed The prior fall) that I’m not optimistic will bloom.

Does that help? And thank you for the resources.
the prior year) and last spring no flowering.


Thanks for getting back to us. The information that you provided clearly sharpens my thinking about your rhododendrons. The fact that over the five years that you have had your rhododendrons there has never been good flowering would rule out the cold temperatures of April 2018 as the only factor though such temperatures certainly did not help matters. I now suspect that one or more of the following may be causes:

1). You have a variety of plant that is not suitable for growth and flowering in Minnesota. If you can determine the exact variety you have, you should be able to Goggle it and ascertain its climate requirements. If it turns out that what you have is not suited for growing zones 4 and higher, then your best course of action should be removal and replacement. Here are some rhodies that do grow well and flower in Minnesota:

https://www.gardenia.net/guide/Azaleas-and-Rhododendrons-for-The-Midwest

2). The soil conditions are not suitable for your plants. Rhododendrons require soils high in organic matter with a rather low pH (between 5.5 and 6). Moreover, the soil should be moist but well-drained. Avoid adding an excess of fertilizer, especially one having a high nitrogen content. The nitrogen will promote leaf growth at the expense of developing flowers. Elevated nitrogen levels might still allow for flower buds to form but prevent their full maturation. It appears that this may be happening to your plants. If you really want to get serious about things, a soil analysis of the soil around your rhododendrons is highly recommended. The following will give some information about these things:

https://www.rhododendron.org/v46n2p77.htm

https://homeguides.sfgate.com/make-soil-acidic-rhododendrons-93095.html

http://soiltest.cfans.umn.edu/testing-services

If you do opt for the soil testing, we would be glad to help you in the interpretation of the results should you wish.

3). Although rhododendrons typically need relatively little pruning, if you have been pruning your rhodies perhaps you have been doing this too late in the season? Rhododendrons develop flower buds on "old wood" as you probably know. If pruning had been done in 2018 after 2019 flower buds had formed, then this would lead to reduced blooming in 2019. Here are a couple of references about pruning:

https://www.gardeningknowhow.com/ornamental/shrubs/rhododendron/pruning-rhododendrons.htm

http://www.harvestpower.com/best-time-prune-azaleas-rhododendrons/

Good luck; happy spring!!