Rhododendron won't bloom

vbellomoDecember 14, 2007

Does anyone have any ideas why my rhodie won't bloom????? I purchased in summer 06 and summer 07, nothing came up at all. When I purchased ithad many, many blooms on it. that was in August. What am I doing wrong????


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rhodyman(SE PA, USDA Z6)

There are two distince possibilities, no flower buds are set or flower buds are set and they don't produce flowers.

1) Failure to set flower buds may be a sign of too much health and vigor in a plant. One solution my be to prune the roots by cutting around the plant with a spade or moving the plant. This will check foliage growth and encourage production of flower buds. Application of nitrogen rich fertilizers are the main cause of vigor which suppresses flower bud production. Deadheading flowers as soon as they wilt can promote flower bud production. Too much shade, a cool wet summer, or inadequate phosphorus or potassium in the soil may also suppress flower bud production. There are a number of other reasons for a lack of flowers. The effect of each variable depends upon the variety of the plant. The effects include:

* Pruning. The buds are formed in late summer and early fall so pruning then or later is not advisable since it will remove flower buds. New leaf buds will form in the spring, but new flower buds won't form until the next year.

* Fertilizing. Nitrogen promotes leaf and branch growth and discourages flower bud production. It can also force late season growth that gets killed or stunted by frost damage. Phosphorus promotes flower bud production and hardiness. Potassium is necessary for well being.

* Weather. Cold weather can kill flower buds. Usually you see the brown buds in the spring. Cold spells in the fall or spring can damage buds that are not hardened off. Bud blast (blooming in fall or winter) uses up good buds which are then not available at the normal blooming time.

* Sun & Shade. Some rhododendrons need full sun to bloom and others can take fairly dense shade. In general, the more sun the more flower buds but also the greater exposure to damage from desiccation in summer or winter. More shade produces tall spindly foliage and less flowers.

There are many other cultural variables that influence the plant's health and hence, its ability to produce flowers.

2) Failure of flower buds to open could be due to a number of reasons. On a mature plant if they ever bloomed they will have a few of the seed pods still here and there. If you can't find any old seed pods, then they may have never bloomed. In any case, here are a few suggestions that may help:

* Bud blast. Disease may attack the buds before they open. If it is a fungal infection, the dead bud will be covered with short hair-like structures.

* Bud set. The buds could be foliage buds rather than flower buds. In this case check the previous section about flower buds not setting.

* Fall Blooming. Some causes of fall blooming include a dry summer and moist fall and/or warmer climates including a warm fall. For some reason, fall blooming is more common in Georgia according to Dr. Sandra McDonald. Plants which are not sufficiently hardened off or are exposed to unseasonable warm spells can start bloom prematurely. These blooms are seldom satisfactory and many times get frozen before opening fully. In any case, the seasonal bloom is lost. Avoid application of nitrogen after late spring, but phosphorus and potassium may be applied throughout the growing season. Application of nitrogen too late in the season can hinder hardening off in the fall.

* Low temperatures. The buds could be flower buds that froze. Early frosts are especially destructive. Plants harden off progressively in the fall. If a frost occurs before hardening is complete, the frost can kill flower buds. Late frosts in the spring after dormancy is broken is also a problem. This is especially true of early bloomers such as PJM that break dormancy very early. Cold climates may be too cold for many rhododendrons. Most rhododendrons have a low temperature at which the flower buds are damaged and will not produce flowers. It varies greatly from variety to variety and somewhat from season to season. Flower buds can also be damaged by cold, dry winds, particularly when warm winter weather is followed by a period of bitter cold.

* Nutrients. Improper nutrients my be a problem that affects cold hardiness and flower bud set. A few things you can do are to fertilize with phosphorus (super-phosphate) per directions to increase hardiness and flower bud set. This can be done any time. Do not use nitrogen rich fertilizers as they may inhibit flower bud production and also reduce cold hardiness. Lawn fertilizers are notoriously high in nitrogen and should be kept away from flowering plants.

* Acidity. Measure the pH and acidify if necessary. Flowers of sulfur (powdered sulfur) or iron sulfate are the best chemicals to use to increase the acidity [lower the pH]. Do not use aluminum sulfate since aluminum salts build up in the soil and eventually becomes toxic to many plants including rhododendrons and azaleas. If soil is too acid, the symptoms can be the same. Very acidic soil can prevent the roots from taking up nutrients. As many of my rhododendrons are planted in very acidic forest soil, an application of Dolomite and a light topdressing of mushroom manure in late spring is all they need. Sprinkle the lime on in late winter, very early spring. Don't overdo it - just a light sprinkle. If it is mid-spring, get the lime on right away so the rhododendron roots will be able to take up the soil nutrients in time for new growth. If you don't have rain, water it in well.

* Protection. If the plants are wrapped in burlap during the winter, they may gain a few more degrees in hardiness.

* Drought. When soil moisture is too low, the buds will not open. Watering will usually resolve this condition if detected soon enough. Also, summer drought with a moist fall can contribute to fall blooming.

* Deer Damage. Deer and rabbits may eat many of the flower buds as they browse in the winter, particularly if the weather is harsh and other food is scarce.

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

    Bookmark   December 14, 2007 at 4:29PM
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I have noticed almost without fail that a rhody purchased and planted when full of blooms will produce exactly nada (OK maybe one or two) the following year. My guess is that the rhody does not produce flower buds when adjusting to its new surroundings. Indeed sometimes it takes two springs for the plant to bloom again but usually after missing out on one years spring flowers you should be A OK.

    Bookmark   January 16, 2008 at 12:25PM
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rhodyman(SE PA, USDA Z6)

That is sometimes because they use a lot of fertilizer in greenhouses after the buds are set to force lots of growth. This fertilizer inhibits bud set the following year. I get all of my plants from friends and local nurseries where they don't overdo the fertilizer and I never see this problem.

    Bookmark   January 16, 2008 at 1:48PM
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my rhodo is 3m tall. the buds are small and lots of them are blackish

    Bookmark   April 27, 2011 at 2:25PM
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luis_pr(7b/8a Hurst, TX)

It sounds like the shrub got stressed for some reason and aborted some of them. While I would be tempted to prune them, I would just let them be. After the blooming period is over & all the ones that could bloom bloomed, you can prune any stragglers left in the plant.

In the meantime keep the soil moist, not wet; maintain 3-4" of mulch; do not overwater; do not fertilize now as the plant seems to be stressed; check for fungal infections and insects; and hope there is no bad weather with wildly fluctuating temperatures.

    Bookmark   April 28, 2011 at 3:16AM
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rhodyman(SE PA, USDA Z6)

If there is some green, the bud is still viable and should be left.

If the bud is brown or black and covered with hair like structures, it is diseased and should be removed and destroyed.

If the bud is brown but not hair like structures on it, it is frost damaged and can be left or removed.

When removing buds, try not to damage the new growth that is just coming out, or the buds at the base of the flower buds that will be the new growth.

    Bookmark   April 28, 2011 at 12:43PM
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