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Rhododendron fragrantissimum/no buds?

Posted by wobur 7/8 CA Sierras (My Page) on
Tue, Oct 16, 07 at 6:51

Would my R. fragrantissimum have buds by now if it was going to bloom in the spring? I am trying to decide whether or not I need to move it. Thanks!


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RE: Rhododendron fragrantissimum/no buds?

Definitely, it would have buds now. At this point in time it is difficult to tell whether buds are going to be foliage buds or flower buds. The flower buds usually do not start swelling up until early spring.

If a rhododendron is not producing flower buds, it can be a number of problems. Typically, the two most common problems are not enough sun or the wrong nutrients.

Most rhododendrons like "high shade". Hence, if the shade is caused by trees, removing the lower branches of the trees is a good solution. Of course, if the tree is like a Norway Maple, then moving is the only solution.

Fertilizing or not fertilizing can both be problems. Too much 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. Phosphorus can be applied anytime and is slow to reach the roots. So it is good to apply phosphate fertilizers now for next spring. Potassium is necessary for well being. Of course, the soil needs to be acidic for the fertilizers to do any good.

Good Luck!

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


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RE: Rhododendron fragrantissimum/no buds?

  • Posted by wobur 7/8 CA Sierras (My Page) on
    Tue, Oct 16, 07 at 19:28

Great info and link. I have pruned the tree branches of the overhanging Liquid Amber every year for three years thinking it may need more light. This summer it suffered some sunburn on about 5% of it's leaves, so I have thinned enough! My other Rhody and my azaleas all bloom and thrive and all have nice green leaves, including the R. frag. I do give them all a healthy dose of homemade finished compost twice a year, but otherwise haven't fertilized. And they are mulched additionally with pine needles. The growth seems healthy and not excessive, but something obviously isn't working. Maybe more research on ferts is in order. I will look into the phosphorous and potassium as you suggest. Thanks Rhodyman! I sure do love my R. f. when it blooms...or I think I did... Wobur ;-]


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RE: Rhododendron fragrantissimum/no buds?

  • Posted by bboy z8 WA USA (My Page) on
    Fri, Oct 19, 07 at 11:54

Sample soil and have it tested before fertilizing much, beware of overdoing phosphorus in particular. 'Fragrantissimum' (it is a hybrid cultivar, rather than a species R. fragrantissimum) is rated hardy to about something like 15F, wonder if you are actually having flower buds form some years and then freeze out - without the plant being damaged. (This does happen with other rhododendrons). This cultivar should bud pretty readily.


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RE: Rhododendron fragrantissimum/no buds?

Bboy, I am very surprised at your recommendation. Rhododendrons require phosphorus, as well as nitrogen, and adequate sunlight to produce flower buds. Not always understood is the length of time required for phosphorus to reach the root system and be taken up by the plant. As long as six months may be necessary for this process. Rhododendrons which have formed few, if any, flower buds by fall should receive an application of granular phosphate some time during the winter to assure flower bud development during the following summer months. No need to be concerned about applying too much; a rhododendron is not a phosphorus glutton. It will feed on no more than required.


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RE: Rhododendron fragrantissimum/no buds?

  • Posted by bboy z8 WA USA (My Page) on
    Sat, Oct 20, 07 at 22:06

If rhododendrons have an internal barrier to uptake of excess phosphorus then that occurrence alone wouldn't be a concern. Otherwise

"Phosphorus is used in the plant in several ways. However, the high energy organic complexes, ATP (Adenosine triphosphate) and ADP (adenosine diphosphate), provide the energy for several chemical reactions within the plant. A phosphorus deficiency, even though very mild, will reduce this energy transfer system and slow growth functions of the plant. It is therefore very important to supply the proper amount of phosphorus. However, excess phosphorus is equally detrimental to plant growth. Excess phosphorus combines with calcium, iron and other micronutrients to form insoluble complexes of these elements. Thus, excess phosphorus generally is observed as stunting and deficiencies of several micronutrients. Phosphorus is normally found in plant tissues at only about one-tenth to one-eighth the level of nitrogen, comprising 0.14 percent to 0.32 percent of the dry weight of leaves."

--Establishment and Maintenance of Landscape Plants, Carl E. Whitcomb

Things seldom happen in isolation, piling it on might have other deleterious effects besides poisoning the rhododendron directly.

"If phosphorus levels are too high, however, the roots do not exude the organic acids and mycorrhizal
connections do not form. This forces the plant to put more resources into root growth to compensate for
the lack of mycorrhizae. So in a sense phosphorus will increase root growth but at an added cost to the
plant. The resources expended by the plant in growing additional roots to take the place of mycorrhizae
are not available for other plant needs.
Shrub and tree species that are mycorrhizae-dependent have a difficult time surviving in soils where
mycorrhizae cannot develop. In particular, seedlings and newly transplanted materials are less efficient in
absorbing water and minerals from the soil and are more likely to suffer transplant shock than plants
where mycorrhizae are present. Adding mycorrhizal spores to soils where phosphorus is too high is
ineffective the spores will remain dormant"

Here is a link that might be useful: The Myth of Beneficial Bone Meal


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RE: Rhododendron fragrantissimum/no buds?

  • Posted by wobur 8 CA Sierras (My Page) on
    Sun, Oct 28, 07 at 9:01

Thanks for the suggestons bboy, and Rhodyman and the interesting discussion.

The low 20's is as cold as it has gotten since I have lived here, and that is fairly unusual. A USDA site puts me in zone 7 or 8, but another one says 8 or 9, which makes more sense, I think. We do have very hot summers....90's and about 10 days over 100, but that doesn't seem to bother my other Rhody and 3 azalias. Maybe I just need to keep my fingers crossed more and I will reevaluate the fertilizer, which as I said has been just top dressings of compost. Thanks again! Wobur


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RE: Rhododendron fragrantissimum/no buds?

  • Posted by morz8 Z8 Wa coast (My Page) on
    Sun, Oct 28, 07 at 12:13

Wobur, you might consider winter protection for your R fragrantissimum if your plant looks healthy otherwise and see if that makes a difference. As bboy pointed out, it's buds are less cold tolerant than most and icy winter winds, overnight drops in temp could be affecting it and not others.


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