Alexander Pensky wrote:

I have an azalea in front of the house which is in its 4th season
after being purchased in a gallon pot, and it has never bloomed.
Each year it puts out new leaves and grows a bit larger, but no
flower buds. I don't know the exact cultivar but it is one of
the deciduous ones with a very open habit and peach-colored
blossoms (well, they would be, if any ever appeared). It is
on the southwest side of the house, Zone 5-6 (Northern Ohio),
gets about 3-4 hours of sun a day, and gets no special treatment
other than watering and very infrequent fertilization.

There is another azalea next to it, planted at the same
time, which is blooming OK. It is a "Hershey" red, one of the
boxwood-like evergreen ones.

Do azaleas need to establish for a few years before they begin
to bloom? Or is mine unhappy about something (soil pH, light
exposure, etc.)

This could be one of 3 distinct problems:
1) Bud Blast, 2) No Buds, or 3) Buds Dying.

1) BUD BLAST is a symptom of the fungal disease Pycnostysanus, but may
also be caused by a late frost or application of a nitrogen containing
fertilizer too late in the season which prevents the buds from hardening
off. In all cases the buds turn brown or black. If it is a Pycnostysanus
infection, the dead bud will be covered with short hair-like structures.
Pycnostysanus is best controlled by sanitation, but may be reduced by
spraying buds with fungicide. Avoid application of nitrogen after late
spring, but phosphorus and potassium may be applied throughout the
growing season.

2) 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.
* Variety. Some plants will never bloom. Some rhododendron that come
from the seed of a hybrid plant will look good butwill never produce
flowers or will produce very poor flowers. To come true to the parent
plant, a hybrid may be propagated by cuttings or tissue culture but not
from seed. A good hybrid seedling only comes about once in a while. For
that reason it is important to know that you are getting a good named
variety or a good species.
* 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.
* Age. Most rhododendron take 2 to 3 years to bloom from a rooted
cutting unless forced. Some take longer and some bloom sooner. From
seeds the plant may take 1 or 2 additional years.
* Exposure. Some rhododendron 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 more foliage and less flowers.
* Inspection. You can usually tell if the plant has ever bloomed. A
rhododendron that has bloomed will have the seed pods on it unless it
has been dead-headed. If dead-headed too late after blooming, new flower
buds can be damaged.

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

3) 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 set. The buds could be foliage buds rather than flower buds. In
this case check the previous section about flower buds not setting.
* Bud blast. Plants which are not sufficiently hardened off or are
exposed to unseasonal 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. Also, disease may attack
the buds before they open.
* Low temperatures. The buds could be flower buds that froze during the
winter. Cold climates are 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.
* 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) is the best chemical 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
rhododendron 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.

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