(Lucy) wrote:
I moved into a home with previously planted george tabor rhodendrons,
I have been here through last fall, winter, spring, and still no
blooms yet. They are planted underneath a stand of oak trees and get
afternoon sun. Any suggestions?
Too much shade or too much fertilizer. Or possibly the previous owner
pruned the azaleas in mid summer and cut off all the flower buds. That
is highly likely since they may have done the pruning to enhance the
appearance of the property to help sell it.
These are the two possibilities.
1) the plants aren't setting flower buds
2) they are setting flower buds, but the flower buds aren't surviving.
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:
* 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.
* 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.
* Pruning. The buds are formed in mid summer to 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 rhododendrons that
come from the seed of a hybrid plant will look good but will 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.
* 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 rhododendrons 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.
* 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.
* 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.
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 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 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. 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. 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.
* 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.
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