Rhododendron & Azalea News

Rhododendron and
Azalea News

Spring 2009 Vol. 12 No. 1

ARS Home Page R&A Index People and Events Gardens Ideas for Chapters

Plant Tips
Dear Dr. Rhody...root rot...	Dear Dr. Rhody, Yes, we really need your help. We seem to have root problems in our rhodies. We have lost five in about five years. One every year and one of my favorites is beginning to roll its leaves...according to the web the first signs of the problem. On the web, it is called Phytophthora and they recommend drenching with fungicides...such as subdue, turban, or terrazole. Any idea who might carry this stuff? We originally took it to the extension office and he thought it was the fungus that affects the Port Orford cedars and said there was nothing we could do...but the web description sounds like what it happening with ours. Thanks. Vickie
no remedy for Phytophthora...	Dear Vicki, The conditions you describe could indeed be caused by Phytophthora root rot. Symptoms of the disease include: stunting yellowish-green leaves, branch dieback, wilting of, and eventually death of the plant. Once the plant dies the leaves hang on to the branches instead of falling off. If you inspect your plant's root systems, the roots will be destroyed (rotted) starting with the smallest roots and progressing to the larger ones.
destroy plant and some of soil around...	Once the plant acquires Phytophthora...there is no remedy. Remove and destroy the plant. Phytophthora can remain the soil...so removal of the nearby material may be necessary...if you wishes to plant in the location again. Certain varieties of rhododendrons are more resistant to the disease than others. Try to choose healthy, resistant plants.
weather conditions causing root rot...	Root rot seems to occur most often when the weather is very warm and the plant's root system get "soggy". Good drainage will definitely help present infection. Good gardening! - Dr. Rhody

Crash course in fertilizer nutrients...	The Pilchuck Chapter's newsletter, Pollinator, shared a few "crash" ideas for your spring gardening...specifically about fertilizer nutrients! A bag of fertilizer has three numbers prominently featured on the label...something like...5-2-0. It's important to know what those numbers mean...because the wrong combination can do more harm than good. The guaranteed analysis indicates the amount of three major plant nutrients: nitrogen, phosphorus, and potassium ...abbreviated NPK. One way to remember what those things do, and keep them straight is the phrase "up, down, and all around." Nitrogen is needed for green, leafy growth...the up. Phosphorus helps produce healthy roots...the down. Potassium is important for overall plant health and resistance to water or insect stresses, so it's...the all around. Plants need anywhere from 14 to 18 plant nutrients for best health and production. Magnesium and sulfur comprise the macronutrients along with NPK. The micronutrients include: iron, manganese, boron, zinc, copper, molybdenum, and maybe chlorine. Testing your soil is the way to determine what is needed.

Plants from containers	During the last fifteen to twenty years, the nursery industry has changed the way they grow and ship rhododendrons. Instead of in-ground growing, they have switched to growing the plants in containers with an artificial mix as a growing medium. This technique allows them to produce a saleable plant quickly, efficiently, and economically. There is only one problem...the gardener who purchases the plant in the Spring has a terrible time keeping it alive after he has planted it in his garden. Many containerized rhododendrons purchased in the Spring...do not survive.
reason for low survival...	Why? Because the mix in which the roots are growing in the container is so different from natural spoil. Water will not move into the root zone of the plant after it has been planted. When the gardener plants a containerized plant, he creates three different soils: the mix in which the plant is growing, the backfill, which should be made of a mixture of top soil and organic matter, and the great mass of exiting soil in the garden. Roots have not yet penetrated the backfill and capillary action does not carry water from the mass of garden soil to the root ball of the newly-planted rhododendron. Sprinkler and rainwater that falls outside of the root ball has not way to move to the roots because of the umbrella effects of the leaf canopy of the plant. Essentially, the plant has to survive on the moisture in the containerized mix. Most casual gardeners are not willing to do that. Most have not been told that it is necessary.
root balls need to be vigorously attacked...	In the Portland, Oregon, area it is best to plant rhododendrons in the Fall. Fall planting allows the plant to develop a good root system for the dry season coming the next summer. However, if improperly planted a good root system will not develop. Spring or autumn, the root ball of a container-grown plants needs to be vigorously attacked. Remove the plant from the pot and examine the roots. The extreme root ends should be white. Remove some of the outer layer. In the case of plants that have become pot-bound, the outer roots should be trimmed and freed from the container mix. Experienced rhododendron enthusiasts have even recommended splitting the root ball and flattening it out. Cut root ends, quickly make new fine roots that will penetrate the planting site.
planting hole and drainage...	Prepare a hole at least three times...that is three times...the diameter of the root ball. The planting area should provided abundant organic matter. Mix some of the surrounding soil. Bark is readily available. It last for a long time...compared to sawdust (three years) and other materials. Provide good drainage. THIS IS ABSOLUTELY NECESSARY! Backfill with a mixture: one-half soil and one-half organic matter. Firm the backfill around the root ball...but do not stomp it down. The top of the root ball should be at ground height or ½ inch above...never deeper. Soil should never be placed on top of the root ball...but a layer of mulch is beneficial. Be sure the root ball does not dry out. It shows sign of wilting, you have not kept it moist. Hand water, if necessary. Herb Spady of the Wilmette Chapter wrote this article and several chapters have included this helpful hint in their chapter's newsletter.

Reading labels...so important	Questions: Reading the label on an insecticidal soap, came across "potassium salts of fatty acids." Tell me what those are...and how they kill insects? Can one use dishwashing liquid as a substitute for insecticidal soap? G. C., Hollywood CA
an interesting answer...	Potassium salts of fatty acids are created by adding potassium hydroxide to fatty acids obtained from animal fat or plant oils. The resulting "soap salts" are most effective in controlling soft-bodied pests, such as: aphids, scale, and mealy-bug crawlers, thrips, whiteflies, and spider mites. Generally, they have little effect on beetles and other hard-bodied insets (an exception being cockroaches). The soaps must come into direct contact with the pest to be effective. The soap penetrates the out cuticle of the insect's body and dissolves or disrupt the cellular membranes, causing the dehydration and death. Soaps can also block the spiracles, or breathing pores, the in the insect's body, which interferes with respiration. In come cases soaps may also act as an insect growth regulator, affecting the metabolism of cells and metamorphosis.
be careful in using common dishwashing soaps...	Certain common dishwashing liquids and laundry detergents, mixed with water, have also shown insecticidal and miticidal properties. When applied to an assortment of vegetable crops, Palmolive, Dawn, Joy, Ivory, and Dove, for example, have effectively reduced populations of whitefly, aphids, and spider mites. However, dishwashing and laundry detergents are not labeled as insecticides. Although they may be insecticidal, they are chemically different from the registered insecticidal soaps. Furthermore, they may prove phytotoxic, causing injury by dissolving the waxy cuticle of the plant's leave surfer. It is better to save these soaps for the chores for which they were designed. - Horticulture Magazine

Planting elepidotes in sunny locations	This is a real pitch for early bloomers by Marianne and Bruce Feller of the New York Chapter. They wrote about it in the New York Chapter's newsletter of October 2002. Just listen! Although opinion sometimes varies among growers of rhododendron with respect to the finer points of cultural requirements and preferences...we are largely of one mind when it comes to the advantage of high canopy shade for elepidotes...particularly from afternoon sun. The absence of shade...however...need not preclude elepidotes altogether.
open exposures present challenges...	Yes, these are some of the challenges with open exposures... accelerated water loss higher ambient temperatures direct effects of full day sun exposure on foliage and bloom. Accordingly, your strategy for sun tolerance needs to factor in all of these issues. Assuming the availability of irrigation, water loss can be addressed directly. Use of heavy mulches will also reduce evaporation and moderate soil temperature year round.
issue of higher ambient temperature...	The issue of higher ambient temperature poses a more serious challenge. Perhaps, the most heat tolerant rhododendron, R. hyperythrum, is part of the solution. This species has been used in hybridizing a number of heat-tolerant offspring, including, R. 'Hypermax', R. 'Charles Loomis', and R. 'Peppermint Twist'. Of course, don't overlook the obvious advantages of using lepidotes and deciduous azaleas as companion plants in open sunning settings.
open sun gives abbreviated bloom time...	Our own experience suggest that the most serious effects of direct sun on established rhododendron is largely a much abbreviated bloom period...the flowers seem to last only a day or so in hot weather before collapsing. While foliage can actually burn in periods of extreme heat and direct sun exposure, this seems less a problem than the effect of sun on the flowers.
considerations for planting...	Bearing this in mind, consider planting very early blooming elepidotes in sunny locations. April bloomers are far less likely to encounter the high temperatures that wilt flowers later in the season. May want to try R. 'Taurus' or R. 'Grace Seabrook'...two excellent early reds, and/or R. 'Babylon', a huge early white bloom with burgundy blotch. Other early blooming elepidotes include: R. 'Bosutch', R. 'Christmas Cheer', R. 'Jacksonii', R. 'Strawberry Swirl', R. 'Vernus', and R. 'Spring Glory'...all well-suited to our Long Island climate. R. 'Hypermax', mentioned above, is also an early bloomer with the added advantage of R. hyperythrum parentage for basic heat tolerance.
strength the case for early bloomers...	Strengthening the case for early blooms are a number of other advantages. Their foliage develops and matures earlier...before the strongest periods of Summer sun...and often before the host of chewing insects reach their destructive peak. They enjoy longer flower life...in sun or partial shade...and are rarely affected by petal blight.
best of all...no competition in the garden...	Our obvious affection for early blooming elepidotes is also based on the fact...they are unrivaled in the garden at that time of the year...when they can be most appreciated without competing influence at the very outset of the Spring bloom period. Plant and enjoy...early bloomers!
Dr. Rhody question...split bark...	Dr. Rhody, This year I have noticed a number of our rhodies have what appears to be split bark. Most exhibit satisfactory growth...despite the appearance of the bark. However, one, a 'President Roosevelt', rather suddenly exhibited signs of leaf and truss stress and was soon about as moribund as a plant gets. During the ceremonial removal of the plant, a post-mortem examination showed that the split bark actually exposed dead wood...in contrast to other healthy plants with bark disruption exposed stems that were clearly viable in that the underlying stem was green when scratched. Why does bark split? Apparently some hybrids are more susceptible than others to these phenomena. For example, I have been told by a respected student of rhodies that Naselle is frequently lost because of bark split. How can we identify which plants are likely to suffer a similar fate? How can he establish the difference between benign splits and those that sentence the plant to the great beyond? A really long-winded youth want to know.
Dr. Rhody has the answer	Dear Youth, Bark split usually occurs when a plant has high water content and suddenly experiences a drastic drop in temperature...to well below the freezing point of water. Water does a very unusual thing when it freezes...it expands. The sudden expansion can cause cell destruction and damage to the surrounding wood. If it is severe enough, the cells that move the water are ruptured...and may cause the bark to actually split or break loose from the woody part of the stem. When all of the transporting cells on a stem rupture...the life above that point will cease.
partial bark split...	Partial bark split can occur and the upper portion of a plant may continue to thrive. If the damage goes all the way round the stem it will die. We usually don't notice the dark damage until after the temperatures begin to increase and the plant needs water from the root system. In the western Oregon climate, plants can live quite well with water supplied to the leaves from the moisture in the air. When it warms up, we notice the leaf stress.
really want to save plant?	If you really want to save your plant and you notice the problem soon enough, prune the limbs below all visible bark split. You may have to wait to have a beautiful plant again...it can survive. One way to help prevent bark split is to reduce any artificial watering as Fall progresses. Of course, if it rains hard and then freezes quickly, you have no control of what happens. In reference to your President Roosevelt, damage is frequently caused by stems having too much weight...flowers...or by wind blowing on the very, very brittle stems and causing the actual stem to break or split.
other suggestions...	I have raised hundreds of plants of 'Naselle' and have never had a plant die due to bark split. The one plant that I lost many, many of due to bark split was 'Crater Lake'...one of my favorites. I pruned some back drastically and they eventually survived. We all experience different weather...different plant locations...and different results. So, don't give up. Good Growing! Dr. Rhody

Spring thoughts!	If thoughts were flowers... How easy they bloom Into bouquets of prose and rhyme. Should words be as petals... How softly they fall gently to earth passing time. The language of nature Written in color Interprets the glory of spring. A blossom, A quill, Transcribe the beauty! Celebrate the life that they bring. - Kristi O’Donnell, Meerker Magic Whidbey Island Chapter, Newsletter, March 2008. Thanks, Kristi, for bringing Spring to the world. Hope each reader, reads again your expression of Spring. It is truly a new awakening!