Rhodie help requested

The upper leaves of one of my rhodies, about three feet tall, are turning yellow getweing the veins, leaving a kind of green "skeleton" in the center.
I judged it as a need for more acidic soil, and added a mulch of used coffee grounds several months ago, but the condition seems to be worsening.
Does it need something stronger, or a different kind of remedy? I'd appreciate advice on what to do next.
Thanks. vince norris
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Hi Vince,
I don't know where you live, but Kathy Van Veen in Portland, Oregon, uses coffee grounds in her rhododendron nursery and she finds: 1) it helps to aerate their clay soil. 2) slugs don't like to go through. (So you can see they have both mixed in and put on top.) 3) It does help to make the soil more acidic. But it does not replace fertilizer.
Warning, you don' t mix anything into the soil around a planted rhododendron. They have very shallow roots. She obvioiusly mixes it in her planting soil before she plants.
What you have, yellowing of a leaf between dark green veins, is called chlorosis and is usually caused by an iron deficiency. Many conditions can be responsible for an iron deficiency. Poor drainage, planting too deeply, heavy soil with poor aeration, insect or fungus damage in the root zone and lack of moisture all induce chlorosis. After these conditions are eliminated as possible causes, soil testing is in order. Chlorosis can be caused by malnutrition caused by alkalinity of the soil, potassium deficiency, calcium deficiency, iron deficiency or magnesium deficiency. Iron is most readily available in acidic soils between pH 4.5-6.0. When the soil pH is above 6.5, iron may be present in adequate amounts, but is in an unusable form, due to an excessive amount of calcium carbonate. This can occur when plants are placed too close to cement foundations or walkways. Soil amendments that acidify the soil, such as iron sulfate or sulfur, are the best long term solution. Foliar sprays of iron sulfate or chelated iron can reduce symptoms. A combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Chlorosis caused by magnesium deficiency is initially the same as iron, but progresses to form reddish purple blotches and marginal leaf necrosis (browning of leaf edges). Epsom salts are a good source of supplemental magnesium. Chlorosis can also be caused by nitrogen toxicity (usually caused by nitrate fertilizers) or other conditions that damage the roots such as root rot, severe cutting of the roots, root weevils or root death caused by extreme amounts of fertilizer.
There is a tonic that remedies some cases of chlorosis. It was devised by Diane Pertson, of Vancouver Island, BC. Purchase a bag of Epsom Salts crystals (magnesium sulfate) (available here in bulk at farm-and-feed outlets), about $4.00 for a 5 lb. bag - and a bottle of FULLY Chelated Iron & Zinc (this is a very concentrated liquid - the chelation means it is in a form that can be readily absorbed by the plant), about $7.00 for 1 quart; In a one gallon watering can, put in 2 Tbsp. of Epsom Salts crystals and 2 Tbsp. of Iron and Zinc liquid - fill with warm water and stir to dissolve; Sprinkle this over the rhododendron - by that I mean drench the leaves with the solution and pour the remainder around the drip line of the root ball. In 1-2 weeks, the leaves should be nice and green. You could repeat the process at this time if the leaves aren't fully green.
She warns that in some areas where she lives the problem is too much acidity and she must use domonitic limestone to keep the soil from being too acidic. I have never witnessed that problem, but depending upon where you live, you could have that also.
I hope this help. Good luck.
--
Pardon my spam deterrent; send email to snipped-for-privacy@earthlink.net
Visit my Rhododendron and Azalea web pages at:
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thank you, Stephen. I was hoping you'd respond to my query. You've provided a wealth of information, as usual.
vince norris
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.