One of my rhododendrons is showing some typical chlorosis on its newest leaves (I'll try to get a pic to post tomorrow, just to be sure; but they look identical to many online photos -- green veins with yellow between). My soil was tested in January: pH 7.0 and iron at 60.9ppm.

Is chlorosis likely with these numbers? I know the rhodos like a more acidic soil, and this one is closest to the lawn and the indiscriminate liming that the lawn company did prior to my giving them the boot last summer.

What is the best way to treat the rhodo? Foliar? Soil treatments? What should I use and how much? I bought chelated iron, but with the high temps here recently (woo hoo -- it's finally summer here!), I haven't dared use it for fear of burning things up.

I wasn't planning to adjust my lawn soil pH, since it will probably drop with time due to the amount of rainfall we have here (the area is known for its naturally acidic soils). But I think I need to do something for the rhodo and its soil; it's looking pretty bad. Any help would be greatly appreciated.

Thanks!

Can I gently disagree? I have Rhodo's and Japanese Andromeda that are over 100 years old, and my soil is pH 6.8. I go once a month or so a throw a handful or two of Blood Meal (or Dried Blood) and they never show signs of Chlorosis any more. I think that trying to manage pH in a 10 sq ft area is impossible long-term.

I guess. Its not easy to do all that to 100+ year old rhodo's that are 8'-9' tall. I go for the simplest solution that solves the problem (thank you, Mr. Occam) and I've found that to be Blood Meal.

Camellia, Azalea, and Rhododendron fertilizer works good too....

Makes tasty blueberries too....

Of course -- I have no problems maintaining a low soil PH... If I just leave it be -- it stays around 5.0.... Acid lovin' stuff just doesn't get any Lime like the lawn and garden does....

Thanks

MorpheusPA wrote:Foliar apps (same rules; not over 85 degrees, although you can cheat a bit by applying it early in the morning and washing it off as temperatures approach 85) will help a lot. Temporarily. The end solution is to acidify the soil.

I have applied chelated iron as a foliar spray twice in the last month to try to get some instant relief. There was no change at all in the yellowing of the leaves (I applied when the temps were around 70-75F). I should also note that the "chlorosis" is not uniform on the plant -- just in some areas. Does this indicate it might not be a pH/iron issue? Should I have seen some green-up if it was iron-related? I used the recommended amount for shrubs that was listed on the iron chelate container.

I did fertilize with rhodo fertilizer after they bloomed this spring, and was careful not to use more than the suggested amount.

The plant is at the edge of the garden right up against the driveway. The leaves closest to the driveway are the most yellow and then the yellow parts seem to brown/burn.

This is a current photo -- the yellowing is much more pronounced now than when I first posted. So, I guess my questions are: 1) could this still be iron/pH-related, even if the iron foliar spray didn't help? 2) are there other things that might cause this? I will be getting some peat this week to mulch this area.

Thanks!

The plant is at the edge of the garden right up against the driveway.

How long has the plant been in that spot, and what is the driveway constructed from (material)?

andy10917 wrote:How long has the plant been in that spot, and what is the driveway constructed from (material)?

Since it was planted, 6 years ago. The driveway is exposed aggregate concrete. It does not get any salt in winter (usually not enough snow, and when there is, we just shovel rather than use salt or other such products). This rhodo does get the late afternoon sun directly on the yellowing leaves, but it has had that amount of sun for 6 years. This is the second year of the yellowing (especially the new leaves).

Hmmm - who did the soil test? Was the soil from the area as close to the concrete as the Rhodo? What were the levels of the following nutrients: Calcium, Magnesium, Iron, Potassium and Boron?

If the Rhodo is really important to you, we can do a few things that will take a bit more time. Like boiling peat moss. Curious?

The soil test was done by a lab called Exova (they have a lab here in Surrey). They do a lot of testing for agriculture in the area. The soil samples were mainly from the lawn and weren't taken very far from the driveway -- the total lawn area is only about 500sf and I took about 15 different core samples from the entire area, but I don't think any of them were taken as close to the driveway as the rhodo is.

Calcium: 1800 ppm
Magnesium: 214 ppm
Iron: 60.9 ppm
Potassium: 164 ppm
Boron: 0.40 ppm

I'm actually very curious, Andy -- I'd love to help/save the rhodo if possible, as it is gorgeous when in bloom. You could barely see the green this spring, it had so many flowers. Boiling peat moss -- hmmmm....well, my hubby already thinks I'm nuts for putting milk, molasses, coffee grounds and grains on the grass. Boiling peat moss wouldn't be much different!

I'm also planning on using Logan Labs this fall, and if necessary would get a separate soil sample from that garden area. I'm interested on hearing your ideas!

Actually, I have a couple of ideas.

Call or email Logan Labs and ask them if they can do a plant tissue analysis for plants from Canada. Soil I know they can, but plant tissue Idunno.

Now the peat. Actually, you don't have to boil the peat - but that's the fastest way to do this trick. Either boil 3-4 pounds of peat in a Big pail of water, or pour boiling water slowly over a screen with the same amount of peat again and again, or get one of those 5 gallon buckets from the big-box and soak the peat for a week. The resulting water should be like dark tea. Keep feeding the peat tea (not the peat itself) to the Rhodo every few days - start with a couple of gallons and then go to a gallon a few times a week. If you happen to have R/O water all the better to make the tea. The tea is extremely soft water and naturally acidic with tannic acid.

So how do I know that? Google "blackwater aquarium peat". In a small area like a single plant it is a great trick. Keep it up for a while.

PS: In your first 2 gallon dose, dissolve in a teaspoon of Epsom Salts (Magnesium Sulfate), a tablespoon of Iron Sulfate, and four ounces of Milk. Take soil samples that you're going to send in BEFORE doing this.

I'll be very interested in hearing what happens.

Thanks for the ideas!! I have a few follow-up questions/comments:

Andy:
1. I will contact Logan to see about the tissue sample. If they can't, I'll try to find one here that isn't too expensive.
2. I'll probably use the 5-gallon pail method since my biggest pot probably won't hold 3-4lb of peat. Is this un-aerated? Just let it sit?
3. I'm assuming I use the peat tea as a soil drench only, not a foliar app?
4. For a soil sample around a rhododendron, do I still try to take the soil 3-4 inches deep? Would this still be the same soil test that Logan offers for the lawn service?

bpgreen:
1. I used ~5 drops of baby shampoo on the second spraying (in 1 gallon of water). I forgot it on the first and wondered if that was why the first one didn't show any improvement. But the second one didn't either. Maybe I didn't use enough shampoo?
2. I'll try the coffee -- we only have it on the weekend, as only my husband drinks it, but I'll stop pouring the remains down the drain. No real chance to move the plant, as I don't have a spot to put it.

Thanks again! I'll head out to buy Iron Sulfate and Epsom Salts tomorrow, and I guess I better get my soil sample.

I haven't done the peat tea thing, but the purpose is to try to acidify the soil, so you're right that it would be a soil drench rather than a foliar app.

Yes, it is. Some of the tannins behave like humates, which is a side-benefit. I never use teensy amounts like 5 drops, Rhodo's have waxy leaves, so I'd go to 1/2 oz or even an ounce. Let your eyes tell you - if it isn't sheeting, it ain't working.

Another thing to consider is that not all chlorosis is caused by iron deficiencies. This is especially likely if mature leaves are showing signs of chlorosis (iron deficiency tends to hit new leaves hardest). Magnesium deficiency is another cause of chlorosis and can be caused by a lack of magnesium or by magnesium that is unavailable due to high pH. That's why Andy is recommending the Epsom salts. I didn't notice that he was suggesting adding that to the peat tea. With the Epsom salts in it, a foliar application may help for a quick greenup, followed by a longer term help from the magnesium that goes into the soil as well as a slight acidifying effect from the Epsom salts.

BP knows exactly where I am going. Photosynthesis and Chlorophyll creation are very complex processes involving as many as dozens of compounds and elements. If any one is missing, the process stops at that point. Assuming Iron is the broken link is simplistic. Iron isn't getting to the leaves, but the question is Why. If a car won't run, it might be out of Gas, but it also might be any other item in the chain of things that have to happen. That's why I asked for all of the PPM's on the measured micro's. I added Magnesium through Epsom Salts. I have a hunch that the concrete's Calcium may be displacing Magnesium, but it's just an educated hunch.

... and the mention of the driveway was why I immediately asked "what is it constructed from". My mind jumped right to the possibility of concrete.

This sounds very promising. I bought my iron sulfate and magnesium sulfate today and will pick up the peat tomorrow to get that going. Thank you so much!!

While the peat is soaking for the week, would there be any harm doing a foliar spray of some of the epsom salts, if magnesium is the problem? If that would be ok, what kind of ratios would I use?

Thanks again. I'll take my soil sample before I start and will document my progress with photos.