I just got my favorite gardening magazine and a reader asked the question, “The leaves of my roses are yellowing but the veins are green. What causes this?” The given answer is, “This is called chlorosis and is caused by a deficiency of iron”. The answer might be true, or it might not be true. It is certainly an incorrect statement. Find out the truth about chlorosis.
Chlorosis – What Is It?
According to all the dictionaries I could find including ones dedicated to botany, chlorosis is a yellowing of leaves due to a lower than normal amount of chlorophyll.
It is incorrect to define chlorosis as a yellowing of the leaf but not the veins. When the veins stay green the proper term is interveinal chlorosis. This might seem like a trivial matter but the difference can be important if you are using this as a diagnostic tool.
Chlorosis – Is it an Iron Deficiency?
No! An iron deficiency can cause interveinal chlorosis but it does not cause chlorosis.
What causes Interveinal Chlorosis?
A lack of iron in the soil can cause interveinal chlorosis but so will a number of other soil issues. Just because you have a plant with inverveinal chlorosis does not mean you have an iron deficiency. Each of the following conditions can produce the same symptoms.
- manganese deficiency
- a high soil pH
- zinc deficiency
- herbicide damage
- wet soil conditions
- compacted soil
- trunk-girdling roots
- plant competition
- high organic content in soil
- high salts
- high levels of phosphorus, copper, zinc or manganese
Some plants are more sensitive to iron deficiency at higher pH than others. Many acid loving plants have trouble getting enough iron from the soil at higher pH and therefore show interveinal chlorosis while their neighbors don’t.
It should be obvious from this list that adding iron to the soil may not solve the problem. But what if iron is deficient–will adding more iron solve the problem? Not necessarily. If your soil has a high pH, or high levels of some of the other nutrients mentioned above, then the iron you add will be bound up in the soil so tightly that your plants can’t use it. In these situations, adding iron will not help.
Will a Foliar Spray Work?
Spraying an iron solution on the leaves may make them green up in the short term. But since you have not fixed the underlying problem, interveinal chlorosis will return in a few weeks and any new leaves will immediately show interveinal chlorosis.
The second problem with foliar sprays is that there is a small difference between concentrations that work and ones that damage the leaves. It is just too difficult for home owners to apply the right amount.
Chlorosis – What Causes it?
This can be caused by a number of things.
- Early blight
- Low light levels
- Low nitrogen
- Low potassium
- Low magnesium
- Poor drainage
- Damaged or compacted roots
- High soil pH
The Cure for Chlorosis and Interveinal Chlorosis
If the symptoms really are chlorosis, try adding nitrogen to the soil. It should solve the problem.
If the problem is interveinal chlorosis, then the solution is more complex. If all plants seem to be affected, get a soil sample tested and follow the recommendations from the lab. It is unlikely you will solve the problem on your own, unless you are watering too much, or adding far too much organic matter.
If only a few plants are affected, do some research on the plants and see if they like acidic soil. If they do, you probably can’t grow these plants. Don’t fight mother nature–grow something that does well in your soil.
If you are like me, you won’t take this advice and you’ll try to grow the plant anyway. You can try adding iron sulfate around the plant. This will add iron, in case you do have a deficiency. It will also add sulfur which might help lower your soil pH. You can also try just agricultural sulfur which will lower the pH. When the pH goes down, plants have an easier time getting at the existing iron. In a future post I will have a closer look at acidifying soil–but it is more complex than most references suggest. It really is much better to just grow a different kind of plant.
References:
1) Photo Source: Scot Nelson
Firstly, thank you for a fantastic website.
Secondly, however, this page isn’t quite correct. Depending on plant type and severity of iron deficiency, it absolutely can and does cause chlorosis of the entire leaf. Therefore the most easily distinguishable difference between N and Fe def. is that one affects the oldest leaves and the other affects the new growth.
https://www.haifa-group.com/online-expert/deficiency-pro/fe-iron
Your link is to a commercial company – do you have a link to a government site, university or study to confirm what you say?
Could it be the leaves are bleached by the sun coupled with high heat conditions. I’ve had a few do that when it was in the 90’s and direct sun
My old corrugated iron tank collapsed and I have all this iron sludge left behind as well as iron bits from the tank itself. Can I use it in the veg garden or in the compost?
I assume the tank was used for something? Maybe Oil storage? I would not use the sludge from a tank in the garden unless I knew for sure the tank never contained anything except food grade products. Why risk contaminating your soil?
The metal itself will decompose very slowly. If your plants need iron now, then use a soluble source eg iron sulfate fertilizer.
very interesting article! I have several clematis plants, as well as several hydrangeas, all planted intermittently along a fence, on the north side. its a part sun location. two of the three clematis plants, as well as two of the three hydrangeas have what I call, “bleached leaves”. plain white, with no green veins. as if ALL color has been removed. ive been trying to find something on this condition but ive had little to no luck. I keep coming up with, “yellow with green veins”, which is not what im experiencing. have you ever heard of leaves turning all white?
Sorry – I have never heard of this condition.
hm. is there a way to upload a photo, for you to take a look at? not that it matters if you haven’t heard of my problem, simply looking at a white leaf wont help me much, but at least you’ll know im not crazy!
I don’t think there is. You might try joining a gardening Facebook group, like Garden Professors, and uploading your question.
What makes “adding … organic matter” into “adding far too much organic matter”? Does it depend on what form the organic matter is in?
I am not clear on where you are getting the quote from, but too much organic matter in the soil will cause problems. Soil should have no more than 5% organic matter. Different types of organic matter can cause different types of problems. for example if you add a lot of saw dust, it robs the soil of nitrogen and your plants will suffer from a nitrogen deficiency. saw dust breaks down fairly slowly, so it is a type of organic matter that does not cause other problems.
Too much manure, compost, plant material etc can all cause problems since they require nutrients, and cause an explosion of microbe life. As the organic matter decomposes it can actually produce high levels of certain nutrients which can be toxic to plants. Too much organic matter will also affect soil structure over time, which is not good for plants.
Since different forms of organic mater decompose at different rates, and contain different amounts of nutrients, they have slightly different affects on the soil. As long as you add no more than an inch or two each year you should be fine.
For reference, I was quoting from the third paragraph from the bottom.
I understand about the potential short term problems with adding carbon, as with your example of sawdust, and that large additions of compost/manure/etc, may potentially result in short-term toxic levels of nutrients. But to generically say that OM levels above 5% are problematic, that’s something I don’t understand. Is there a different effect than the “nitrogen robbing” and “excess nutrients” effects?
I have made raised beds in my garden that were filled entirely and exclusively with compost (available to me at low cost from a local farmer), and the veggies seemed to grow quite happily. I didn’t measure the organic matter content, but it seems safe to assume that it would have been above 5%. It’s that experience that makes me wonder about the threshold.
Excess nutrients are not necessarily a short term problem. Many nutrients do not leech out of soil quickly and are very difficult to get rid of once they are at high levels. Phosphorus, for example, moves very slowly through soil.
The raised bed is no longer soil–it is an artificial environment. As the compost degrades you would add more compost, and that will degrade also. Whatever nutrients the plants don’t use will be left behind. A couple of years of this and everything looks great. But over time, the excess nutrients will start to accumulate where the compost and soil meet. You will create a high nutrient layer between the two. This layer can become toxic over time.
Healthy, natural soil has 5% OM.
Much obliged!
My understanding is that an OM content up to 10% is ideal. Some East Anglian soils are much higher than this due to their peat content. A limit of 5% seems arbitrary.