The word chlorosis comes from two Greek parts. The first, chlor-, means green. The ending, -osis, indicates a state or condition, usually implying a less than desirable or abnormal condition. Thus, it is a little odd that the English definition of chlorosis literally means “the condition of being green,” but for plants it is “the state or condition of lacking necessary or desirable green.”
Almost anyone who has grown a garden has heard of chlorosis. Although lack of iron is a popular diagnosis, it turns out that there might very well be complications with other nutrients, whether in excess or depletion, instead or in addition to deficiency of iron. Understanding some of the chemical reactions in the plants and the soil can help avoid making the problem worse or spending money for no reason.
First of all, chlorosis can manifest in various patterns, in different parts of the plants, and in distinct time periods. For instance, the chlorosis associated with iron deficiency is particularly “interveinal.” This means that the veins of the leaves remain predominantly green, but the rest of the body of the leaf yellows. According to Professor Linda Chalker-Scott in the book How Plants Work, a lack of other nutrient metals, such as magnesium, manganese, or molybdenum can also lead to this unique pattern. Environmental variables like temperature, current water, and pH of the soil affect how any of these heavy metals are absorbed by plants.
Becoming aware of all of this could make one wonder how anything grows at all, and if there is any way to counteract these imbalances, at least from a plant’s perspective. Soil tests are often recommended, but in my garden it is not uncommon for the same exact species to be healthy within six inches of one that isn’t. One example from my garden this year was pole beans. When I think of testing my whole acre square foot by square foot, I quickly realize this in not practical.
Some of the advice about growing plants that easily live where you want to grow things is helpful. A gardener must be very devoted to try to grow something like blueberries in naturally alkaline soil. On the other hand, I have never had any trouble with chlorosis in broccoli or zucchini. Azaleas sold at local nurseries are only there because there is always someone who wants to prove everyone else wrong, but my hybrid roses always seem to have an easy time being green, if they survive the harsher winters.
Shrubs or perennials can be frustrating, not only because they are a more expensive experiment, but because I have seen them change right before my eyes. One year a particular bed will be a healthy green, but the next most of the plants will be sickly yellowish, and me not having done anything different there for several years. I have a couple of garden beds that bring out the latent chlorotic tendencies of nearly any plant I put there, except this year the tomatoes are thriving. There is an ancient sycamore tree that is actually getting greener, even though I haven’t done fed it anything in the 20 years we have lived here. Is it patience or a game of roulette?
One thing that cheered me up in reading about all of this was that part of the trouble is sometimes too much of other nutrients, such as phosphate, copper, manganese, or zinc. The main caution here is to NOT go willy-nilly adding nutrients to the soil in hope that something will help. The saying that the poison is in the dose is also true for plants. Interestingly, phosphate can also be concentrated in chicken manure, and the area where I have the pole beans is in an old chicken pen. I know from watching my chickens that having a food dish or water in a certain spot could lead to that location being “more fertilized.” But, then, it might have been a combination of that and the rainy spring, because it wasn’t an issue there last year!
The idea with water seems to be that more heavily saturated soil results in more of some substances dissolving, which in turn may alter pH or interfere with absorption of necessary nutrients. Weather adds other factors like temperatures affecting growth rate and sunlight available for young, vulnerable plants.
As mentioned, chlorosis can look different depending on what is causing it. If lack of nitrogen is the problem, a more overall yellow is likely. Unlike iron, nitrogen can travel around the plant and will be shuttled to newer, growing parts if at all possible. Sulfur, like iron, is less mobile, but is hardly ever missing in the soil. The infamous pole beans mentioned above that were chlorotic, were pale from their first sprout, and stunted, but then newer leaves came in as a dark, vibrant green. They are now producing fine beans, although the plants are not as full as the plants that were never chlorotic. It is still a mystery to me if this was due to iron deficiency, the intricacies of weather, roots branching out, or other unknown factors.
The suggestions for “treating” chlorosis range from spraying on chelated iron to refraining from applying the ubiquitous triple nitrogen-phosphorus-potassiium (NPK) fertilizers. Even the type of mulch you use can make a difference. Anything like plastic that blocks oxygen or water can poorly affect a plant’s ability to get it’s dinner, or may overheat soil organisms that are trying to help! Organic mulches tend to offer both slow release and friendlier root conditions. If you have a favorite plant that is declining or an eye-sore that is really bothering you, and you are convinced you need to add iron, you might try reading one of the articles below to learn more about application options. I also highly recommend the book by Professor Chalker-Scott cited above. I found it easy to understand and entertainingly written.
The next time I am faced with serious and fairly defined iron interveinal chlorosis, I think I will try the iron chelates, as they seem to offer the most hope. Meanwhile, I think I need to go reexamine some leaves and growth patterns. Plus, there is the somewhat humorous fact that grass is one of the easiest plants to treat for iron deficiency, so maybe more lawn in some places where I am having trouble growing other things?