When you drive around your neighborhood in Wyoming, you’ll see a common and disturbing sight. Trees with pale, yellow leaves in the middle of summer. It’s very common in maple trees, but even here in Pine Bluffs, we see it in the cottonwoods. Many other plants can suffer from chlorosis, slowing their growing and dulling their color. The condition you are observing is called Chlorosis.
Symptoms of Chlorosis
Chlorosis is a condition in which leaves are unable to produce sufficient chlorophyll, resulting in pale, yellow leaves. In sever cases, the leaves begin to brown at the tips, limbs die back, and eventually the entire tree dies. Lots of things can cause chlorosis, but here in Wyoming, it’s almost always from an iron deficiency.
The Cause of Chlorosis
Our soils generally have enough iron in them, but the plant is unable to absorb it. This is because we have something called alkaline soil. Our pH is often up near 8 or 9. That’s almost the same as baking soda. Soils with a pH that high don’t like to release certain micro-nutrients, particularly iron and manganese. Plants need iron and manganese to make chlorophyll for energy production. While manganese may contribute to the problem, iron is the primary culprit in Wyoming. Without these trace elements, the leaves turn pale and die. There are a few ways you can fix the problem.
You can spray the sick leaves with an iron chelate. Foliar spraying works fast, within a day or two, but the symptoms return in a couple weeks. I don’t recommend this option.
Applying Iron Chelate
Another option is to add chelated iron to the soil. “chelated iron” is iron that is in forms plants and animals can use. Don’t just go to your local home improvement store and buy plant iron, though. Most forms of iron fertilizer come in the form EDTA. I don’t want to into too much boring chemistry and this article is already borderline nerdy, so I’ll just say EDTA is useless in our soil. The only form that works to its full potential is EDDHA iron. I have not been able to find it in local stores, but you can easily order it on the internet. Just search for “EDDHA iron chelate”. If you dissolve it in water and pour it on your plant, it will green up. Chelates applied to the soil only last for about one season, so you must do it every spring and the stuff is expensive.
A long-term fix that might or might not work is to change your soil pH. Don’t bother buying “soil acidifier” or peat moss at your home improvement store. It would take literally tons of the stuff to even make a dent. The only viable way to change the soil pH in a significant way, is to add elemental sulfur.
Change Soil pH with Sulfur
You can permanently change the pH of soil with applications of elemental sulfur. In a nutshell, soil bacteria break down the sulfur into sulfuric acid, which reacts with the calcium in your soil, lowering the pH. It’s hard to make a recommendation on how much it will take because it depends completely on the exact constitution of you soil. Most places don’t recommend applying more than 20 pounds per 1,000 square feet at a time. Continue adding the maximum amount in the spring and fall until you see results. The process takes months, so be patient. It might take a lot. It works best to mix the sulfur into the top six inches of soil. Scattering it on the ground is OK, but it takes a lot longer to react. Your local ag coop should be able to get bags of sulfur for you for a reasonable price.
Direct Trunk Injections
Here is what I did. I have a cottonwood in my backyard that stubbornly stayed yellow. I even applied several hundred pounds of sulfur to the backyard. Still, the tree had yellow leaves. I did some reading and found something called trunk injections. It can be a bit complicated, involving tubes and needles – like an I.V.. Only certified arborists could get the supplies. After a little more searching, I found these things called systemic tree implants. They’re nothing more than pill capsules filled with iron citrate. You drill a hole in the tree and insert the implant. Both option work, but there is a very effective DIY method.
DIY Trunk Injection
- Drill a hole 3 inches deep into the base of the tree trunk with a ½” drill bit. Aim the drill down at a 45-degree angle. For trees smaller than 3 inches, only drill halfway into the tree and use a ¼” drill bit.
- Insert a small funnel into the hole. Homemade funnels made from paper even work.
- Pour EDDHA powder into the trunk through the funnel. Use a pencil or something like it to pack the powder into the trunk. I used EDDHA because it’s a lot easier to find than iron citrate. EDTA would work too.
- Start by using 1 teaspoon of EDDHA per 1 inch of trunk diameter. Use more if you don’t see results within six weeks. The iron leaches into the tree slowly and a little bit goes a long way.
- You will need to drill more than 1 hole for trunks larger than 4-6”.
- The closer you can drill to the ground the better. As you move up the tree, the iron distribution in the leaves will get less uniform and you will see patchy results.
- Start with less. You can always add more but overdosing the tree could kill it.
- If you still don’t see any results after the first season, try another implant with Manganese chelate in addition to the iron.
- Remove the funnel and pack the powder into the trunk so you have all but the last ¼” of the hole.
- Fill the remainder of the hole with tree wound repair paint to seal in the iron. Latex paint works OK too. You just need to seal in the iron, so it won’t wash away.
- Observe the tree and repeat every 5 years or as needed.
A Long Term Solution
The DIY injection method has proven to be the most practical in inexpensive for me. It only takes about a half hour every few years. After a couple years of applying the chemical into the trunk, it will permeate a large area of tissue on the tree and give long term effects. The University of Wyoming has reported symptom-free cottonwoods even after five years.