Chlorosis

In some sense, this post is another chapter about the improper use of fertilizer. For this discussion we will consider chelated iron.

Chlorosis is a condition where leaves are abnormally yellow and their veins are prominent. This is not the onset of pigment loss in the fall, but a problem that occurs during the growing season. Most often, the cause is a lack of iron or, better said, the perception of a lack of iron by the plant.

Plants suffering from iron deficiency will not thrive. A yellow leaf is not photosynthesizing properly; it is not making as much food as it could be. This sub-optimal condition leads to a weak plant.

Almost all soils contain enough of the micro-nutrient iron for normal growth. The problem begins with the soil’s pH. pH is a number scale used to represent degree of acidity or alkalinity. 7 is neutral, 0 is extreme acidity and 14 is extreme alkalinity. Everything has a pH: your hair, water, and soil.

Almost all of Calgary’s soils are alkaline, some extremely so. Soils I have tested in Varsity Acres in northwest Calgary came back as pH 8.2. Growing in that yard was a beautiful cut-leaf birch. Beautiful as it was, you might have called it a yellow birch. The soil test done at a agricultural lab revealed that there was plenty of iron in the soil. The problem was the pH, not the lack of iron.

Many are the times a distressed Calgary gardener has enlisted a spray service to apply chelated iron to a Chlorotic plant, only to have that plant spiral into decline from iron poisoning.

So we have enough iron but the pH of the soil is inhibiting its availability. If we could practically lower the pH, then all should be good. The best answer I found to that problem was the application of elemental sulphur. Sulphur compounds are naturally acidic. Reaction of the sulphur with bacteria and other soil components will result in sulphur compounds to lower the pH. What I came up with, after a number of trials, was a broadcast application method of small pellets of elemental sulphur. Describing the dose is difficult. What I did was to walk back and forth systematically, one hand carrying bucket of sulphur, the other distributing a steady rain of small pellets. I applied the equivalent of a small handful per square foot. If you got down and looked, there was a nearly even layer of pellets in the base of the grass, one pellet deep. An alternative method would be to punch one six-inch hole in each square foot of the turf and dump the sulphur pellets into the hole. I never tried the hole method.

Now we have the area under the drip-line of the birch covered with a layer of tiny sulphur pellets. For that two-foot diameter tree, I have used close to 100 lbs of sulphur pellets.

The next step is watering it in. Set up your watering equipment so you can water the entire area to which you applied sulphur. Water for 3-4 hours. WARNING: do not skimp on the watering or you will burn your lawn. This long duration watering will saturate the soil, allowing the soil’s components to make intimate contact with the sulphur pellets.

This treatment is not a pill; it does not happen overnight. Perhaps in a month, for sure next year, your tree will be looking much better.

And that’s what happened: that big tree in Varsity turned back to its natural deep jade green, and has been grinning ever since.

(Photo credit: “Raspberry vein chlorosis virus NT5 (1)" by Selso, licensed under CC BY-SA 4.0.)