Why is My Tree Yellow? Iron Chlorosis Explained

chlorotic pear tree

chlorotic pear tree

Spring’s arrival is ushered in by warming temperatures and verdant greens.  But amongst the landscape, you spot some very yellow leaves.  Very.  Yellow.  That particular tree with the extremely yellow leaves is not a species known for that particular hue.  Instead, it should be a typical tree green.  Just what is going on?

To sum it up, iron chlorosis.  This malady generally strikes during the spring.  The reason that it may be more noticeable in spring is that the chlorosis tends to be exhibited in new growth at branch tips.

yellow leaf with green veins

yellow leaf with green veins

The characteristic look of iron chlorosis is a yellow leaf with green veins.  If this is left untreated and it worsens, the leaf color will become a pale yellow to even whitish in appearance.  However, the leaf veins will remain green.  You may even notice angular brown spots between the veins and a scorched look along the leaf margin.  Other symptoms of an untreated tree are poor growth (compared to a healthy tree).  The leaves themselves may curl, dry, and drop from the tree.  And if the tree bears fruit, the fruit itself may be smaller than normal and have a bitter flavor.  In severe cases (those left untreated for years), limbs may die or perhaps the entire tree.

The reason that chlorosis is so damaging to a tree is that iron is needed in order for chlorophyll (which is responsible for the green leaf color) to form as well as for photosynthesis to take place.  Once the plant is stressed from chlorosis, it loses vigor, may become prone to winter injury, and becomes susceptible to insects or other diseases.

Causes of Chlorosis

  • high soil pH can cause chemical reactions that make iron unavailable to plants
  • conditions that restrict air movement through soil, such as plastic sheeting laid down over a soil surface as a manner of weed suppression or soil compaction
  • cool soil temperatures
  • eroded soils (or top soil scraped away) that reveal a lime enriched subsoil
  • low pH loving plant material planted in high pH soils
  • regular overwatering

To rule out other culprits that may look similar to iron chlorosis, such as certain cultivars bred to have yellow foliage, improper herbicide application, fungus, or insect infestation, have your soil tested.  Iron deficiency is usually found in soils with a high pH (7.0 or greater).

 Types of Available Treatments

  • trunk injection – holes are drilled into the tree trunk and iron compounds are placed in the holes. The compounds may be liquid or dry based upon the manufacturer.  If this is the selected treatment, go with a brand that requires small holes which will minimize damage to the tree as well as lessen the area for insects to infiltrate.  Some brands will specify that the holes should be made just above the soil surface, made at a certain angle, and at a specific depth.  (Professional arborists may be able to perform trunk injections for very large trees.)  For best results, apply in early spring and follow label instructions.
  • foliar treatment – a compound is mixed with water and sprayed directly onto the affected leaves.  For best results, spray on a cool, cloudy day or in the evening.  This will reduce the likelihood of leaf burning from the application.  Of all treatment types, foliar typically shows the quickest response, though is may be spotty and temporary.  Iron additives are typically in the form of iron sulfate or iron chelates.  Repeat applications are generally needed for lasting results.  Please note that on large trees, it may be difficult if not impossible to reach all affected leaves.
  • soil treatment – a compound is mixed with water and applied directly to the soil, typically at the drip line (the outer reach of the branches) of the chlorotic plants.  This type of treatment is quick and easy to apply, whether it is for an individual plant or a group.  NOTE: there are treatments in a stake form which can be pounded into the soil, but those are falling out of favor due to the iron not traveling as well through the soil compared to compounds that are mixed in water and applied.  Iron additives for treatment can be in the form of iron chelates, iron sucrate, or even iron sulfate plus sulfur.  For best results, consult with a nurseryman and read the label for proper application rate.

    applying soil treatment for iron chlorosis

    applying soil treatment for iron chlorosis

  • lowering the soil’s pH – this may be the most impractical method, especially if the soil contains free-lime (calcium carbonate).  According to Colorado State Extension Service, you can test for free-lime by placing a “rounded tablespoon of dry, crumbled soil in a small cup.  Moisten the soil with vinegar.  (The soil needs to be thoroughly moistened, but not swimming in vinegar).  If the soil-vinegar mixture fizzes or bubbles, it has free-lime.  High lime content is typical of soils with a pH above 7.5.”  If your soil does not contain free-lime, you can use sulphur products to lower the soil pH.    Be aware though that sulphur treatments are typically effective over several years.  Read label instructions and retest soils in a few years.

If you have heard the stories about using metal shavings or  rusty nails as treatment for iron chlorosis, ignore them.   According to Utah State University Forestry, high soil pH causes a chemical reaction that makes “iron solid and unavailable to plant roots.  Such iron will be tied up indefinitely unless soil conditions change.  Iron released by these materials immediately forms solids that are unavailable to plants”.


While there are no quick and easy ways to treat iron chlorosis, there are steps you can take:

  • test your soil’s pH
  • plant material that is suitable for the pH
  • do not overwater
  • do not compact the soil
  • begin treatment at the first signs of chlorosis

With proper treatment and patience, your plant(s) can return to their normal color and back to a healthy state.


Don’t Fear the Swarm


It begins this time of year in early spring.  You may glance over your shoulder or try to peer around hedge.  Could one be over there?  Nope.  Just a grouping of brown leaves.  Wait… what’s that noise?  The hum of a motor?  An overhead light buzzing? You ponder staying indoors for the next month or longer.  Surely those late-night science fiction movies on this very topic you’ve watched in the dark are based on science, right?   But before your fear inhibits your enjoyment of the outdoors, just breathe deeply and repeat after me, “Don’t fear the swarm”.

One of the most mesmerizing images in nature is a honey bee swarm.  It is a ball of living, breathing bees all tightly clustered together.  Often in odd locations.  Hanging off the side mirror of a car.  From the bottom of a mailbox.  A branch of a dead tree.  Perhaps even the gutter of a house?  Forget the horror films that vilify a swarm, in reality, it is truly a sight to behold.

honey bee swarm

honey bee swarm

Just what is a swarm you ask?  It is a natural event in which a colony of bees creates a new colony.  Overcrowding is what kicks off this event.  There just simply isn’t enough room in the colony (hive) for the growing number of honey bees.  At this point, some of the workers begin to create queen cells or cups (in which new queens will grow).  These cells are quite distinct… they are typically hang vertically from the lower portion of the honeycomb and are much larger than the cells from which a worker bee will emerge.  And if the large cells aren’t enough of a clue, they have another distinguishing feature…. these cells look like peanut shells, dimples and all.

As the queen cells are being made, other bees begin scouting flights… searching for a potential new home.

Prior to swarming, the departing bees will gorge themselves on honey.  Think of it as one-for-the-road.  It may be a day or two (after they leave the colony) before they settle into a new home.

When a swarm happens, approximately 50% of the bees (workers as well as drones) leave the colony with the old queen.  The air is filled with bees as they exit their home… whether it is a hollow tree or a beekeeper’s hive.  This mass of bees travels together like a cloud.  Generally a short distance from their old home, the bees cluster together, hanging off of an object such as a tree branch.  Within this cluster, the queen is in the middle… protected.  Scout bees leave the cluster in search of a new home.

honey bee swarm on tree branch

honey bee swarm on tree branch

Some people are terrified when they see the cluster.  They believe that the bees are just waiting for them.   But unless you start swatting or poking at the swarm, they are content to leave you alone.  They are ‘homeless’ for the time being and therefore not defensive about their location.  Remember those scouting bees?  The cluster is waiting for them to return and do their dance to indicate potential new locations.

What are the scout bees looking for?  Specifically a place that will provide protection from the elements.  Also… the new location must have not only enough space for the swarm, but also for the new bees that will be hatched from this homeless colony.  And once a place is found, the cluster will break apart and travel as a cloud of bees to their new home.  (Finding a new location may only take about an hour upwards to a day).

So friends, don’t fear the swarm.  It is a natural event that begins in spring.  These bees are simply looking for a new place they can call home.

Natural Finish for Beehives

Natural Finish for Beehives

Keeping backyard bees is one of my greatest pleasures.  Sitting on the patio with a cup of coffee in hand, I watch their comings and goings daily.  Foraging bees return with water, pollen, and nectar.  Departing bees head out in a direction based upon the dance they watched in the hive.  In spite of the activity, they never fly into each other. It is very much like watching the planes at a very busy airport, but on a much smaller scale.

Besides being a beekeeper, I am also an organic and sustainable gardener.  All of my actions are thoughtful and deliberate.  A healthy environment is good for man and insect.  With a newly constructed hive waiting for a finish, there is no doubt that the coating will be natural and non-toxic for the soon-to-be inhabitants.

To start off the process, I consulted our small library of beekeeping books, read through various bee forums, and consulted with long time beekeepers.  The one finish that was referred to over and over was a combination of linseed oil and beeswax.

Why linseed oil?  It a natural product made from flaxseed.  This oil has been used as a wood preservative as well as providing water resistance for centuries.  As far as beeswax goes, it has been used as a wood conditioner for ages.  It helps keep wood from drying out and also protects against moisture.

But before you create your natural finish, please be aware that there are a few potential issues when working with linseed oil.  (For me, the benefits far outweigh these issues).

Potential Issues for Linseed Oil

  1. Surfaces may attract mildew.  Not as much of an issue in drier climates.
  2. No protection against ultraviolet light so wood fibers can deteriorate.
  3.  It can be difficult to remove from wood if you change your mind and want to apply something else.
  4. And most notably… it takes a long time to dry.  It may take from a few weeks depending on how thickly it was applied.  For best (and quick) results, apply in very thin coats.

    applying a thin coat

    applying a thin coat

It is worth noting that the type of linseed oil I used is raw, not boiled.  It was my personal choice to stay with raw linseed oil.  Boiled linseed oil has metallic dryers added which help speed up the drying process where raw linseed oil has no driers added.  Examples of oil-soluble metal salts include: manganese with zirconium, cobalt, and lead per  Steven D. Russell.

Benefits of linseed Oil

  1. Seeps into the wood which enhances the look of the grain.
  2. It is water-resistant.
  3. Easy to apply.
  4. Continues to protect as the wood expands and contracts depending on conditions.

Linseed Oil/Beeswax Recipe

  • 1 ounce beeswax, shredded or in pellet form
  • 4 Cups linseed oil

Melt the beeswax slowly, taking care not to take it over 160F.  It is combustible at that point.  You can melt the beeswax  and linseed oil in a double boiler or you can melt it in a pan on the stove, but at a low temperature setting.  You could also melt the beeswax separately, but it will begin to harden in clumps once the cool oil is introduced to the pan.  By melting them together… no more clumps.  Even when the mixture cools, there are no clumps of beeswax, it is one unified blend.

melting beeswax with linseed oil

melting beeswax with linseed oil

You are now ready to apply the mixture to the exterior of the hive.  A brush or a rag work equally well.  Remember to apply a thin coat to the unfinished wood of your hive.  Once it has dried, you may add another coat, but be prepared to wait a week or more for it to dry before you can apply the second coat.

unfinished hive with cloth and linseed oil beeswax mixture

unfinished hive with cloth and linseed oil beeswax mixture

Add this recipe to your natural beekeeping arsenal.  This mixture is non-toxic to bees, provides moisture protection, acts as a wood conditioner, and wood preservative.  Sure it may take some patience as you wait between coats for the finish to dry, but your efforts will be greatly rewarded.  What you end up with is a beautiful finish that will last for years that enhances the natural wood grain.

cedar beehive with linseed oil-beeswax finish

cedar beehive with linseed oil-beeswax finish