Japanese maple trees are prized for their stunning foliage color and graceful form. It’s disheartening when owners begin to spot patches of unsightly lichen growing on the bark. So what causes this stuff to appear?
Why is there lichen on my Japanese maple? Lichen commonly appears on trees that are already weak or stressed due to factors such as drought, poor soil conditions, weather damage, or disease. Lichen growth is surface level and will not harm your tree directly, but it is often indicative of an underlying health issue.
It may not appear very beneficial, but the presence of lichen on a healthy tree can indicate low levels of air pollution in your area. Unfortunately, lichen growth tends to be most common on unhealthy trees.
Keep reading to find out the possible causes behind lichen on your Japanese maple, how to spot the difference between moss and lichen, care tips, and more.
Japanese maples are no different from other trees in that they are susceptible to various problems. In this article, 16 Common Japanese Maple Problems: Causes & Easy Solutions, I go over the most common issues they face.
Lichen on Japanese Maple
Lichens can be a repulsive sight on your beautiful Japanese maple, but this growth is not always a cause for concern. Let’s learn what lichen is plus how to remove it (and whether or not you should).
What Is Lichen on Trees?
Lichen are non-parasitic organisms that grow on trees as well as shrubs, rocks, and fences.
They can appear as hardened gray, green, yellow, or orange-encrusted masses but may also have a leafy, moss-like appearance.
Lichen vs. Moss
While moss is a dark-green flowerless plant, lichen is a partnership of fungi and algae. Lichen also comes in a variety of colors — unlike moss.
Additionally, moss will only grow on natural surfaces like tree trunks and the odd rock while lichen will happily latch onto wood, rock, cement, and metal due to certain conditions.
What Causes Lichen on Trees?
Lichen favors damp and damaged or dead wood and will commonly appear on trees that are already weak, stressed, or lacking in vigor due to maturity or unfavorable conditions.
The appearance of lichen is a symptom that a tree is unhealthy rather than a direct cause of its decline.
Will Lichen Harm a Japanese Maple?
Lichen is generally not harmful to Japanese maple trees as this plant-like organism is thought of as an epiphyte.
This means it grows on a host (a tree or shrub), but unlike a parasite, it grows on the surface and does not penetrate the tree tissue or draw nutrients from it.
Lichen thankfully lives off the rainfall and air-borne nutrients, not your Japanese maple!
Should Lichen Be Removed From Japanese Maple?
In most cases, lichen will not pose harm to your tree to the extent it requires removal, and doing so could do more harm than good.
Japanese maples have quite thin and tender bark, so scrubbing away at this harmless growth could injure the bark, allowing disease to enter.
In rare cases, lichen growth may be excessive to the point that the tree is not getting adequate sunlight or moisture.
If you are concerned the growth could be getting out of hand, it’s wise to get a professional opinion from a local tree surgeon for a proper diagnosis.
How To Remove Lichen From Japanese Maple
If you must remove lichen on your tree, gardening experts Plant Harvests recommend gently scrubbing the area using a soft bristle brush and a solution of water and mild detergent, rinsing afterward to remove residue.
As for excessive lichen on the trunk or branches, affected branches may require pruning, and you should consider improving your tree’s growing environment to help increase airflow and prevent overly moist, humid conditions.
Underlying Issues Leading to Lichen Growth
Lichen is a sign that your tree is struggling due to issues such as poor root health, environmental stressors, or simply age. Here are the following factors behind lichen growth on your Japanese maple.
1. Drought Leading to Root Loss
A bad drought can leave the soil parched, which in turn can cause significant root loss in trees.
With fewer nutrients being sent up to the branches, this results in dead or decaying twigs and areas of branches, inviting lichen.
2. Saturated Soil Suffocating Roots
Japanese maples appreciate moist soil, but waterlogged conditions make it hard for oxygen to enter, causing the roots to become suffocated.
Living in excessively wet soil for long periods can also risk the development of root rot and other diseases that will severely weaken a tree.
3. Compacted Soil Limiting Root Growth
Japanese maples require rich, airy soil to thrive, so lichen growth could be a sign that tree roots are suffering due to low oxygen caused by a compacted soil type.
Mulching can help improve soil quality, but consistent issues may require replanting.
4. Slow Growth
If your tree is growing slower than normal or it is naturally slow growing, like the Japanese maple, bark can take longer to shed and be replaced with new growth, presenting an opportunity for lichen to grow on the bark.
5. Disease or Pest Infestation
Underlying diseases or damage caused by a pest outbreak can weaken and stress your tree.
In this case, it’s important to investigate the source and take corrective measures, preferably with the help of a professional arborist if the damage is widespread.
6. General Tree Stress
Trees can easily become stressed when growing conditions are far from ideal (poor soil quality, lack of sunlight, etc.), if it suffers the brunt of storm damage, or has to compete for resources with nearby plants and lawns.
As with age, a stressed tree can result in weaker, more brittle bark, resulting in a cracked surface to which lichen can readily attach itself.
7. A Change in Bark pH
As tree bark ages, it tends to become more alkaline, and some species of lichen need alkaline conditions to thrive. Ash trees (which have a high-alkaline bark) have alone been associated with 536 lichen species!
How To Improve Health of Japanese Maple
To help ensure unsightly lichen doesn’t appear on your Japanese maple, you need to keep it in top shape. Here’s how to show your maple tree some TLC:
- Plant it in spring or fall – This helps the roots settle before the growing season as planting in winter can shock the roots.
- Suppress weeds and maintain moist soil by adding quality mulch – Add about 3 inches of compost and other organic materials like well-rotted conifer bark around the base. Keep mulch a few inches from the trunk to prevent the risk of rot.
- Prune heavily in late winter just before the leaf buds open – Take note of any scrawny or broken interior twigs and branches crowding the space, and cut these back to improve airflow.
- Provide deep watering in drought periods – Water at the root zone slowly for optimal soil absorption.
- Shield your maple from heavy wind and frost damage by planting them near a tall fence or one side of your home.
Is Tree Lichen Harmful to Humans?
Types of lichen that contain large quantities of vulpinic acid are believed to be toxic to humans, and some lichen is thought to be harmful when ingested.
Research into lichen toxicity is fairly limited, however, as the majority of lichens have not been tested for edibility or safety.
Does Vinegar Kill Lichen on Trees?
Vinegar can kill lichen on trees, but it can take a few days to have an effect. Make up a solution of 1 ounce of dish soap and 2-3 cups of white vinegar in a bucket, and pour it into a spray bottle.
After a couple of days, the dead lichen can be scrubbed off or removed with a pressure washer.
Lichen may not be a pleasing sight on your beloved Japanese maple, but it thankfully isn’t likely to do any harm.
The appearance of lichen growth can be taken as a warning sign that your tree is under stress due to compacted or waterlogged soil, dry conditions, and general stress, so revising your care regimen can help to fix these issues.
This harmless organism may only cause problems with your tree directly if the growth is excessive enough to inhibit sunlight exposure and moisture to your tree.
If this is the case, a professional tree surgeon can help assess the damage and provide the right treatment.