Moss or Lichen on Your Tree in Richmond Hill?

Look closely at almost any older tree in Richmond Hill and you will find something growing on it. Soft green moss on the shady side of the trunk. Flat grey-green crusts. Little leafy, frilly growths on the twigs. People often call us worried that these are killing the tree. They almost never are.

What Moss and Lichen Actually Are

They look similar from the ground, but they are two very different things.

Moss

Moss is a small, simple plant that needs moisture and shade. It has no roots that go into the tree. It simply sits on the bark where water collects, which is why it gathers on the north side of trunks and at the base. A yard where moss grows on the trunk usually has moss on the fence posts, the shady side of the roof and the patio stones too.

Lichen

Lichen is a partnership between a fungus and an alga, living together as one organism. It makes its own food from sunlight and takes moisture from the air. It comes in crusty patches, leafy rosettes and hairy tufts, in shades from grey-green to bright yellow and orange. Lichen grows slowly, and it grows best in clean air and good light.

Why They Don’t Hurt the Tree

Neither moss nor lichen takes anything from the tree. They don’t reach through the bark, they don’t feed on the wood and they don’t block the tree’s pores in any way that matters. You can see heavy lichen on healthy oaks, maples and fruit trees that live for decades. In a sense, lichen is a compliment: it doesn’t grow well where air quality is poor.

When It Is a Clue

There is one situation where lichen is worth reading. Because it loves light, it spreads quickly onto branches that have lost their leaves. A tree that is declining for some other reason, from root damage, drought or age, opens up its crown, more sun reaches the bark, and lichen moves in. Then it looks as if the lichen did the damage.

It didn’t. It arrived after. So if you see lichen thickly coating branches that also have few or no leaves, the question to ask is why those branches are bare. That is common on older blue spruce in Richvale and Crosby, where the inner needles drop with shade and age, and on old apple and crabapple trees in backyards that have seen better days.

A Quick Check

• Moss or lichen on a tree with a full, healthy crown: leave it alone.
• Lichen on bare twigs of an old spruce: normal ageing. The lower bare branches can come off for looks and clearance.
• Lichen covering limbs with no buds in spring: those limbs are likely dead. Have the tree checked.
• Moss plus soft, spongy wood, cavities or mushrooms: the moss is a side note. The rot is the problem.

What Not to Do

Don’t scrape, wire-brush or pressure-wash bark to get rid of moss or lichen. Bark is the tree’s skin. Damaging it opens the way for insects and disease and does far more harm than anything growing on the surface. Skip the sprays and powders sold for moss on roofs too. They aren’t meant for trees and they aren’t needed.

Letting in More Light and Air

If moss bothers you, or your yard stays damp and dark all summer, more light and airflow help. That might mean thinning out a dense crown so wind and sun reach the inner branches, raising low limbs, or cutting back shrubs crowded against the trunk. It is the same work that helps a crowded tree stand up better in storms. Our crown thinning page explains how we do it without overcutting.

In the older parts of town, in Mill Pond and Observatory and along streets with big mature canopies, a little thinning goes a long way toward a brighter, drier yard.

Richmond Hill Notes

Thinning and normal pruning are routine care. If a tree turns out to be in decline and has to come down, private trees 15 centimetres or wider at chest height need a City permit under Tree Preservation By-law 19-25. City boulevard trees are the City’s to look after: contact Access Richmond Hill at 905-771-8800.

Moss on the Roof and Deck

Sometimes the real complaint isn’t the tree at all. A heavy canopy hanging over a roof keeps shingles damp, and moss follows. Branches resting close to the house also drop needles and leaves into the eavestroughs, which hold water and feed more moss. Lifting or shortening those limbs lets the roof dry between rains. That is pruning for the house rather than the tree, and it is a common reason Richmond Hill homeowners in shaded older streets call us.

Asking for an Honest Look

If the lichen sits on bare branches, or you’d simply like a second pair of eyes, send a photo of the whole tree to (289) 475-5822. Scott is happy to drop by the same day and give you a free opinion and quote; the line is open daily from 8am until 8pm. More often than not, the honest answer is that your tree is fine and the green stuff can stay.