Liking the Lichens

The questions that I get asked about gardening and horticulture get more and more sophisticated as gardeners gain more and more experience. This is reflected in our garden spaces and the plants that we experiment with and try to grow. Twenty years ago I would have never been asked how to grow lichens, but now the subject comes up regularly.

Lichens can be a wonderful component of our landscape, though they are often seen, noted and then passed by. The yellows, grays, greens and silver hues contribute a subtle beauty all year. In the dead of winter as they peek out from rock tops or on the trunks of woodland oaks and even garden furniture, they garner interest. To say that they are misunderstood is an understatement (they are pronounced like-en) because they are not classified in any of the plant communities that we are familiar with. They can be found growing on rock, the bark of trees and shrubs, leaves, stained glass windows, fence posts, garden furniture and gravestones.

Amazingly, there are more than 16,000 species worldwide occurring in both macro and micro forms. In recent years it’s been discovered that lichens are a very important indicator of air quality because they are very sensitive to air pollution, especially sulfur dioxide, a common pollutant from automobiles. You’ll be hard-pressed to find lichens growing in Queens or Brooklyn, but as you travel east on Long Island they become more common and they seem to thrive on the South Fork. Now that it’s cooling, but still humid, the growing conditions and colors are peaking.

If you remember any of your biology or botany, the lichens can be perplexing because these organisms can be considered plants, but at the same time they can be thought of as fungi. In actuality, they are both. Lichens grow in an unusual and very special way. They are classified as a cryptogram. This class of organisms includes the lower or non-flowering plants such as algae, fungi, mosses and liverworts. Lichens form a symbiotic relationship in which two or more organisms simultaneously exist. There can be a benefit to each partner, yet neither is harmed.

A lichen has an algal partner and a fungal partner. The alga has the ability to make its own food and it photosynthesizes. The alga is provided with a home and the fungus is provided with nutrients it could not have derived on its own. Fungi do not make their own food but rather derive it from their environment.

As far as we know, the lichens are long lived perennials that grow very slowly and they can be inhabitants of the harshest environments. They can be found in places that are extremely wind-swept, droughty or both. The optimal conditions, though, seem to be low light—the north side of an oak or a shaded stone wall or monument—high humidity and cool temperatures.

Water uptake is critical and can be a limiting factor to their growth and development, something to consider if you are planning on growing them. They lack the ability to store or conserve water and they will absorb it quickly from the environment when available. This occurs mostly from moisture laden air be it from high humidity, dew or precipitation.

When moisture is not available, the lichens have the ability to go dormant. Then, within hours of the moisture returning, they revive. They have also been known to inhabit the exact same site for years and decades while some that inhabit boreal, arctic or alpine sites seem to stay in the same spot for hundreds of years.

Lichens form thalli (plant bodies) that occur in four forms: foliose, fruiticose, crutose and squamulose. Foliose, as the name implies, simply means foliar, or leaf like. The thallus, or plant body, of a lichen is often divided into lobes and the width of these lobes is used in identification. A fruiticose form is shrub-like in structure, forming small, scaled down, miniature bodies. They can be hairy and bushy, attaching themselves to rocks and trees. A crutose form is one that forms a crust on the surface of rock, bark, etc. Squamulose lichens have small separate lobe-like structures that form their bodies.

Apart from their natural beauty and complexity, you probably don’t realize how important the lichens are economically. They are used in the production of perfumes, medicines, dyes and poisons as well as for food for reindeer and humans. Litmus paper, used to determine the relative acidity or alkalinity of a solution, relies on a lichen extract to indicate the change of pH. Essential oils contained within lichens are use as perfume bases and as fixatives, which mellow and preserve fragrances.

A yellow European species of lichen is used to create an effective antibiotic salve. Usnic acid is the active ingredient that is extracted. Cetraria islandica (Iceland moss) is still actively used in Chinese medicine as an expectorant. The Harris tweeds from Scotland utilize a lichen to achieve those characteristic hues. In Africa, it’s smoked. A mash is made to produce alcoholic beverages. And there is even a biblical connection—it’s thought by some that the manna that appeared to Moses and the Israelites was actually a form of lichen that had been blown down from the trees or from the mountains and down to the flat plains.

So, how do you get it to grow where you want it? Remember, it doesn’t grow from seeds, so you can’t go that route. It doesn’t grow from spores, so that option is out also. In humid weather they can be moved from one site to another, but the substrate—be it rock, bark or exposed wood—and the exposure needs to be nearly identical in the new location. You’ll have little luck if you try to move lichen from a rock face to a fence post. One strategy to consider if the lichen is growing on wood, bark or small rocks is to remove a small piece of the wood, bark or the rock to the new home and hope for colonization, but again, the original growing conditions are imperative. Don’t expect the lichen to live if you move it from the north side of an old oak to the south or west side of your prized beech (or beach).

One thing that we do know for sure is that lichens can reproduce like many mosses do: from broken pieces. These small pieces often produce microscopic “buds,” each of which is actually a piece of algae and fungus threaded together. These pieces will then start growing together whenever the conditions are just right. There’s some anecdotal information that if you paint an area with fresh yogurt then apply the lichen pieces it will enhance the chances for success. But so far, all I can find is references to those who have tried this method, not to anyone who has had success with it.

So, here’s your new challenge in the garden to add some new color and texture to your rocks, fence posts and bark. Lichens really thrive out here so you may find it an easy task. And if you’ve done it before or are giving it a try now, please drop me a line so we can follow your progress. Keep growing.