Every winter, homeowners notice and ask the question, “What is the blue-gray and green stuff growing on my trees, stone walls, fence posts, walkways and lawn?”

The answer is it’s probably one or all of these three things – algae, lichen or moss.

Algae are threadlike green plants that form a slimy green film on rocks and decks during warm and humid conditions and on soils that are compact and waterlogged. During periods of dry weather, this algal growth forms a dry, cracking crust on the surface of the lawn that repels water and impedes recovery.

For algae control of interior or exterior surfaces around the home, oxygen bleach (hydrogen peroxide) is preferred as it will not harm you, your pets or your plants.

Control options for algae in the lawn include: ammonium sulfate and hydrated lime or fungicides. If using fungicides, then make applications on a 10 to 14-day interval during warm, humid weather.

Lichens are a composite of a fungus and either a green or brown algae capable of producing food by photosynthesis. Lichens are located on every continent including the Antarctic. They survive in all climates and are found on undisturbed surfaces, such as bark, wood, rocks and soil. Lichens do not parasitize plants nor are they associated with any plant diseases. Instead, lichens live in symbiosis with trees and shrubs, often facing north.

When looking at a cove of trees covered in lichen, people mistakenly blame them as the cause for the decline.

In reality, decline may occur from a combination of poor location and soils that are waterlogged and compact with limited light penetration.

Lichen did not cause branch decline, but one of the effects of the plant decline was an increase in lichen growth. To improve tree health, thin out dead trees and limbs, prune off additional limbs for more light penetration and apply fertilizer to promote more growth.

Mosses are small green plants that do not produce seeds or have a vascular system like most plants. Mosses produce spores as a method of reproduction and are part of the Bryophyte division. Mosses are competitive and grow in clumps or mats in cool moist shady areas of woodlands and forests with nearby water.

If you desire to reduce or eliminate your mossy area and take back control of your lawn, then the following practices will help to prevent and control moss:

Take a soil sample to determine proper lime and fertilizer needs. Lime raises pH and helps to lower soil acidity. Changing the soil pH and nutrient levels will minimize weed encroachment and enable grass seeds to germinate and grow in less stressful conditions.

Options for removing moss include: physical removal (e.g., hand or rake) or chemical control with copper sulfate or ferrous sulfate. Read the label for specific instructions for appropriate concentrations and safety.

Afterwards, you may need to remove the moss by raking to allow recovery of the area. Once the moss is gone prepare a good seedbed by tilling in the appropriate amount of lime and fertilizer and reseed bare areas with a shade-loving turf grass.

In addition, for areas already covered in turf, aerify (core) compacted soils. If limited light is an issue then increase light penetration and air movement in shady areas by removing a few trees or limbs, along with unnecessary undergrowth. If sitting water is an issue, consider improving drainage and avoid excessive watering by altering irrigation schedules.

For more information on care of your garden and home orchard, contact Christy Bredenkamp, NCSU Extension horticulture agent, at 586-4009.