Algae

The fish tanks of our youth were often coated with algae.

As gardeners, you may see algae growing in planter pot saucers, rain barrels, or birdbaths. You may also see it growing on your soil.

But what do you really know about this plant family? And what does it do in your garden?

Algae growing on damp concrete (Kate Russell)

Algae plants

Algae are a large group of plants most commonly found in water. Most seaweeds are algae, but I doubt any of us are growing any seaweed in our gardens. Unlike moss, which prefers shaded areas, algae thrive in direct sunlight. Algae can also become a problem in greenhouses and on houseplants. By learning more about how these plants grow, we can find ways to reduce a few garden problems.

Algae are simple plants that contain chlorophyll and perform photosynthesis, the same as your tomato plants. Some of them absorb nutrients through osmosis, sucking, or surrounding and incorporating smaller life forms. Algae need water more than they need heat. This is why algae is often seen in spring and autumn on soil with drainage or overwatering problems. Algae do not have true stems, roots, leaves, or vascular tissues.

There are green, brown, red, and golden algae. There is also something called blue-green algae that is more closely related to bacteria than plants. These microorganisms are all believed to be some of the first lifeforms on Earth. But we probably don’t want them growing in our birdbaths or on our soil.

Algae growing on soil with poor drainage (Kate Russell)

Algae on soil

A thin layer of green slime on exposed soil is usually algae. Algae won’t harm your plants directly, but it does compete for nutrients and water, and often attracts fungus gnats and shore flies. As the algae dry out, they can form a dark, dry crust that makes it difficult for water and gases to penetrate in either direction.

Algae prefer neutral to alkaline soil pH, so acidic soil is less likely to have a problem with algae. If your soil is heavy or compacted, adding compost can improve drainage. If you have an area that stays wet, you may want to consider installing a rain garden there. Rain gardens are sunken areas that put native plants to work to absorb excess water.

Algae in plant containers

Algae can grow on vermiculite, peat moss, and perlite, as well as soil. If plant containers and seedling pots are not allowed to dry out between waterings, algae spores floating in the air will take up residence. Rather than watering containerized plants from above, add water from below. This encourages the root system to expand downward and makes life more difficult for algae.
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​Algae in birdbaths

If your yard features a birdbath, keeping it clean is necessary for bird health. Red algae commonly grow in birdbaths and should be removed by scrubbing with a mixture of 9 parts water and 1 part vinegar. Birdbaths placed in sunny areas will have more of an algae problem than birdbaths placed in the shade. Position your birdbath accordingly.

Red algae bloom in concrete birdbath (Kate Russell)

​If you see algae in your garden soil, try aerating the area. If you see algae in potted plants, let the soil dry out between waterings. If your birdbath is demanding more time than you want to give, move it to a shadier spot.

And if you haven’t seen the fish in your tank lately, it may be time for a good scrubbing,