Aquatic Plant Primer: How To Control Moss

Fish and Lake Management
Best of several worlds. Notice the peripheral plants, all native, with a purpose of holding soil in place. They look natural, which they are. But, see the green water? That fertility is the base of the food chain, plus it blocks sunlight from the bottom in water two feet deep and deeper. Good plan.

Late spring, early summer is the time of year our phone rings off the hook from anxious pondmeisters who are concerned about "too much moss" in their precious ponds. I know, I know—we've written about this topic many times over the years, but it just doesn't seem to go away, does it?

The more you know, the better decisions you can make, even if the subject seems redundant.

Underwater plant growth seems to follow that line of thinking—redundant, and abundant.

We collectively need to know more about what makes plants do what they do.

Right now is the time to decide what to do about your plants, so right now is a good time to increase your awareness level, seek knowledge, and plan what to do.

I know. I can read your mind. "We don't have a problem. We don't have too many plants." My answer, "Not yet, but you will."

Understand what to do before you have a problem. When those inevitable phone calls come, biologists have a process. It starts with defining that word, problem. To most pondmeisters, plants are a problem when they can be seen, or when their lures inevitably snag and drag. Instead of catching a big fish, you haul in a bundle of salad.

Biologists see these plants through different eyes.

That pond pro knows that some level of native plant life is both natural and needed. Different species of native plants work with a pond to establish much-needed habitat for newly hatched fish, to give them a fair shake at substantial time and food to play a better role (whatever that role is) in a pond's fish population.

The pondmeister, on the other hand, is influenced by how much those plants impact pond usage. If one can't cast a line, drive a boat, swim, or enjoy the way a pond looks because of its excessive underwater salad bar, then that's when plants become the problem.

So, what do you do? The biologist thinks a pond needs it, the pondmeister doesn't like too much of it.

Unlike our current Congress seems to think, compromising is a good idea. Relegate weeds where they're best suited, but not in conflict with end user benefit.

Remember this: as long as 20-25% of a pond's area has adequate habitat, things click. A percentage of that habitat can be aquatic plants. So, the reality is this. If a pond truly has that magic number for habitat, less than a fourth of that needs density as thick as underwater plants. Interpretation? If a pond has 5-10% coverage of submersed plant life, that's good. The rest of the habitat can be in the form of ridges, humps, creek channels, timber, artificial structure, and such. Since each pond is its own entity, and is autonomous, the true percentage is a reflection of that pond. Interpretation? Some ponds will have more plants, others will have less.

So, enough of the theory. What's the reality?

Right now, early spring, plants will begin their annual arousal. Three things have to come together for plants to grow. Plants need sunlight, temperature, and food. When that combination happens, plants grow. Different plants have different requirements of any of the Big 3, or some combination. Algae grows in cooler water. American pondweed waits until its warmer. Filamentous algae can glean its nutrients from either the mud or the water. Bushy pondweed is fed from nutrient-rich pond bottom mud. Cattails spring up, almost overnight, where they were last year, once the temperature warms to their magic number.

If you want to avoid plans for buying stuff like this weed rake, plan now. You'll be glad you did.
If you want to avoid plans for buying stuff like this weed rake, plan now. You'll be glad you did.

Job One for pondmeisters is to understand that concept.

Job Two is to understand that plants are never the problem. They aren't. Plants are a symptom of the problem. If you drill your thought process down to understanding what plants need in order to thrive, you're a long way into managing them. Remove any one of the Big 3 and you've eliminated the plants. Sounds easy, doesn't it?

That's one reason knowledgeable pond builders recommend 3:1 slopes for ponds. Get to deeper water fast and sunlight can't penetrate to the deeper water, so you prevent unwanted plant growth. That's also a reason some biologists recommend fertilizing ponds in the proper circumstance. Decrease visibility in water to prevent plants.

What about temperature? Can't do much about that. Food? As ponds age, nutrients roll in with rainfall runoff. Aeration can mitigate food for plants by keeping some amount of nutrients suspended in the water column, feeding plankton and microscopic stuff. Otherwise, heavy work is needed to get rid of nutrient-laden pond bottom muck. Not easy.

Assess your situation right now, while water temperatures are moderately cool and making their annual climb. Even if you simply climb in your boat and drag a hook along the pond bottom, go look for plants. When you find something, figure out what it is. Take a photo and compare it to some of the sites online. Once you understand what you have, it's up to you to interpret what it means, and then project what will happen. If it was bad last year, expect the same this year, but now you get a jumpstart and can decide what you want to do.

This is where I turn up the pond music and break into the song and dance of how to deal with plants. This time of year, prevention is definitely the best way to go. Decrease visibility with fertility. Think about dye, but don't do it if your fishery is important. Dye a pond to minimize ultraviolet light penetration from the sun only if you don't care about your fish.

When you have plants, prepare to deal with them. First, identify the plant species. Learn if they are native or exotic. Learn if they are invasive or not. Then, decide what to do. There are three basic types of plants: emerged, submersed, and floating plants. Emerged plants tend to grow around the perimeter. Those are cattails, bulrushes, lilies, lotus, arrowhead, and primrose, to name a common few. Submersed plants are the pondweeds, algaes, coontail, milfoil, and others. Floating plants include duckweed, watermeal, azolla, and others.

There are three fundamental ways to deal with aquatic plants. There are physical ways, such as with cutters, rakes, and underwater mowers, not to mention the creative things I've seen over the years. One of my faves was the guy who used a big chain-link fence gate tied to a rope on the back of his tractor—with two high school kids to toss the gate over the moss, and then dig it off the gate when the tractor pulled it out. Biological remedies are mostly limited to white amur, also known as grass carp. Approved herbicides are abundant and specific for each type or species of plants. Ironically, none of the control methods solve the problem; they are just temporary ways to deal with unwanted plants until we grasp the fact that the Big 3 is actually the problem.

Once we understand that, we can go head to head with plants.

Now is the time to put that thought process into place.

Reprinted with permission from Pond Boss Magazine