Algae in hydroponics: why does it appear and how to prevent it?

Algae in hydroponics: why do they appear and how to prevent them?

You lift a grow basket and discover a green film on the sponge. Or perhaps the walls of your reservoir are starting to turn green.

Don't panic: seeing algae appear does not mean your hydroponic garden is doomed.

To grow, algae notably take advantage of the light and nutrients present in the water. Yet your garden deliberately brings these elements together... to grow your plants.

The goal is therefore not to make the system sterile.

It is mainly about preventing light from unnecessarily reaching the nutrient solution and keeping the setup clean.

Why do algae appear in a hydroponic garden?

A plant and an alga obviously do not have the same structure, but they share certain needs.

Algae notably use light and the nutrients available in their environment to grow. Agricultural extension organizations also observe that algae blooms are favored by the availability of nutrients and that certain species grow particularly well in nutrient-rich waters.

In a hydroponic garden, the water contains hydroponic nutrients intended for the plants.

If this water is also exposed to light, the conditions become interesting for algae.

This is why they often appear:

around an unused growing site;

on a highly exposed germination sponge;

on a constantly lit damp area;

or inside a reservoir if enough light penetrates it.

The light reaching the water is therefore the first thing to check.

Are algae harmful to plants?

A few green traces do not automatically constitute an emergency.

A thin layer around a germination sponge has nothing to do with a system completely covered in algae.

However, it is better to avoid letting the problem take hold.

Strong algae growth can change the conditions in the water. Algae notably consume oxygen when they breathe, and their decomposition can also contribute to a decrease in available oxygen.

This phenomenon is particularly well documented in aquatic environments: large blooms followed by their decomposition can lead to a decrease in dissolved oxygen.

In a small indoor garden, there is no need to wait until it gets to that point.

If you observe significant green growth, clean it and especially look for the cause.

How to prevent algae in hydroponics?

The simplest method is also the most logical:

prevent light from reaching the water where it is not useful.

Your leaves need light.

Your roots and your nutrient solution do not.

1. Cover unused sites

Does your garden have more sites than you want to use?

Do not necessarily leave the openings free to expose the water to light.

An opaque cover adapted to the system allows you to limit this exposure.

This is particularly useful if you are growing a few large plants rather than filling all available sites.

A 14-site garden does not necessarily need to contain 14 adult plants.

The density must first be adapted to the crops.

2. Avoid unnecessarily exposing the sponges

At the beginning of germination, a hydroponic sponge can remain damp and receive direct light from the lamp.

This is precisely the area where a small green deposit can sometimes be observed.

Once the seedling is sufficiently developed, its foliage generally ends up casting more shade around the grow basket.

Before that, simply check that the sponge is correctly positioned and that it does not unnecessarily protrude from the basket.

Do not try to completely enclose the young plant, however: it obviously needs light and space to grow.

3. Keep the reservoir away from light

An opaque reservoir is preferable to a transparent container directly exposed to horticultural lighting or a window.

If you use your own hydroponic setup, think about this point from the design stage.

A pretty transparent jar filled with nutrient solution can be photogenic.

To limit algae, it is much less interesting.

What to do if algae are already present?

Start by looking at their quantity.

A few traces on a sponge or around a basket do not require the same intervention as a reservoir whose walls have turned green.

For a light deposit, remove what is easily accessible and correct the light exposure.

If the algae are much more prevalent, take the opportunity to perform a more complete cleaning of the system in accordance with the manufacturer's recommendations.

You can notably:

• remove accessible residues;
• clean the surfaces concerned;
• renew the nutrient solution if its condition justifies it;
• check the pump and the areas where debris can accumulate;
• restart the system with clean water and the appropriate nutrient dosage.

The goal is not only to remove the visible green.

You must remove the condition that allows it to return.

The recommendations for managing algae in aquatic environments go in the same direction: acting only on visible algae without treating the conditions that favor their growth often leads to having to start over.

Should you put an anti-algae product in your garden?

This is not the first reflex to have.

Your hydroponic garden is used to grow plants that you may eventually eat.

Adding randomly a product intended for a pool, a decorative pond, or an aquarium is therefore not a good idea.

Some treatments used against algae in aquatic environments can have effects on other organisms and their dosages depend on the context of use. Penn State recommends, for example, strictly following the labeling of algicides used in ponds and highlights the necessary precautions with certain substances.

For a small home garden, start rather with the simple levers:

light, cleanliness, water circulation, and regular maintenance.

Only use a treatment if it is explicitly intended for your system and your use.

Green water, white deposit, or brown roots: do not confuse everything

Every color change is not an alga.

A whitish deposit can be linked to something else, notably minerals present in the water.

A discoloration of the roots can come from the nutrients, their natural aging, or, in some cases, a root problem.

And water slightly colored by a nutrient solution is obviously not necessarily dirty.

Algae generally have a characteristic green color and can form a film on lit and damp surfaces.

Before treating anything, therefore take a few seconds to identify what you are really observing.

→ Read our guide on brown roots in hydroponics

How often should you clean your hydroponic garden?

There is no universal frequency adapted to all systems and all crops.

A small garden with three young herbs does not get dirty exactly like a setup accommodating several large adult plants.

The right reflex is rather to regularly observe what is happening under the leaves.

When you fill the reservoir, take the opportunity to look at:

the condition of the water;

the accessible walls;

the grow baskets;

the sponges;

the roots;

and the operation of the pump.

Between two crops, a more complete cleaning allows you to start over with a clean setup before introducing new seeds.

This little routine takes less time than waiting for a problem to become well established.

So a hydroponic garden requires maintenance?

Yes.

Hydroponics removes soil and traditional daily watering, but it does not remove maintenance.

You must always fill the reservoir, add the appropriate hydroponic nutrients, monitor the plants, and clean the system when necessary.

The difference is mainly in the nature of the actions.

On the Belverdia models equipped with a pump, water and nutrients circulate in the system. The Verdia Mini, for example, has a 1.6 L reservoir and three sites; the Verdia One uses a 5 L reservoir with 14 sites. Both have integrated horticultural lighting.

This makes indoor growing easier, but does not make the plants autonomous.

→ Download the free guide

What to remember if you see green in your garden?

Three things.

First, a few traces of algae do not mean your crop is lost.

Next, look where they appear. An empty site or a directly lit sponge often gives an immediate clue.

Finally, do not only look to clean.

Look to prevent light from unnecessarily reaching the water and maintain a regular maintenance routine.

In hydroponics, small problems are generally much easier to manage when you notice them early.

And lifting a grow basket from time to time to look at what is happening underneath is probably one of the best habits to take.