Wetting Agents in Hydroponics

In this blog we break down a misunderstood but essential tool in hydroponics: wetting agents, also known as surfactants.

These substances act like specialised soaps, helping water behave the way growers want it to—whether that’s re-wetting hydrophobic media, improving foliar spray performance, or supporting pest control.

Let’s explore the three main types of surfactants, their uses, and some big mistakes growers should avoid.

What Are Surfactants?

Surfactants change how water interacts with surfaces. In horticulture and hydroponics, they’re used to:

• Re-wet dried or compacted growing media
• Improve water penetration
• Help nutrients penetrate soil or substrates
• Enhance pesticide coverage
• Break down insect wax layers (in insecticidal soaps)

They fall into three main categories:

1. Cationic Surfactants (Positively Charged)

Mnemonic: “Cat = +”
Think of a cat with a plus sign on its back—silly, but it helps.

These should almost never be used in horticulture.

They are extremely strong antimicrobials capable of killing:

• Plants
• Algae
• Microbes
• Beneficial biology

They are typically reserved for industrial disinfection, not growing.

2. Anionic Surfactants (Negatively Charged)

These are the most commonly used surfactants in hydroponics and horticulture.

Why growers use them:

• Re-wets hydrophobic media (soil, peat, coir, compost, even some synthetic media)
• Helps open up compacted, dried-out substrates
• Used in certain wetting agent formulas
• Used in insecticidal soaps (if formulated safely)

Eutrema manufactures two popular anionic surfactants:

• Clay Drainer – improves drainage and re-wets soil or dried growing media
• Yucca Extract – a natural anionic surfactant derived from saponins

Yucca is widely respected for being gentle, effective, and plant-safe.

3. Non-Ionic Surfactants (No Charge)

These are mostly found in:

• Foliar sprays
• Pesticide mixes
• Herbicide formulations

They help chemicals spread, adhere, and penetrate plant surfaces.
They are not typically used as growing-media wetting agents.

Why Growing Media Becomes Hydrophobic

Over time, many types of substrates shrink, compress, and dry out. This causes water to bead on the surface instead of soaking through.

Common hydrophobic media:

• Peat
• Coir
• Compost
• Soil mixes
• Long-standing substrates used in pots or beds

If this happens, even heavy watering won’t help—water simply runs off.
This is when anionic wetting agents are essential.

Do Fertilizers Contain Surfactants?

Some brands include surfactants in their nutrients.
At Eutrema we do not add them too fertilizers because:

• They can cause excess foam in recirculating systems
• They remove grower control
• Many systems don’t need them continuously

The Hidden Danger: Sodium-Based Surfactants

Avoid sodium-lauryl-sulfate-based insecticidal soaps.

Why?

• Sodium is as toxic to plants as arsenic is to humans
• Sodium accumulates in media
• It prevents nutrient uptake
• It causes leaf burn and long-term stress

Shockingly, many expensive “garden safe” products contain it. If in doubt, check the Safety Data Sheet (SDS).

Choose sodium-free alternatives instead.

Eutrema’s own Insecticidal Soap is one such option, designed to dehydrate pests without damaging plants.

How Insecticidal Soaps Work

Surfactants break down the waxy coating on soft-bodied insects such as:

• Aphids
• Whitefly
• Mites
• Thrips

This causes pests to dehydrate and die.
But the formulation must be precise—too strong and it harms plants as well.

Key Takeaways

• Cationic surfactants: Avoid them; they’re too harsh for horticulture.
• Anionic surfactants: Best for wetting agents and insecticidal soaps.
• Non-ionic surfactants: Best used as adjuvants in pesticide mixes.
• Avoid sodium-based formulas: They are plant-toxic.
• Natural yucca extract: A safe, effective anionic surfactant for hydroponics.

Wetting agents may be “glorified soaps,” but they’re powerful tools—when used correctly. Whether you’re re-wetting hydrophobic media or enhancing pesticide performance, knowing the right surfactant type can save crops and improve yields.

Article by Dr Russell Sharp

If you would like to keep up to date with subjects just like this, you can listen to both our podcasts! Links can be found bellow:

Hydroponics Daily Podcast: https://podcasts.apple.com/us/podcast/hydroponics-daily/id1788172771

Cereal Killers Podcast: https://podcasts.apple.com/us/podcast/cereal-killers/id1695783663