Slugs and Snails in Hydroponics: Why It Happens and How to Stop It

Unexpected Visitors: Slugs in Hydroponic Systems?

Hydroponics is often touted as a pest-free method of growing—but this blog will prove otherwise. A grower contacted Eutrema after discovering slugs invading their NFT (Nutrient Film Technique) system—something most hydroponic growers don’t expect.

These weren’t aquatic snails or fish-tank pests—they were full-on land-dwelling slugs, actively munching on crops in a clean, controlled grow environment.

Why Slugs and Snails Invade Hydroponic Systems

The culprit? A perfect storm of moisture, plant matter, and possibly the use of seaweed-based fertilizer, which may have created the ideal conditions for slugs to thrive.

While less common than in soil gardening, slugs and snails can still invade:

• Densely humid grow environments
• Organic or seaweed-rich nutrient inputs
• NFT or DWC setups with consistent moisture and minimal barriers

Biological Control: Nematodes

The go-to biological defence is a parasitic nematode with the tongue-twister name: Phasmarhabditis hermaphrodita. These beneficial nematodes infect slugs, leading to septicemia (blood poisoning) and eventually death.

However, there are limitations:

• 🧊 Cold temperatures reduce effectiveness
• 🌊 Nematodes may drown in NFT systems
• 📦 Limited seasonal availability

Commercial alternative nematode species like “Nemaslug 2.0” exist, but buyer beware: they’re often marketed more for IP protection than superior performance.

Ferric Phosphate-Based Sprays

I would recommend Slugger, a liquid ferric phosphate solution developed at Eutrema. It’s currently the only liquid form available in the UK and:

• Can be sprayed on lower plant stems and surfaces
• Works better than dry pellets, which slugs often avoid

Why Not Slug Pellets or Salt?

• Metaldehyde-based slug pellets, though highly effective, were banned in the UK in 2018 due to toxicity to pets, humans, and water systems.
• Salt kills slugs, but also kills plants and is cruel. Sodium is highly toxic to plant roots.

Myths and Ineffective Controls

Many traditional “slug deterrents” just don’t work:

• 🧣 Copper bands – Slugs crawl right over them
• 🍺 Beer traps – Most slugs drink and walk away
• 🧵 Sheep wool barriers – Ineffective in high-moisture setups
• 🔦 Night patrols – Effective but labor-intensive

If you’re going manual, do it humanely—slugs feel pain due to their opioid receptor nervous system.

Alternative Natural Deterrents

Some plants naturally repel slugs due to high caffeine content or secondary metabolites:

• ☕ Coffee grounds or cold tea sprays
• 🍃 Plantain (Plantago) – rich in caffeic acid
• ❌ Avoid hostas, lettuce, and delphiniums if you’re slug-prone

Warning: Not All Slugs Are Slugs

Some sawfly larvae mimic slug-like appearances, especially on orchard crops like cherries and pears. These pests:

• Look glutinous to avoid predators
• Eat from the inside out—damage often unnoticed until it’s too late
• Require regular visual inspections to catch early

Dr. Sharp’s Final Advice: Daily Monitoring Is Key

While hydroponics can be highly automated, pest monitoring isn’t. AI cameras may be improving, but nothing beats a human eye—for spotting:

• 🐌 Slugs/snails
• 🐜 Thrips
• 🕷 Spider mites
• 🐛 Sawfly larvae

“Don’t water every day, but do check your plants every day.”

Closing Thoughts: Slugs in Hydroponics—Who Knew?

Slugs may seem like a soil-only problem, but even high-tech hydroponic systems can fall victim. If you notice damage or slime trails:

• Don’t panic
• Identify the pest
• Use biologics or safe chemicals like Slugger
• Stay consistent with plant inspections

And remember—never assume pests can’t reach your clean room. They will find a way.

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://open.spotify.com/show/207T7p7fw9sPjINfSjVXW2

Cereal Killers Podcast: https://t.co/eSEbBkTVHl