Phosphites in Hydroponics: A Powerful Biostimulant

Phosphites in Hydroponics: What You Need to Know

Often confused with phosphates, phosphite’s (HPO₃) are actually a unique class of compounds with compelling biostimulant properties, especially valuable for hydroponic and horticultural growers aiming to maximize root development.

What Are Phosphite’s?

Phosphite’s are chemically different from phosphates, despite the similar names. While phosphates are PO₄-based and essential for flowering and fruiting, phosphite’s (HPO₃) function more as biostimulants than nutrients. In simple terms, they’re as different as water (H₂O) is from hydrogen peroxide (H₂O₂). The form most commonly used in agriculture is potassium phosphite, a clear liquid often formulated into various plant products.

How Phosphites Boost Root Growth

Phosphite’s are particularly effective at promoting early-stage root development. They’re commonly used in root crops like potatoes and in hydroponics to establish a strong root base before flowering begins. A healthy root system not only supports better nutrient uptake but also helps plants outcompete pests like slugs and nematodes.

This early root vigor is crucial in many crops, especially in controlled environments where every growth stage must be optimized.

Myth Busting: Phosphites ≠ Phosphates

It’s a common misconception that phosphite’s can act as a direct source of phosphorus for plants. While they contain phosphorus, phosphite’s do not convert easily into usable phosphate. So if you’re after a phosphorus supplement, you’re better off sticking with actual phosphate fertilizers.

Some marketers falsely claim phosphite’s provide “readily available phosphorus” or promote their fungicidal effects. However, scientific studies, including research from the University of Nottingham, show phosphite’s work more as biostimulants than fungicides.

Phosphites vs. Glyphosate: A Note of Caution

Interestingly, glyphosate, the well-known herbicide, shares part of its molecular structure with phosphite’s. Both belong to the phosphonate family. However, unlike glyphosate, phosphite’s do not kill plants—they stimulate growth. That said, if you’re cautious about chemical inputs, you may want to explore organic alternatives like:

• Amino acids
• Humic acids
• Seaweed extracts

These offer similar root-boosting benefits without synthetic chemical origins.

The Takeaway: Are Phosphites Right for You?

If you’re struggling with weak root systems, battling soil pests, or looking for a growth edge in early crop stages, phosphite’s may be worth considering—particularly in non-EU regions where they remain legal. They’re powerful, low-toxicity biostimulants that can offer hydroponic growers a real advantage.

However, they are not a substitute for phosphorus nutrition and are not organic. Always read the label and verify claims—especially around fungicidal effects.

Final Tip
If you’re focused on flowering, don’t be quick to grab that PK booster. In many cases, dialling back nitrogen and focusing on micronutrients like iron (such as using a product like Slugger) may be more beneficial than loading up on phosphorus.

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