Why Sulphur is Essential in Hydroponics.

When most hydroponic growers think of essential nutrients, nitrogen, phosphorus, and potassium usually top the list. But there’s another critical element often overlooked: sulphur.

Whether you spell it sulfur (US) or sulphur (UK), this secondary macronutrient plays a major role in plant vitality, especially in hydroponic systems. In this article, we’ll explore why sulphur is important, what deficiency looks like, and how to ensure your plants are getting enough.

What Does it Do in Plants?

Sulphur is indispensable in several key plant processes:

• ✅ Protein Synthesis – Some amino acids (like cysteine and methionine) require sulphur, making it essential for building proteins.
• ✅ Enzyme Function – Sulphur is a component of enzymes involved in metabolism and plant growth.
• ✅ Photosynthesis Efficiency – Even if your plants are packed with chlorophyll, without sulphur, they can’t properly convert sunlight into energy.
• ✅ Chloroplast Function – These are the powerhouses of photosynthesis, and they can’t operate correctly without sufficient sulphur.

Symptoms of Deficiency

Unlike nitrogen deficiency (which causes yellowing), sulphur deficiency results in:

• 🟢 Light green or dull green leaves
• 🌱 General lack of vigour
• ⚠️ Often mistaken for other nutrient deficiencies

In hydroponics, this is one of the more common deficiencies, especially when using nutrient regimens that lack sulphur entirely.

Why Sulphur Deficiency Is Common in Hydroponics

Many granular and liquid fertilizers do not include sulphur. Manufacturers often assume you’ll supplement it or that it’s present in your water supply—but that’s not always true.

For example, some hydroponic lettuce growers in the U.S. assumed sulphur was present in their irrigation water. Unless you live near a volcano, your water probably isn’t supplying much sulphur. Once they began supplementing sulphur (or better yet, switched to a complete feed like Liquid Gold), their crops recovered almost overnight.

Avoid These Common Sulphur Mistakes

✅ Don’t burn elemental sulphur in grow rooms with crops present—it can form sulphuric acid, damaging plants.

✅ Avoid powdered sulphur on soil or media—it breaks down too slowly and can lower pH drastically.

✅ Do use soluble sulfur forms or a complete nutrient mix that includes sulfur in bioavailable form.

Pro Tip: Secondary Macronutrients Matter

Sulphur is a secondary macronutrient, but that doesn’t mean it’s optional. It’s required in significant amounts, and deficiency can limit your plant’s performance—even if everything else is dialed in.

A good rule of thumb: if your leaves look dull and growth is slow despite full feeding, check your sulphur levels.

Final Thoughts

Sulphur often flies under the radar, but without it, your plants won’t thrive. It’s essential for vibrant, healthy crops—especially in hydroponics where assumptions about your feed or water can backfire.

If you’re experiencing slow growth or pale leaves, sulphur might be the missing link in your nutrient strategy.

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