The Truth About Foliar Sprays in Hydroponics

In today’s blog, we’re diving deep into one of the most debated topics in plant nutrition — foliar sprays. Whether you’re a home grower, commercial cultivator, or somewhere in between, understanding the true benefits and pitfalls of foliar applications can make or break your grow.

What Are the Benefits of Foliar Sprays?

1. Fast-Track Nutrient Delivery
Foliar feeding allows nutrients to be absorbed directly through leaves. This can bypass nutrient lockout in the soil or hydro system — especially useful for:

• Iron deficiencies
• Zinc and calcium deficiencies
• Silicon applications to strengthen cell walls

2. Powerful Biostimulant Delivery
Biostimulants like seaweed extracts, amino acids, and aloe vera can be absorbed more effectively via the leaves. These help boost:

• Growth rate
• Plant resilience
• Protein synthesis

3. Pest Monitoring and Houseplant Health
Regular foliar spraying helps:

• Spot spider mite webs early
• Remove dust and debris from houseplants
• Act as a therapeutic, hands-on activity for growers

4. Mildew Control (In Some Cases)
Spraying can trigger mildew spores to germinate prematurely, preventing outbreaks — although this comes with risks (more on that below).

The Downsides: When Foliar Sprays Backfire

1. Poor Leaf Absorption
Not all plants absorb sprays efficiently. Hairy or waxy leaves (like lupins or some brassicas) may cause the solution to bead off and become ineffective.

2. Increased Risk of Disease & Scorch
Spraying in high humidity can promote fungal diseases. Likewise, applying foliar sprays during intense light or heat can cause:

• Leaf scorch
• Nutrient burn (especially with nitrogen, calcium, sulphur)

3. Expensive and Diluted Products
Many “ready-to-use” (RTU) foliar sprays are just diluted base nutrients — often sold at a premium. Some even contain unpreserved ingredients or dangerous heavy metals like:

• Copper
• Cobalt
• Nickel
• Zinc (in high concentrations)

These should be avoided, especially if you’re spraying in enclosed grow rooms or near vents.

Pro Tips for Using Foliar Sprays Safely

• Test first: Try on a few leaves before spraying an entire crop.
• Spray during cooler parts of the day: Early morning or late evening is best.
• Avoid spraying flowering plants: Prevents bud rot and residue buildup.
• Check ingredients: Avoid harmful metals and opt for biostimulant-rich formulas.
• DIY if possible: Understand what you’re applying — and why.

Final Thoughts

Foliar sprays have their place in precision horticulture, but they’re not a silver bullet. Use them wisely, understand the science, and never overpay for watered-down products.

Have you had success (or disasters) with foliar feeding? Get in touch with Dr. Russell Sharp on social media via Liquid Gold (UK) or Gold Leaf (US). And don’t forget to follow Hydroponics Daily for daily insights into the world of soilless growing.

Any if you are looking for an excellent fertilizer to feed the roots while you feed the foliage with your new knowledge of folia spraying, check out Liquid Gold

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