Can Epsom salt be used in hydroponics?
Written by
Olivia Mitchell
Reviewed by
Prof. Samuel Fitzgerald, Ph.D.Epsom salt (magnesium sulfate) is an effective remedy for magnesium deficiencies in hydroponics if used correctly. This inexpensive material is effective for interveinal chlorosis (green veins and yellow areas between them). Dissolve separately from other solids before addition to avoid precipitation problems.
Deficiency Identification
- Interveinal chlorosis on mature leaves
- Reduced fruit/flower production
- Leaf curling without necrosis
- Slow growth despite adequate nutrients
Safe Usage Guidelines
- Dissolve 1g per gallon in 100°F (38°C) water first
- Add during reservoir changes only
- Limit applications to twice monthly maximum
- Flush system after 3 consecutive uses
Risk Mitigation
- Test magnesium levels before each application
- Monitor sulfur accumulation monthly
- Avoid with high-sulfur nutrient formulas
- Discontinue if EC increases over 10%
During a serious deficiency, I rescued pepper plants with Epsom salts. Yellowing leaves turned to deep green in five days. This quick fix saved the crop but required careful monitoring to prevent the buildup of sulfur, which could cause a lockout of calcium.
Epsom salt should be considered targeted therapy, not a general routine application of magnesium. Effects of magnesium deficiencies often indicate insufficient/imbalanced base nutrients as a primary concern. Always address a primary formula issue before addressing additives or remedial therapies. High rates of magnesium can cause lockouts of potassium (Efficiency) and calcium (Root health), both of which can stymie root gains.
Always confirm deficiencies by conducting a test on leaf tissue. Symptoms of iron deficiency and nitrogen deficiency can appear similar. Misdiagnosing a non-magnesium chlorosis will often lead to excess incorporation of magnesium. Epsom salt is ineffective in correcting any chlorosis where magnesium is not the contributing factor and may compound other true deficiencies.
Store Epsom salt in tightly closed containers to prevent moisture from entering. The crystalline form remains stable for years when kept dry, unlike liquid nutrients, which can degrade over time. The containers should be labeled with the date of purchase and used within three years for best results.
Read the full article: Hydroponic Nutrient Solutions: The Complete Guide
