Does Epsom Salt Help All Plants Grow Better?
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The Verdict: Mostly busted. Epsom salt provides magnesium and sulfur, but most California soils already have plenty of both. Applying it without a deficiency can cause more harm than good.
Why People Believe This
Epsom salt (magnesium sulfate) has been promoted as a garden cure-all for decades. Social media posts claim it makes tomatoes sweeter, roses bushier, and peppers more productive. It is cheap, easy to find, and feels like a wholesome, old-fashioned remedy. The National Gardening Association has called it one of the most persistent garden myths in America.
What the Research Says
UC Master Gardeners and Washington State University Extension have both cautioned against routine Epsom salt use. Most soils in California, including those in the Santa Cruz area, are not deficient in magnesium. UC ANR soil surveys show that Central Coast soils typically have adequate to high magnesium levels. Adding more when it is not needed can disrupt the calcium-to-magnesium ratio, which can actually damage soil structure and reduce water infiltration.
A controlled study cited by the University of Saskatchewan found no yield benefit from Epsom salt applications in tomatoes or peppers when magnesium was already adequate in the soil. Linda Chalker-Scott, a horticulture professor at Washington State University, has published extensive reviews debunking Epsom salt claims, noting that excess magnesium can compete with calcium uptake and contribute to blossom end rot, the very problem many gardeners are trying to solve.
What to Do Instead
Get a soil test before adding any mineral supplement. If your test shows a genuine magnesium deficiency (uncommon in our area), then a targeted Epsom salt application makes sense. For general plant health, focus on the basics: compost for fertility, consistent watering, and appropriate fertilization based on what your plants actually need. For tomatoes and peppers in your Santa Cruz garden, a balanced organic fertilizer with calcium is a safer bet than Epsom salt.
This week: Put the Epsom salt back under the bathroom sink. Order a soil test or pick up a basic soil test kit to check your magnesium levels before supplementing.
For more on feeding your garden, check out our free California Garden Planning Guide at Your Garden Toolkit.
Frequently Asked Questions
Does Epsom salt really help all plants grow better?
Mostly no. Epsom salt provides magnesium and sulfur, but most California soils, including those around Santa Cruz, already have plenty of both, so applying it without a deficiency can do more harm than good.
Can Epsom salt actually harm my plants or soil?
Yes. Adding magnesium when it is not needed can disrupt the calcium-to-magnesium ratio, damage soil structure, and reduce water infiltration. Excess magnesium can also compete with calcium uptake and contribute to blossom end rot.
Should I use Epsom salt on my tomatoes and peppers?
A controlled study cited by the University of Saskatchewan found no yield benefit from Epsom salt in tomatoes or peppers when soil magnesium was already adequate. A balanced organic fertilizer with calcium is a safer choice.
How do I know if my garden actually needs Epsom salt?
Get a soil test before adding any mineral supplement. If the test shows a genuine magnesium deficiency, which is uncommon in the Santa Cruz area, then a targeted application makes sense.
