You need to know when not use Epsom salt so you do not hurt your garden. Skip it when your soil already has enough magnesium, when your tomatoes show blossom end rot, and when you have not done a soil test yet. These three cases cause most of the damage from wrong Epsom salt use.
The top epsom salt risks garden growers face is the calcium problem. I learned this two summers ago when my tomatoes got dark sunken spots on the fruit. Forums told me to add Epsom salt, so I did. The blossom end rot got worse on every plant within two weeks. Magnesium and calcium both fight for the same entry points on your roots. Pushing more magnesium into soil that already has enough blocks calcium from reaching your fruit.
Clemson Extension says too much Epsom salt creates a salty zone around your roots that blocks water uptake. Your plants wilt even though the soil stays damp. UMN Extension warns you not to apply it when soil tests show enough magnesium. SDSU says you should never use it unless you can see clear signs on your leaves. All three agree that blind use without testing hurts more than it helps.
You can spot too much epsom salt plants have taken in by watching for a few key signs. Your leaves turn a dark blue-green color. Leaf edges go brown and crispy. Growth slows down even though you water on schedule. These signs show up within 3-4 weeks of over-use. You may also see a white crust on the soil near the base of your treated plants.
Epsom salt also does nothing for your plants in soil with a pH below 5.5. At that acid level, your roots cannot grab magnesium no matter how much you add. The right fix is dolomitic lime, which raises your pH and adds magnesium at the same time. Epsom salt cannot change your pH at all, so it will not solve this problem for you.
Get your soil tested through a real lab before you spend money on Epsom salt. Clemson Extension warns that home test kits give bad results. A lab test costs about $15-$25 and tells you the exact numbers for magnesium, calcium, and pH in your soil. If magnesium comes back as enough or high, skip the Epsom salt. You save money and keep your plants safe from salt stress that damages their roots.
Read the full article: Epsom Salt for Plants
