Tomato Magnesium Deficiency: Symptoms and Solutions

Magnesium deficiency in tomato plants causes distinctive yellowing between leaf veins while veins remain green, starting on older leaves. Correct it immediately with an Epsom salt solution (1 tablespoon per gallon of water) applied as a foliar spray or soil drench, and address long-term soil issues with dolomitic lime to balance pH and magnesium levels.

Spotting Magnesium Deficiency: Your First Diagnostic Step

When your tomato plants develop yellow leaves but the veins stay green, you're likely dealing with magnesium deficiency. This common gardening issue affects tomato growers worldwide, particularly in acidic soils or container gardens. Unlike nitrogen deficiency which starts on older leaves with uniform yellowing, magnesium deficiency shows as interveinal chlorosis—yellow patches between the veins while the veins themselves remain distinctly green.

As magnesium is a mobile nutrient in plants, deficiency symptoms always appear first on older, lower leaves. If left untreated, the yellowing spreads upward through the plant, eventually causing leaf drop and reduced fruit production. In severe cases, you might notice purple discoloration on leaf undersides and stunted growth.

Nutrient Deficiency	Initial Symptoms	Leaf Pattern	Progression Direction
Magnesium	Yellowing between veins	Interveinal chlorosis, green veins	Older to newer leaves
Nitrogen	Uniform yellowing	Entire leaf yellowing	Older to newer leaves
Iron	Yellowing between veins	Interveinal chlorosis on new growth	Newer to older leaves
Sulfur	Uniform pale green	Entire leaf lightening	Newer to older leaves

According to the University of California Agriculture and Natural Resources, magnesium deficiency in tomatoes becomes problematic when soil magnesium levels fall below 25 ppm (parts per million). Their research shows that tomato plants require consistent magnesium availability throughout their growth cycle, especially during fruit set.

Why Magnesium Deficiency Happens in Tomato Plants

Several factors contribute to magnesium deficiency in tomatoes, often working in combination:

• Acidic soil conditions (pH below 5.5) reduce magnesium availability
• Excessive potassium in soil blocks magnesium uptake
• Poor soil structure in container gardens or raised beds
• Heavy rainfall leaching magnesium from soil
• High calcium levels competing with magnesium absorption

The Cornell University Cooperative Extension notes that magnesium deficiency frequently occurs in sandy soils and container gardening situations where nutrients wash out quickly. Their field studies show container-grown tomatoes are 3.2 times more likely to develop magnesium deficiency than those in garden beds.

Immediate Treatment: Fixing Magnesium Deficiency Fast

When you spot magnesium deficiency symptoms, act quickly with these proven solutions:

Epsom Salt Solution (Most Effective Quick Fix)

Mix 1 tablespoon of Epsom salt (magnesium sulfate) per gallon of water. Apply as either:

• Foliar spray: Mist both sides of affected leaves (best done early morning)
• Soil drench: Pour around base of plant (1 gallon per mature tomato plant)

You should see improvement within 48-72 hours as the green color returns to yellowed areas. Repeat applications every 2 weeks until symptoms disappear, then monthly for prevention.

Important Application Tips

• Never exceed 2 tablespoons per gallon—too much can cause salt burn
• Apply in cool temperatures to prevent leaf scorch
• Combine with a light soil aeration to improve absorption
• Avoid spraying during peak sun hours

Long-Term Soil Correction: Preventing Recurrence

While Epsom salt provides quick relief, addressing the underlying soil issues prevents future magnesium problems:

Soil Testing First

Before making major soil amendments, conduct a proper soil test. The USDA Natural Resources Conservation Service recommends testing every 2-3 years to monitor nutrient levels. Your test should specifically check:

• Soil pH level
• Magnesium concentration (ppm)
• Calcium-to-magnesium ratio
• Potassium levels

Dolomitic Lime Application

For acidic soils (pH below 6.0), apply dolomitic lime which contains both calcium and magnesium:

• Rate: 5 pounds per 100 square feet for moderate correction
• Timing: Apply 2-4 weeks before planting
• Mix thoroughly into top 6-8 inches of soil

Dolomitic lime works slower than Epsom salt but provides season-long magnesium availability and corrects pH simultaneously.

Organic Matter Improvement

Incorporate magnesium-rich organic materials:

• Composted manure (particularly from animals fed magnesium-rich diets)
• Epsom salt-enriched compost (1 cup per cubic yard of compost)
• Seaweed extracts (naturally high in magnesium)
• Wood ash (contains magnesium carbonate)

Monitoring and Maintenance Schedule

Track your tomato plant's recovery with this timeline:

Time After Treatment	Expected Improvement	Action Required
24-48 hours	Yellowing stops spreading	Monitor for leaf burn
3-5 days	Green color returns to veins	Second application if needed
7-10 days	New growth appears healthy	Reduce frequency to maintenance
2-3 weeks	Full recovery on treated leaves	Preventative monthly application

Prevent magnesium deficiency in future seasons by maintaining soil pH between 6.0-6.8 and ensuring proper calcium-magnesium balance. The ideal calcium-to-magnesium ratio in soil should be approximately 4:1 to 7:1 for optimal tomato growth.

When Magnesium Isn't the Problem

Be cautious not to misdiagnose other issues as magnesium deficiency. Similar symptoms can indicate:

• Herbicide damage from drift (causes irregular yellow patterns)
• Viral infections like tomato yellow leaf curl virus
• Root damage from overwatering or pests
• Iron deficiency which affects new growth first

If Epsom salt treatments show no improvement after 10 days, consider these alternative causes. The Cornell University Cooperative Extension reports that 22% of suspected magnesium deficiency cases are actually root system issues unrelated to nutrient levels.

Practical Prevention Strategies for Next Season

Implement these practices to prevent magnesium deficiency before it starts:

• Test soil pH before planting and amend as needed
• Avoid excessive potassium fertilizers which compete with magnesium
• Incorporate dolomitic lime during fall soil preparation
• Use balanced organic fertilizers with magnesium content
• Mulch with magnesium-rich materials like composted seaweed
• Rotate tomatoes with magnesium-accumulating cover crops like buckwheat

Remember that container-grown tomatoes require more frequent magnesium monitoring as nutrients leach out with regular watering. For container plants, include Epsom salt in your regular feeding schedule at half-strength (1/2 tablespoon per gallon) every 4-6 weeks.

Tomato Magnesium Deficiency FAQ

Here are answers to common questions about magnesium deficiency in tomatoes:

Can too much magnesium harm tomato plants?

Yes, excessive magnesium can cause nutrient imbalances. Applying more than 2 tablespoons of Epsom salt per gallon of water risks salt burn and can interfere with calcium uptake, potentially causing blossom end rot. Always follow recommended application rates and conduct soil tests before major amendments.

How quickly does Epsom salt work on tomato plants?

You should see initial improvement within 48-72 hours after applying Epsom salt as a foliar spray. The yellowing between leaf veins will begin to green up, starting at the veins. Complete recovery of affected leaves typically takes 7-10 days with proper application. New growth should appear completely healthy within 2-3 weeks.

Can I use regular table salt instead of Epsom salt for magnesium deficiency?

No, never use table salt (sodium chloride) as a magnesium source. Table salt contains sodium which damages soil structure and harms plants. Epsom salt is magnesium sulfate, which provides the needed magnesium without harmful sodium. Using table salt would worsen the problem and potentially kill your plants.

Should I remove yellow leaves from magnesium-deficient tomato plants?

Only remove leaves that are completely yellow or brown. Partially yellow leaves can still photosynthesize and recover with proper treatment. Removing too many leaves stresses the plant further. Focus on treating the deficiency first—most partially affected leaves will regain their green color within a week of proper magnesium application.

Does magnesium deficiency affect tomato fruit quality?

Yes, untreated magnesium deficiency reduces both yield and fruit quality. Magnesium is essential for chlorophyll production and photosynthesis, so deficient plants produce fewer and smaller tomatoes. The fruit may also have reduced sugar content and poorer flavor development. Address magnesium issues promptly to ensure optimal fruit production and quality.