Troubleshooting Nutrient Deficiencies in Tomato Plants: A Comprehensive Guide

Troubleshooting Nutrient Deficiencies in Tomato Plants: A Comprehensive Guide

Tomato plants are a favorite among home gardeners, but they can be particularly sensitive to nutrient deficiencies. Today I'll be going into crop science in continuation of the previous Tomato blog (if you haven't read that one it's linked here!)

Identifying and correcting these deficiencies is crucial for a healthy, productive crop. All of the nutrient deficiencies that tomato growers in Texas fall into 2 categories Macronutrient and Micronutrient. Most of these can be tackled with a good fertilization schedule and patience. Do not expect the problem to be resolved within a week and remember soil is the most forgiving media on Earth!


How to diagnose your plant:

Nutrient deficiencies are the most common hinderance to plant growth and fruit development. When plants run out of essential nutrients they throw up their own warning flags to help the grower diagnose the issue. So let's go back to biology and chemistry class...

The big takeaway I want everyone to get from today is that most crops will exhibit these signs at some point due to either stress, a virus, or lack of nutrients. Due to this we must eliminate the possibility of a pathogen issue, like the mosiac virus prior to assuming we have a nutrient related issue.

The plant will translate this into either chlorosis (yellowing) or necrosis (dying) of leaves. The chlorosis and necrosis can occur in either in the leaf tissue or the leaf veins itself. Now, the big thing you should pay attention during the early stage of a undiagnosed deficiency is how it progresses. These things cannot be corrected overnight and you will generally observe more progression of symptoms as days go by.

I recommend making use of a flow chart like the one provided below by FloraMax




Another often overlooked cause of "deficiency" is soil pH, which results in some nutrients becoming non-bioavailable to plants. In acidic soils (low pH), essential macronutrients like nitrogen, phosphorus, and potassium (NPK) become less available. In Central Texas alkaline soils (high pH), micronutrients such as iron, manganese, and zinc are less available, leading to potential deficiencies. Maintaining an optimal pH range (typically 6.0 to 7.5 for most plants) is crucial for ensuring balanced nutrient availability and promoting healthy plant growth.

PRO TIP: When using liquid fertilizer applications, it is important to balance the pH after mixing up your solution. Adding ANY fertilizer to soil will alter the pH, however soil has an incredible ability to "buffer" the pH to more neutral levels. If you are doing surface application or side dressings this is not something to worry about.

For example look at how Phosphorus looses availability from [pH 7.5-8.3.

Credit: RX Green Technologies 

Keep all of these in mind if you are reading this to troubleshoot, the last thing you want to do is misdiagnose your plant and complicate your issues. It is much harder to reverse the effects of overfeeding than underfeeding!


Here is a breakdown of what nutrients ALL plants need, and more importantly, if they are mobile or not.

HINT: All Macronutrients are considered MOBILE, except for Calcium**

Macro Nutrients:

  • Nitrogen (N)
  • Phosphorus (P)
  • Potassium (K)
  • Magnesium (Mg)
  • Sulfur (S)
  • Calcium* (Ca)

Micro Nutrients:

  • Iron (Fe)
  • Boron (B)
  • Copper (Cu)
  • Manganese (Mn)
  • Zinc (Zn)
  • Molybdenum (Mo) - my favorite one to say.


1. Nitrogen (N) Deficiency (most common)


  • Yellowing Leaves: The deficiency starts with yellowing on the lower leaves and progresses up the plant.
  • Stunted Growth: Plants appear smaller and weaker than healthy ones.
  • Reduced Fruit Production: Poor flowering and fruit set.
Identifying nutrient deficiency in Plants / Tomato plants
Credit: Charlotte County Weather

Causes: Nitrogen deficiency often occurs due to poor soil quality, inadequate fertilization, or leaching from heavy rains. Leaching is the most common cause for Nitrogen depletions in soil.


  • Quick Fix: Foliar spray application of Seaweed or Kelp at dusk for quick correction.
  • Fertilization: Use a balanced fertilizer with a higher nitrogen content, I love FoxFarm Grow Big! Organic options include compost, manure, or blood meal.
  • Side-Dressing: Apply nitrogen-rich fertilizers to the soil surface around the plants and water it in.

2. Blossom-End Rot (Ca)


  • Dark, Sunken Spots: Black or brown spots develop at the blossom end of the fruit.
  • Fruit Deformity: Affected fruits may appear distorted and unusable.
Blossom-End Rot Tomato

Causes: Blossom end rot is primarily caused by calcium deficiency, which can be exacerbated by irregular watering, excessive nitrogen, or acidic soil.


  • Consistent Watering: Maintain consistent soil moisture. Avoid letting the soil dry out completely or become waterlogged.
  • Calcium Supplementation: Use calcium sprays or a product called CalMag
  • Mulching: Apply mulch to retain soil moisture and regulate temperature.

3. Phosphorus (P) Deficiency


  • Purple Leaves: Lower leaves turn dark green to purple, especially the veins.
  • Slow Growth: Plants exhibit slow, stunted growth.
  • Poor Root Development: Roots may be underdeveloped.

Causes: Phosphorus deficiency can result from cool soil temperatures, poor soil quality, or imbalanced fertilization. Phosphorus also needs to be built up in the soil, it undergoes rapid transformations into unavailable forms within weeks of applying!


  • Soil Amendments: Add bone meal, rock phosphate, or manure.
  • Proper pH: Ensure soil pH is between 6.0 and 6.8 for optimal phosphorus availability.
  • Use a late stage fertilizer like Fox Farm Tiger Bloom

4. Potassium (K) Deficiency


  • Leaf Edges Yellowing: Older leaves show yellowing or browning at the edges, eventually leading to necrosis (death).
  • Weak Stems: Plants have weak, brittle stems.
  • Poor Fruit Quality: Fruits may be small, misshapen, or have poor flavor.
Potassium Deficiency

Causes: Potassium deficiency is often due to poor soil structure, excessive rainfall, or inadequate fertilization.


  • Potassium-Rich Fertilizers: Use fertilizers high in potassium, such as potassium sulfate or wood ash (potash)
  • Regular Watering: Maintain consistent moisture levels to prevent nutrient leaching.
  • Soil Conditioning: Improve soil structure with organic matter to enhance potassium retention.

5. Magnesium (Mg) Deficiency


  • Interveinal Chlorosis: Yellowing between leaf veins, starting with older leaves.
  • Leaf Curling: Leaf tips may curl upward (praying leaves) and show necrotic spots.

Credit: University of Maine

Causes: Magnesium deficiency can be caused by acidic soil, high levels of potassium or calcium, or poor soil quality. I recommend adding Epsom salt to your planting hole at the beginning of the season.


  • Epsom Salt: Dissolve Epsom salt (magnesium sulfate) in water and apply as a foliar spray or soil drench.
  • Lime: Add dolomitic lime (dolomite) to the soil to increase magnesium levels and adjust pH.

6. Iron Deficiency


  • Interveinal Chlorosis: Yellowing between veins on new leaves, with veins remaining green.
  • Stunted Growth: Plants exhibit poor growth and vigor.

Causes: Iron deficiency is often due to high soil pH, poor drainage, or low organic matter.


  • Iron Chelate: Apply iron chelate to the soil or as a foliar spray.
  • Acidify Soil: Lower soil pH with sulfur or acidifying fertilizers.
  • Organic Matter: Add compost or organic matter to improve soil structure and nutrient availability.


Properly diagnosing and correcting nutrient deficiencies is vital for the health and productivity any plant. By understanding the symptoms and causes of common deficiencies like nitrogen, calcium (blossom end rot), phosphorus, potassium, magnesium, and iron, you can implement targeted solutions to address these issues effectively. Regular soil testing, consistent watering, and balanced fertilization are key practices to ensure your tomatoes thrive and produce abundant, healthy fruit sets.

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Tomatoes on the vine

 Other applications for this blog:

You can apply the nutrient deficiency troubleshooting techniques discussed for tomato plants to the following plants:

  1. Peppers (Capsicum spp.)
  2. Cannabis (Cannabaceae)
  3. Eggplants (Solanum melongena)
  4. Cucumbers (Cucumis sativus)
  5. Squash (Cucurbita spp.)
  6. Melons (Cucumis melo)
  7. Beans (Phaseolus spp.)
  8. Peas (Pisum sativum)
  9. Corn (Zea mays)
  10. Potatoes (Solanum tuberosum)
  11. Spinach (Spinacia oleracea)

For more gardening tips and expert advice, visit our website. Join our community of home gardeners and share your experiences and solutions to common gardening challenges.

For more expert tips on gardening in Texas, check out our guide on growing vibrant and flavorful peppers in your garden!



Additional Resources:

  1. US Dept. of Agriculture -

    Identifying nutritional deficiencies in backyard plants

  2. Texas A&M Agrilife Extension - Diagnosing Nutritional Deficiencies 
  3. West Virginia University - Nutrient Deficiencies in Plants
  4. Royal Horticulture Society - Nutrient deficiencies
  5. Michigan State University - 6 Steps to identifying nutrient deficiencies


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