Tomato nutrient deficiencies show up as leaf color changes, and where they start tells you which nutrient is short. Pale yellow lower leaves usually mean nitrogen, yellow between the veins of lower leaves means magnesium, and yellow between the veins of new leaves points to iron. Pick where you see it and what it looks like to find the likely cause.
Try a preset:
Your entries stay in your browser. Nothing is sent to a server or saved to an account.
What Your Result Means: the tool names the nutrient that most often causes that pattern, explains why, and gives a first step. It also flags when your soil pH, rather than a shortage in the soil, is the likely reason the plant cannot take a nutrient up. Confirm with a soil test before adding anything.
How Do You Spot a Nutrient Deficiency in Tomatoes?
Look at which leaves changed first and what the change looks like. Those two clues narrow most deficiencies down to one or two nutrients, because some nutrients move inside the plant and some do not.
- Find where it started: the oldest, lowest leaves, the newest leaves at the top, or the fruit.
- Describe the pattern: whole leaf pale, yellow between green veins, mottled, purple, or brown edges.
- Add your soil pH if you know it, since pH often locks nutrients up even when the soil has enough.
- Read the result, then confirm with a soil test before you feed.
What Each Result Means
| Result | What It Tells You |
|---|---|
| Likely nutrient | The nutrient most often behind that pattern |
| Match | Whether it is a classic pattern or a less typical one |
| Why it shows there | How the nutrient moves inside the plant |
| What to do | A first step, before any big change |
| Soil pH note | Whether pH may be blocking uptake |
Tomato Nutrient Deficiencies at a Glance
The common deficiencies in home tomatoes, where they show first, and what they look like.
| Nutrient | Shows First On | What It Looks Like |
|---|---|---|
| Nitrogen (N) | Older leaves | Whole leaf pale green to yellow, plant stunted |
| Phosphorus (P) | Older leaves, seedlings | Purple leaves or reddish-purple undersides |
| Potassium (K) | Older leaves | Browning that starts at the leaf edges |
| Magnesium (Mg) | Older leaves | Yellow between the veins, veins stay green |
| Iron (Fe) | Newest leaves | Yellow or whitish between green veins |
| Manganese (Mn) | Newest leaves | Checkerboard yellowing near the main veins |
| Calcium (Ca) | Fruit | Blossom-end rot: dark, sunken fruit bottom |
How Does the Deficiency Checker Work?
It uses the rule extension services teach for reading leaves: mobile nutrients show on old leaves first, and immobile nutrients show on new leaves first. The leaf pattern then separates nutrients that share a location.
Newest leaves first -> an immobile nutrient: Fe or Mn
Pattern picks the nutrient: pale = N, purple = P, brown edges = K,
yellow between veins = Mg (old) or Fe (new), checkerboard = Mn
Soil pH above 7.0 -> iron and manganese are locked up
Soil pH below 6.0 -> magnesium is harder to take up
When your answers do not fit a classic pattern, the tool says so and suggests the most likely alternatives, such as disease, root stress, or fertilizer burn.
Worked Example
Say the newest leaves at the top of your plant are turning pale yellow while their veins stay dark green, and a soil test showed pH 7.6. Newest leaves first means an immobile nutrient, and yellow between green veins on new growth is the classic sign of iron deficiency. With pH above 7.0, the soil likely has iron but the plant cannot take it up. The fix is a chelated iron feed for a quick response and lowering the pH over time as your soil test advises, not adding more general fertilizer.
Factors That Change the Result
- Soil pH: above 7.0 locks up iron and manganese; below 6.0 makes magnesium harder to take up. Tomatoes do best around 6.0 to 6.8.
- Cold soil: early in spring, cold soil slows phosphorus uptake and turns seedlings purple, even when the soil has enough phosphorus.
- Soil type: light, sandy soils lose nitrogen, potassium, and magnesium to leaching more easily.
- Fertilizer balance: too much potassium blocks magnesium uptake, a common cause of yellowing between the veins during heavy fruit set.
- Water: waterlogged or dry soil limits root uptake, and uneven watering causes blossom-end rot.
Understanding Your Outputs
| Output | Meaning | Best Used For |
|---|---|---|
| Likely nutrient | Most common cause of the pattern | Naming the problem |
| Match | Classic or less typical | Judging how sure to be |
| Why it shows there | Mobile or immobile nutrient | Checking your observation |
| What to do | First step | Acting this week |
| Soil pH note | Whether pH is the real cause | Fixing it long term |
When to Use It
Use it when leaves change color without the spots, rings, or mold of a disease. If you see spots or lesions, start with the Tomato Plant Problem Diagnosis tool instead. For the wider picture, read our guides to yellowing tomato leaves and fertilizing tomatoes. For a firm answer, send a soil sample to your local extension office before feeding.
Common Mistakes to Avoid
- Feeding more nitrogen for every yellow leaf: yellow between the veins is usually magnesium or iron, and extra nitrogen will not fix it.
- Ignoring pH: iron and manganese problems usually come from alkaline soil, not a lack of those nutrients.
- Adding Epsom salt by habit: it only helps when magnesium is actually short.
- Treating purple seedlings with phosphorus: cold soil is the usual cause, and it clears as the soil warms.
- Skipping the soil test: guessing risks adding what the soil already has too much of.
Accuracy and Limitations
This is a guide to the most likely nutrient, not a lab result.
What It Does Well: matches the classic leaf patterns extension services use and points out when soil pH is the likely cause.
What It Does Not Do: measure nutrient levels or rule out look-alikes. Diseases, viruses, herbicide drift, root damage, and pests can all cause yellowing, and a plant can be short of more than one nutrient. Only a soil or tissue test confirms a deficiency. This is general guidance, not professional agronomy advice.
Methodology
Method: a rule-based lookup that combines where the symptom starts (older leaves, newest leaves, or fruit) with its pattern, following the mobile and immobile nutrient rule used in extension diagnostic keys. Inputs used: symptom location, symptom pattern, and optional soil pH band. Coverage: nitrogen, phosphorus, potassium, magnesium, iron, manganese, and calcium (blossom-end rot). pH rules: pH above 7.0 flags iron and manganese lock-up (University of Maryland Extension); pH below 6.0 flags reduced magnesium availability (University of Kentucky). Rates: the only rate given is the RHS magnesium foliar feed of 20 g Epsom salts per litre, used only when magnesium deficiency is the match. Edge cases: combinations that do not fit a classic pattern return a “less typical” result with likely alternatives.
Sources: Cornell Vegetables – Tomato Nutrient Disorders, Royal Horticultural Society – Nutrient Deficiencies, University of Kentucky – Interveinal Chlorosis (Magnesium), University of Maryland Extension – Nutrient Deficiency of Vegetable Plants. Last reviewed: September 28, 2026 · Reviewed by Aiza Anwar.
Frequently Asked Questions
Why are the bottom leaves of my tomato plant turning yellow?
Even, pale yellowing that starts on the oldest, lowest leaves and moves up is the classic sign of nitrogen deficiency. Yellowing only between the veins of lower leaves points to magnesium instead. Brown ringed spots on the yellow leaves mean early blight, a disease, not a nutrient problem.
Why are the new leaves on my tomato yellow with green veins?
Yellow between green veins on the newest, top leaves usually means iron is not being taken up, most often because the soil pH is above 7.0. A mottled, checkerboard pattern on young leaves points to manganese. Test the soil pH before adding anything.
Why are my tomato leaves turning purple?
Purple leaves, or reddish-purple leaf undersides, are a sign of phosphorus shortage. On young plants it is usually caused by cold soil, which slows phosphorus uptake, and it clears as the soil warms. If it persists in warm weather, get a soil test before adding phosphorus.
Why do my tomato leaves have brown, crispy edges?
Browning that starts at the edges of older leaves is the typical sign of potassium deficiency, which is most common on light, sandy soils. Dry soil, fertilizer burn, and wind can also scorch leaf edges, so check watering and recent feeding too.
Should I give my tomatoes Epsom salt?
Only if the plant shows magnesium deficiency: yellowing between the veins of older leaves. The RHS suggests a foliar feed of 20 g of Epsom salts per litre of water in that case. If magnesium is already adequate, extra Epsom salt does not help, so a soil test is the best guide.
Is blossom-end rot a calcium deficiency?
It is a calcium problem in the fruit, but it is usually caused by uneven watering rather than a lack of calcium in the soil. Water evenly and mulch. Adding calcium rarely fixes it on its own.
Which nutrient deficiencies show on old leaves first?
Nitrogen, phosphorus, potassium, and magnesium move within the plant, so it moves them from old leaves to new growth and the old leaves show symptoms first. Iron and manganese do not move, so their symptoms appear on the newest leaves.
How do I confirm a nutrient deficiency?
Get a soil test through your local extension office. It measures pH and nutrient levels, so you add only what is missing. The University of Maryland Extension suggests testing soil pH and nutrients every three years.
Can too much fertilizer cause yellow leaves?
Yes. Too much potassium can block magnesium uptake and cause yellowing between the veins, and too much fertilizer can burn roots and scorch leaf edges. More feed is not always the answer, which is why testing first matters.
Related Tomato Tools
See the Full Problems & Solutions Guide
This tool gives general guidance on the most likely nutrient deficiency from leaf and fruit symptoms, not a lab diagnosis or professional agronomy advice. Many problems look alike, and only a soil or tissue test confirms a deficiency. Follow product labels when feeding. Spotted an error? Tell us here.