Posted on 10 June 2008 by tomatocasual.com

Understanding Yellow Tomato Leaves

By Vanessa Richins

When I went into work today, my friend greeted me with the question:

“Why are my tomato plant’s leaves yellow?”

If only there was a simple answer to this. There are many different factors that can cause tomato plants to develop yellow leaves.

Here are some of the most common reasons:

  • Under-watering: When plants don’t get enough water, they start to wilt and lose color. Under-watered plants are also more prone to attack from diseases and pests.
  • Over-watering: On the flip side, overwatering can also cause yellow leaves. Over-watering can also cause root rots.
  • Aphids: If you see sticky honeydew and small green, black, or red insects, you have aphids. A strong spray of water can knock these off. Ladybugs love to eat aphids.
  • Nitrogen: Another cause of yellow leaves could be a lack of nitrogen. Test your soil with a basic kit available at home improvement stores or nurseries, or you can send in your soil for more detailed testing through your local cooperative extension. The cost varies by location but for example, it costs $15 here in Utah. If this is the case, add compost or a nitrogen fertilizer.
  • Tomato Hornworm: If you see chewed yellow leaves, you may have tomato hornworms. Check the plant for these large, fat green worms. The easiest remedy is to just pick them off.
  • Iron: Another nutrient deficiency signaled by yellow leaves is lack of iron. Add an iron chelate to the soil or the leaves, depending on the form.

These are only some of the causes. Other possibilities include: Early blight, psyllids, sunburn, curly top virus, whiteflies, flea beetles, and Septoria Leaf Spot.

If you are unsure of the cause, you can call a fellow gardener, ask here on Tomato Casual, or consult your local extension office.

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15 Responses to “Understanding Yellow Tomato Leaves”

  1. tomatocasual.com our friend Ben Says:

    Great post, Vanessa! Plant problems are seldom straightforward, and it’s too often the case that opposites (like under- and over-watering or feeding) can produce similar symptoms. We all have to put on our Sherlock Holmes hat (or deerstalker cap, in his case) when it come to diagnosing our plants!

  2. tomatocasual.com Nancy Bond Says:

    This was very helpful!

  3. tomatocasual.com Dani in NC Says:

    You guys are right on time again! I was planning to do some research today on why the leaves on my plants were turning yellow, and here’s your article :-).

    I think my problem may be underwatering. I skipped a few waterings because we keep getting the promise of rain that doesn’t come. I also skipped the Miracle Gro. All the leaves are looking droopy, not just the yellow ones. I hope a little extra water is all they need because my first tomatoes are coming in!

  4. tomatocasual.com John Says:

    I had problems with all of my Better Boys this year. The leaves yellowed, then dried out and fell off. Same thing for the blooms. I’m hoping it was overwatering or their incompatability with desert heat rather than blight. I should find out soon, as I planted a couple of Heatwaves and Sunmasters in the same soil.

    http://desertcontainergardening.blogspot.com/

  5. tomatocasual.com JJ Says:

    From the attached photograph does anyone recognise what may be causing this ‘yellowing’. Apart from the heads turning yellow the plants all seem very healthy

  6. tomatocasual.com recyclerdave Says:

    So what is the concensus on picking off yellow leaves? I don’t mean brown crusty leaves or those already with bugs.

  7. tomatocasual.com randy gardner Says:

    The tomato plants in this photo have yellow leaves because of a soilborne fungal disease, fusarium wilt. Use a resistamt variety.

  8. tomatocasual.com cooknkpl Says:

    Randy…
    If that’s the diagnosis, what’s the treatment?

  9. tomatocasual.com Dave Miller Says:

    Yellow leaves on tomatoes mean so many things.

    The first leaves turn yellow and die off

    Too much water (swamped) is another indicater.

    Underwatering means the whole plant show signs but the leaves are first. Even if not yet yellow, the leaves are droopy.

    Calcium uptake is another issue. There may be a deficiency. Soil tests from you local county extension service can do it or guide you.

    Miracle-gro may work for flowers but it is too artificial for human consumption. There are many better alternatives. Fish emulsion is one King Neptune.

    Contact me: recyclar4dave@comcast.net if you can’t find it locally.

    I am hoping to save some heirloom seeds this year.

  10. tomatocasual.com fraggles Says:

    but do the yellowing leaves affect the fruit? My plant is in a topsy turvy BTW – wondering if that method of plating is causing yellow leaves…(fruit is growing wonderfully and no sign of rot or disease on it)

  11. tomatocasual.com coolpillow Says:

    I have tomatoes in a Topsy Turvey as well.
    The Beefsteak leaves have a yellow/brown problem in several places.

    The Park’s Whopper seem to be doing fine.

    The directions to say to water every day- but a friend told me they had the gizmo last year and it fizzled because the plants got root rot.

    I’m going to cut back to watering every other day for a while and see what happens.

    Thanks for the great posts- and all the comments!

  12. tomatocasual.com Jenn Says:

    How do I keep the rain from flooding my plants? We have been getting too much rain here 🙁

  13. tomatocasual.com Gayka Says:

    You need to have some way of draining the excess water, such as a sandy mixture beneath the top soil.

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