The Q&A Archives: Tomato Leaves Turning Yellow

Question: I started my tomatos from seed in March. They grew very well indoors. They grew to a height of 8 to 12 inches. I brought them outside, left them in the shade for a week, then planted them in the ground (compost + soil + mulch). I noticed the leaves starting from the bottom of the plant, working there way up, are turning yellow. The newest growth appears to be a nice green color. The plants were atarted in newspaper pots, so no the roots weren't damaged during transplanting. It hasn't been sunny for about 1 full week here, and has rained significantly during this week. Also, about 2 weeks after transplanting these plants, when I noticed this discoloration, I fed the plants with miracle grow solution.

why are they turning yellow, and what should i do?

Answer: It sounds as if you are doing everything right with your tomatoes. Yellow leaves can be caused by many things including lack of nitrogen, insufficient light, water-logged soil (plant roots need oxygen to thrive), dry soil, or iron deficiency. If the older bottom leaves are yellow, but new growth is green, it's usually a lack of nitrogen. If new leaves are yellow, with green veins, it's usually a lack of iron. Lack of nitrogen is a more common problem than lack of iron and that sounds like it could be a possibility in your case. However, the lack of sunlight could be a factor, as tomatoes need full sun to thrive. And, if the soil is overly wet from rain, roots could be suffering as they also need oxygen to live. Soil should be kept moderately moist (but not wet) while plants establish. Finally, transplant shock can contribute to yellowing. Since you did fertilize, and new growth shows up as green, that might be the problem. One more thing: are the roots packed within the newspaper pot? Or did you cut the bottom off so they could grow outward? Sometimes it takes longer than expected for newspaper and peat pots to disintegrate and the roots become rootbound. I hope this info helps.

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