I started my basil plants late this year, on May 10. They didn't grow much at all for the first four weeks, and then started to yellow and develop brown patches. But once the constant rain finally moved out, I'm starting to see what looks like healthy new growth on top. Where should I go from here? Should I remove the yellow leaves at the bottom, or leave them be? - Derek
Yellow leaves on basil could be a number of things, so here are a few things to consider.
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Since you planted the basil in May, the weather has been generally cool, cloudy and very wet. The older leaves could be responding to the sudden change in temperature and very hot sun, resulting in sunscald. In this case the plant will grow out of the condition. Just cut off the yellow bottom leaves as they die.
And how is the drainage? Basil needs good drainage.
Next, have you fertilized the plants? With all the rain we have had, they could be deficient in nitrogen. Nitrogen is mobile in the soil and will wash out. Also, too wet conditions can tie up nutrients in the soil that the plants need. Try an application of a balanced fertilizer.
Lastly, check the underside of the yellowing leaves. Are there any spots, fluffy grayish spores, webbing? If so, post again, with a picture of the underside of the leaves.
Hope this helps.
Carole-Johnson County Extension Master Gardener