Basil plant rot
I planted these basils as starters that I bought from a nursery. Healthy when bought. They are on a balcony and get partial sun (late afternoon full sun). The leaves plants are more yellowish in leaves and some stems are brown at bottom. I water a little daily on hot days and skip a day when cooler or after rain. Could I be overwatering? Also there was a similar rot on basil last year, but didn't happen until late summer. I reused the soil in the same pot this year. Could that be problem?
Prince George's County Maryland
It is not uncommon for stems to turn brown like this on basil. Keep the roots moist. Basil doesn't need to be in full sun all day; 3-4 hours of full sun is usually sufficient.
There is a disease called Southern blight that can affect basil plants. You would see blackening of the stems, wilting, white mold, and small, seed-like structures at the base of the stem. We don't think this is occurring in your plant. We also don't see any symptoms of downy mildew, which tends to be a problem in basil later in the season.
We do recommend changing at least some of the soil in your container each year. Add 50% new compost/potting soil and mix it in with the existing soil to add nutrients.
Also, it is not too late to plant more basil from seed. Many gardeners will sow basil seeds in succession (every couple weeks) up to mid summer to keep a good crop of healthy plants going as the older ones decline.
Thank you for your response. I think my basil does have Southern blight because the bottom of stems are black and there were also some fungal growths near them. What can I do?
It is possible that this could be southern blight. A sure way to confirm it would be if you see any small seed-like structures at the base of the plant (they look like mustard seeds). They can be white to reddish tan to light brown in color. These are called sclerotia and they provide the inoculum for the pathogen to carry over to a new crop. They only thing you can do is discard the plants and do not reuse the soil. You can start new plants or seeds into a fresh pot of soil mix.