I grow marigolds every year on my balcony from seed I collect each summer. Last year, the marigolds had a lot of brown bugs. Can I reuse the soil in these pots for my marigolds this year or will the bugs be in the soil?
Soil in containers can generally be used for several years if the plants have been pest and disease free. Given your last year’s bug infestation, I would suggest completely replacing the soil in the pot this year. Wash the pot thoroughly and make sure the new soil is formulated for containers.