I have some sage I grew from seed in a pot on my window sill. I have 2 pots of it. One is almost gone, it’s leaves have turned black and it wilted away, now the second one is about to go. what’s wrong with them? and can they be saved? I also have basil in a pot next to them, will it be affected?
Sage needs a lot of light and prefers excellent drainage. It is difficult to give it enough light indoors, unless you have a sun room or greenhouse. It is also not at all tolerant of over-watering. My guess is that your sage was over-watered, which can cause the roots to rot and then the leaves to wilt. If you catch it soon enough, it is sometimes possible to save a house plant with rotting roots by re-potting. Remove as much of the old soil as possible and expose the roots to air before putting in fresh soil- preferably better draining soil. Try mixing some cactus potting mix or perlite or sharp sand or grit in with regular potting mix to get a better draining mix and look for potting mix with a small percentage of peat moss.
Basil also needs a lot of light but is not as much of a stickler for good drainage as the sage. It will probably be fine, but I would move it outside for the summer to give it some extra light and fresh air.