In trying to grow indoor herbs, we find that they are under attack from some disease. The leaves brown and then die.
We have fungus gnats in the soil. Hydrogen peroxide doesn’t seem to eradicate them, even after repeated use.
We sterilized soil before planting.
Thank-you for contacting Toronto Master Gardeners with your question about growing indoor herbs.
While it can be very satisfying to grow your own culinary herbs indoors, they can be susceptible to various pests and diseases. There are 2 particularly significant issues in attempting to grow herbs indoors. The first is inadequate sunlight. Unlike many other popular houseplants with origins in tropical forests, most herbs hail from sunny, open spaces, and they require more sunlight than most windows can provide. The second major issue is related; most herbs prefer fairly dry conditions. People often make the mistake of watering too frequently and not allowing the soil to dry out between waterings. These 2 issues can lead to weak plants. Overwatering, in particular, is related to infestations of fungus gnats.
Please refer to the link below for a previous post regarding fungus gnats.
Another previous post by the Toronto Master Gardeners discusses some of the issues in growing herbs indoors. Here is the link:
I hope this helps with your problem.