If your home is dry, as it tends to get during winter months, use a humidifier in your home, or mist herbs daily, preferably early in the day so that the herbs are dry when the light is no longer available. If an herb's leaves wither, check to see that it's getting enough, or too much water, and enough light. A lot of us indoor gardeners think insects or disease are causing leaves to wither, turn brown, or develop crisp edges, but this may not be so. The plant may be getting too much heat, or soil temperatures may be fluctuating too much. Lifeless-looking leaves may be the result of too little water.
Buds dropping off usually indicate rapidly fluctuating temperatures.
If stems turn soft, the herb isn't getting enough sun, and it's probably getting too much water. Indoor Pests and Disease Herbs growing indoors are fairly resistant to disease and insects, just as they are outdoors. But, they DO get them. Major indoor herb pests include aphids, mealybugs, mites, and white flies. Insecticidal soaps, used to combat outside pests, are also available in indoor formulas.