One of the nicest benefits that our herb gardens provide, is the growth of our herbal bounty. Herbs that are growing well, need to be divided, that is, dug up and cut or chopped into smaller plants, every second or third year, for overall health. Herbs that have not been divided, will still continue to survive, but they often become stunted and weak. In a container, herbs that are not divided will become rootbound and will either choke themselves out, or will no longer be able to draw nutrients up from the soil, due to the roots filling the container, and allowing little to no soil to remain, for holding moisture and fertilizer.
The best time to divide your herb plants is when they are getting ready to have a growing period. This is usually early in the spring, often when it is too cold out to even consider planting. In my area, zone 5, if you look at an established chive plant in early March, you may think it is still lying dormant, with dead chive leaves the only thing readily visible. If you were to pull aside the dead matter, you would see that the chives were growing vigorously, and were prime for division. Chives are one of the easier herbs to divide. Mint plants and also as easy, mint being invasive and often wanting to take over a garden, if not cut back or divided.
With the energy of the herb in its growth stage, division is less stressful, and you have greater success with keeping the newly divided plants.
