People often ask me what is the best way to transplant herbs. Recently I had to move my herb garden because it was in the area where we want to build our house. This was quite a big job but all of the herbs have been moved to a new area and they haven't turned a leaf or shown any signs of stress.
When it comes to transplanting, herbs are no different to any other plant. Just because most herbs are hardy and can tolerate harsh conditions doesn't mean they don't like good conditions; the better the conditions the more healthy and productive the herbs will be.
Before I transplant a herb from the garden or a pot I always prepare the new garden bed well by digging the topsoil. I never turn it over but loosen it with a spade so the topsoil stays on the top rather than being turned under. Removing all weeds and grass is essential. After this is done I add good compost to it and mix it in well. Adding fertilizer depends on the herbs I'm transplanting; some don't like rich soil such as sage and rosemary while others like comfrey are heavy feeders.
When the new bed is ready I carefully dig the herbs out of the old garden making sure I allow plenty of room around the plant so as not to hurt the surface roots and I dig down deep enough so the tap root isn't damaged. If I'm transplanting potted herbs I wet the soil well so they come out of the pot easily. I always take the herbs I've dug out and the potted herbs to the new garden bed before I've dug any holes for them. This is so I know how big the holes need to be.
After the hole has been dug to a size big enough for the plant I fill it with water and put the plant in. For potted plants I remove them from pots and gently tease the roots out. When the plants are in the holes I sprinkle dirt through the roots until they're all covered then add the remaining dirt up to the original line on the trunk. I water them in well and cover the surrounding dirt with mulch that's no more than 4 cm deep and away from the trunk.
There's one more thing I do to ensure the health and vigour of my plants are not compromised when they're being transplanted and that is I always do it when the moon is waxing (increasing) and close to the full moon. This is when the plants are most vigorous. It's very rare that I lose a transplanted herb. My new garden that contains transplanted herbs such as Echinacea, soapwort, valerian, aloe, comfrey, lemon balm, and lavender, is thriving even in the unseasonal hot and dry weather we're experiencing at the moment.