Transplanting Lemon Grass

My friend who is from Vietnam, likes to grow his lemon grass outdoors in his herb garden during the warm weather. He likes to dig up some of the lemon grass in the fall an pot it up for growing indoors durnig the winter. His problem is that the lemon grass always seems to wilt and die shortly after he transplants the herb. Why does it die off and do you have any suggestions on proper transplanting of lemon grass?

Lemon grass does not root all that readily. It roots best in the spring when in active growth. By transplanting it in the fall, he is picking a time when it is not doing any root growing and once its roots are badly disturbed, they cannot supply the plant with sufficient water and nutrients and the plant dies. On top of this it is moved from a bright, damp, cool environment to a dimly lit (compared to the outside), dry, very warm one. The shock would be big enough if it did not have to regrow the root system. It would have to increase it dramatically to just cope with the new conditions.
To overcome some of the problems, have your friend grow the plant in a large pot and bury the plant pot and all in the garden for the summer. Make sure there is some drainage under the pot to discourage rooting through the hole(s) in the bottom of the pot. In the fall move the plant in its dug up pot to the north side of the house for a week, then move it indoors onto a humidity tray (a tray half filled with pebbles and a quarter full of water) in the brightest window of your living quarters. During a northern hemisphere winter this would be an unobstructed south facing window.
Water diligently, since the plant will dry out faster in the house and if it wilts anyway, cut off the tops of most of its leaves, leaving the bottom 10 to 20 centimeters (four to eight inches), depending on the size of the plant and the severity of the wilting.
If the new growth seems weak and very stretched, you might have to add artificial lights over it to save it. Such lights should be left on 12 to 14 hours a day. A timer will make the lighting supervision less of a chore.
Do not expect too much growth during the winter. The plant may not grow for a long time, but with spring in the air this will rapidly change.