Snake plant by Fuzzy T
A number of readers have asked how to keep old Sansevieria or Mother-in-laws tongue plants happy and healthy. Many readers have inherited family sansevieria plants and want to do the right thing in revitalizing the plants. The best suggestion is to join a Sansevieria society to get their journals that give information about the plants and where you can write to a specialist who works with almost no other plant family. See here.
One question is: What sized pot should it be repotted in? According to the University of Arizona, they recommend that for all plants the †rule is that the diameter of the pot should be about one-third the height of the plant from the top of the foliage to the soil line.†Because Sansevierias have strong roots that can break pots, the Sansevieria International Society recommends planting the plant in a deep enough pot to allow its shoots to reach bottom and turn back upwards.
Light is essential for the growth of the sansevieria, but how much light indoors is enough? Fortunately Sansevieria needs are satisfied with low light. You can grow the plant in a window with a Northern exposure. Or if you only have sunny windows, you could put your Sansevieria near an inside wall or in a hallway. The Sansevieria does not want direct sunlight but it will take dappled sunlight. When you are growing your plant, look at it. It will “tell†you if it is happy because the color will be good, the leaves will be normal size and sturdy. If the light is too bright the leaves might become lighter and not have as much pigment. Too low light and the sansevieria leaves might grow too long and become weak.
Sansevieria do not like much nitrogen which is in fertilizers. They grow in poor soil.  Any soil will work for them though they will be happy with a good loamy soil. Some growers add a little fertilizer to the soil on a monthly basis when the plant is growing. See here.
When indoors, the Sansevieria do not need a lot of water. They will not tolerate soggy soil at any time but they especially do not want much water during the cooler months.   It is best to let the plant dry out between waterings. But underwatering is not good for the roots either, so some people stick their finger or a stick in the soil a few inches to check for moisture. Watering once every few weeks when the plant is indoors- checking the top of the soil in the pot to see if it is dry might be easier for you to remember.
They like it warm indoors. They will not survive in temperatures below 50 degrees fahrenheit so it is best to keep them in warmer environments. They are happy when the temperature indoors is what makes you comfortable and warm- over 65 degrees F.