How To Make Citronella Oil by Pam Haefner, eHow Contributor

Citronella is an oil derived from the leaves and stems of varieties of the nard grass or lemon grass family. Its primary use is as a safe, nontoxic insect repellent. Diluted citronella oil can be applied directly to the skin. Commercial oils manufactured through distillation can be expensive. Making your own citronella oil is a cheaper option, and allows you to ensure the purity of the oil. Add it to candles, lotions or lamps to repel insects.

Instructions: 

1. Combine the olive oil and nard grass leaves and stems in the slow cooker. 
2. Cook the oil and nard grass mixture for four to eight hours. 
3. Strain the mixture using a cheesecloth.
4. Then strained mixture is your citronella oil. 
5. Discard the nard grass. 
6. Repeat the process using the strained mixture with fresh nard grass leaves and stems. 
7. Do not add more olive oil to the mixture. 
8. Repeat the process until your oil reaches the desired degree of fragrance. 
9. Seal and date the citronella oil in a dark jar. 

Tips:

1. Gather your nard grass leaves and stems in the morning when oil is at its peak. 
2. Store citronella oil in a cool, dark place. 
3. Pure citronella oil has a shelf life of six months. 
4. Lemon grass leaves and stems may be substituted for nard grass. 
5. Do not ingest citronella oil.

http://www.ehow.com/how_8349759_make-own-citronella.html