Are you using the same containers that caused the root rot in the past? Because if so, that is probably what is causing your problem.

If the containers are not expensive, you should just throw them out. If they are too expensive to throw out, then you need to empty them out, get rid of all of the soil that was in them, and sanitize them with bleach before you use them again.

Here is a good page about root rot:
http://www.uoguelph.ca/pdc/Factsheets/Diseases/RootRotHouseplants.htm

To avoid root rot with new soil and new pots, you’ll want to make sure the soil drains well. And do not over water. Do not let pots/containers sit in water-filled saucers.

FYI, have you seen these fabric grow bags? They are inexpensive, and I like them. They are quite popular at Clean Air Gardening, where I work.

http://www.cleanairgardening.com/tomato-smart-pot-planter.html

I plant in plastic containers because that is what I am able to afford, however, the last two years of the four that I have been planting herbs and tomatoes I have gotten root rot. I do not want this to happen again this year, so I have limited my items that I have decided to plant. Please give me some instruction on how to avoid the root rot with the plastic planters or let me know what I can do to try to prevent it. I live in Northern NJ and I am in area #6. Just to let you know I have not planted anything yet, I am starting my seeds this week. Thank you so much for your help.

Here’s an article from an old issue of Flower & Garden magazine.
http://findarticles.com/p/articles/mi_m1082/is_3_43/ai_54851905/

And here’s a good one from the University of Illinois extension.
http://www.extension.org/article/20982