Fall isn't actually the end of your herb gardens. Frost is the real killer. There are simple ways to protect your herbs from frost, and knowing them ahead of time is always a garden-saver.  Take a look at some of these ideas to see if they might work in your garden. Sometimes protecting your herbs from frost one night, can mean weeks of extended warm garden time. 

1. Know your weather forecast- All jokes aside, our weather forecasters have become extremely precise at predicting the weather in the immediate area. I suggest getting familiar with your local weather station, or a weather app. I use Weather Live on my Kindle. If it seems like it is going to be chilly (below 55 degrees), I bring my heat loving herb into the greenhouse if possible. These include rosemary, thyme, even sage. All seem to grow all winter with very little shock going from outdoors to the greenhouse.

1. Have a plan - We all get caught once in a while. I have been driving home from dinner and hear on the radio that suddenly we are going to get frost (it's Maine, it happens). Now, I have to go outside after dark and make an attempt at covering what needs to be protected. It really helps to have a supply of things to grab. I use anything available; bed sheets, blankets, carpets, milk jugs, 5 gallon buckets, anything that will keep the frost from actually touching the plants. You can use piles of loose leaves or compost, unless it's particularly windy that evening. The same thing with straw. It's a lovely choice, but it blows around very easily. I think the only thing worse than losing herbs to frost is going through the effort to cover everything and having it blow away. 
2. When to cover - Don't cover your plants too early the day that the frost is going to come. There can be quite a bit of heat and condensation build up under those plastic sheets. This can cause separate problems. I cover when the sun starts going behind the trees here. That is late in the afternoon. There is still enough light if I work quickly, but the worry that I am making little sunrooms on my plants has also passed. 

1. Know when to uncover - Just like covering, there is an optimal time to uncover. Based on the next day's temperatures, you may be able to only cover your plants for the night and have a couple of weeks of Indian summer. That will give you time to move your sensitive herbs indoors before the next frost. Also, if you are industrious enough, you can cover and uncover your herbs for a few weeks to extend the season. Uncover your herbs for the day once the sun has hit that particular area of garden. This may be early morning, or early afternoon for some. Just wait until the frost on the surrounding plants has melted before uncovering your herbs. 
2. When in doubt, protect from frost - Is the weather going to come close to frost temperatures? You may get lucky and have it miss you, but more than likely you will experience some frost damage. Also, once it gets down below 50, your plants aren't productive anyways. To be safe, cover when the temperatures are getting close to freezing and you will be sure to have some plants remaining and no surprises.