Bolting means getting ready to flower, but in a special sort of way. It describes plants that die after flowering (such as parsley) and that often change their flavor when they start to form a flower stalk (I've noticed this with parsley, spinach and other things). With some plants, bolting just seems to be initiated by age. With many others, heat plays a role, so you may see some lettuce varieties described as "slow to bolt" and hence better for warm weather.

There is a "I will not be denied" air to a plant that's bolting -- pinching off the developing flower stem of a parsley plant won't do much to delay the inevitable, or keep you in an endless supply of the herb.

Another explanation is that bolting occurs when a plant goes to flower and seed prematurely - ie before you can use the parts of the plant you really want to use! Coriander and lettuce are good examples, and are notorious bolters. Coriander will often bolt before you can get to harvest the leaves; lettuce will often bolt before a heart is formed.

Bolting is often related to weather conditions such as sudden changes in temperatures, very hot weather etc. It is also associated with transplanting - some plants object to it, and bolt as a protest. Parsley is an example. In short, it can happen to a plant under undue stress.

It's a phenomenon mainly associated with annuals, and in most cases it is a precursor of imminent death of the plant. A last-gasp attempt to reproduce before carking it!

This is my first experience growing herbs in containers. From the question about bolting, I now know that my cilantro plant has done that. What do I do with it now? Is it still usable or do I need to start over and trim it more often?

Cilantro, once it bolts, will not return to the nice green flat leaves you usually harvest. You can cut the thin leaves that are now forming as they have nearly the same flavor as the flat ones. If you leave them to flower, and go to seed (actullay a fruit), you will probably get a good crop next spring, provided the fallen seeds survive your winters. Here, I usually would have a few new plants that show up from the previous summer. Because cilantro bolts, choosing a variety that is slow to bolt is a good choice. For a continous supply, plant seeds about every 3-4 weeks and you can have a good supply all during the growing season. After it bolts and flowers, you can collect the seeds, as coriander, as that is what it is. Oddly, coriander does not have a taste similar to cilantro..

Thanks for the information. I'll try to find one that doesn't bolt so quickly. If you know of one, let me know. I will try to replant the seeds that came from this plant and see how it goes. Since this is in a small container, I'd like to try to keep it growing indoors during the winter.

Yes, you can. From germination to harvest, you have a fairly short time span, so if you do plant all the seeds, expect them to all die out (or bolt) at once. Growing indoors in winter is very tough as they don't usually get enough sunlight to give them their volitile smell and flavor. Growing under artifical light designed for plants would require about 18-20 hours a day.