An annual plant is a one season plant. The goal of all plants is to flower and set seed. When this goal has been reached and the plant is assured the next generation is going to be produced, it often will stop growing. If after a flower has been produced it is prevented from setting seed by removing it, it continues to produce more flowers. An annual plant at the end of the season will die whether or not it has been allowed to flower or set seed. A perennial will do the same, but its roots remain alive, though dormant and will grow again next spring. Al

Adding onto Al"s message. If you cut off the spent blooms on perennials, the plant WILL stay green longer. However the plant energy, will be directed at the roots, new growth instead of creating seeds. This is why so many of us work at deadheading our perennials, to make better plants. Better roots allow better leaf and stem growth to produce more flowers NEXT year.

As Al said, annuals only live one season in most places. Warmer climates may allow some to overwinter, they survived to bloom again. Depends on how your winters go. Some annuals can actually be tender perennials, will survive in warmer winters. I do not count on my annuals being around next year, too cold, frozen ground. You can deadhead annuals, it helps produce more flowers. I regularly trim my salvias, dianthus, marigolds, geraniums and they reward me with more flowers. Many new annual plants are great at deadheading themselves, flowers fall off.

Kind of like mowing grass. The more often you mow a short amount of leaf, the thicker, nicer, lawn grass looks. Not mowing regularly then whacking off large amounts of leaf on grass, makes lawn look kind of tatty, patchy. May go to seed and then dormant. Annual flowers can like being trimmed of dead flowers, will bloom again for you.