The spring equinox for 2010 falls on March 20. What is the significance of this day? Well, as Larry West says in an article on the spring equinox, "equinox" is Latin for "equal night" (as in daylight hours and nighttime hours being equal). Says Larry: "The idea is that on the first day of spring there are exactly 12 hours of daylight and 12 hours of darkness, but it rarely works out that way. There is always a time each spring, and again each fall, when the hours of light and darkness are equal, but it usually occurs before the vernal equinox and after the autumnal equinox."
That's okay with me. All the numbers aside, the fact is, the chief significance of the spring equinox for the plant lover is that it marks the first day of spring! So the spring equinox in 2010 can't come fast enough for me. And as Larry notes, "In spring, the Earth's axis is tilted toward the sun, increasing the number of daylight hours and bringing warmer weather that causes plants to bring forth new growth."
Resource related to spring equinox 2010: Groundhog Day and the Spring Equinox