Spring is an exciting time for gardeners.  Plants begin to wake up from their winter sleep and flowers show their colors.  But this time of year can also be the most dangerous period for plants because the weather can quickly change from nice to nasty.  Planting too early can be hazardous to your plants' health.

As you begin to plant, here are some things you need to know:

Large numbers of landscape plants are damaged or destroyed outright by drastic shifts in the weather.  Most  victims are newly planted plants that have been stuck in the ground by gardeners a little too eager to get a jump on the growing season.  What sends those plants to an early grave are air temperatures that produce either a frost or, worse yet, a freeze.  

A light frost occurs when the air temperature around plants drops to 32 degrees F; at that point, tender plants may be damaged.  A light freeze occurs at temperatures between 29 and 31 degrees, and in that range tender plants may be destroyed; half-hardy plants may be seriously damaged.  Temperatures between 25 and 28 degrees result in a moderate freeze, which can be widely destructive to all kinds of plants, including the top growth of established ones such as fruit blossoms.  A severe freeze producing temperatures of 24 degrees and below will almost certainly destroy newly-planted, non-woody plants and may seriously damage certain established plants

The sun also plays a role in damaging plants.  If the ice crystals in the cells have a chance to melt before the rising sun stimulates the plant into its daily activity, the plant may recover nicely.  But if the sun hits the plant while the ice crystals are still frozen, tissue damage is almost certain.

The extent of damage will obviously depend on the actual air temperature and the hardiness of the plant.  This is the reason only hardy plants--whether annuals, perennials, vegetables, or herbs--should be planted in early spring.  Just because a plant is available for sale at a local nursery doesn't mean it's time to plant it.  In fact, you may have to wait two weeks or more before you should consider planting.  If you have already planted and a freeze is in the forecast, then you should water both the soil and the top growth of your plants.  Cover them with floating row covers, clothes, blankets, mulch or other protective devices.  For herbaceous plants, rest the covers on stakes so that the weight of the cover doesn't collapse the plants  Watch the weather so you will know when a frost or freeze is imminent.