Homeowners usually choose evergreen plants for their year-round color and fragrant needles. Unlike deciduous perennials and shorter-lived biennials and annuals, evergreen plants retain green foliage through multiple growing seasons. These long-lasting shrubs and trees can be hard to kill, but a few things will do them in, whether intentional or not. You can decide which method you need to use, or, on the inverse, you can see which of these techniques might have killed your evergreens.
Consider using an herbicide such as 2,4-D or MCPA to kill weeds around the base of the shrub itself. The herbicide enters the roots of the evergreen and slowly kills it. If you apply herbicide to the ground, the trunk or parts of the plant above ground, it is absorbed into the plant and growth is stopped.
Girdle evergreen shrubs by cutting through the bark about an inch all around major stems of the plant and removing it. This stops the flow of nutrients and water up into the shrub. You will notice the green foliage browning and drying up within weeks, and eventually the wood will rot away.
Spray the shrub with a salt spray such as is used on roadways. The part of the shrub that is sprayed is usually killed, although as with the other methods, it will take several weeks or months before the shrub looks like it is dying.
Burn the shrub. If a plant is small enough, the heat of the fire will do irreparable damage and what is left of the shrub will slowly dry out and rot. Note that this cannot be done in most settings since burning regulations tend to be against shrub burning. Check the burning restrictions in your area before attempting this method.
Cut the shrub down below the surface of the soil. You may occasionally get a few shoots that come up, but they are easily cut back and the shrub's roots will eventually die.