There are many reasons why otherwise healthy plants suddenly die. This could be the result of too little watering, too much watering, fungal disease or pests.
When plants suddenly bite the dust for no apparent reason, gardeners tend to blame themselves for something they did or didn't do. To understand the reason for a plant's demise, you have to do a little detective work, especially with plants that have no apparent signs of insect or disease problems.
There are many reasons for sudden plant death, including gopher damage, microscopic nematodes that attack plant roots, too much fertilizer and so on.
In the vast majority of cases, the cause is as simple as too much or too little water.
Master gardener Paul James planted a carefully coiffed Chamaecyparis 'Boulevard,' but it died from lack of water while he was on an eight-day fishing trip. To find the cause of death, he dug in the soil to a depth of roughly one foot and found it dry as a bone. Unfortunately, his irrigation system didn't reach far enough to water the plant. The opposite happened with a juniper, which received too much water because of a drainage problem.