Crops also fail when floods inundate fields; flooded conditions can also kill shrubs such as lilacs if submerged for only a few days. Most plants need oxygen in the soil to live. Flood waters also compact soil, making it difficult to grow crops in the future until proper tilth is regained.
Soil types can affect plants also. Clay soils bind up nutrients when they are cold in the spring. That is why plant leaves are chlorotic (green veins and yellow on the main part)before soil warms. Nutrient deficiencies also show up as purple, white or yellow leaves. Plants are more susceptible to disease when they aren't growing actively. Tomatoes that are fed low rates of fish emulsion during the summer don't overgrow vegetatively but just enough to fend off leaf diseases. Tomatoes not kept evenly moist when fruiting end up with blossom end rot, black leathery patches that make the fruit unusable. Diseases also enter through roots that are cut during hoeing.
Trees that have roots exposed die but those planted too deep also die - just slowly. Roots disturbed or cut during construction or when making a new flower bed can cause tree death or slow deterioration. It can take years to show up. If you plant perennials or seedlings whose roots are a solid mass or encircle the spot without spreading them out, you will have restricted growth. Trees will develop roots that choke and kill the tree - just when it is giving you shade.
Herbicides are another culprit. 2-4-D sprayed on a windy day may drift to desirable plants. On hot days it can vaporize, causing deformed or cupped leaves, dead spots or yellow and white leaves. If it is your tree or plant, it is an oops; when it is your neighbor's, it can mean legal action. Herbicides can kill plants that you don't intend to affect.
Mulches are good, but when applied too deeply, too close to stems, or covering the plant itself, will cause disease and death of plants. Mice and other creatures can also live there if the mulch composition is not appropriate.
