Lost Foliage, Flowers

When plants change environments, they may lose foliage or flowers if not properly acclimated.  When moved from one location to another, plants want the same type of environmental conditions.  These conditions should only be changed gradually to prevent or reduce shock.  If you buy a plant from a location with bright sunlight, high temperatures, and high humidity, but the environment where you plan to place the plant is different, be sure to allow the plant to adjust to its new location by changing these attributes gradually.

Wilting

Wilting is a tough problem to remedy, because it can be caused by too much or to little water.  Too little water causes a plant to wilt due to water deficiency.  Too much water can cause the plant to wilt due to too little oxygen, as the excess water does not leave room for oxygen in the interstitial spaces in the soil.  Water can also cause root rot.

It is easier to cure an under-watered plant than an over-watered plant.  If your plant shows signs of wilting, check the amount of water the plant should have.  Be sure you are watering the plant properly, and on a regular basis.

Yellowing

Yellowing is a sign of chlorosis, or a lack of minerals and nutrients needed for chlorophyll.  However, knowing which nutrient is defficient is hard to determine.  Lack of nitrogen, magnesium, and iron can cause chlorosis.

Brown Tips

There are three causes of brown tips in plants. 

1. Potassium is one of the three big macro-nutrients that plants require, and is a component of proteins.  It is the third number often listed with fertilizer.  Brown tips of plants often indicate a lack of potassium.  Calcium forms the middle lamella layer that holds cells together. 
   
2. Calcium cannot move through a plant, so calcium defficiency will often lead to brown tips where the plant is growing.
3. Many plants do not survive well in windy, drafty areas.  Often, the tips of plants in these areas will brown.  The Rhapis exelsa is an exception - if you want to put a plant in a drafty, windy area, consider this.

Stunted Growth

Two of the three macro nutrients - Phosphorous and Potassium - can cause stunted growth.  These are the last two of the three numbers you often see listed on fertilizer.  Phosporous is part of the DNA of plants, and Potassium makes up plant proteins.  If you suspect that your plants are suffering from stunted growth, consider fertilizing them.

Brown Edges

Plants lacking Potassium will often show brown edges.  To remedy this, consider using a fertilizer high in potassium.

Necrotic, Light Green

A plant with a necrotic, light green look may be lacking sulfur.  Sulfur is a macro nutrient that is a large component of proteins.