Just a slight imbalance in soil, light conditions, temperature and watering can make a plant sick. So can pests and fungus. Caring for sick plants is a process of diagnosing symptoms and implementing corrective measures. There are standard procedures to follow regardless of whether the sick patient is a houseplant or an outdoor plant. Once you determine the root of the problem, you can take steps to alleviate the cause and nurse your plant back to health.
Look at the soil and base leaves. Are there bits of white moss growing on top of the soil or are the base leaves falling off? This could mean the plant is being over watered. If the roots of the dying houseplant are water logged, transplant into another pot and cut back on watering.
Are the leaves of the plant limp or yellow or brown in color? This happens when the plant is not receiving enough water and nutrients. Placing a water meter in the soil can help you better monitor when a houseplant needs water. Start the plant on a fertilizing schedule so it begins receiving the nutrients it is missing.
Some plants require more alkaline or acidic soil. Use a pH tester and be sure your plant's soil is appropriate for good health. Use soil additives or different potting mixes to bring the pH to the right level.
Examine the plant’s structure. Is its growth thin and weak with wiry offshoots growing upward? This is a sign that the plant is not receiving enough sunlight. If the sick plant is outdoors in an area that gets mostly shade during the day, you may need to transplant it to a sunnier spot. If it is a houseplant, either move the plant to a sunny window or relocate under florescent lights that are on a good portion of the day or night.
If there are burn spots on the leaves, the plant is likely receiving too much sun or is too close to a window where the sun is reflecting too much heat off the glass.
Inspect the leaves of the unhealthy plant carefully. If leaves are damaged, turning brown, or curling up, this could be caused by pests or a pest-caused diseases. Caterpillars, spittle bugs, greenflies, mites, grubs, whiteflies, spider mites and other pests and insects leave signs of their presence, such as tiny holes or half eaten leaves. Look on top and under leaves for signs of pest infestation. If you spot any, apply a pesticide.
Using a magnifying glass, look for signs of fungal disease. This could show up as black or brown spots on leaves, white or gray powdery mildew on leaves and stems, small spots of white foam on leaves, or spider-like webbing on various parts of the plant. Treat with the appropriate fungicide.