Plant food supplements houseplants and gardens where soil needs amending. The composition of plant food varies. There are many types of fertilizer to encourage lush growth, flowering or fruiting, depending on your plants' needs and the condition of your growing medium.
Mineral and non-mineral elements are important for healthy plant growth. Non-mineral elements include hydrogen, oxygen and carbon. Mineral elements come from the soil. They dissolve in water and are absorbed through the plant's roots. Mineral elements include macronurtients and micronutrients. Often, soil does not contain an ideal balance of nutrients. In this case, plant food can provide needed nutrients.
Commercial plant food is always labeled with three numbers separated by dashes. The numbers represent the combination of three primary nutrients: nitrogen, phosphate and potash, denoted by the letters N, P and K. This label is known as the fertilizer grade.
The best way to select the right plant food for your garden is to have your soil tested to find out which nutrients it is lacking. Cooperative extensions may offer this service for a nominal fee, or you can have the soil tested by an independent laboratory. After testing your soil the extension or lab will recommend the best plant food for your needs.
Specific plants require a specific balance of nutrients to perform. For example, rhododendrons thrive in acidic soil, which allows them to efficiently absorb nutrients. The best plant food for them ensures adequate soil acidity. Additionally, for early flower buds, incorporate phosphorous into rhododendron soil. To ensure adequate magnesium, which helps keep their leaves green, add Epsom salts. Researching the nutrient requirements of specific plants allows you to select the best plant food to encourage lush growth.
Avoid overfeeding plants--too much plant food will cause a negative effect, called "burning." Burned plants will show yellow leaves and quickly die. Feed plants at the right time of year. Early spring and autumn are typical feeding times for outdoor plants. Houseplants may require weekly or twice monthly feeding. Consult plant food instructions and research the needs of your specific plant to determine the best amount and time to feed.