Plants require the proper nutrients in order to thrive. Houseplants in particular are prone to nutrient starvation, since they quickly deplete the food stored in the potting soil. Vegetables and herbs grown in containers also require frequent feeding to stay healthy for much the same reason as houseplants. Many fertilizer types exist on the market, but soluble liquid fertilizers are some of the simpler ones to use and they come in formulations for houseplants, flowering plants and vegetables.
Measure out 1 teaspoon of balanced, soluble fertilizer, such as 20-20-20 analysis. Alternately, follow the measurement recommendation on the fertilizer package if using a different analysis.
Dissolve the fertilizer in 1 gallon of water. Use a watering can that is set aside only for fertilizer applications and isn't used for daily watering, as fertilizer left in the watering can may lead to over-fertilization later if it is re-used accidentally.
Water the plants from the top with the fertilizer water. Water until the excess drains from the bottom of the pot. Avoid getting water on the leaves of the plants as the fertilizer may burn them.
Empty the drip tray under the pots one hour after watering. This allows all the excess to drain out and prevents diseases from breeding in the standing water.