Farmers and gardeners have used whey to water their plants for many years, with healthier plants as evidence that whey is beneficial for their plants. Whey contains nitrogen, phosphorus, potassium, magnesium and other minerals that are essential to plant growth. However, when watering your plants with whey, moderation is key. Small amounts of whey will fertilize your plants. But excessive amounts of whey in the soil can actually decrease the amount of nutrients available to your plant.
Place a rain gauge near the plant(s) that you intend to water. While a small amount of whey is beneficial to plants, too much whey is detrimental. The rain gauges will help you determine exactly how much whey you are giving your plants. If you cannot find a rain gauge, simply tape a ruler to the side of any clear, cylindrical container.
Fill your watering can with a solution that is one part whey and one part water. Ideally, use a watering can with a spray head so that the whey is evenly distributed.
Give each plant 1 inch of the whey water solution (stop when the water gauge is filled with 1 inch of water). Avoid wetting the plant's foliage if possible. Instead, spread it evenly around the soil around the plant, taking care to cover all of its roots.
Repeat steps 1 to 3 weekly.