Day lilies are an easy to grow perennial flower and can easily thrive with little or no attention from the home gardener. But an application of the right fertilizer at the right time can take your day lilies from ho-hum average to an eye-popping spectacular show of bright blossoms. A well-fertilized day lily will be healthier, produce bigger blooms and bloom more often. Caution should be used when fertilizing day lilies—too much fertilizer will actually harm the plant, cause fewer blooms and could even result in plant death.
Test garden soil first to see what nutrients your day lilies will need for optimum growth. There is no "one size fits all" approach for day lilies. Take a soil sample to your local County Extension office for testing, or use Scotts/Miracle-Gro mail-order service to get results without leaving home. (Testing fees vary from state to state; Scotts' testing costs $15.) Soil testing can provide you with an analysis of pH, phosphorus, potassium, calcium, magnesium, organic matter percent, acidity and more.
Buy the appropriate chemical fertilizer for your day lily garden. Fertilizer is labeled with a three-number system, such as 25-0-12, which stands for the ratio of nitrogen-phosphorus-potassium (K) in the mix. A 10-pound bag of 25-0-12 would have 25-percent nitrogen, no phosphorus and 12-percent potash, a source of potassium.
Determine the amount of fertilizer to apply according to the package directions. Sprinkle the fertilizer by hand while wearing gloves or with a spreader over the entire garden in the spring. If the plants are already growing (you can see their leaves poking through the soil), carefully sprinkle the fertilizer next to, not on, the plants.
If you prefer to fertilize your day lilies twice per year, cut the amount of fertilizer applied in half. Apply the first dose in the early spring as above, and apply a second dose in mid-summer.
Water the day lilies to dissolve and dilute the fertilizer. This step will help the fertilizer reach the plant's root system while ensuring that the chemicals do not accidentally burn the plant's tender leaves.