The Best Azalea Fertilizers—and How to Use Them for Bigger, Better Blooms

While azaleas don't always need an added boost from store-bought fertilizer to produce beautiful blooms, choosing the right product—and applying it in the right way, at the right time—can help these bright bushes reach their full potential.

Give your spring stunners a little extra support with these fertilizing tips from gardening experts, from choosing the right nutrient balance and fertilizer format to sprinkling it safely during the correct part of the plant's growing season.

Why You Should Fertilize Azaleas

Like most plants, azaleas grow best when given the right amounts of three essential nutrients: nitrogen, phosphorus, and potassium, says Jim Putnam of Encore Azalea. "Nitrogen promotes overall plant growth and fuels the development of healthy stems, leaves, and roots," he says. "Phosphorus plays a vital role in flower and seed formation and promotes strong root development, allowing plants to better access water and other nutrients from the soil. Potassium allows plants to utilize water more efficiently, better withstand drought stress, and improve overall resilience and resistance to pests and pathogens."

Types of Azalea Fertilizers

Azalea fertilizers should contain consistent amounts of nitrogen, phosphorus, and potassium (labeled NPK on the packaging). "Look for a mix that is well-balanced," says Putnam. "The three numbers on the packaging should be the same or similar"—for example, 10-10-10 or 10-6-8. He recommends a granular azalea and rhododendron fertilizer or a premium slow-release formula over liquid options. "Liquid fertilizers tend to push plants, while slow and steady growth is the best way to go," he says.

Organic Azalea Fertilizer

Azalea fertilizers labeled as "organic" are made from naturally occurring ingredients, says Putnam. Think compost, manure, and plant debris. "These materials break down over time, releasing nutrients into the soil," says Putnam. "[This makes] them an attractive option for gardeners who prefer a more natural approach."

However, organic fertilizers can come with one drawback: "The nutrient content in organic fertilizers can vary, making it trickier to determine the exact amount of nutrients your plants are getting compared to synthetic fertilizers with specific NPK ratios," says Putnam.

Inorganic Azalea Fertilizer

In contrast to the natural ingredients used to make organic azalea fertilizer, inorganic—or synthetic—fertilizers "are manufactured through chemical processes," says Putnam. These fertilizers "are often available in concentrated forms, like granules or water-soluble solutions, which makes them easy to measure, store, and apply." They also typically have exact nutrient ratios on the packaging.

While these manufactured fertilizers may seem more reliable, they offer a few down sides, says Putnam, including the potential buildup of salt over time; the possibility of harm to helpful organisms, like earthworms and microbes; and the introduction of too-harsh chemicals into your gardening routine.

When to Fertilize Azaleas

The best time to fertilize your azaleas is in spring or early summer, just after they bloom, says Putnam. "Generally speaking, mid- to late-summer fertilizing can encourage new growth going into the colder parts of the year, when that new growth will be more susceptible to cold damage," he says. "Many people like to plant azaleas in the fall (and indeed, it’s a terrific time of year to plant them!), but it’s important to avoid fertilizing them at this time, as the colder seasons are just on the horizon."

How to Fertilize Azaleas

Before choosing an azalea fertilizer, test your soil. "A soil test will tell you what kind of nutrients your soil needs in order for your azaleas to do their best—or whether or not they need to be fertilized at all," says Putnam.

Check the pH Levels

Azaleas thrive in acidic soils, which create the ideal environment for nutrient absorption, says Fidel Perez, the horticulture manager at Bellagio Resort & Casino in Las Vegas. "An acidic fertilizer will help to maintain the right pH so that the plant can uptake nutrients," he says. If your soil's pH comes back between 4.5 and 5.5, you can opt for a regular slow-release fertilizer that you would use with other plants; otherwise, choose an acidic fertilizer, says Putnam.

Apply the Fertilizer

Before applying fertilizer based on your product's instructions, wear gardening gloves and moisten the soil around your plant. Then, "spread in a light layer around the base of the plant and extend several feet out from the center of the plant," says Kristen Pullen of Star Roses and Plants. "Azalea have fibrous roots that are shallow and pull in nutrients from beyond the foliage area of the plant."

Water the Plant

After applying the fertilizer, says Putnam, "Water it in very thoroughly, and make sure to wash any fertilizer off the leaves that may have gotten on them, because some fertilizers can cause leaf burn."

Watch Your Blooms

Keep an eye on your azalea during the summer to determine whether it will need fertilizing the next spring. "If a second application is needed, do so in mid to late summer before the end of July," says Pullen; a later application will interfere with the plant's cold-weather preparation.

Plants that are thriving in the summer are unlikely to need fertilizer in the spring. "If your azaleas look healthy and have flowers in the summer, then you have done your job as a gardener and created the ideal soil conditions," says Putnam.