How to Fertilize Hydrangeas for the Best Blooms

Full blooming colorful hydrangeas are a sight to behold! Large blooms are rewarding, but gardeners often struggle to get hydrangeas to bloom every year. Although hydrangeas aren’t considered high maintenance plants and can thrive in many different climates, they do require some TLC. More importantly, gardeners must understand how to fertilize hydrangeas properly to achieve big blooms every year. 

Understanding how to fertilize hydrangeas also requires knowing what variety of hydrangea it is. Each type of hydrangea may have different needs when it comes to fertilization. Improperly fertilizing hydrangeas can affect the health of the bloom and the number of blooms that cover the plant. 

This article will guide gardeners on how to achieve gorgeous blooming hydrangeas simply by using the correct fertilizer at the right time and applying it in the proper way to help the hydrangeas reach their maximum growth potential.

The Different Types of Fertilizer

Different methods for how to fertilize hydrangeas:

Organic Fertilizer

adding compost

Organic fertilizers are great for your budget, and if you prefer a chemical-free option that can bring your soil up to optimal health. One drawback is that organic fertilizers may not be as strong as chemical ones. However, organic materials can still benefit the condition of the soil and add necessary nutrients to help plants thrive. 

Natural fertilizer may contain earthworm castings, animal manure, or compost ingredients. As hydrangeas flourish in an acidic environment, gardeners can fertilize hydrangeas with coffee grounds, adding extra acidity to the soil and helping repel certain insects like ants and slugs. Another option is to add distilled vinegar to the water to add acidity to the ground and infuse some iron.   

Inorganic Fertilizer

hand applied plant fertilizer

Inorganic fertilizers are commercially prepared with specific chemicals to help hydrangeas achieve their full growth potential. Hydrangeas need nitrogen, phosphorus, and potassium to develop well.

Look for an all-purpose, balanced fertilizer which would typically be labeled 10-10-10 for each of the ingredients by weight. Chemical fertilizers have timed-release ingredients designed to dissolve more slowly to feed the hydrangeas over a more extended period, like a few weeks or months. 

Fertilizer comes in three forms:

Liquid

liquid plant fertilizer

Liquid fertilizers give a fast-acting nutrient boost to a plant’s roots and leaves. They are usually in concentrated form and must be diluted before being used to fertilize plants. 

Granular

miracle grow fertilizer for hydrangeas

Granular fertilizer is sprinkled around the hydrangeas and worked into the soil. The solid granules take longer to absorb into the ground. Because of this slow release of chemicals, the fertilizer doesn’t need to be applied often and lasts longer. 

Spikes

fertilizer spikes

Spikes are similar to granular fertilizers in that they dissolve slower and provide nutrients to plants over a longer period of time. The spikes are pushed into the soil around the base of the plant.

When to Fertilize Hydrangeas

Hydrangeas are deciduous shrubs, so they naturally lose their foliage and go dormant in the wintertime. Hydrangeas begin preparing for dormancy in the fall season. Stop fertilizing hydrangeas at least two months before the expected time of receiving the first frost in your area. 

Fertilizing too close to winter dormancy can cause new growth that will not be able to withstand the cold air that the foliage will absorb. The risk is that the entire plant will wither and die during the winter. 

Best Time for Fertilizing Hydrangeas 

1. Early Spring

Early spring is the best time for the first application as the hydrangeas are coming out of dormancy. 

2. Before the Hydrangeas Bloom

When hydrangeas bloom will depend on the type of hydrangeas planted. Each type of hydrangea has a different bloom time. There are five varieties of hydrangeas generally found in North America.

Types of Hydrangeas

Bigleaf Hydrangeas

Also known as French Hydrangeas, they are the most common type of hydrangeas found in the United States. Endless Summer hydrangeas are a popular variety of Bigleaf (PDF). They generally bloom from late spring to midsummer. The second fertilizer treatment should be just before they begin to flower.

Panicle Hydrangeas

They are known for their cone-shaped flower heads. They generally have white-colored blooms but turn pinkish as they age. Popular varieties include Limelight, Bobo, and Phantom hydrangeas. Blooms start appearing in July and last until the fall. Panicle hydrangeas require two fertilizer applications in April and June right before they bloom in July. 

Smooth Hydrangeas 

Smooth hydrangeas are named so because of the texture of their large leaf. Smooth hydrangeas also have large, globe-shaped white flower heads. Annabelle hydrangeas, also called snowball bush, are a popular type of smooth hydrangea. Smooth hydrangeas start blooming in late June and continue to bloom intermittently throughout the summer, so the second fertilizer application should be no later than mid-June.

Oakleaf Hydrangeas

The leaves are shaped like those of a red oak tree, hence the name. These are the only types of hydrangeas that naturally change color in the fall. The Oakleaf variety blooms from early summer in southern regions and midsummer to early fall in the Midwest and northern states. 

Climbing Hydrangeas

Climbing hydrangeas grow like vines as they tend to grow upward around structures. They also have large blooms. These hydrangeas bloom from late spring until midsummer. 

Factors that Affect Hydrangea Bloom Time

Pruning 

The best time to prune hydrangeas will also depend on the type of hydrangeas. Hydrangeas are woody shrubs. Some varieties of hydrangeas grow on old wood, and others bloom on new wood. 

Some shrubs bloom on new wood, which means that the flowers bloom on buds formed in the current season. Since the buds formed after the winter, hydrangeas such as Smooth and Panicle hydrangeas need to be pruned in late winter or early spring just before the new growth starts. Pruning at this time will help the hydrangeas reach their full growth potential and the number of flowers that it produces. 

Hydrangea shrubs blooming on old wood have flower buds that form shortly after blooms fade in the summer. So the buds and the stems of the plants have to survive the winter to get blooms for the following spring or summer season. Hydrangeas such as the Bigleaf, Oakleaf, and Climbing hydrangeas variety, should be pruned once the flowers have died. The pruning must be done before the new buds form. Otherwise, it will be too late because of the risk of pruning off next year’s flowers. 

The flowering season or time of the first bloom can be affected by pruning or lack of pruning. Pruning some hydrangeas in the spring can delay their blooms. The delay in the flowering would also delay the time to fertilize the shrubs. 

Temperature

The climate affects the timing of when hydrangeas bloom. In different areas of the country, the same type of hydrangea will bloom at different times. Hydrangeas planted in warmer climates will bloom earlier and for longer than hydrangeas planted in colder, more northern climates. 

Inappropriate Care

A hydrangea’s ability to bloom every year can be affected by the amount of sun exposure, being under or overwatered, and over-fertilizing the plants. 

Tips on How to Fertilize Hydrangeas

It is essential to understand where the drip line is of the shrub to know where to place the fertilizer. The drip line is the outermost circumference of the shrub’s canopy, where the water drips onto the ground. A light fertilizer coating should be spread around the drip line and never placed at the trunk or next to the stems. 

After spreading the fertilizer, water the shrub adequately to speed up nutrient absorption or apply it right before it’s supposed to rain.

For the first dose in early spring, use an all-purpose, balanced fertilizer with nitrogen, phosphorus, and potassium and a ratio of 10-10-10. A strong fertilizer without timed-release that slowly feeds nutrients to the plants will cause mainly the leaves to grow and provide little support to getting big blooms. 

For the second treatment, before the hydrangeas bloom, apply a fertilizer with a higher phosphorus level in the ratio. Phosphorus helps with plant growth and bigger blooms. A fertilizer mix of nitrogen, phosphorus, and potassium and a ratio of 10-30-20 will help grow big blooms.

Be mindful of the amount of fertilizer applied because too much can leave the foliage looking scorched. 

Fertilizer Can Change the Color of Hydrangeas

Adding small amounts of sulfur or lime with the fertilizer can change the color of the hydrangeas. Hydrangeas treated with sulfur will stay or turn blue or purple. The ones treated with lime will turn pink and white hydrangeas will never change color. 

Conclusion

The best practices for hydrangea care include fertilizing hydrangeas twice a year. The first time should be in early spring with an all-purpose, balanced fertilizer, and the second time should be just before the shrubs start to bloom with a phosphorous heavy fertilizer mix. 

Gardeners who follow the correct hydrangea care and fertilization advice provided can expect to see big beautiful blooms in the next season. 

Fequently Asked Questions

Can you fertilize hydrangeas when they are blooming?

This depends on when your hydrangeas bloom. If they bloom in the later spring to early summer, then you can fertilize them prior to blooming. Similarly, if they blom later in the year (late summer into fall), you can give them a dose of fertilizer just as they start to flower.

Is Miracle Grow good for hydrangeas?

Yes Miracle Grow can be good for hydrangeas. Just make sure to select the right formulation. Usually a 10-10-10 is best for a first dose, and 10-30-20 for a second dose.

Are Epsom salts good for hydrangeas?

Yes Epsom salt can be good for hydrangeas. It contains sulfur and magnesium sulfate. Both of these minerals will help lower the pH of your soil. We have a full article on how to make your soil more acidic if needed.

Can I use rhododendron fertilizer on hydrangeas?

Yes, you can use rhododendron fertilizer with hydrangeas. They have similar nutritional needs.

Can you overfeed / fertilize hydrangea?

Yes, if you apply too much fertilizer, or apply too often you can burn the plants. Always follow methods outlined in this article with the proper fertilizer.

References

USMASS Extension Growing Tips : HYDRANGEAS Color + Fertilizing (PDF)

https://ag.umass.edu/sites/ag.umass.edu/files/pdf-doc-ppt/fs5_hydrangeacolorfert14.pdf

University of Tennessee Institute of Agriculture: Hydrangea Production (PDF) https://plantsciences.tennessee.edu/wp-content/uploads/sites/25/2021/11/Hydrangea-Production_Species-Specific-Production-Guide-PB1840-B.pdf