How and When to Fertilize Hydrangeas For Brighter Blooms

Not sure when or how to fertilize your hydrangeas? While the fertilization process is straightforward, there is some basic information that's important to know. In this article, gardening expert and hydrangea enthusiast Jill Drago walks through the best times of year to fertilize your hydrangeas, and how to do it by following a few simple steps!

Purple Blooming Fertilized Hydrangeas in Garden With Green Foliage

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Hydrangeas are a garden favorite. Their large flowers can be the showstopper in the garden or a gorgeous accent plant lining borders and pathways. They grow in most locations and almost every part of the United States. There are many different types of hydrangeas, most of which are tolerant of almost all conditions.

Hydrangeas are relatively low maintenance, but even the lowest maintenance plants need a little boost every now and then. Fertilizing is an easy garden task, and sometimes it is not even necessary. But how do you fertilize them, and when should you fertilize them for the best results?

Keep on reading to learn everything you need to know about fertilizing your hydrangeas. You’ll learn about different fertilizer types, as well as the best time of year to start fertilizing. We’ve also put together a step-by-step guide of how it’s done.

Should You Fertilize?

Fertilized Hydrangeas with Blooming Purple Flowers. The flowers are a light lavender color, with yellow at the centers where some of them are still less mature and have not fully bloomed. Green foliage is at the base of the bloom.
Fertilizing can have many different benefits, including longer, bigger blooms.

Plants don’t always get the nutrients they need to survive, and thrive. In many areas of the world, the soil can be lacking in critical nutrients that plants need to thrive and bloom. Fertilizer helps supplement missing nutrients in the soil, which can help your hydrangeas build a stronger plant foundation and encourage bloom production.

Not every gardener should fertilize, and not every gardener needs to fertilize. But usually, most soils do not have the perfect nutrient profile.

When you fertilize your hydrangeas, you’ll see several benefits. Your plants will bloom for longer periods, have bigger blooms, and have bloom colors that are incredibly vivid, making your plants the envy of your visitors.

When to Fertilize

Hydrangeas blooming in blue and purple in the garden. Some of the flowers are yellow on the flower clusters, which are young and not yet mature. There are hundreds of small flower blooms on each cluster.
Don’t fertilize after August, as this can cause new plant growth.

When you are fertilizing, you do need to keep the time of year in mind. You will be safe as long as you don’t apply any fertilizer after August.

The reason for this is that once your hydrangea has stopped blooming, the fertilizer will cause your plant to produce a lot of new growth. This new growth may not have time to harden off before the temperatures drop. This can cause winter damage to your plants.

How to Fertilize

Fertilizing is fairly straightforward. You’ll follow five simple steps, along with a bonus step if you are fertilizing to change your hydrangea’s color. Let’s take a look at how it’s done, step-by-step.

Step 1: Test Your Soil

An closeup image of a soil pH meter. There is dark, rich soil on the ground with the soil meter. You can see the meter measuring the soil pH, showing a rating of 7.
Before proceeding with the selection of fertilizers, it is recommended to conduct a soil test.

While this is not a required step when it comes to fertilizing hydrangeas, it is recommended. Soil tests can provide you with a lot of information about what is going on in your soil. This information can help you make a more efficient plant care plan.

There are a variety of ways to have your soil tested. You can purchase a test right online or at a garden center. Or you can go through a lab or a local extension office. You will learn about your soil pH, as well as the levels of nutrients in your soil.

You may have more than enough nutrients in your soil and can skip fertilizing altogether. Or you could be really lacking something important and can supplement as needed.

Step 2: Choose Your Fertilizer

There is a fertilizer for every need these days. You should choose the fertilizer that is right for your soil chemistry and the needs of your plant. You’ll need to decide between organic or non-organic and quick versus slow-release. Let’s take a look at the different options.

Inorganic vs. Organic

A gardener holding two handfuls of fertilizer. The gardener is wearing a green sweatshirt and the image focus is on the gardener's hands holding granules of fertilizer. The fertilizer has many different colored granules.
Organic fertilizers work more slowly but have added benefits.

Inorganic fertilizers are made up of synthetic components. Hydrangeas benefit from a 10-10-10 NPK fertilizer. If you are looking to boost your blooms, you will want a higher phosphorus fertilizer, something like a 10-20-10 NPK would be great.

Often, inorganic fertilizer is slow-release which many gardeners see as a benefit because you do not need to reapply throughout the season.

Organic fertilizers also have amazing benefits. They are better for the environment and keep your plants healthy and strong. Keep in mind that because there are no synthetic components to these fertilizers. This means the results may not be quite as “big” as inorganic results.

When you are choosing a fertilizer for hydrangeas, look for something labeled for acid-loving plants. If you would like to boost your blooms, try fish bone meal product, which is high in phosphorus.

Slow-Release vs. Quick-Release

A gardener is wearing yellow rubber gardening gloves pouring liquid fertilizer into a small cup. They are holding a yellow plastic container pouring it into a small plastic cup. On the ground is a blue container near green garden shrubs.
Fast-acting liquid fertilizers can provide a boost of instant nutrition.

Slow-release fertilizers are of the inorganic variety. They are small granules that are coated to prevent the fertilizer from releasing all at once. When applying, it is important to scratch the soil surface beforehand. Soil contact helps the fertilizer release.

Quick-release fertilizers come in all varieties: liquid and granular. Liquid fertilizers are usually in a foliar feed.

They could also be organic or inorganic. Whichever fertilizer you choose, these quick-release options will provide your plants with instant nutrition. These types of fertilizers are great if your hydrangea needs a quick pick me up or if you don’t mind making multiple applications per season.

Step 3: Water Your Plants

A gardener his holding a blue watering can pouring water on pink blooming hydrangea bushes. The gardener is wearing a blue shirt, and is standing in the middle of the garden pouring water on the plants.
Before fertilizing, make sure that the hydrangea has received sufficient water.

Before you apply your fertilizer, no matter what time of the year, it is a good idea to make sure your plant isn’t dry. If the roots are dried out, fertilizer can burn the plant. You will see fertilizer burn as dried brown spots on the leaves.

Hydrangeas require about one inch of water a week from rainfall or irrigation. Keep on top of your watering before you fertilize for the best results.

Step 4: Apply Your Fertilizer

Hand of a gardener in gloves holding granulated fertilizers. The gardener is holding a green trowel that has fertilizer on it over the soil next to green garden shrubs.
It is recommended to wear gloves when fertilizing.

The application of fertilizer will differ greatly depending on what product you have chosen for your garden.

The label on the back of your product should be your bible. Follow the guidelines to avoid damaging your plant or the surrounding areas.

You may need to hook your fertilizer up to your hose, or you may need to use a measuring scoop or spoon to apply granular fertilizer. Wearing garden gloves is always recommended.

Step 5: Add Compost

A gardener's hand is holding compost next to the garden bed. In the compost is rich brown organic matter with worms crawling around in the composting mixture.
Compost is able to improve the structure of the soil by saturating it with nutrients.

Adding compost is an amazing way to boost everything in your garden. It provides essential nutrients in a safe way and improves the structure of your soil.

Adding compost yearly to all of your gardens is great. Some years I will add compost to the entire surface of my gardens. Other years, I will just add it around each individual plant. Either way, I have great results with the growth of my plants.

I can also personally testify to the improvement of soil. Many gardens are very sandy. After about ten years of adding compost, I can see layers of both sand and compost when I dig holes for new plants.

Step 6: Fertilizing to Change Color (Optional)

Shrubs are blooming with pink and blue flowers. The blue flowers are turning pink based on the soil pH. There are several blooms, some of which are half pink and half blue.
Bigleaf hydrangeas change color depending on soil pH.

Beyond improving plant health, you can also fertilize bigleaf hydrangeas and mountain hydrangeas to change their bloom color. These types of hydrangeas may bloom in shades of white, pink, purple, red, or blue.

Their bloom colors are dependent on the pH of your soil. Lower pH will create more acidity. Soils that have a pH of 5.5 or lower will support blue flowers, where soils that have a pH of 6.5 or higher will support pink flowers.

This is an instance where a soil test is especially helpful. You could also use a pH gauge, which looks like a thermometer that you just stick into your soil and get a read on your pH.

If you are looking for blue blooms you will want to use aluminum sulfate, or a soil acidifier. Follow the labeled instructions. I like to follow a less is more approach with these products, because you don’t want to alter your soil too much.

It’s easier to add more than it is to take away. If your plant is dry, water before applying this solution. This method should only be used twice a year, once in April and once in May.

When it comes to brightening the pink flowers on your hydrangeas, garden lime will be your best tool. Apply a powder form of lime to the base of the plant in April and again in October.

Final Thoughts

However you decide to fertilize your hydrangeas is your choice. By following the above tips, you will have set yourself up for success. Make sure you’ve picked the right type of fertilizer, and plan on fertilizing at the time during growing season. Their blossoms will be bigger, leaves greener, and the plant will be healthier overall!

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