Hydrangeas should be fertilized twice yearly – once in early spring to promote flowering and once in early fall to finish the season. In my experience, well-performing Hydrangeas only need a low-concentration, balanced fertilizer with equal NPK values, while a 15-30-15 fertilizer higher in phosphorus will improve flowering. But, it’s also possible to overdo it, potentially ruining your hydrangea flowering season and future ones if you’re not careful. In this article, I’ll run through everything you need to know about when and how to fertilize hydrangeas to get the most out of your plants.
Signs Your Hydrangeas are Lacking Nutrients
Regular fertilizing is best for getting the most out of your plants. But, if you’ve planted in nutrient-deficient soil or have forgotten to fertilize for a while, your Hydrangeas will quickly give you signs that they’re in trouble.
The first thing most notice is a lack of flowers. There are many causes for this common issue, from lack of sunlight to incorrect pruning techniques. Lack of nutrients could also be the culprit, particularly a lack of phosphorus. A quick soil test will tell you the problem, allowing you to target the proper nutrient.
Yellowing leaves are another concerning sign, usually indicating a deficiency in iron or possibly nitrogen, although that is less common. The yellowing will appear mottled while the veins remain green, a condition known as chlorosis. Root rot or heavy shade can also cause leaves to turn yellow, but it is not as common in Hydrangeas. The leaves will also be completely yellow rather than a mottled yellow.
Overall lack of growth can also indicate a nutrient deficiency. Each Hydrangea species and your chosen cultivar will have a mature height. If growth has slowed without reaching that full height or the leaves and flowers look small and diminished, look to your soil’s nutrient content for the answer.
How Often Should You Fertilize Hydrangea Plants?
Hydrangeas must be fed at different times during the season for different purposes. In spring, a flower-focused fertilizer can encourage more blooms throughout summer. At the end of the season, an additional dose will help maintain health until growth picks up again the following spring.
If your plant is not performing at its best, apply a lower-strength liquid fertilizer towards the end of spring. This can significantly impact your flowering season, but it’s also important not to overdo it. Overfertilizing is challenging to resolve and can ruin the rest of your season or permanently damage your plants if used excessively.
After the final dose of fertilizer in the fall, applied a few weeks before the plants die back (and are ready for cutting back), there is no need to fertilize over winter. Depending on the performance of the Hydrangeas, you can fertilize them again in early spring to kickstart the season. Late autumn is also a good time to consider moving or transplanting your hydrangeas if needed.
The Best Types of Fertilizer
If your Hydrangeas are planted in fertile soil and are flowering well, a balanced fertilizer with equal parts nitrogen, phosphorus, and potassium is suitable. Look for a fertilizer with an NPK ratio of 10-10-10 for the best results.
For those that need to give your Hydrangeas an extra bloom boost, you can also look for a fertilizer with a higher phosphorus value, like a 15-30-50. The higher concentrations and extra phosphorus will push the plant to develop even more flowers, ensuring you get the most out of your season.
Slow-release fertilizers are best as they will sustain the plant throughout the season. These break down slowly over time whenever you water hydrangeas, giving plants the nutrients when they need them. If your plant is lacking flowers, a low-concentration liquid fertilizer can also be added toward the end of spring for quick absorption.
Try these options specially formulated for Hydrangeas and other flowering shrubs (via Amazon):
- Shake ‘N Feed Flowering Trees and Shrubs Plant Food
- Miracle-Gro Water Soluble Flower Food
- Jacks Classic 10-30-20 Blossom Booster Fertilizer
How to Apply Fertilizer
The application process will depend on the type of fertilizer you choose. Slow-release fertilizers can be added to the soil and gently mixed in to cover all the roots. Make sure the fertilizer extends to the edges of the growth. Keep the pellets of the stem to prevent scorching.
Other fertilizers should be diluted in water and applied to the soil when you water. Always dilute according to the instructions and never add more to prevent overfertilizing.
There are a few tips and tricks to be aware of when fertilizing Hydrangeas:
- When growing any color-changing Hydrangea species, remember that some fertilizers are formulated for specific colors. For example, if you want your fertilizers to turn blue, use blue hydrangea fertilizer to make the soil slightly more acidic.
- Fertilizers can’t make up for inadequate soil. Amend your soil with compost and mulch throughout the season with organic materials to maintain soil health.
- If you notice any signs of nutrient deficiency, eliminate any other potential causes first. Removing it from the soil is challenging once you’ve applied too much fertilizer.
- It’s worth noting that hydrangeas are considered toxic, so it’s prudent to wear a pair of gardening gloves throughout the process.
The Role of Fertilizing in Plant Health, Growth, and Development
Nutrients are an essential component of growth, flowering, and their associated benefits – the part many Hydrangea growers look forward to. There are many different nutrients that all plants require, grouped into three categories: macronutrients, secondary nutrients, and micronutrients.
Macronutrients are those plants need in the largest amounts, vital to essential processes within the plant. If you’ve seen the letters NPK on a package of fertilizer, it’s these three nutrients that they refer to.
The first is nitrogen, which plays a prominent role in leaf and stem growth. Phosphorus is next, a big part of flowering and fruiting. Finally, potassium contributes to overall health and root growth. While these nutrients have a particular function, they all work together to keep the plant healthy and thriving.
The second category is secondary nutrients like calcium and sulfur. They are needed in slightly smaller amounts than the three macronutrients but are also essential in plant health. Finally, micronutrients like iron and boron are needed in tiny amounts. Even though they are required in lesser amounts, a deficiency in any of them can cause serious health issues in your plants.
Plants absorb these nutrients from the soil. But, when hydrangea soil lacks nutrients, one way to boost it is to add fertilizer to the soil. Some are diluted in water to be immediately available to the roots, while others break down slowly over time and enrich the soil.
The Final Word
Fertilizer is essential in getting as many flowers from your hydrangea plants as possible. Monitor their performance to apply the best fertilizer for your specific species at the right time.
To enjoy the fruits of your labor for longer, see our essential guide to drying and preserving hydrangea flowers at home.