The Ultimate Growing Guide - Macrophylla Hydrangeas
GORGEOUS SKY BLUE BLOSSOMS
Easy to shift from pink to blue, you’ll soon enjoy the color of the sky down at eye level.
OUTSTANDING IN GARDENS FROM MICHIGAN TO FLORIDA
Trust this extensively trialed hydrangea to grow beautifully in your own garden.
DURABLE BUDS MEAN MORE BLOOMS
Cold hardy flower buds and an ability to continue to produce new flowers means you’ll have loads of flowers to enjoy and share.
Everyone loves blue hydrangeas, and that’s what you’ll get – in abundance – with these gorgeous rebloomers. Trialed extensively for garden performance from Michigan to Florida, these hardy, reliable hydrangeas are spectacular across their entire hardiness range from zones 4 to 9.
THE SCIENCE OF HYDRANGEA COLOR
The color of bigleaf and mountain hydrangeas, in particular, can change depending on the soil's chemistry. In addition, the genetics of the specific plant will influence color intensity.
Here's a quick explanation:
- Blue flowers occur in acidic soils (below 6.5 pH).
- Pink flowers occur in alkaline soils (above 7.5 pH).
- Mixed colors or purple flowers happen in neutral soils (6.5 to 7.5 pH).
So why does soil pH determine color? In acidic soil, aluminum is more readily available for hydrangeas to absorb. The aluminum interacts with the pigments in the petals, leading to a stunning blue color.
Important: Only bigleaf and mountain hydrangeas can change their color in a predictable, controllable way. Smooth and panicle hydrangeas undergo some color change as they age, but their flowers cannot be turned blue.
HOW TO ENCOURAGE BLUE HYDRANGEA FLOWERS
When you buy your hydrangea plants the flowers may be pink. Keep reading to learn how to change the color over time.
Determine Your Soil's pH
Understanding your soil's pH is essential when aiming to grow blue hydrangeas. Follow these simple steps to find out the pH level of your soil:
- Buy a soil test kit: You can purchase these kits at gardening stores or online. They don't cost much and are easy to use.
- Collect a soil sample: Take a small amount of soil from your garden using a clean trowel. For the best results, collect the sample from near your hydrangeas or from the spot you want to plant them.
- Conduct the test: Always follow the kit instructions, but generally, you'll mix your soil sample with a testing solution or place it onto a test strip.
- Read the results: After a specified time, the solution or strip will change color. Match this color to the provided chart to determine your soil's pH.
Remember, if you want blue hydrangeas, you'll need to have a soil pH of 6.5 or lower, and aluminum must be present.
Adjust Your Soil's pH
So what if your soil pH isn't low enough for blue flowers? To turn hydrangeas blue, you'll need to make your soil more acidic.
You may have heard of tricks like adding coffee grounds, vinegar or even pennies or a bundle of rusty nails to the soil. However, it’s best to use aluminum sulfate, which is a proven method for changing flower color.
Achieving the desired shade of blue in your hydrangeas is a process that requires patience. It may take up to a year for hydrangea flowers to transition to the stunning blue that gardeners covet.
Here are a few crucial points to keep in mind:
- Your hydrangeas won't turn blue instantly. The transformation is a gradual process that takes time.
- It might require multiple applications of aluminum sulfate to make your soil acidic enough for blue hydrangeas. Re-test your soil's pH and adjust your treatments as necessary.
- If your hydrangeas already bloomed pink, you probably won't see blue flowers until next year. Soil amendments affect the developing buds, not the flowers that have already bloomed.
- Be careful! If you lower the pH too much or too quickly, your plants may have trouble absorbing the nutrients they need. If the pH does become too low, apply lime to raise it back up.
IDEAL GROWING CONDITIONS FOR BLUE HYDRANGEAS
- Sunlight: Thrive in areas with morning sun and afternoon shade.
- Temperature: Prefer temperate climates, but can adapt to a range of zones.
- Soil: Fertile, well-draining soil rich in organic matter.
- Soil pH: Acidic soil (below 6.5 pH) is necessary for blue blooms.
- Water: Keep soil consistently moist. Hydrangeas need regular, deep watering but avoid waterlogging.
- Mulch: Use organic mulches to retain soil moisture, and regulate temperature.
Enjoy Dreamy Blue Hydrangeas All Summer
- Abundant, mophead flowers are easier to shift from pink to blue
- Blooms in summer; rebloomer
- Cold hardy buds and stems
- Smaller size makes it versatile in containers and landscapes
- Thrives in part sun to full sun
- Perennial in USDA zones 4-9
Care:
PLANTING
Macrophylla reblooming hydrangeas typically grow in USDA zones 4-9. In cooler climates, they grow and bloom prolifically in full sun but will also flower in as little as four hours of direct sun. If you live in a warm climate, it’s a good idea to provide some shade during the hottest part of the day. No matter where you garden, your hydrangea will benefit from a 2-3″ layer of mulch to keep the roots cool and moist.
Ideally, this type of hydrangea prefers rich, acidic soil that remains consistently moist. Acidic soils (pH less than 7.0) free up the aluminum present in the soil so the flowers bloom sky blue. When the soil is alkaline, the plant is not able to absorb aluminum as easily, so the flowers bloom purple or pink. You can shift the pH of your soil somewhat to make your hydrangea bloom more blue or pink using a product like Espoma’s Soil Acidifier. One thing that makes this hydrangea so unique is that the soil won’t need to be very acidic for the flowers to turn blue. That makes doing so more achievable across wider swathes of North America.
Good drainage is important for hydrangeas even though they like the soil to stay consistently moist. If you garden in heavy clay, plant them in a raised bed or plant “high”. Planting high means instead of positioning the shrub even with the ground level like you would other plants, dig a slightly shallower hole and position it so that the base of the plant is a bit higher than the ground. This encourages water to drain away from the plant rather than settling around it. Mulch well after planting
MAINTENANCE
Reblooming hydrangeas like macrophyllas produce flowers on both old and new wood. That makes it tough to find a good time to prune them without sacrificing some flowers. We suggest that you avoid pruning reblooming hydrangeas at all except to remove any completely dead branches in the spring once the plant starts to leaf out.
One common misconception about hydrangeas is that you can prune them throughout the season to keep them shorter. Hydrangeas are not like other shrubs, such as boxwood or holly, which can be pruned to maintain a smaller size. If you prune your hydrangea down, it will quickly grow right back to its original size.
Fortunately, macrophylla hydrangeas are a shorter variety that grows just two to three feet tall – short enough to fit under a window ledge. Choose a place where it can flourish without needing to be pruned to size.
If, for some reason, you do need to cut your macrophylla hydrangea back, understand that you will be sacrificing some of the flowers when you do so. Do not cut the stems back by greater than one third as that can produce soft, floppy growth.
COMPANION PLANTS
Which companions you choose for your macrophylla hydrangea depends on where you live. In the North where it grows best in full sun to light shade, choose sun-loving companions. In the South where it needs some afternoon shade, pair it with more shade-loving plants.
NORTH: Keeping in mind that most macrophylla hydrangeas grow 2-3’ tall and bloom from summer into fall, look for sun-loving companions that are shorter and taller to create a grouping.
Pearl Glam® beautyberry (Callicarpa) grows 4-5’ tall and has dark foliage flushed with purple tones that complement blue and pink hydrangea flowers. In the fall, bright purple-violet berries carry the visual interest into early winter. It would make a perfect backdrop for your garden bed. In front, try growing a few shorter plants around its feet like Magic Show® ‘Pink Potion’ speedwell and Supertunia Mini Vista® petunias.
FREQUENTLY ASKED QUESTIONS
How often should I apply soil amendments to maintain blue hydrangeas?
Apply soil amendments according to the product's instructions, typically once or twice a year. Test your soil's pH regularly to avoid over-acidification.
Can all hydrangeas change color or just certain types?
Not all hydrangeas change color. It's primarily bigleaf (Hydrangea macrophylla) and mountain hydrangeas (Hydrangea serrata) that can shift from pink to blue based on soil pH.
How can I ensure the blue color of my hydrangeas is vibrant?
To get a vibrant blue color, keep your soil consistently acidic, make sure your hydrangeas can access enough aluminum, and take good care of them with appropriate watering, sunlight, and nutrients.
Will my hydrangeas turn blue if I plant them in pots?
Yes, hydrangeas will turn blue in pots if you use a potting mix with an acidic pH and enough aluminum availability.
Can I change the color of my hydrangeas mid-season?
Changing the color mid-season is challenging, as soil changes affect developing buds. For a color shift, start adjusting the soil's pH before your hydrangea sets its buds.
How can I safely lower my soil's pH without harming other plants in my garden?
Use soil amendments specifically designed to lower pH, like sulfur or aluminum sulfate, and apply them directly around your hydrangeas. Avoid spreading these materials throughout the entire garden, which could harm plants preferring neutral or alkaline soil.
What should I do if my hydrangeas are not turning blue despite acidic soil?
Even with acidic soil, hydrangea blooms might not turn blue if aluminum is not available. If this is the case, consider applying an aluminum sulfate soil amendment.
Does the change in hydrangea color affect the health or growth of the plant?
The color change in hydrangeas is a natural response to soil conditions and doesn't negatively impact the plant's health or growth. It's a unique characteristic of certain hydrangea species.
Growing beautiful blue hydrangeas can indeed be an art, but with the right knowledge, it's within reach for many gardeners. Embrace the learning process, enjoy the journey, and prepare for a garden full of stunning blue blooms!
QUESTIONS? Please email them over to helpdesk@provenwinnersdirect.com and we'll get back to you! We love helping our garden friends.
Contributors: Susan Martin