There is no shrub that adds elegance and Old World charm to a garden like the luxurious, bloom-filled hydrangea. With many colors, leaf shapes, and sizes to choose from, these stunners will please even the most minimal garden aesthetic.
Hydrangeas prefer moist, nutrient-rich soil and can thrive in both full sun and partial shade, depending on the variety. They are, however, quite sensitive to over-fertilizing.
In recent times it has become fashionable for gardeners to experiment with the color of hydrangea blooms by adjusting soil pH. But often, consequently, they can be found asking themselves “Why is my hydrangea not blooming anymore?” In this article, I’ll guide you through the most common reasons hydrangeas stop flowering and how to fix them.
Why Is My Hydrangea Not Blooming?
A lack of blooms on your hydrangeas could have one or several causes. When making a determination, the following factors should be considered:
- Incorrect pruning — According to the University of Maryland, only specific varieties require pruning in order to bloom.
- Winter damage — Freezing temperatures can damage varieties grown outside of their natural hardiness zone and result in a lack of flowers.
- Old wood vs new wood growth — With different pruning seasons for each type, ill-timed pruning can lead to fewer blooms.
- Disease or pest infestations — These can have a detrimental effect on a hydrangea’s ability to produce buds.
- Incorrect fertilizer — Hydrangeas thrive on a balanced fertilizer. Unbalanced nutrients can lead to an abundance of foliage but few blooms, if any.
- Not enough water — Healthy circulation of water and nutrients is required for proper bud production. In times of drought, hydrangeas forego bud production in order to conserve moisture and energy.
Cold Weather Damage
Winter temperatures alone can damage hydrangeas that are not bred for that climate. When coupled with freezing winds, even local varieties can be in peril if not properly mulched.
Due to cold climate species going dormant in winter, signs of damage won’t be evident until spring when there is a lack of foliage and buds.
Damage occurs when sub-freezing temperatures crystalize water within the plant, damaging cell walls and potentially halting the internal processes that keep it alive in dormancy.
To prevent this, I recommend a thick layer of straw, hay, or gathered autumn leaves. This practice mimics the same natural, nutrient-recycling process found in the wild and provides effective winter protection.
Depending on the variety, an unexpected early autumn frost can decimate new buds. Discontinuing fertilization around the middle of August will slow new growth and buds that may be vulnerable to an early frost.
Your Hydrangea Is Not Climate Hardy
Not all hydrangea plants are made equal. While they’re all beautiful and colorful, some are more cold-hardy than others.
Big leaf varieties perform best in temperate climates. Panicled types are the most cold-tolerant. If your hydrangeas are not blooming, it may be that it’s just not suited to your hardiness zone.
A ‘hardiness zone’ indicates the climate where specific plants grow best. In the US, these zones are numbered from 0 to 13 and are ranked by an area’s lowest average temperature. The higher the number, the warmer the climate.
To promote abundant blooms, choose varieties bred for your specific climate. Local garden centers will be your best bet. When ordering online, determine your hardiness zone first.
Late Spring Frost
In hardiness zones 10 or lower, spring can bring surprising and unexpected freezing temperatures that can shock hydrangeas.
This can stop new buds in their tracks. Keeping an eye on the weather forecast can give you enough time to run out and protect your plants.
Burlap, bed sheets, or even leftover painting tarps work well. Just cover plants at night to protect them from the season’s coolest temperatures.
If frost damage occurs, simply prune where the damage ends and healthy growth begins. Along a damaged stem, scrape a bit of bark with your fingernail and look for healthy, green tissue. Make your cut where it turns brown.
Any buds along the still-green part of the stem should continue developing into flowers.
To maintain adequate water and nutrient circulation throughout, hydrangeas need to be watered well.
As they rise from winter dormancy, hydrangeas benefit from deep watering to encourage new root growth. This practice is also recommended for new plantings.
Watering during the cool morning hours will allow roots to absorb the amount given with less evaporation. Early morning watering is also recommended in hot summer climates to prevent leaf wilting.
If you do see midday wilting, wait until evening to determine if watering is needed. Wilting is a plant’s way of conserving moisture.
There is a fine balance, though. Overwatering can impact leaf growth and structure. Root rot caused by continually soggy soil will cause foliage to yellow, followed by leaves dropping prematurely.
Overwatering may also result in blooms being few and far between due to nutrients and food created through photosynthesis being flooded out.
Effect Of Soil pH On Hydrangea Flowers
Hydrangeas thrive in a pH range between 6.0 and 6.2. This supports optimal plant health and an unrestricted flow of other vital nutrients.
Amending soil with well-aged compost will naturally lower soil pH over time.
This method also helps limit the change in pH to just these plants. Fertilizers may leach through to other plants that don’t do well with a lower pH.
A 6.0 pH allows hydrangea roots to absorb more aluminum from the soil, resulting in blue flowers. A 6.1 pH displays a purple hue, and in 6.2, you get pink.
Note that soil pH only affects bloom colors in some hydrangea cultivars. In fact, the majority of hydrangea varieties out there are visually unaffected by small pH changes.
Pruning Hydrangeas At The Wrong Time
For a big show of summer blooms, pruning hydrangeas at the proper time is a must. Too early, too late, or when it’s not needed may result in a sparse display. In my experience, improper pruning is the biggest culprit when it comes to hydrangeas not flowering as expected.
Best Time To Prune Hydrangea
Optimum pruning times depend on the hydrangea variety you’re growing. Some set buds on old wood, some on new growth, while others set buds on both. So, how do you know which one you have?
Pruning should be done in late summer or early fall, after blooming has ended, and only when necessary.
This is important because, in spring, new buds are forming inside mature stems where you might not see them. Spring pruning means risking the removal of branches that have a ton of buds waiting to emerge. It may also leave cut branches vulnerable to spring frost.
Hydrangeas that fall under the ‘old wood’ category include:
- Mophead Hydrangeas
- French Hydrangeas (Bigleaf)
- Oakleaf Hydrangeas
Pruning new wood bloomers should be done in early spring, just before the emergence of new growth. If pruned too late, next year’s blooms could be delayed. Autumn and winter are when new wood bloomers gear up to produce next year’s buds. If pruning is done during this time, the plants need to start all over again.
New wood bloomers include:
- Panicle Hydrangeas
- Smooth Hydrangeas
Both New and Old Wood
This type sets buds on both old and new wood, producing several larger blossoms in cluster formations. They should be pruned in early spring, prior to the appearance of new growth.
- Endless Summer Hydrangeas
What Happens If You Don’t Prune Hydrangeas?
Old wood bloomers don’t actually require pruning. Only branches damaged by winter cold, disease, or pests should be removed.
Deadheading flowers is fine up until late fall. But cutting into your hydrangeas after this leaves them vulnerable to freezing temperatures.
New wood bloomers do benefit from a good pruning. Buds emerge from new growth sprouting from the plant’s base. Significant pruning triggers the growth of strong branches and stems.
Without proper pruning, weaker stems will grow from the tips of old branches that are unable to support large blooms.
Smooth hydrangeas can be pruned down to 12” above the soil surface. But panicle varieties only need roughly ⅓ of their overall size pruned back.
Poor Nutrient Balance
When grown in fertile soil, hydrangeas typically won’t need any fertilizing. Otherwise, a balanced fertilizer can help support increased plant health.
Which balanced fertilizer to use depends on soil condition. If your soil needs a small boost, then a 10-10-10 fertilizer will provide enough nutrients for optimal health without overwhelming your plants.
In poor soil, a 20-20-20 fertilizer applied just after planting will help hydrangeas become well-established. You can then switch back to a 10-10-10 formula.
Without vital nutrients, plants begin to show signs of distress. Without nitrogen, leaves may start to yellow and drop mid-season.
A lack of phosphorus, which plays a key role in bud and flower production, will result in an equally lackluster show of blooms.
Potassium is responsible for the circulation of water and other vital nutrients throughout plants. Inadequate access to potassium will result in poor plant health, including a lack of blooms.
Too Much Nitrogen
Of course, too much of a good thing is never a good thing. Balanced nutrition is important because too much of one macronutrient can cause an imbalance in plant processes.
Too much nitrogen will force the plant’s energy toward foliage growth, with little to none left for bud and flower production. Excess nitrogen will also create a burnt appearance on flowers that do manage to grow.
If too much phosphorus or potassium is applied, foliage growth and photosynthesis will fail.
With equal parts of each macronutrient, every aspect of your hydrangea’s growth will function effectively.
As I mentioned, if you have established hydrangeas growing in fertile soil, you probably won’t need to fertilize. They’ll get all they need for lush foliage and blooms from the soil. If they do need it, a fertilizer for hydrangeas with a balanced NPK ratio will support those processes.
The most effective time to fertilize is in early spring for both old and new wood bloomers, just as new growth is emerging. Avoid adding extra phosphorus to increase flowering.
Scorched By Too Much Sun
Hydrangeas flourish in locations with partial sun and shade throughout the day. Sunlight encourages blooms while shade protects them from dehydration and scorching.
If your plants have burn marks, this may be due to excessive sunlight and they would do better in a shadier spot.
Scorching is also common during hot summers when moisture evaporates faster than you can replenish it, causing rapid dehydration.
It’s best to water hydrangeas during cooler times of the day, applying it directly to the soil. Intense sunlight can cause evaporated water droplets on foliage to leave scorch marks as well.
To further protect against dehydration, the soil around hydrangeas should remain moist but not soggy. Maintaining this balance will encourage a beautiful summer show.
While hydrangeas prefer at least 3 hours of shade per day, most varieties won’t bloom in full shade. As with most flowering plants, sunlight triggers bud production and increases color vibrancy.
In full shade, foliage color may turn pale and, once a plant fails to bloom, it may not do so again unless moved to a partial-sun location.
This is especially so for those growing farther from the equator. The closer to the poles they’re growing, the more sunlight they’ll need.
Also be mindful when planting hydrangeas under young trees. The older and fuller they grow, the more sunlight they will block.
If planting in shade is your only choice, smooth and oakleaf hydrangea varieties are the most shade-tolerant.
Newly Planted Hydrangea Not Flowering
Nursery-propagated hydrangeas are subject to the same flower-busting risks as older, established plants, such as damaging temperatures and improper pruning. But how long it takes for these to bloom will also depend on the variety.
It can take 1 to 3 years for root systems to become established. Only then will they begin to bloom.
If a hydrangea was moved from growing in a pot to the ground, it may bloom from buds that set while in the pot. But it may not bloom again for a year or two while it gets established in the larger space.
Try not to measure their progress by height or the number of blooms. Overall plant health is what will provide that highly anticipated show.
Hungry Deer, Slugs, Or Snails
Deer typically prefer other plant varieties over hydrangeas. But if food is scarce, your hydrangeas can suddenly become their favorite meal.
If you live near a large deer population, planting oakleaf hydrangeas will significantly cut down on munching. The smell of the foliage and flowers tell the deer this plant won’t sit well with them.
Hydrangeas wouldn’t be the first choice of slugs and snails, either. But, again…if their preferred meal of decaying plant material isn’t available, hydrangeas can get decimated pretty quickly.
These are most effectively eradicated when removed by hand, at dusk or on cloudy days when they’re active. A mixture of egg yolk and water or just plain soapy water has proven effective in warding off snails, slugs, and deer.
When Should Hydrangeas Bloom?
As we’ve seen, how much and when hydrangeas flower can be influenced by a number of different factors. This is why pinning down an exact bloom time for different varieties is often difficult. The closest we can get is mid-spring through late summer or early fall.
One factor to consider is where they’re growing. For example, old wood bloomers may flower earlier and for longer in warm climates than in cooler ones, despite them being the exact same plant.
New wood bloomers can flower in mid-spring but stop in the heat of summer. Then, continue flowering in autumn.
The one reliable exception to all this madness would be endless summer varieties that are bred to bloom several times in one season.
Origins Of Hydrangea Plants
The earliest,fossilized hydrangea specimens are found on the west coast of North America, dating back to between 40 and 65 million years ago. Slightly younger discoveries were made in China, Japan, Taiwan, and the Philippines, demonstrating that these blooming beauties have been inhabiting the earth far longer than we have.
The first hydrangea variety to arrive in Europe, Hydrangea hortensis, was transported from Japan in 1788, where it was botanically named, studied, and documented.
There are roughly 75 different hydrangea species in total but only a fraction of those will be found in home garden and landscape designs. In these environments, lace-cap, oakleaf, and large-leaved hydrangeas are the most common varieties to offer color and drama.
Final Thoughts On Why Hydrangeas Won’t Bloom
In the depths of winter, when many plants are sound asleep, we dream of giant clusters and spires of color on a wide variety of hydrangeas. In order to better secure the fruition of those dreams, there are a number of helpful practices to put in place:
- Plant the best variety for your hardiness zone
- Protect them from winter damage and spring frost with mulch and protective materials like burlap and canvas tarps
- Create a beneficial watering regimen, based on your climate and daily temperatures
- Choose a planting location with at least 3 hours of shade and 4 hours of sun
- Apply proper nutrition with a balanced NPK fertilizer
- Prune in the correct season for both old wood or new wood bloomers
- Know how to protect plants from pests and other intrusive wildlife
And, most importantly, gauge the success of your hydrangeas by overall plant health instead of by size and bloom numbers.