Hydrangeas can withstand some frost. While some varieties of hydrangeas can withstand cold temperatures and frost better than others, preparing them properly for winter can reduce the possibility of any significant harm.
Hydrangeas can recover from minor winter damage, but not from severe winter dehydration or damage to the roots.
It’s simple to prevent winter kill on these plants, so heed my advice if you want to consistently enjoy your hydrangeas’ gorgeous blossoms.
How cold must it be for hydrangeas?
Many people were dissatisfied last year because their hydrangea shrubs produced few, if any, flowers. It was assumed that the particularly hard winter was to blame.
There are numerous hydrangea species, but the majority of them that are grown by homeowners in their gardens belong to the genus Hydrangea macrophylla.
The two groupings of H. macrophylla are distinguished by the appearance of their flowers. The mopheads have a broad, rounded shape and can range in color from red to pink to white to blue to green and many colors in between. Similar in color, the lacecaps are flattened corymbs with fertile blooms in the center and spectacular clusters of sepals of various sizes around them.
Hardiness zones 6 to 9 apply to H. macrophylla. A hydrangea should, in theory, be able to withstand temperatures as low as -10 degrees. However, in the real world, temperatures as low as 12 degrees and freezes in the late fall or early spring may limit this hydrangea’s ability to flower.
H. macrophylla forms its bloom buds in the summer and the fall in response to the shorter days and chilly temperatures. To achieve bud dormancy, the bud must be refrigerated for 1,000–1,200 hours, or roughly seven weeks.
As the weather gets warmer, buds open, shoots appear, and blooms grow. Flower buds and vegetative stems will perish if this happens at the end of February, as it did last year and may do this year as well. In the spring, the plant might grow again from the root, but it won’t produce flowers. It has sturdy roots, but delicate flower buds.
On fresh wood, on the woody stems from the current year, H. macrophylla flowers. If a shrub needs to be pruned, it should have been done last year when the blooming season had just ended. Avoid pruning it. You will now remove any budding flower buds.
I have been growing my favorite variety of H. macrophylla for almost 15 years, and it is called “Blue Billows.”
Dr. Richard Lighty of the Mount Cuba Center in Hockessin, Delaware, originally grew this lacecap, Hydrangea serrata, from seed gathered in the Korean mountains. The inner fertile flowers are a darker blue than the outer sterile blossoms, which are blue with a pink blush.
Before relatively recently, the taxonomists classified the H. serrata variation as a distinct species from the macrophylla. It possesses each of the traits that distinguish H. macrophylla from other species. The leaves are smaller, though, and it has a stunning copper-red fall color. From June to October, the plant blooms; as fall approaches, the blossoms turn over to reveal pink undersides.
It is situated for me in some moderate shade with drained soil. They call it a “robust plant.
Most recently, the big root ball split in two when I moved it to a shadier spot. I then discovered that it had sucker-grown or air-layered three smaller plants.
It is a dense shrub that grows to be about 3 feet tall and wide, and it is so covered in leaf and flowers that I was unaware I had four additional plants until I started to move it.
This low-maintenance shrub works well as a border shrub or as a foundation plant. And it will offer you profusion that you can keep or gift to others as a reward. It was chosen by the Pennsylvania Horticulture Society in 1990 as a Gold Medal Plant.
Depending on the amount of aluminum ions in the soil, the color of the flower varies. In more acidic soils, the concentration is higher, whereas in more alkaline soils, it is lower. For the majority of H. macrophylla and H. serrata cultivars, acidic soil (pH 5.5 and below) will result in blue flowers, whereas neutral to alkaline soils (pH 6.5 and higher) will typically result in pink flowers. The blooms will be purple or a combination of blue and pink blossoms will be seen on the same plant between pH 5.5 and pH 6.5.
The most constant guideline for growing hydrangeas, though, is that there is a lot of variety and no absolutes.
At this time of year, Hydrangea arborescens is another hydrangea that merits discussion. It also appears as lacecap and mophead flowers. The names “Annabelle,” “Invincible Spirit,” and “Grandiflora” are a few well-known cultivars. All of these flower on fresh wood. Cut them to the ground now, in late winter, and apply a mild fertilizer.
Place a support structure around the plant before it starts to grow since the flowers are frequently too heavy for the stems to keep the plant upright.
The new plant will start to bloom in June or July and continue to do so for several weeks.
As the petals wilt, cut the stem at the base and remove the leaves if you want to dry them. Cut them to the length you want, then hang them backwards. They make wonderful dried flowers and can be sprayed with spray paint to add color.
Do my hydrangeas need to be covered tonight?
To protect the roots of the hydrangea, cover the entire root zone with a thick layer of mulch that is at least 4 inches deep. Although bare earth absorbs heat more quickly, it also lets heat escape more quickly. For optimal results, cover the soil at night after allowing it to absorb heat from the sun throughout the day. However, you can use any material you have on hand, like compost, leaves, and straw. Shredded bark mulch works nicely.
Do hydrangeas need to be protected against frost?
Here is professional guidance on how to put hydrangeas to bed for the winter season from guest bloggers Megan Nichols and Jessie Jacobson of Tonkadale Greenhouse in Minnetonka, Minnesota. (They may have more hydrangea trees and shrubs in their zip code than almost anywhere else in the United States, so they are aware!)
The temperature has dropped, and autumnal symbols can be seen everywhere. The garden needs to be put to bed soon. Hydrangeas reward us with large, stunning, and prodigious blooms all season long. You may say that they are givers. It’s time to return the favor now. It’s time to tuck the hydrangeas in with kisses and wishes for sweaty dreams.
Here in Minnesota, our moods can fluctuate as drastically as the unpredictably harsh winter weather extremes, snowfall, and freeze/thaw cycles. Despite the fact that many hydrangeas are regarded as hardy, all of this can confuse them. To survive the winter and come back bigger and better the next year, they require some care. Although hydrangeas cultivated in warmer areas don’t need as much post-season primping as those grown in our zone, there isn’t a single thing that wouldn’t appreciate a little tender loving care right now.
Utilize these suggestions to get the most out of your hydrangeas so that you can be the one to present at this time next season!
(Is pruning in order? No and yes. Here is our recommendation for which hydrangeas should be pruned right away and which should wait until spring.)
Don’t Stop Watering
Make a commitment! I shall water my hydrangeas till the earth freezes solid, you declare while raising your right hand. really good Hydrangeas are thirsty plants by nature, so it’s essential to give them regular, deep watering. We don’t need to get all linguistically nerdy right now, but their name literally means “hydration.” Winter’s cool, dry winds completely drain the moisture from the vegetation, and hydrangeas don’t use lip balm. It need not be heated in order to be dry!
If a freeze is not a concern where you live, water deeply but sparingly during the winter depending on how much rain you get.
This is how: Making a small hole in the side of a 5-gallon bucket, filling it with water, and placing it at the base of the plant while it slowly drips out of the bucket is one method. Another option is to lay your hose at the base of the plant for about an hour with the water turned on to a gentle drip.
Give Them One Last Hearty Meal
Composting your hydrangea beds in the fall will give them a boost for the upcoming growing season. Everyone feels better after a full night’s sleep and a filling breakfast. This also applies to hydrangeas. After a lengthy winter’s hibernation, they will be ravenous for some nice compost. Compost can decompose during the winter if it is used now, making nutrients easily accessible in spring. A few inches of compost is advisable even in regions without a deep cold. Only compost is being discussed here! Don’t give your hydrangeas fertilizers that are high in nitrogen because this can encourage them to produce new foliage growth.
This is how: Before laying down mulch in colder climates, top dress the area with compost, well-aged manure, or other organic material after the ground has frozen. This organic fertilizer, which is rich in nutrients, will decompose over the winter, making nutrients available to the plant in the spring. Apply compost in the late fall or early winter in zones that are warmer.
Mulch Matters
Mulching helps keep moisture in and weeds out in warmer climates while shielding the crown and roots of your hydrangeas from harsh winter temperatures in colder climates. Snow serves as a natural insulator if everything goes as it should. Plants suffer during strange winters with little snowfall and extreme temperature changes. Apply a thick layer of mulch around the plant’s base to offer hydrangeas the best chance of flourishing. While decorative mulch is useful, straw, marsh hay, or dead leaves are suggested instead.
This is how: Apply a 6–8 layer of mulch once the ground has frozen (or late fall or early winter in zones with milder winters). This shields plants from the heave-ho of springtime freeze/thaw cycles, which can yank them out of the ground. Inviting mice to make this their snug winter home, causing rotting and illness, or tricking the plant into believing it’s time to bud, are all consequences of mulching too early. Be patient; you don’t have to do things early simply because your neighbors are.
Keep Them Cozy
The amount of winter cold determines whether or not hydrangeas require protection. Winter protection is not required in zone 7 if the air temperature stays above zero degrees. Wrap or totally cover barely hardy hydrangeas in chilly areas. This is crucial for plants that bloom on old wood, such hydrangeas with mop heads and large leaves (Hydrangea macrophylla). The most recent types of mop head/big leaf hydrangeas, however, bloom on both fresh and old wood, so it’s important to keep that in mind. In their favor and ours! Hardier hydrangea varieties like the paniculata and arborescens don’t often require additional winter care, although really low temperatures might cause its limbs to die back. Consider covering if a colder than usual winter is forecast.
This is how: Wrap plants loosely in a few layers of burlap, making sure to tie it off with strong twine. Making a mulch mountain and covering the majority of the plant is an additional choice. Smaller, newly planted specimens respond well to this technique.
There’s Still Time To Plant!
The first three varieties of hydrangeas can be grown here in Zone 4; oak leaf hydrangeas can also be grown in warmer climates (zones 5 to 9). The optimal time to plant shrubs is in the fall. Just make sure to do all of the aforementioned things, including watering and mulching.
Here are some of our favorites that you can plant now for stunning blooms the following spring.
Panicle Hydrangeas
These late blooming hydrangeas, sometimes known as PeeGee hydrangeas (summer into early fall). They are covered in elongated, conical flower heads that emerge white or green and blush into pinks and peaches as the season goes on.
Will hydrangeas survive a freeze?
A few nights at or just below 32 degrees Fahrenheit are unlikely to kill or seriously harm a hydrangea over the long term. Root hardiness for hydrangeas that bloom on old wood ranges from USDA zones 5 to 6, or minus 20 F to minus 15 F. New-wood bloomers may tolerate colder temperatures—zone 3 or minus 40 F—better. Any new leaves or buds that your hydrangeas are pushing out could die back if the cold weather arrives after they’ve started to send up vulnerable growth. In a light frost or freeze, the foliage becomes purplish-red and may wilt or collapse and turn brown or black. Both stem tips and buds get a dry, black appearance. Find the end of the hydrangea frost bite damage by running your fingertip across the stems to check if they are still green beneath the bark. Move from the tip down toward the base until you reach green.
Can I put my hydrangea plant in a pot outside?
Mophead hydrangeas can be cultivated outside wherever the wintertime temperature stays above -15oC because they are hardy (5oF). However, as they were grown in greenhouses and given fertilizer to induce early flowering, potted hydrangeas sold as houseplants may require some time to acclimate to life outside before being put out. Place them outside in their pots during the day and bring them inside at night to harden them off for one to two weeks before to planting. Hydrangeas that have been grown for outdoor planting can be planted immediately. Mid- to late April, when the soil has had time to warm up, is the ideal time to plant mophead hydrangeas outdoors.
The optimal conditions for hydrangeas are shade from the sweltering afternoon sun and moist, well-drained soil. They are therefore excellent alternatives for shady gardens, and in mid- and late-summer, their dramatic spherical flowerheads are absolutely gorgeous. Regularly water hydrangeas, especially during dry spells, and in the spring or fall, mulch with compost or other organic material.
Because of the soil’s pH (acidity or alkalinity), pink and blue mophead hydrangea blossoms have the unusual ability to change color. The blossoms will be a deeper shade of blue the more acidic the environment is. Flowers turn a gorgeous pink on alkaline soil. The color of white mophead hydrangeas doesn’t alter.
Can hydrangeas be kept in pots?
Do hydrangeas thrive in containers? Given that potted hydrangeas received as gifts rarely survive longer than a few weeks, it’s a reasonable question. The good news is that they can, given the proper treatment. Growing hydrangeas in pots is a great idea because they can grow to be fairly large and have beautiful blossoms all summer long. Learn more about container-grown hydrangea plants and how to take care of hydrangea in pots by reading on.
How do I keep my hydrangeas safe during the winter?
Stakes can be used to create a frame around the plant to protect it throughout the winter. To create a cage, encircle the stakes with chicken wire. Pine needles and/or leaves should be stuffed inside the cage to completely insulate your plant.
Because they do not settle as quickly as other materials, oak leaves perform nicely. As the insulation settles during the winter, keep a bag of leaves from your fall leaf raking pile to fill the cage.
As you fill the cage, take care not to snap off the ends of the branches because if you do, it will all be for nothing and you won’t have those magnificent blossoms the next summer.