How to Grow Hydrangea Serrata (Mountain Hydrangea)

It's no surprise you can see hydrangea shrubs in gardens worldwide. Despite their showstopping appearance, they need minimal maintenance, and the beautiful clusters of flowers provide a centerpiece in any landscape.

There are around 75 different hydrangea species and many more cultivars. One lesser-known species worth considering is the hardy mountain hydrangea (Hydrangea serrata). With the right care and conditions, the delicate globes of blue or pink lacecap flowers bloom from early summer right through to fall.

Their compact, rounded habit and glossy green foliage make them a great choice for low privacy hedging, mass planting, foundation plantings, or even in containers on your patio. As a bonus, lacecap hydrangeas, like Hydrangea serrata, are great for attracting pollinators to your yard.

Plant these fast-growing plants in fall or early spring and expect around 2 feet of growth annually.

All hydrangeas are known to be mildly toxic to humans and animals, so it's best to keep this shrub away from curious kitties and canines.

Hydrangea Serrata Care

It's all about location when it comes to caring for mountain hydrangeas. If you provide a sheltered spot (on a patio or protected side of a house) with filtered sun and moist, well-drained soil, you should be rewarded with abundant summer blooms. Space them around 3 to 5 feet apart to give them room to grow.

Light

Choose a filtered sun spot which receives morning sun and afternoon shade., especially in the warmest growing climates. Although not as tolerant of extreme hot and dry regions as their bigleaf mophead hydrangea cousins, they can survive in full sun providing the soil is consistently moist.

Soil

Pick a spot with rich, well-drained soil. Aside from this, they aren't fussy, but soil pH does impact bloom color. Strongly acidic soils produce blue flowers, while mildly acidic or alkaline ones result in pinker shades. Add a little aluminum sulfate to the soil to produce slightly bluer shades. Amending with lime will encourage pinker shades.

Because these shrubs like fertile conditions and consistent moisture, add some organic matter to the soil in the spring and layer a few inches of mulch around the base of the plant (taking care not to mulch up the stems).

Water

One of the quickest ways to kill off your Hydrangea serrata is by watering incorrectly. Consistent, even moisture is key. Waterlogged soil rapidly results in root rot, but letting the plant dry out affects bloom production, and leaves will start to scorch and drop.

Once the top 4 inches of soil feel dry, it's time to provide a deep watering, saturating but not flooding. You'll probably have to get the hose out at least once a week during hot summers.

Temperature and Humidity

Known for being one of the hardier hydrangea species, these shrubs are still sensitive to windy, hot and arid conditions or extreme hard winters. Temperate climates work best for mountain hydrangeas.

Providing a layer of mulch helps protect against frost and retain the moisture they love. Although mature plants are hardy down to −13 °F when dormant, harsh spring frosts can kill off new growth.

Fertilizer

While you don't want to go overboard with feeding, fertilizing your Hydrangea serrata during the growing season boosts growth and healthy bloom production.

Applying a balanced fertilizer in early spring, alongside amending the soil with organic matter, should be enough to see you through the season. Don't apply any fertilizer in late summer. You don't want to encourage late new growth, which hard winter frosts can kill off.

Steer clear of fertilizers high in nitrogen as this focuses energy on foliage growth rather than bloom production. Selecting a higher phosphorous bloom-boosting fertilizer with a 10-20-10 NPK encourages more abundant flowers.

Types of Hydrangea Serrata

Most mountain hydrangeas are lacecap form (featuring flat bloom caps with edges of larger, showy flowers), but some cultivars have the traditional large globe mophead form. Even though this isn't the most well-known hydrangea species, there are still several cultivars to choose from. These include:

• Hydrangea serrata 'Blue Bird': A compact shrub with delicate lacecap flowers ranging from light blue to pale pink, depending on the soil pH. Popular for their long bloom season, flowers appear from early summer to early fall. The leaves turn a striking red in the fall, providing additional seasonal interest.
• Hydrangea serrata 'Tiny Tiny Stuff': Perfect for small patios, this particularly compact mountain hydrangea cultivar (reaching 24 inches height maximum) is also very cold hardy and produces long flowering, bright blooms.
• Hydrangea serrata 'Pink Dynamo': Eye-catching upright lacecap variety with striking pink flowers, white central accents, and red stems.

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Pruning

Pruning requirements for hydrangeas vary. Because mountain hydrangeas bloom on old and new wood, little pruning is required.

It''s mostly a case of removing weak, damaged, or dead growth in the spring and cutting back older growth every few years. After flowering, it's also possible to cut back flowering stems on old growth, leaving healthy buds on the lower part of the stem to direct the energy there.

Deadheading spent flowers isn't essential, but it can give your shrub a tidier appearance.

Propagating Hydrangea Serrata

Because most mountain hydrangeas are cultivars, growing from seed won't produce a true to type plant. So propagating your hydrangea from softwood stem cuttings is recommended. Before doing this, check the cultivar is a non-trademarked variety, or you risk infringing copyright law.

Follow these steps for a chance of success:

1. Start the process in early summer to give the cutting ample time to root before planting in the fall.
2. Cut off a healthy stem tip (around 6 to 8 inches long) with sharp, sterile pruning shears or a knife.
3. Select a stem without any growing blooms but with at least one node (a knobby growth line running across the stem). Leave around 2 inches of stem below the node.
4. Take the leaves off the bottom half of the cutting, leaving two to four on the top half.
5. Dip the cut stem end in rooting hormone.
6. Use a small pot with sterile potting mix and put a small hole in the center to insert the cutting, ensuring you bury the node under the soil. Pat the soil down.
7. Select a warm location with bright but indirect sunlight and keep the soil moist but not waterlogged.
8. Putting a loose but secure clear plastic bag over the cutting can help to retain moisture and promote growth.
9. Check moisture levels regularly and water when the top of the soil begins to get dry to the touch.
10. New roots should form within a month, and you can transplant well-developed cuttings outside in the fall.

Overwintering

This is one of the hardier hydrangea varieties, but if you expect late frosts, use a layer of burlap to wrap the plant and fill the inside space with straw. This provides additional protection, reducing the risk of dieback and promoting consistent blooming the following summer.. Some other hydrangea winter care tips include planting the shrub near a heat retaining wall and away from harsh winds, and generously mulching around the plant base.

Common Pests and Plant Diseases

Mountain hydrangeas aren't particularly susceptible to major pests or diseases. However, it's worth keeping an eye out for aphids, bacterial wilt, and leaf spot. These shrubs are also more prone to powdery mildew than Hydrangea macrophylla because their leaves aren't as thick.

How to Get Hydrangea Serrata to Bloom

With the right care and conditions, you'll be treated to a stunning fragrant floral display from early summer through to the fall.

Although they stay dormant longer than bigleaf hydrangeas, this means mountain hydrangeas bloom later so the tender buds are less likely to be killed off by late spring frosts.

If you're hydrangea isn't blooming the way you expected, consider the following:

• Protect your shrub from harsh winter conditions by overwintering in a greenhouse or covering it with burlap, insulating, and mulching.
• Keep your hydrangea out of intense, direct afternoon sunlight.
• Provide consistent moisture but don't leave the roots soggy.
• Use a fertilizer with a higher proportion of phosphorous to encourage blooming.
• Be patient—it can take newly planted shrubs up to two years to establish and produce blooms.

Common Problems With Hydrangea Serrata

Part of the popularity of hydrangea shrubs is they are fairly easy to maintain. However, there are a few signs that indicate developing problems.

Yellowing Leaves

Yellowing leaves can be an indication of a few different issues. Examine whether you're offering your mountain hydrangea too much or too little water or if you're over-fertilizing it.

Drooping Leaves

If you're leaves droop during the day but then perk up again after dusk; there's no need to panic. This is a built-in protective measure the shrubs have in hot weather. If they don't perk up, it's often a sign you're not providing enough water. Remember to water deeply when the top few inches of soil are dry.

Browning Tips

Although fertilizing can help your plant produce abundant healthy blooms, going overboard can result in the tips of the foliage scorching, as can too much intense, direct sunlight. If you're adding aluminum sulfate to change the color of your hydrangeas blooms, take care not to add too much too soon, as this can also scorch the tips of the leaves.