How to Grow and Care for Mophead Hydrangeas

Spread the love

Mophead hydrangeas (H. macrophylla) are the most well-known variety of the bigleaf hydrangeas. They are the most commonly grown hydrangea shrubs, and there are hundreds of cultivars to choose from. 

These gorgeous shrubs are instantly recognizable from their mass of round clusters of blooms and green leaves. Mophead hydrangeas are perennials and have long-lasting flowers. Their blooms are held on strong stems, so they make excellent cut flowers. 

You can change the color of a mophead hydrangea’s flowers from blue to pink and vice versa by altering the pH level of the soil. The exception is that if the flowers are white, they will remain white and can’t be changed by adjusting the soil pH level.

History

The mophead hydrangea was introduced to Europe in the mid-1800s from Japan. Once the flowers arrived in France, they became so popular that they became known as French hydrangeas. They are known as mopheads because of the shape of their flower heads.

Plant Facts

Scientific nameHydrangea macrophylla
Common namesBigleaf hydrangea, French hydrangea, Hortensia, Mophead Hydrangea, 
GenusHydrangea
FamilyHydrangeaceae
Height3 to 6 feet
Width3 to 6 feet
USDA Plant Hardiness Zone6 to 11
OriginJapan, China, Korea, Southeast Asia
Flower colorsPink, Purple, Blue, White
Blooming seasonSummer
Plant/Flower special featuresCut flower, long-lasting, dried flower

How to Plant and Grow Mophead Hydrangea

Many mophead hydrangeas in gardens are old, large shrubs. Learning how to grow hydrangeas will reward you with a beautiful colorful garden.

Make sure that you plant your mophead where it will have sufficient space to spread. Plant breeders have created smaller hybrids that retain the showy blooms. Cultivars such as these make excellent pot plants.

Where to plant

H. macrophylla or mophead hydrangeas need to be sheltered from the strong afternoon sun and flower best if they receive morning sunshine. 

Mophead hydrangeas are generally hardy in USDA zones 5 to 9 and can also be planted in pots or containers. In containers, they do well and are a good choice if you are looking for a patio plant since they can be protected during a cold spell.  

When to plant

The best time to plant your mophead hydrangea bush is in the spring or fall. 

How to plant

Before you plant the mophead hydrangea shrub, gently remove its root ball, trying not to break the tiny roots. Leave the root to soak. 

For a standard-sized mophead hydrangea plant, the hole should be 2 feet in diameter. If the soil is too light, you should enrich it with compost. If it is too heavy, mix a little sand into it. The ideal pH level should be around 6½, which is slightly acidic.

If necessary, enrich the soil with organic matter, which will stop the soil from drying out.

When it’s time to plant the mophead, untangle any roots. The soil should be soft and crumbly, as this will give the new plant a better chance to establish itself.

Give the plant a soak immediately and make sure that the top of the root ball is level with the surface of the soil. 

In containers

Mophead hydrangeas do well in containers, but the pot needs to be well-drained and three inches bigger than the root. The soil will dry out quicker than garden soil. Move the potted hydrangea out of the sun on hot days, to prevent it from wilting.

When you re-pot your mophead hydrangea, the new container should have adequate drainage. Leave about 1 inch from the top when filling, then, when you water, you can fill the pot, and after it has drained you can re-water.

If you have chosen a dwarf variety, you don’t need to prune it. If a standard size, you can prune it to keep it to a good size for the pot.

Care and Maintenance

All different types of hydrangeas are easy to care for, but there are some tips to get the best from your mophead hydrangea shrub.

Soil

Although hydrangea shrubs aren’t particularly fussy, they do need well-drained soil. Heavy soil quickly becomes saturated. The roots will rot and this will kill your mophead hydrangea plant.

If you want to keep the flowers of a blue mophead hydrangea shrub blue, you should use ericaceous compost. This is compost designed for acid-loving plants such as rhododendrons. Ericaceous compost will also make mophead hydrangea flowers turn from pink to blue, or if they are already blue, will make sure they continue to be blue.

Water

A newly planted mophead hydrangea shrub needs to be watered regularly. Once established, it will absorb nutrients and moisture through its roots. 

The best way to water mophead hydrangea shrubs is to soak the plants, then allow the surface water to drain away. You should then re-water. 

If you are feeding mopheads, choose a specially designed composition. Too much nitrogen in the mix will give you beautiful, enormous leaves – at the expense of flowers. 

For blue flowers, your fertilizer formulation should be one designed for acid-loving plants such as rhododendrons and azaleas. You can fertilize once in the spring with a fertilizer low in phosphorous. 

If your hydrangea flowers are pink, then the composition doesn’t need to be so low in phosphorous (the middle number). 

Whichever fertilizer you select, if it is granular, use at the rate marked on the packet and mix it into the top couple of inches of soil or compost. Always water the plant thoroughly after applying fertilizer to prevent the possibility of the fertilizer burning the roots.

Sunlight

The mophead hydrangea doesn’t need sunlight to survive. It will thrive in shade, but will not flower well.  

Mophead hydrangeas, like other bigleaf hydrangeas, need sunlight to produce their beautiful, showy blooms, and the most common reason for a lack of flowers or no flowers at all is insufficient sunlight.

As already stated, you need to protect your hydrangea bush from the heat of the strong afternoon sun, so ideally plant in a spot where it will receive plenty of morning sunlight.

Temperature and Humidity

The mophead hydrangea bush will survive in USDA zones 6 to 9. Although the plant should survive even if temperatures fall to minus 10, if there is an extended cold spell, this can greatly reduce the number of flowers the following year.

It is during winter dormancy that the flower buds form. The hydrangea needs about six or seven weeks with a cool temperature for this formation. Then, as the day starts to lengthen and the temperatures warm up, the buds will break and flowers start to develop. These new buds are very tender, and this is why flowering is susceptible to a late spring frost.

During hot weather, keep the base of the plant cool. The soil should be moist but not wet. If the plant has wilted, watering will not help. Once the hydrangea cools down, the leaves and flowers should recover.

The hydrangea bush mustn’t sit in waterlogged soil or the roots will rot, and the hydrangea will die in just a few weeks.

Pruning Mophead Hydrangea

Mophead hydrangeas don’t have to be pruned at all. They will flower happily without any pruning. 

Almost all mophead hydrangea (H. macrophylla) varieties bloom on old wood. So it is during late summer when flower buds develop. If you prune your mophead after these buds have formed, you will not have flowers the following year.  

If you do want to prune your mophead hydrangea bushes, you need to do so immediately after flowering. This will make sure the following year’s flowers are preserved, and will also encourage new growth.

If you just wish to trim your hydrangea, the best time to do so is very early in the spring, when you can cut off any old flower heads that are still on the plant.

Repotting and Transplanting

Select a pot that is about 3 inches larger than the root ball of the plant. Even a dwarf plant needs this amount of room to be able to spread its roots. Remember to water well before removing the plant from its pot, as this makes it easier to remove the plant without damaging its roots. You should water again once you have transplanted it.

Keep some original compost to mix with the new, so that the change of growing medium will not shock the plant too much.  

How to Propagate Mophead Hydrangea Shrubs

There are several ways in which you can propagate your mophead hydrangeas successfully, and the easiest method is by layering. 

It is easy to identify potential branches for layering in the spring because there won’t be too much foliage. Low-lying branches are easy to peg into the ground. Put a bit of compost over each peg and tiny roots should start to form fairly quickly. Once they are developed, you can detach them from the main branches and pot them up. Put them in a cold frame or unheated greenhouse and leave until the autumn before planting out. 

Alternatively, take softwood stem cuttings in the spring. To do this, you need to work somewhere cool. Always select cuttings from healthy plants. 

The cuttings should be a few inches long and taken from tender stems. Cut below a leaf node and remove all but the top two leaves from your cutting, which you should cut in half.

Dipping the cuttings into hormone rooting powder will speed up the process. But it’s not essential, as the hydrangeas will still root without it. Make a small hole in the potting compost with a pencil or stick. Let the cuttings drop into the holes and firm the surrounding compost gently.

If you put the cuttings in a cold frame, mist them regularly. You want to keep them just moist but not overly wet, or they will rot. They should be in a fairly well-lit and warm environment, out of direct sunlight and extreme heat.

Although the cuttings will start to form tiny roots after just a couple of weeks, don’t disturb them until they are around two months. At this stage, they will have healthy roots, and you can plant them out in the garden or into larger containers. 

Pest and diseases

The great thing about mophead hydrangeas is that, like all hydrangeas, they are not troubled too much by pests. Pests will cause little more than cosmetic damage to your plants. Aphids, weevils, spider mites, and beetles can sometimes build up to quite important levels but often can be eliminated or reduced by a simple spray jet from a powerful garden hose. None of these insects will adversely impact the plant’s health in the long term, although they can cause unsightly blotches on the leaves.

The most likely problems are caused by excessive water, whether caused by rain or overwatering. Fungal diseases may cause spots on the leaves and a furry covering on the flowers. The spores of the fungus can be spread to healthy plant tissue by the wind.

Mophead hydrangeas can suffer from powdery mildew too, but this is more of a cosmetic problem than something that affects the long-term health of the plant. 

The most serious problem is root rot, which is caused by letting your plant sit in waterlogged soil. If you have heavy soil, you need to improve and lighten it to improve drainage. 

Uses of Mophead Hydrangeas

These plants produce beautiful, large blooms and epitomize summer with their colorful display. Much loved by florists, mophead hydrangea flowers make extravagant floral displays, both fresh and dried. 

Common Varieties and Cultivars

Newer cultivars of the mophead hydrangea flower more reliably than traditional varieties. They also often have a tidier habit than their predecessors. Some start to flower earlier in the season, some will flower in shade, and some are bicolored with colorful leaves and stems too.

A few of the more attractive and useful mophead hydrangeas to consider are listed below.

  • Hydrangea macrophylla ‘Big Daddy’

This is a beautiful mophead hydrangea with huge flowers. The flowers can be pink or blue depending on the acidity of the soil and are long-lasting. Because of the strong stems which support the flowers, they are popular with florists as they make excellent cut flowers. This variety will grow about 6 feet tall and is hardy in USDA zones 5 to 9.  

  • Hydrangea macrophylla ‘Nikko Blue’

If you keep your soil acidic, this cultivar can produce the bluest of hydrangea flowers. Less hardy than other varieties, so you need to protect it if you are in USDA zone 5. 

It flowers earlier than many varieties and, like most mopheads, it flowers on old wood. This is why the forming flower buds are susceptible to frost damage in the spring.

  • Hydrangea macrophylla ‘Little White’

This is a compact, white-flowered mophead. It is a perfect choice if you are looking for a hydrangea to plant in a container on the patio. It is fully hardy, and the blooms are long-lasting. This variety makes ideal cut flowers too.

  • Hydrangea macrophylla ‘Kanmara’

This hydrangea shrub will only grow to about 2 feet in height and spread, and has been developed so that it will even flower in partial shade. It flowers for an exceptionally long time.  Like all white hydrangea bushes, its flowers will remain white.

Conclusion

Mophead hydrangeas include many hundreds of cultivars, and they are long-lived plants. Requiring little in the way of care, they are sure to bring joy with their long-lasting display of summer flowers. Whether you want the show of the large mophead flowers or a more compact, upright plant for a patio or deck, there is a mophead to meet your needs. You can also grow lacecap hydrangeas as companion plants next to your mopheads.