Hydrangea (Hydrangea Macrophylla) – The Complete Guide

Hydrangeas are real miracles of flowers. These beautiful plants are also known as hortensia, bigleaf hydrangea, French hydrangea, lacecap hydrangea, mophead hydrangea, and penny mac.

Their gaudy hues enchant every observer. But the splendor of color does not come by itself.

You need to consider some factors in the care and selection of the site so that the semi-shrub grows vigorously.


The hydrangea is also known by the name of hortensia. Its Latin name is Hydrangea macrophylla. It is considered the most famous representative within the hydrangea genus.

Its triumphal march through the gardens of Europe and America began in the early 20th century. During this period numerous cultivars and hybrids were created.

Before that, the plant was cultivated in its original area of distribution in Japan.


Hydrangeas develop opposite deciduous leaves composed of petiole and leaf blade.

Its petioles are short, appear fleshy, and end in a simply constructed blade. It has a sharply toothed leaf margin and is traversed by a raised median vein from which numerous lateral veins branch.

The oval to ovate leaves are slightly wider or narrower, depending on the variety. They can grow up to 6 inches (15 cm) long.

The base of the leaf blade has a blunt wedge shape with a pointed end. The deciduous leaves come in dark green with a shiny upper side.


The hydrangea shrubs develop numerous single flowers that cluster together in umbrella-like inflorescences. The shrubs sit on thick branches.

Coma flowers occupy the outer edge of an inflorescence. The flowers have a scooping function with the outer flowers consisting of four sepals. These sepals are conspicuously large and brightly colored.

The color of the sepals varies depending on the pH value of the soil.

If hydrangeas grow in acidic soils, they develop a blue coloration. Alkaline soils result in red flower color.

The intensity of the coloration varies depending on the variety. Some specimens bloom pure white.

As the flowering period draws to a close, a fascinating play of colors occurs. The colors change to green and finally to rusty red. In the new Hovaria varieties, this phenomenon is particularly intense.

Inside sit fertile flowers, which are responsible for reproduction. Their calyx is small and bell-shaped. The individual sepals are short and triangular in shape.

In Japan, hydrangeas bloom between June and August. The flowering period of plants cultivated in America or Central Europe extends throughout the summer and continues until October. The flower buds are formed in the previous year.


The wild form of the hydrangea grows as a half-shrub. The old shoots become woody in the second year, while the fresh shoots are herbaceous.

They are deciduous and grow upright with dense branching. After flowering, the inflorescences remain on the plants.

The bark of young branches is greenish in color, but with age, it becomes brownish. Strong branches appear light brown. They are covered by a felt-like bark, which is easy to peel off.


Hydrangeas reach growing heights of up to 7 ft (2 m) in their original range. Heights vary depending on cultivar and site conditions.

The summer bloomers have a large space requirement, which is determined by the height of growth. Garden hydrangeas grow at least as wide as they are tall.


These summer shrubs have a rustic character. They are suitable for planting in perennial beds that ensure partial shade conditions.

Under taller growing shrubs, the summer bloomers cut a particularly good figure. They beautify small front gardens and bring colorful accents to the dark corners of the garden.

Other hydrangea species prove to be optimal planting partners. You may plant them in small clumps and rows, creating a dense hedge over time.

Hydrangeas feel at home next to rhododendrons and other plants in shady to semi-shady locations. Between hostas, astrantias, goat’s beards, spireas, or astilbes, the splendor of the flowers comes out perfectly.

Is Hydrangea Poisonous?

Like all hydrangea plants, Hydrangea macrophylla contain various toxins. They are weakly concentrated in all parts of the plant.

In addition to prussic acid, hydrangenol, saponins, and hydrangin are present. Normally, poisoning does not occur after the consumption of small amounts.

Only large quantities cause symptoms of poisoning. Sensitive people may have an allergic reaction upon skin contact.

Possible symptoms of poisoning are:

  • Feeling of anxiety
  • Circulatory problems and dizziness
  • Shortness of breath
  • Cramps

Hydrangeas are also mildly toxic to horses, dogs and cats, birds, rabbits, hamsters, and guinea pigs. The toxins can cause circulatory problems or gastrointestinal discomfort.

Serious symptoms of poisoning occur only after eating large quantities. Often the bitter taste of the plant deters animals.

Which Location is Suitable for Hydrangea?

Hydrangeas have special requirements for the location. They originally grow along watercourses and moist forest edges.

Semi-shrubs prefer a sheltered place with partial shade conditions. A north or west-facing spot with no drafts is optimal. The plants also grow under strong sunlight.

Under these conditions, the need for water increases sharply. In the absence of water, the garden hydrangea droops its leaves and gets a sunburn.

What Kind of Soil Does Hydrangea Need?

The substrate should be low in lime, rich in humus, and moist. The ideal pH is between 4.5 and 6.

At a low pH, the semi-shrub blooms blue. Higher values produce purple, pink, or red tones. White flowering varieties do not change their flower color, though.

Propagating Hydrangea

The easiest method is to propagate cuttings with fresh shoots cut in July. But make sure the shoots do not have flower buds.

Divide the shoots into small sections, each with two pairs of leaves. Then remove the lower pair of leaves and shorten the upper leaves by half.

This will give the cuttings more room to spread out in the planter and put more energy into root development.

Put the cut shoots in a growing medium and then water the substrate. To maintain humidity, it is a good idea to place a plastic bag or screw-top jar over the planter.

Ventilate the plant daily to prevent mold from growing. Place the planter in a warm and shady spot in the garden or on the patio. The cuttings only need a little time for root development.

Pricking Out Hydrangea

When the cuttings have developed roots, prick them and transplant them individually into small pots. The planting pot should have a diameter of 4 inches (10 cm).

To prevent sunburn, place the pot in a shady place. For further cultivation, you do not need to cover the seedlings with foil.

You should keep in mind that young hydrangea plants are sensitive to frosty temperatures. Therefore, place the planter in a cool and frost-free place indoors in the first winter.

By next spring, the plants will have developed enough to be ready for planting out in the garden.

Sowing Hydrangea

Propagation by seed is proving difficult. Many double varieties do not develop seeds.

Primitive varieties and the wild type carry seeds inside the withered inflorescences. But they are difficult to collect because they are very hidden and are hardly noticeable. A good alternative is to buy seeds in specialized stores.

Here is a short guide on how to sow the seeds:

  • Fill planting container with growing soil.
  • Scatter the seeds.
  • Cover them lightly with soil.
  • Moisten them with a spray bottle.
  • Cover the plant pot with foil.

Hydrangea in a Pot

Hydrangeas are ideal for cultivation in pots. They beautify balconies, house entrances, and terraces.

You can also often find potted hydrangeas in stores. Potted hydrangeas are also varieties of Hydrangea macrophylla.

Hydrangea in the Greenhouse

A greenhouse provides optimal conditions for pre-growing hydrangeas. Potted hydrangeas from the store, which are already in full bloom between February and April, were usually grown in the greenhouse.

These specimens are sensitive to late frosts and require winter protection. Greenhouse-prepared hydrangeas should not be planted in the garden during the first year. They are very sensitive to cold at first.

Pruning Garden Hydrangea Properly

Hydrangeas do not need to be pruned. In the spring, you should only remove the wilted flower spikes so that the fresh buds can unfold unhindered.

It is also a good idea to cut back dead and frostbitten branches. You can identify these by their gray-brown discoloration.

If you are unsure, you can lightly scratch the bark. If the tissue underneath is yellow-green in color and appears dry, the shoot is dead.

Proceed with caution when thinning. Most varieties develop their flower buds already in the fall. Pruning in the spring will thus reduce flowering.

But there are also special cultivars that will develop new flowers even after severe pruning.

Fertilizing Hydrangea Properly

Hydrangeas enjoy a special fertilizer for hydrangeas or rhododendrons. To promote blue coloration, the fertilizer should contain alum. This aluminum salt contains water-soluble crystals that have an acidic effect.

Fertilize free-growing hydrangeas for the first time in spring. then provide them with a second fertilizing in early summer.

Use a slow-release fertilizer, which the plant will feed on throughout the growing season. Give potted plants a liquid fertilizer at regular intervals between March and August.

But you should stop fertilizing as soon as the summer comes to an end. Then the fresh shoots have enough time to lignify. The shoot tips will remain unwoody, which is typical of semi-shrubs.

Watering Hydrangea

Semi-shrubs have a high water requirement. When exposed to direct sunlight at the growing site, the plants require larger amounts of water.

Water the plants thoroughly so that the soil is well moistened. The root ball should never dry out completely.

Check the substrate more frequently during hot summer months to prevent drying out. You should water hydrangea grown in pots twice a day during the summer.

Do not use chalky water for watering as it will change the pH in the substrate. It is better to use soft rainwater.

Avoid waterlogging as it will damage the roots of the hydrangea.

Wintering Hydrangea

Potted hydrangeas should overwinter indoors in cold winter regions. An unheated greenhouse is the ideal place if it is protected from direct winter sun. As a result, temperature fluctuations will be lower.

Dark overwintering is also possible. In this case, pay attention to low temperatures that do not rise above 41 °F (5 °C). Under these conditions, the garden hydrangeas stop their metabolism.

Bright and warm wintering is suboptimal, as pests quickly attack the shrubs. The lack of dormancy also inhibits the development of new flower buds.

Specimens growing outdoors need additional winter protection when young. A layer of fir branches or brushwood is ideal.

Older plants do not need winter protection in regions with mild winters. But make sure to protect the plant during severe frosts.

Fungal Infestation

Hydrangea species can be affected by both powdery mildew and downy mildew.

Powdery mildew is a fungus that spreads during dry and warm weather conditions. You can recognize an infestation by the white coating that resembles a layer of flour.

Downy mildew requires moisture. It leaves a silvery-gray fungal turf on the underside of leaves.

Here’s how to fight powdery mildew:

  • Cut off infested areas and destroy them.
  • Means containing neem oil or silicic acid help against powdery mildew.
  • Garlic or onion decoction helps against downy mildew.

Brown spots on the leaves indicate gray leaf spot disease. This fungal disease develops when there is a poor nutrient supply.

Just like this fungus, gray mold also spreads during humid weather conditions. Infestation is evident by the gray turf that covers flowers, leaves, and shoots. The plant parts will wither if the plant is not treated.

Optimal care with a good supply of nutrients and water will prevent these fungal diseases. Plants should generally be well ventilated.


Chlorosis is a relatively common disease in hydrangea that manifests itself as green discoloration of the leaf veins. The leaves turn yellow over time.

Chlorosis is due to an iron deficiency, but alkaline soil can also lead to this disease. Work rhododendron soil or peat into the soil to lower the pH. A fertilizer containing iron will provide a quick remedy.

Certain mycoplasmas or viruses cause virose in hydrangeas. Diseased plants have small and stunted inflorescences. The plant parts take on reddish hues.

Since this disease spreads quickly to other plants and cannot be controlled, you must quickly remove the affected plant and burn it if possible.

Good to know

Support the inflorescences of large-flowered varieties with a curved perennial support, as their stems can easily snap off, especially after heavy rains and in windy conditions. Remove broken shoots. The plant usually regenerates quickly.


There exist numerous varieties of hydrangea that come in different colors and shapes. Some interesting varieties are:

  • Endless Summer: This variety works well for sunny locations. It is very well tolerant of pruning and blooms reliably after pruning in spring. Also, this variety is especially hardy.
  • Forever & Ever: Another variety for sunny locations. It also has a good pruning tolerance and blooms reliably after early pruning. The plant blooms twice a year and is quite easy to care for.
  • Glowing Alps: A variety that is suitable for sites exposed to wind. It is fast growing and blooms crimson between July and September. The foliage is dark green. It can grow to a height of 50 to 60 inches (120 to 150 cm).
  • Hovaria Hobella: It blooms in pastel shades of pink with flowers up to 10 inches (25 cm) tall. The fFlowers turn green and red. The plant grows between 45 and 60 inches (100 and 150 cm) tall.
  • Hovaria Love you kiss: The plant blooms white with red toothed edges between June and October. Bloom lasts four to six weeks, then the flowers turn green and red. It reaches heights of growth between 45 and 60 inches (100 and 150 cm).