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Growing Guide

Growing Guide


1. Chapter – Hortensia (Hydrangea)

1. Hortensia (Hydrangea)

What are Hortensias?

Everlasting® Hydrangea is a new series of outstanding hortensia that is being introduced into the American market. This series comes from a long line of florist's hydrangeas. Some of you may know this plant by the name of mophead hydrangea, big leave hydrangea, but the technical name is Hydrangea macrophylla. The international market designation is hortensia. To be consistent and to avoid potential mix-up with other important horticultural crops such as oakleaf hydrangea (Hydrangea quercifolia) and panicled hydrangea (Hydrangea paniculata), I prefer the name hortensia. This is important since unlike the other species of hydrangeas, hortensia is designed for commercial greenhouse production as well as for outstanding garden performance. With the introduction of Everlasting® Hydrangea you have access to professional grade cultivars that are stunning performers in your garden and easy to take care of.


Hortensia is a fun plant to grow in pots, containers, and in the yard. It is an interesting plant to grow or to just watch grow since it responds to various manipulations - small differences in soil pH affect flower color. For instance, growing the same cultivar in acidic garden soil may result in blue flowers. While growing it in more neutral soil (pH around 7) the plant will burst into pink flowers. White cultivars on the other hand remain white and cannot be manipulated into changing flower color. The characteristic of a high quality hydrangea flower is the clear coloration which is perfectly contrasted by the dark green foliage. Hydrangeas flower as small plants and increase their show from year to year as they slowly grow into a medium size bush over time. Depending on the cultivar this process will take several years – they don’t mind confinement of a large pot or garden container, faithfully flowering year after year. For the gardening adventurer and advance gardener the ultimate project is growing single stem standards and large patio containers. This certainly falls into the long-term category of horticulture bliss. Reportedly some of these supersize bonsai have been growing in their pots for decades. Americas culture and lifestyle has changed and keeps on changing. Trends are fast, and products that fit this development become extremely popular – hydrangeas are an example that has undergone this cycle several times. The new hybrids of the Everlasting® Hydrangea have been selected and bred for traits that make them virtually care free. These plants are deer resistant, and extraordinarily defiant to disease and adverse environmental conditions. With little effort, anyone can enjoy this beautiful flower.


Background Information

Hortensia is a group of cultivated varieties of the genus Hydrangea. There is conflicting information regarding the number of named cultivars which is estimated by some to range in the hundreds. Formerly this genus was included in the Saxifragaceae; today they have been assigned to their own family Hydrangeaceae. The genus hydrangea includes some 70 species many of which are native to East Asia, and can be found in countries such as Japan, China, and Korea, to name just a few. Hydrangea macrophylla is native to Japan and was cultivated for some time prior to its first description by Carl Peter Thunberg in the 1700's. Thunberg discovered these early cultivars near the city of Nagaski on the Kyushu island of Japan. Due to some confusion during categorization, these plants were classified with the genus Hydrangea and not as initially proposed Hortensia. Since the discovered material were cultivars and not species, an interesting debate incurred. Systematics is a fascinating topic and I can recommend reading the stories early explorers wrote – they are not boring scientific papers. Most are written in prose and are, at times, very witty. In the decade of 1790 to 1800 some plants were brought to Europe where they were used as the initial breeding stock. Much of the early breeding work occurred in France where they were grown in botanical gardens and by some plant collectors. By the late 19th century hortensia found its way into the horticulture trade. In a relatively short time hundreds of new cultivars were bred in floriculture hotspots such as Belgium, the Netherlands, Germany, and France. Interestingly these new western cultivars eventually were brought back to Japan where they are called Seiyou-ajisai and are popular additions to the original assortment. Western, as well as the original Japanese cultivars, will grow into attractive, several feet tall shrubs in the garden. Surprisingly, this fact of using potted plants in the house or the patio which may be later transplanted into the garden is still not known by the average gardener in the USA. For example, which average consumer would know to use hortensia as an indoor plant in the winter? To transplant it into the garden after the frost and eventually harvest cut flowers from this plant for indoor decoration for years to come?

A Botanical Profile of Hortensia

The plants are deciduous and the pattern structure of the foliar arrangement is opposite. The dark green foliage is large and to some degree serrated. The typical florist’s hydrangea produces a large inflorescence on the end of relatively long stems (twigs). The size of the spherical bloom is massive and may have a diameter of 5 to 10 inches. The flower head can be described as an umbelliform cyme consisting of numerous small florets. Most interestingly to growers, a modification of the florets resulted in sepals to be the dominant part of the flower and it is the sepals that are responsible for the show of the flowers. The petals on the other hand are small, insignificant, frequently completely missing. The blooms are white, pink, deep rose nearly red, and blue. Unlike petals, the size of sepals may be modified through cultural practices. In other words, a grower can specifically modify the pigmentation of the flower (except white cultivars) as well as increase the size of the sepals with improved cultural practices.

General Environmental Requirements

The native habitat of hortensia is situated in wooded areas near the ocean. There, it is an understory shrub protected from the elements such as too much direct sunlight and wind. The climate is mild, perhaps closest described as Mediterranean with a touch of a northern temperate climate. Winters are cool, with temperature remaining just above freezing. The summers are warm yet some level of precipitation continues and the relative humidity is high. This is essential for hydrangea. As the name may suggest, they require a constant supply of water. So be careful; they do not appreciate “wet feet” for any amount of time.

I try to encourage people to be inquisitive and to find out where plants came from – some really enjoy learning. In order to grow excellent garden plants one ought to learn about their origin. The botanical name and information about the native habitat provides valuable hints for what might work in a garden – the differences of cultivars withstanding, it reveals clues to cultural requirements and the temperament of the plant. In the case of hydrangea, the very specific environment hortensia evolved became imprinted into the species, even into the current cultivars. Hydrology, soil composition, and temperature range of the natural environment defines the species. Modern cultivars thrive when these environmental factors are met. For example, flower initiation occurs in the late summer or early autumn as soon as average day temperatures range 55°F to 60°F – the optimal temperature is 59°F. Unlike temperature, photoperiod does not seem to be an obligatory factor – while some discussion remains, for the consumer this debate is of little applicable interest. The bud remains dormant throughout the winter and requires temperatures just above freezing to complete vernalization. It will produce a flower the following spring. Frost and untimely pruning destroys the flower buds thus the plant will fail to bloom the flowing spring. Some remontant (ever blooming) strains will set new flowers in the spring but are generally not well suited for forcing. For example, a good potting media and garden soil should exhibit similar properties as forest soil – plenty of organic matter, good water retention to remain moist, yet well draining to prevent waterlog. The plants prefer acidic media to facilitate iron uptake, while pH effects flower pigmentation. This information is simply obtained by learning about the natural habitat as well its history and cultural context.

Growing Pink and Blue Hortensia

Buying and Planting

Young plants should be bought from reputable suppliers only, particularly if your goal is to grow vigorous and healthy hydrangea in your garden. Finding such a supplier can be challenging – sometimes the material is badly conditioned, other times cultivars are mixed up, or they are just weak and in overall bad condition. Breeding new cultivars is a costly investment so more and more cultivars are protected by breeder rights and patents. Everlasting® Hydrangea are also protected by patents and taking cuttings for commercial purposes is prohibited.

Potting Media – Garden Containers

In contrast to most standard pot plants, hortensia frequently will stay in containers for several years. Selecting the right growing media is of paramount importance. You must select a media that does not shrink over time. As indicated above, hortensia require plenty of water without being submitted to waterlogged conditions. Potting media amendments may include coarse and stable materials such as haydite, pine-bark compost, and coarse sand. Peat moss should be used sparingly due to the fine particle size. In many of my long-term corps, including hortensia, I incorporate some percentage of topsoil into the potting mix. Frequently, I test a few formulas before settling, assessing recipes that work best under my growing conditions. The media should receive an initial starter charge and the pH needs to be adjusted if necessary. The final pH for blue flowering container plants needs to be adjusted to 5.0 to 5.5. A pH over 6.0 inhibits the uptake of aluminum ions, the flower will not turn completely blue, often resulting in a muddy blotched wine color. Choosing the proper cultivars is the most important aspect for designing your garden. The following are considerations for identifying suitable cultivars:

Consult with your supplier and identify cultivars suitable for setting – they need to be sufficiently vigorous if planted in the garden. While compact cultivars are better suited for container growing. Everlasting® Hydrangeas are a new generation of hydrangeas. They incorporate the best traits of the older cultivars. To bring it to a point, they are truly multipurpose and perform exceptionally in pots, in the garden, as well as cut flower. When reviewing the cultivars the following my be a guideline for making your decision:

  • White cultivars cannot be turned blue.
  • Not all pink and rose colored cultivars will produce a clear blue, even under perfect conditions.
  • Trial cultivars - not all cultivars perform equally well in the different climatic zones.

Pigmented hydrangea flower either pink, dark rose, some cultivars nearly red. Depending on your cultivar and the intensity of the pigmentation, the flowers may turn blue; some cultivars produce an almost violet/purple. Changing the color from pink to blue depends on the pH and concentration of aluminum ions present in the media or garden soil. Nonetheless, not all pigmented cultivars make great blue flowers. Consult with your supplier and identify the best cultivars for your area.

Once you have identified suitable cultivars for your garden or container, adjust the pH and apply Alum. Make sure to maintain the proper pH throughout the growing cycle. Adjust the pH with lime or Alum to a value between 4.8 and 5.5. Alternatively, aluminum-sulfate works just as well and can be used to correct the pH down. When growing blue flowers, the pH should never exceed 5.5. On the other hand, reducing the pH below 4.8 may damage plants and growth is impaired. At a pH over 6.5 not only will flowers not turn blue, iron becomes unavailable, consequently the foliage may become pale and chlorotic. In short, both aluminum potassium sulfate (Alum) KAl(SO4)2 and aluminum sulfate Al2(SO4)3 are essential tools in manipulating the flower color of hortensia. They are used to control pH and to add sufficed quantities of aluminum ions to the media. Since the optimal concentration is based on pot size and cultivars, consult with your supplier for appropriate rates. In addition to the initial treatment, you need to apply alum or aluminum sulfate in September and November of each year, and again in March and May. Missing an application and/or untimely application of Alum, frequently results in a muddy blue color of the flower. Follow the schedule and increase the amount of Alum in situations where irrigation water is hard (containing high amounts of calcium). Under some circumstances it may be advisable to use rain water for irrigation in order to limit the calcium accumulation in containers.

Water, Temperature, and Light Management

Proper water management is essential for growing excellent hortensia. The availability of water affects sepal size which can be manipulated by providing the optimal amount of water. However, the threshold of optimal and too much water, is slim. At best, excessive water will lead to blind stems and flower bud abortion. Most commonly Pythium blight will take hold in your container or flower bed. To prevent fungal disease, watering with drip irrigation is preferred – avoid overhead irrigation. Keep irrigation zones small to allow custom watering schedules. Make sure your containers are free draining and have plenty of drainage holes. Elevating the pots onto a low platform can help. Alternatively, placing containers onto a gravel bed helps to drain extra water away. Controlling water is extremely important. Many hydrangea cultivars are highly susceptible to root rot. Especially Pythium thrives in waterlog conditions. Free standing water and splashing may quickly spread this pathogen throughout your flowerbed. Good water management is of upmost importance for your plants to succeed.

Although hydrangea requires medium-high light levels, too much direct sun will damage foliage and flowers. Plant your hydrangea in a semi shaded area. Protect the flowers from direct midday sun. Direct sun, overhead irrigation, and strong wind are the most common culprits, causing (sun) burn and fungal infections of flowers and foliage.

Space Requirements

On average, plants are spaced to 1 plant per 5 square feet, depending on cultivar. Make sure to include ample space for the plant to grow. The flower bed should be 4 to 5 feet wide. The flower bed dimensions need to be adjusted according to the vigor of different cultivars. The shrub can be pruned to maintain a certain shape and size.


Hortensia do not tolerate strong frost. Everlasting® Hydrangea are tested and rated for USDA zone 5 so they should be protected with mulch and burlap to protect the twigs. Freezing temperatures in the spring may damage the flower buds. A temperature range of 35°F to 40°F during the fall and winter is necessary to initiate flower bud development. This is why the Everlasting® Hydrangea is rated up to USDA zone 8 and to some degree zone 9. If you are located in Zone 9 or above your plants will certainly grow but may not produce flowers. Hortensia need about 1000 hours or about 6 weeks of cold to complete this process. If you are located too far south your plants may not flower. If you grow your plants in planters you can force hortensia into flower out of season and providing winter storage, grow beautiful flowers in USDA zone 5 and below. For blooming hortensia out of season, bring your planter indoors. Make sure your plants received sufficient cold to ensure flower bud formation was completed. Raise temperature to 65°F during the day; drop the night temperature to 60°F. This temperature range will initiate shoot growth. It will take you about 1 week to see the first signs of development. The flower bud will enlarge and start to break open. Once the first small foliage becomes visible, drop the night temperature to 55°F (the day temperature remains at 65°F). After about 3 weeks, short shoots should have grown, and at this time you can lower the temperature during the day to 55°F. Your plant will flower within 6 to 8 weeks after starting the temperature treatment. Hortensia should not be pruned after August since flower bud development for the next year will begin at that time.

Harvest and Post-Harvest Guidelines

Harvest your stems early in the day when it is still cold – essentially follow the cut rose protocol. The addition of post-harvest flower preservatives, such as Chrysal, has worked well. During peak season expect to harvest fresh flowers 2 to 3 times a week. When cutting flowers make sure you leave 4 to 6 inches of the stem with the plant.

Common Diseases and Pests of Hortensia

Spidermites, aphids, mildew, gray mold and Pythium blight are the main adversaries of hortensia. Good water management and sanitation are your first line of defence agains Pythium blight, gray mold and mildew. The Everlasting® Hydrangeaseries has a strong resistance to many soil borne pathogens such as Pythium blight and other common problems such as mildew. Deer and rabbits usually do not bother hortensia and leave them alone.