Hydrangea’s Hidden Potential

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Hydrangea ‘Everlasting Ocean’ flowers change to dark pink and develop creamy picotee markings.

Even while the market continues to look for a wider selection of high-quality crops, hydrangea remains underused, both as a cut flower and a pot plant. Until recently it was next to impossible to get properly prepared rooted cuttings for a blue hydrangea program in the U.S., so that is likely a factor. Why should you go through the trouble of changing your assortment and production schedule? It is potentially a high-margin crop, so in my opinion, it is worth consideration.

The international market designation for Hydrangea macrophylla is hortensia. This is important, since unlike the other species of hydrangeas, hortensia is designed for intensive forcing programs that include both pot and cut flower production. Many years ago, it was part of the core assortment of floriculture crops.

Production of hortensia requires thorough knowledge of production methods. A high-quality hortensia plant has clear coloration of the flower; a muddy, blotchy color is the result of poor pH management, as well as mistakes in fertilization. Depending on the product line, it may take up to 15 months, sometimes more, to grow a market-ready product. Single stem standards and large patio containers certainly fall into this long-term category. Pot production averages nine to 12 months. The largest time investment is in developing a cut-flower program, which might take as much as three years from cutting to a size that supports profitable cut-flower harvests.

Is Hortensia A New Cash Crop?

Will a time investment of this size pay off? There is opportunity; hortensia is not yet a commodity. Post-harvest traits of cut hortensia are acceptable but have limitations. Often the locally-grown material is of much better quality than flowers imported from halfway around the world. This characteristic especially provides an opportunity for small and medium-sized operations serving a regional market – a market traditionally underserved with top-quality flowers from local production.

Propagation Of Blue Hortensia

Rooted cuttings should be bought from reputable suppliers only, particularly if your goal is to produce blue hydrangea. Finding such a supplier can be challenging – sometimes the material is badly conditioned and unsuitable for blue hydrangea production. Since obtaining high-quality propagation material can be tough, some operations maintain their own stock in-house. Having stock certainly has advantages, such as not being affected by availability of certain cultivars or quality issues. However, increasingly the new cultivars are protected by breeder rights and patents. Taking cuttings from such material is prohibited. Check thoroughly before establishing your own stock plants and make sure to work with free-market cultivars only.

Purchasing rooted cuttings may be the least complicated option for starting a hortensia cut flower program. Rooted cutting liners should be available for delivery in late autumn; if weather permits, winter shipments are possible. Transplant swiftly since the plants need space – crowded conditions encourage gray mold and mildew. Transplant rooted cuttings into a moderately-sized pot before going into the final pot size. For cut-flower greenhouse production, pot one plant per 3- to 5-gallon container, depending on the vigor of the cultivars. If the climatic conditions of your area allow field production, skip the last step and plant the well-established plants outdoors.

Potting Media – Greenhouse Production

In contrast to most standard pot crops, cut flower plants frequently stay in
containers for several years. Selecting the right growing media is of paramount importance. 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 crops, including hortensia, I incorporate some topsoil into the potting mix. The media should receive an initial starter charge, and the pH needs to be adjusted if necessary.

Turning Hortensia Blue

Choosing the proper cultivars is the most important aspect in setting up a cut flower program. The following are considerations for identifying
suitable cultivars:

  • Consult with your supplier and identify cultivars suitable for greenhouse cut-flower production – they need to be sufficiently vigorous.
  • White cultivars cannot be turned blue. Not all pink and rose-colored cultivars will produce a clear blue, even under perfect conditions.
  • Trial cultivars in small numbers; not all cultivars perform equally in the different climatic zones.

Pigmented hydrangea flower either pink, dark rose or some cultivars nearly red. Depending on the cultivar and the intensity of the pigmentations, 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. 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 blue cut-flower production, adjust the pH and apply aluminum potassium sulfate (alum). Adjust the pH with lime or alum to a value between 4.8 and 5.5, and be sure to maintain it throughout the growing cycle. Alternatively, aluminum-sulfate works just as well and can be used to lower the pH.

When growing blue flowers, the pH should never be above 5.5, but reducing the pH below 4.8 may impair growth. At a pH over 6.5, not only will flowers not turn blue, but iron becomes unavailable; consequently the foliage may become pale and chlorotic. 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. A poorly-timed or missed application 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 alkaline (containing high amounts of calcium). Under some circumstances it may be advisable to use rain water or chemically softened water for irrigation in order to limit the calcium accumulation in containers.

Managing Water And Light

Proper water management is essential for growing excellent hortensia. However, the threshold between optimal and too much water is slim. At best, excessive water will lead to blind stems and flower bud abortion. Drip irrigation is preferred, and 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. Controlling water is extremely important. Many hydrangea cultivars are highly susceptible to root rot, especially Pythium. Good water management is of utmost importance for your crop to succeed.

Although hortensia requires medium to high light levels, too much direct sun will damage foliage and flowers. Supplemental lighting may improve early growth of the crop during the low-light winter months. As soon as days get longer and the intensity of the sun is increasing, provide shading, especially in the spring and early summer. Protect the flowers from wind drafts and direct sun. For most areas, a 50 percent shade cloth will do the job. Direct sun, overhead irrigation and wind draft are the most common mistakes, causing (sun or wind) burn and fungal infections of flowers and foliage.

Temperature

High-performing forcing cultivars do not tolerate frost. Maintain a temperature range of 35°F to 40°F during the vernalization treatment of the crop. Hortensia needs about 1,000 hours or about six weeks of cold treatment. This is a rough estimate and works for many cultivars; however, the actual duration depends on the specific cultivar. Forcing of hortensia can start in February allowing harvest of the first flowers for the early season cutting dates. Raise the temperature to 65°F during the day; drop the night temperature to 60°F.

Once the first small foliage becomes visible drop the night temperature to 55°F, while the day temperature remains at 65°F. After about three weeks, a short shoot should have grown; now you can lower the day-time temperature to 55°F. This will conserve energy as well as improve quality of the crop. By bringing on the flowers slowly and limiting the number of stems per plant, the size and the quality of flowers is enhanced. For growing cut flowers, the stem length is very important. A zero DIF environment promotes stem elongation.

A good relationship with your supplier and experts who have experience growing hortensia is important. Over the years, an enormous number of cultivars were released into the market. Some cultivars are very specific in purpose and are designed to perform only as a potted hortensia crop. Others may work only for outdoor or field production since they may not tolerate confinement in containers. Your supplier, and perhaps, your Extension agent might be good resources for selecting cultivars.

Juergen Steininger is a grower at Longwood Gardens in Kennett Square, Pa. He can be reached at juergensteininger@yahoo.com.

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