Hydrangea

Approximately 80 species occur, many with potential as cut flowers, either fresh or dried. The most popular is Hydrangea macrophylla (bigleaf hydrangea). Long staples of landscape horticulture, these mopheads, as they are also known, have become the darlings of the florist industry. Other useful species of this fine genus include H. arborescens (smooth hydrangea), H. paniculata (panicle hydrangea), and H. quercifolia (oakleaf hydrangea). All have undergone significant selection, and many cultivars are available.

Hydrangea macrophylla     
big leaf  hydrangea     Hydrangeaceae    woody, Zones 5-8     hybrid origin     many colors     3-5’/5’ (0.9-1.5 m/1.5 m)
    
The buying public has become enamored with hydrangeas of all kinds, in the garden, in commercial landscapes, and in vases and bouquets. Mopheads have always had a place in cut flower coolers, but broadened demand and choice of cultivars have enhanced the reasons a grower should invest capital and time in a crop that requires 2-3 years before the first flower is cut. Inflorescences consist of showy sterile flowers and small fertile flowers. When the head is made up mostly of sterile flowers, and the fertile ones are hardly noticed, the rounded flower head is referred to as a mophead; when only the outer ring of the inflorescence consists of sterile flowers, and the center is flattened, the head is referred to as a lacecap. The fullness of the mop-heads has made that form most popular in the cut flower trade.

Propagation

In general, 1- or 2-node softwood cuttings are used from May to early July in most areas of the country. Don Mitchell of Flora Pacifica in southern Oregon de-veloped his own method of propagation, the “box” method, which he shares as follows. Take tip cuttings (usually in April and May) and with a sharp knife, cut and remove about 50% of the leaf tissue. Dip the entire cutting in a mild systemic fungicide, allow the excess to drain, then dip the stem end in rooting hormone solution. Place the cuttings in a waxed cardboard box, close the lid, and place the box in an undisturbed location at room temperature (55-75F, 13-24C is ideal). In approximately 10-15 days the cuttings should be calloused, with small roots starting. Plant these cuttings in 4” pots in a protected area until fully rooted and ready to harden off. Paul and Jhon (1992) found that only 27-33% of control cuttings rooted, and that the use ofIBA, regardless of node numbers, resulted in far better rooting, with more roots per cutting and longer roots than cuttings receiving no dip.  The greatest number of roots (about 21) were produced by 1- or 2-node cuttings treated with 1500 ppm IBA. Dirr (1998) recommends 1000 ppm KIBA and media consisting of 3 parts perlite to 1 part peat under mist; roots occur in 10-20 days.

Growing-on

Pot up rooted cuttings in well-drained medium. Plants may be grown on in large containers. Most cultivars flower on the previous years’ wood and require at least 2 years to flower.

Environmental Factors

Most research on flowering centered on how to force containerized hydrangeas as gift plants for Mother’s Day or Easter. The resulting forcing schedules were attempts to simulate what happens naturally. Essentially, hydrangeas begin flower initiation in late summer and fall, as photo-period shortens and temperatures fall. As plants go into winter, leaves fall off and flowers are completely formed. Winter cold is necessary to break the dormancy of latent buds; plants flower as temperatures warm up. In greenhouse forcing, flower induction, initiation, and development are done under 8-hour photoperiods at night temperatures be-low 65F (18C) (Dole and Wilkins 1999). Plants are moved into cold storage areas, where leaves abscise naturally or with the help ofethylene gas or an ethylene-inducing chemical, such as 2-butyne-l,4-diol (Blom and Smith 1994).

Defoliation is necessary; otherwise, botryris will spread rapidly in the cooler and seriously damage plant quality. Without a chilling period, flowers will abort in most cultivars (Guo ec al. 1995). A common cooling regime is around 40F (4C) for 6-8 weeks, although less time and colder temperatures can be used. Upon removal from the cooler, planes are placed into final containers and forced
around 60-62F (15-17C) (Bailey 1989).

Field Performance

Most hydrangeas grown for cut flowers are field-produced, so nature provides the environment necessary for flower initiation, breaking dormancy, and flower formation.

Spacing
: Spacing varies, 3-4’ (0.9-1.2 m) between plants and 5-8’ (1.5-2.4 m) between rows. The more stems re-moved, the closer the spacer can be; however, too dense a planting results in thinner stems and more disease problems. At Flora Pacifica, plants are spaced 3’ (90cm) apart in 8’ (2.4m) rows.Harvesting: Flowers are generally harvested so that 2-4 nodes remain on the stem. Many flowers are dried, and stem length for dried flowers is not as important as it is in other plants. Most fresh cuts are harvested with stem length of 18- 30” (45-75 cm); for dried flowers, 6-12” (15-30 cm) seems are adequate. At Flora Pacifica, har-vesters cut alternate rows back to about knee height on alternate years. They find that this opens up the field for better air circulation and keeps the plants at manageable heights. In southern Oregon, flower size can be too big for fresh cuts, and this method of cutting also helps to keep flower size smaller.

Support: Not all growers use support; those that do recommend using supports along the rows to a height of  18-24” (45-60 cm).

Shade: Hydrangeas perform best when provided with afternoon shade; the further south one grows hydrangeas, the more important shade becomes. Even in the Northwest, some shade is used. Natural shade is preferred, but shade cloth over frames is also useful. Recommendations of 30-50% have been made. White hydrangeas appear to need more shade; around 40-50% would be appropriate.  In some areas, shade is employed only when the daytime temp-erature reaches 85F (29C) and above.

Flower color. The concentration of free aluminum in the soil can strongly affect flower color. The concentration of aluminum is highest in acid soils and lowest in alkaline soils. In general, blue flowers will occur in acid soils, pink in alkaline soils. In greenhouse-forcing cultivars, Blom and Piott (1992) suggested that application of aluminum sul-phate (approximately 0.5 oz/6” pot, 14 g/15 cm pot) induced blue coloration. Not all flowers have sufficient pigment to change colors, however, and many will remain the same color regardless of aluminum or pH.

Greenhouse Performance

Most cultivars require a cold treatment before flowering, although new cultivars for which no cold is necessary have been selected. Hydrangeas (and other woodies) are particu-larly good candidates for outdoor “moveable” greenhouses or tunnels, in which in-field plantings can be covered and forced when prices are at their peak. If noncooled hydran-geas are moved into a greenhouse in the fall, provide about 6 weeks of40-45F (4-7C) in the greenhouse, cooler, or outdoors.  Plants are usually in containers, so they can be moved in or out of the greenhouse as needed. Flowers can be harvested, depending on cultivar, 4-8 weeks after temp-eratures are raised.

Stage of Harvest

Fresh: Cut flowers when they are completely open. But keep in mind Don Mitchell’s experience: “Sometimes we have ‘gotta have’ customers, who have to have hydrangeas before they are ready. [We’ve] cut them with considerable white showing on the inflorescence, and they still make a good cut flower, though in my opinion not the best.”

Dried: Hydrangeas for drying are not ready for harvest until about 1 September, depending on locale. Generally, they are not ready to harvest until the true flowers in the center of the colorful inflorescence have dropped off and the flowers feel rubbery (not papery) to the touch. With experience, a harvester can readily tell by the feel of the flowers. If har-vested too soon, they shrivel into the unattractive product sometimes creatively marketed as “crinkles.”

Postharvest

Fresh: Defoliate and bunch in groups of 10 in the field. As soon as practical get them to the barn and place them in buckets with about 5-7” (13-18 cm) of hot water (110-120F, 43-49C) and immediately place them in a 34-36F (1-2C) cooler. They should remain in the cooler at least 8 hours or until they are shipped. Don Mitchell jinds that hydrangeas conditioned in this way ship well and considers floral preservative optional. Customers should be told to recut the stems and immediately put them in similarly heated water (110-120F, 43-49C). Using this procedure, completely wilted flowers will revive and become turgid. Vase life of conditioned flowers is easily 7-14 days. A word of caution to florists: hydrangeas need lots of water and do not do well in floral foam; the seem needs to be in water.

Dried: Mopheads are far better for drying than lacecaps, lacecaps dry poorly.  Wait until flowers feel somewhat leathery or rubbery before harvesting. If cut too early, the petals shrivel. When flowers are harvested as outlined earlier, they can be stripped of leaves and bunched in threes using a rubber band. Hang upside down on a drying rack, in a warm, dry, dark place. A barn loft or an attic work fine. It is the combination of repeated drying and rehydration as well as sunlight that causes the loss of color. Don Mitchell has found that if placed in a dryer, the flowers will dry overnight, and the stems may take 2 or 3 days. Add fans for ventilation and a dehumidifier to reduce humidity. Direct sunlight results in discoloration; dampness results in flow-ers turning brown. Some growers, such asj. B. Barzo-Reinke of Small Pleasures Farm in Bandon, Ore., dry thousands of flowers in 2 days in a 20 X 16’ room. And Don Mitchell has the last word on drying: “I have no idea where this idea originated, that you need to place hydrangeas in a vase of water to dry. Other than perhaps a backyard operation, this is pure bunk. Try drying 100,000 hydrangeas in vases of water! I understand Martha Stewart suggested putting vodka in the water to increase uptake. I say, drink the vodka and hang the hydrangeas!”

Cultivars

‘Ayesha’ bears pink or blue semi-double flowers.
‘Deutschland’ has pink flowers. Good hydrangea for outside cultivation.  
‘Dooley’ has handsome blue flowers and is distinguished by having many flower buds on the flowering stem. If a late frost kills the terminal buds, the additional buds will subsequently develop.  
‘Glowing Embers’ is floriferous, but stems are short. The mostly red main flowers on the top of the bush do not dry well (they tend to be muddy-looking); however, the more protected flowers develop an attractive buttery yellow-green color. One of Don Mitchell’s top 5. 
‘Green Shadow’ produces greenish red flowers in summer, dried in autumn.  
‘Hamburg’, Don Mitchell’s favorite, is excellent for early fresh cut flowers and drying. It has good-sized flower heads (6-10”, 15-25 cm), and the individual florets are fairly large. Flowers develop nice burgundy tinges as they mature.
‘Kuhnert’, another of Don Mitchell’s top 5, is an excellent mid-blue hydrangea with small flowers
(6-8”, 15-20 cm) that also dries well. In southern Oregon, plants flower all winter, though with all the heavy rain, the flowers are of poor quality.  
‘Nikko Blue’ is a popular small-flowered blue hydrangea. Perfect for florists who prefer small flowers.
‘Red Star’ is late-bloomer with mid-blue flowers. Good as a fresh cut, with large (8-12 “,20-30 cm) flower heads. As a dried flower, it tends to have a floppy head; however, the blue color seems to hold with much less burgundy coloration than ‘Hamburg’. In Don Mitchell’s top 5.
‘Regula’ is a nice white that flowers later in the season and continues on into the winter. It is a good fresh cut, and the mature flowers turn an attractive green. In Don Micchell’s top 5.
‘Romantic Fantasy’ is a picotee form, red-violet with a white edge.  

Old Wood, New Wood
     
Hydrangea macrophylla produces flower buds on stems in late summer and fall. These buds go through the winter, which breaks their dormancy, then go on to form flowers next spring, on “old wood.” Outdoors, when plants are pruned hard in winter (after the buds have set), or late frosts kill back stems, or deer eat the plants to the ground, flow-ering is nil or very sparse. Plants are still healthy and a few flowers may form, but flowering is significantly diminished. Plants that flower on old wood flush only once a season. This is also why plants forced in the greenhouse must undergo a cold treatment on the old wood, or flowering
is unsatisfactory.
    
A few cultivars seem to be able to flower without cold. Buds are formed on developing stems (“new wood”), and cold is not necessary for flowering. Butterfly- bush and deciduous hollies also flower on new wood; with such plants, greenhouse forcing is significantly easier, and additional flushes may occur throughout the season. Very few cultivars of Hydrangea macrophylla that bloom on new wood are available in adequate numbers, although a few, such as ‘Endless Summer’ and ‘PennyMac’, are being investigated and may prove useful.

Additional Species

Several species can be used for cut flowers; some bloom early, others do not bloom until the fall. Hydrangeas, as cuts, have been looked at as a possible alternative source of income for row crop farmers (Wolfe and Dunwell 1999), but in general, literature on growing a diverse range of      
Hydrangea species as cuts is scanty. Products like hydrangeas and peonies fit well into a niche market.      
    
Hydrangea arborescens is hardy in Zones 4-9. ‘Annabelle’, the most readily available cultivar, bears large, 10-12” (25-30 cm) wide, creamy white flowers in late June through September. Plants flower on new wood and, therefore, may be cut to the ground in late winter; the resulting growth will produce sufficient flowers for cutting. A second flush of flowers is possible in southern climates in September if the first flush is removed by early July. The inflorescences are excellent for drying.
    
Hydrangea paniculata is hardy in Zones 3-8, the hardiest of all hydrangeas, and also flowers on new wood. ‘Grandiflora’ (PG, peegee hydrangea) is very common and bears large panicles of white, sterile flowers in early to mid summer.  The panicles are usually 6-8” (15-20 cm) long but can reach 12-18” (30-45 cm) in length if branches are selectively pruned; such large inflorescences maybe too big for the cut flower market. ‘Kyushu’ has white pyramidal plumes of flowers from late June to late summer. ‘Praecox’ is similar to ‘Grandiflora’ but flowers approximately 2 weeks earlier. Tardiva’ bears numerous sterile flowers on a 6” (15 cm) long inflorescence; its late-flowering habit (late September) makes it a useful option for extending the hydrangea market. ‘White Diamond’ and ‘Pink Diamond’ have become quite popular as easy-to-grow cut flower candidates.  ‘Unique’ produces white flowers in July-September, which dry to pink in September-October. See Dirr (1998) for additional cultivars.
     
Hydrangea quercifolia (oakleaf hydrangea) is a stoloniferous shrub with few branches when young but significant branching at maturity. White flowers are formed in long terminal panicles on old wood. The outer showy flowers are sterile, the inner nonornamencal ones, fertile. Plants are hardy in Zones 6-9, marginal, at best, in Zone 5 and below. Cultivars include ‘Alice’ (long panicles), ‘Snowflake’ (double flowers), and ‘Snow Queen’ (heavier flowers than the species); all are better candidates than the species for cut flowers. Needs shade.

Pests and Diseases

Bud blight, leaf spots, rust, mildew, and assorted thrips, aphids, and whiteflies have all been known to associate with hydrangeas. Slugs and snails are particularly nasty pests, and botrytis is a serious problem. Petal spotting, in which distinct, multiple purple spots (like chicken pox) occur on the flowers, has been reported (Leite and Barreto 2000); J. B. Barzo-Reinke actually points affected plants out to her customers: she finds that they love her “printed mops.”

Grower Comments

“My hydrangeas are planted in rows 7’ apart, plants 4’ apart in the rows. I trim back to 2 or 3 nodes every winter. This gives me lots of nice long stems for cut flower production. I have been using 33% shade but am changing to 50% this year.” Ray Gray, Sunset Flowers of New Zealand, Oregon City, Ore.
    
“I’m selling to a wholesaler for $4/5 stems. These are somewhat small, 30” stems, from tree PGs sec out this spring. Larger stems I would sell for $ 1/stem. They liked them cut about half green, half white.” Ron Smith, R. Smith Farm, Renfew, Pa.

Reading

• Bailey, D. A. 1989. Hydrangea Production. Timber Press, Portland, Ore.
• Blom, T.J., and B. D. Piott. 1992. Florists’ hydrangea blueing with aluminum sulfate applications during forcing.
• HortScience 27(10): 1084 1087.
Blom, T. J., and R. B. Smith. 1994. Ethylene gas for defoliation of hydrangeas.
• HortScience 29(6):636-637.
• Bucks, C. 1998. Simply hydrangeas. Organic Gardening 45(2):23-27.
• Dirr, M. A. 1998. Manual of Woody Landscape Plants. 5th ed. Stipes Publishing,  Champaign, 111.
• DoleJ. M., and H. F. Wilkins. 1999. Floriculture: Principles and Species. Prentice Hall, Upper Saddle River, N.J.
• Guo, Z., M. Goi, M. Tanaka, and S. Fukai. 1995. Effects of temperature and photoperiod on the bud formation of Hydrangea. Tech. Bul. Fac. Agric. Kagawa Untv.47(l):23-3l.
• Leite, R. S., and R. W. Barreto. 2000. Petal spotting of hydrangea flowers caused by Corynespora cassiicola: old pathogen—new disease. Mycologist 14(2):80-83.
• Paul,T.M.,andA. Q.Jhon. 1992. Influence of node number and 1BA treatments on rooting of Hydrangea macrophylla (Thunb.) cuttings. Advances in Plant Sciences 5 (2):619 -622.
• Wolfe, D., and W. Dunwell. 1999. Production of cut flowers from field-grown hydrangeas. HortScience 34(3):476 (abstr.).
Many thanks toj. B. Barzo-Reinke, Don Mitchell, and Bob Wollam for reviewing
this section.