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Growing Knowledge Into the blue A comparison of substrate amendments for the adjustment of hydrangea flower color oregon state university By Heather Stoven and Jim Owen New hydrangea cultivars are being introduced on a regular basis, many of which have sepals that vary in color based upon the characteristics of the growing media. It is important to under- stand the color changing mechanism in order to facilitate the desired flower color for production and sales. The availability of aluminum (Al) is what causes a change of color in the sepals from varying shades of pink to blue. However, the availability of this element is dependent upon the substrate pH. More Al is available to the plant at lower pH, resulting in blue flowers, and less Al is available at higher pH, resulting in pink flowers. The Ball Redbook, a popular grower reference manual, suggests pink flower- ing hydrangeas be grown in a pH of 6.5 Growing hydrangeas that bloom the desirable “true blue” color requires the right soil conditions and amendments. It is not always easy to achieve. and blue at 5.5. Drenches or substrate amendments of aluminum sulfate (AlSO4) are com- monly used in the industry to provide aluminum and to lower pH, producing 27 ▲ An ongoing series provided by Oregon State University 50 ▲ in partnership with OAN APRIL 2010 ▲ DIGGER 25 Bringing Growth, Ingenuity and Experience to Market. Ben Piper - 503.710.1778 | Ken Doubrava - 503.866.6116 | Jim McKay - 503.710.1777 Woodburn, OR | Phone: 503.981.3521 | Fax: 503.981.5747 www.wilburellis.com WILBUR-ELLIS Logo and Ideas to Grow With are registered trademarks of Wilbur-Ellis Company. K-0310-377 Nursery Containers For All Your Growing Needs • Greenhouse pots, bedding plant inserts and trays, W propagation trays, tree cell trays and liner pots NE • Outdoor nursery containers from 1-300 gallons • Wood tree boxes, stakes and trellises • Shade cloth, ground covers and growing systems Biodegradable Rice Hull Pot! Trust & Reliability for Over 40 Years Fertilpot! 100% biodegradable Preserves natural root and compostable structure and decreases landﬁll waste Inside Sales: Erin Rivers at 888-981-1727 e-mail: firstname.lastname@example.org Outside Sales: George Graeber at 916-616-4281 e-mail: email@example.com 2830 Progress Way, Woodburn, Oregon www.trlcompany.com Toll free: 888-981-1727 26 APRIL 2010 ▲ DIGGER ▲ INTO THE BLUE Clay amendment No amendment 0 AISO4 blue flowers. However, it is not always easy to achieve the clear blue color that is desirable even with aluminum sul- fate applications and a sufficiently low pH. Also, if the pH gets too low, plant growth and quality can be insufficient. Testing with pozzolan clay In order to address the issue of blue hydrangea flowers, a study using pozzolan clay (diatomaceous cal- 6 lbs/yd cined clay containing 10 percent Al by AISO4 weight) was established at the North Willamette Research and Extension Center in Aurora, Ore. Due to the amorphous structure and high Al content of the clay, it was hypothesized that hydrangea flowers could be produced with a truer blue color and at a higher pH than can be 12 lbs/yd done with typical grower practices. AISO4 Previous studies have been done with zeolite (Opena and Williams, 2003) and kaolinite (Handreck, 1997) clays to pro- duce blue flowers; however, it was only possible at low pH levels. Hydrangea macrophylla Endless Summer® was potted into three Scientists at Oregon State University found that these conditions of amended soil and aluminum sulfate resulted in different Douglas-fir-bark-based substrates with hydrangea bloom colors as shown. different amendments in #2 containers on June 1, 2007. Nine substrate treat- ments were used in the experiment, and each was replicated 10 times. 5 The substrates were as follows: 9:1 (by volume) DFB to pozzolan clay (Western Pozzolan Corp., Doyle, Calif.), 4 7:3 (by volume) DFB to sphagnum peat moss , and 3:2 (by volume) coarse DFB Color Rating to fine DFB. Three rates of AlSO4 were 3 0 AIS04 added to the three substrates: a high rate of 12.5 pounds per cubic yard; a medi- 6 AIS04 um rate of 6.3 pounds per cubic yard; 2 and a control treatment (no AlSO4). 12 AIS04 A requisite amount of dolomite lime was added to each of the treat- 1 ments to equalize pH across treatments. Dolomitic lime was incorporated at a rate of 1.2, 0.90, and 0.60 pounds per 0 cubic yard for the high, medium, and Clay Peat None control AlSO4 treatments, respectively. Figure 1. Effect of substrate and aluminum sulfate (AlSO4) on color rating of Micromax micronutrient package was hydrangea Endless Summer® flowers 28 ▲ APRIL 2010 ▲ DIGGER 27 ▲ INTO THE BLUE Harmony Hill Hydrangeas incorporated at 1.5 pounds per cubic yard into the substrate for all treat- ments. Hydrangeas were top-dressed with a medium-high rate of a controlled release fertilizer and were overhead irri- gated following industry standards. Growth index [(height + mean width)/2] and flower color were record- ed when the plant was determined to be at a saleable stage on May 21, 2008. At this time substrate solution pH was measured via pour-throughs. Flower color and customer appeal were evalu- ated independently with a rating system of 1-5; with 1 being the least blue and 5 being most blue or most appealing. Substrate and AlSO4 had a signifi- cant effect on ratings for sepal color (Fig. 1). Increasing AlSO4 and pozzolan clay amounts increased the blue color rating of hydrangea sepals. At each AlSO4 concentration, the highest color ratings for all substrates occurred in combination with clay. The addition of the peat amendment did not significant- ly affect flower color compared to the unamended treatment. Scientists found they could improve hydrangea flower color by adding calcined As AlSO4 rates increased, the flower clay to the growing medium. color was rated as more blue. The same effect was also seen when the AlSO4 rate was 0, the addition of clay pro- 5 duced blue flowers which were rated higher than the flowers from the peat and none substrates. When the flowers were ranked for customer appeal, blue 4 flowers were preferred (Fig. 2). Customer Appeal Rating As AlSO4 rates increased, the flower color was rated as more blue and con- 3 sequently appeal ratings also increased. 0 AIS04 The clay amendment treatments had the highest color and appeal ratings, with 2 6 AIS04 the clay with high AlSO4 combination 12 AIS04 rated highest overall. The pH varied slightly between 1 6.63 and 7.02 for the different sub- strate treatments, and was significant. However, we hypothesize the differenc- 0 es in soilless substrate solution pH were Clay Peat None due to discrepancies in the dolomite Figure 2. Effect of substrate and aluminum sulfate (AlSO4) on customer and aluminum sulfate rates. appeal rating of hydrangea Endless Summer® flowers 30 ▲ 28 APRIL 2010 ▲ DIGGER 2011 OAN NURSERY GUIDE DEADLINE MAY 3, 2010 Don’t miss this once-a-year ry o mukiede urseeices tG a ! opportunity to keep your message oppo 1 Ond NanNand s rrv ject a success front of the decision makers who in fr 201 FiA pl ts ss or p o are responsible for Oregon green industry sales of nearly $1 billion. ind sine your bu This Th key reference tool reaches more mo than 7,000 buyers and offers a comprehensive selection of Northwest plant material, N services and supplies. se Targeted display advertising T along with listings provides G uide.com year-round exposure. e: www .Nursery lin Search on Y RESERVE YOUR SPACE TODAY! For Display Advertising Contact Chris Sweet at firstname.lastname@example.org. 800.342.6401 Listing Information Contact Debbie Hopkins at 503.682.5089 email@example.com. www.oan.org ▲ INTO THE BLUE Harmony Hill Hydrangeas Acknowledgements: We would like to thank Marta Mielcarek, Jackson Kowalski, and Kim Phillips for assistance, Bailey Nurseries, Inc for providing plant material and North Pacific for pro- viding the clay aggregate from Western Pozzolan Corporation. Additional Reading: • Ball, V. 1991. Ball Red Book: Greenhouse Growing. Geo.J. Ball Publishing, West Chicago, IL. • Handrick, K.A. 1997. “Production of Blue Hydrangea Since the variability of substrate pH of this would be the possibility of a Flowers Without Aluminum was not great, it likely did not affect chemical interaction between injected Drenches.” Communications in flower color or growth. The mean AlSO4 and liquid feed. An easy solution Soil Science and Plant Analysis height (22.6 inches), mean width (35.7 to this problem would be to incorporate 28:1191-1198. inches) and mean growth index (90.8 the granular form of AlSO4, controlled • Opena, G.B. and K.A. cm.) was not significantly different release fertilizer or both. Williams. 2003. “Use of between treatments, meaning that the Aluminum availability is directly Precharged Zeolite to Provide substrate amendments and aluminum responsible for the production of blue Aluminum During Blue sulfate rate did not affect plant growth. hydrangea flowers. Results demonstrat- Hydrangea Production.” ed that pozzolan clay is one method Journal of Plant Nutrition Conclusions that can be used to produce enhanced 26:1825-1840. The incorporation of pozzolan clay, blue sepal color in container-produced • Stoven, H.M. and J.S. in addition to AlSO4 in the substrate, hydrangeas. Nursery growers who Owen. 2008. “Comparison assists in changing of hydrangea sepals observe poor growth from low substrate of Substrate Amendments to a blue color even at high pH levels pH or have difficulty achieving blue for the Adjustment of without negatively affecting growth. hydrangea sepals could successfully use Hydrangea (Hydrangea This will give more leeway in the pro- an amorphous aluminosilicate macrophylla (THUNB.) SER duction of blue hydrangeas, allowing clay (approximately 10 percent alumi- ‘Bailmer’, Endless Summer® for the desired flower color without the num) to amend their substrate, thus Flower Color.” SNA Research complications of maintaining a low pH. alleviating these issues. Conference 53:30-33. If reoccurring issues with aluminum availability and flower color occur, the Jim Owen is an assistant professor of evaluation of growing practices other nursery crops at Oregon State University than pH management may be war- and the North Willamette Research and ranted. Although we found that conven- Extension Center in Aurora, Ore. He tional substrate components (i.e. bark, can be reached at jim.owen@oregon- peat) do not appear to affect aluminum state.edu. Heather Stoven is a research availability, there are other areas of pro- assistant at the North Willamette duction that can. Research and Extension Center in Fertilizer programs can interfere Aurora, Ore., and can be reached at with aluminum availability; an example Heather.Stoven@oregonstate.edu.” 30 APRIL 2010 ▲ DIGGER
"Into the blue"