POWDER KEG®, CADDO SUGAR MAPLE;
Lengthy Adventure to Develop a Superior Landscape Tree.
Carl E. Whitcomb, Lacebark Inc. Stillwater, OK
When I arrived at Oklahoma State University in August 1972, I found what appeared to be some severely stunted tree seedlings in small containers. I was told they were two year old Caddo sugar maple seedlings and even though only 12 to 16 inches tall, were growing exceptionally well. The seedlings, from my perspective and experience, were --- well, depressing. Soon an assortment of stories were shared about the grandeur of Caddo sugar maples in the fall and their toughness in withstanding heat and drought and that it would be a great tree to incorporate into my research. As experience was gained with Caddo’s – I was hooked. But few trees produced seeds and those collected season after season, had little or no germination and the few that did germinate ended up as runts with little or no vigor.
Eastern sugar maple, Acer Saccharum, are native in Eastern Oklahoma but are rarely grown in central and western parts of the state because they do poorly. Heat, drought, drying winds, and alkaline soils were listed as culprits. So when an opportunity to obtain over two hundred bare root seedlings 3 to 4 feet tall from Ozark Nursery in spring 1974, I was ready. The seedlings were planted in three adjacent rows and were watered in several times by hand and all received a moderate rate of fertilizer. Drip irrigation was provided for 1/3 of each row. Drip irrigation plus mulch was provided for 1/3 of each row, while the remaining 1/3 of each row was neither irrigated nor mulched. With 25 trees in each of the three replications, I expected to learn something about planting and growing sugar maple seedlings.
And I did. All of the seedlings survived and looked good during April and May. But with the arrival of heat and desiccating winds of summer, leaves of all of the seedlings began to yellow, then blacken along the margins and developed leaf tatter. Within three to four weeks, trees turned from attractive to ugly. Trees with drip irrigation or drip plus mulch were just as ugly as those with no irrigation or mulch. Yet, all of the seedlings survived. I included the statement in my notes “these trees have a lousy top but a very good root system.” The file on eastern sugar maple seedlings was put to rest for the next 36 years but interest in the amazingly tough Caddo with spectacular fall colors continued.
Most years there were so few seeds from Caddo trees to collect, so they were mixed together, cleaned and planted only to have low germination and only a few with even modest vigor. But 1986 was an exception as Caddo seed population was higher. I collected seed from 14 trees across the state, kept the seeds separate in hopes that a superior parent could be found. And, indeed, seeds from one tree in Stillwater germinated better and produced a higher number of stronger seedlings from all others. That became my primary seed tree until it was destroyed in a storm in 1996.
Seeds collected from this primary Caddo seed tree in 1994 were especially good, resulting in 28 exceptional seedlings. These were grown first in containers, then in the field for a number of years. But with each year’s evaluation, one to several seedlings would be culled and discarded until only five remained. To clear the field for other research, the five were transplanted to a partially shaded lawn area south of the Lacebark main office and evaluations continued. In all aspects of desirable tree form, dark green foliage color, resistance of leaves to heat, wind and drought but most spectacularly, fall color, one tree consistently stood out. This most select tree would remain dark green all summer and into very late fall, then after nearly all other trees around had lost their leaves, ---- Pow--- an explosion of color
beginning at the top and progressing slowly downward, first as shades of yellow and light orange, then to dark oranges and reds (Figure 1). And the spectacular color continued for two to three weeks or longer, depending on the season. Thus the registered trademark name Powder Keg®.
But sugar maples are notorious for being difficult to propagate, especially from cuttings. And Powder Keg® was true to form. After a number of years of taking cuttings and using every trick in the book and beyond, the cuttings would root reasonably well, but, would not survive the first winter. I preferred to have the tree on its own roots but after hundreds of rooted cuttings but only one survivor, the idea of budding or grafting Powder Keg® onto some other species seemed worth trying. And, it was during this period when I recalled the study from 1974, and after several days, located the file and all the details.
The Oregon climate is ideal for growing an array of trees and other nursery stock and lots of trees are propagated by transferring a bud from a select parent tree onto selected seedlings. I contacted Keith Warren with J. Frank Schmidt Nursery near Boring, OR. He was interested and had tried budding a selection of Caddo onto Caddo seedlings, but growth was poor. I asked about budding a Caddo selection onto eastern sugar maple seedlings. He was concerned about performance of the eastern sugar maple root system. I related the results of my study from years ago and he agreed to give it a try. My hope was to get Powder Keg® seedlings two to three feet tall in one growing season following budding onto easterns.
Budwood from Powder Keg® in Oklahoma was shipped to Oregon in late July 2011. The budding proceeded ---- then it was wait and see! An email in September 2012 related that the buds were doing well. In October, another email also had photos of the budded trees with excellent growth, stem taper and branching. In one growing season the buds grew six feet or more and were excellent branched trees ready to be harvested bareroot and shipped back or Oklahoma or wherever they were wanted. The combination of a very heat and drought tolerant top that consistently yields spectacular fall color on a tough eastern sugar maple root system is adaptable to a wide geographic range. Even in eastern areas where eastern sugar maple foliage is affected in droughty areas or heat from parking lots Powder Keg® will shine. Hardiness is from zone 5 through 9.
It takes time to build up sufficient population of parent trees of a selection in order to bud enough seedlings to meet demand thus it will be a few years before significant numbers of Powder Keg® Caddo sugar maple trees are available. However, put Powder Keg® on your wish list, as it will be worth the wait.
2104 N. Cottonwood Road
Stillwater, OK 74075
Where Did That Originate? #1
Ground Pine Bark in Container Growth Media
Carl Whitcomb PhD, Lacebark Inc. Stillwater, OK
I first became interested in growing plants in containers is the late 1950’s. Placing productive field soil in containers worked fair at best, but only inside a greenhouse where water could be carefully monitored. Adding peat moss or other organic matter to the field soil was of little or no assistance. Adding sand was also of no benefit.
A search for answers in the library turned up the John Innes mix from the UK, introduced in 1934. One "potting compost" consisted of; "7 parts medium loam, by volume, 3.5 parts peat, by volume and 3.5 parts sand, by volume. To each cubic yard add 2 pounds of hoof and horn meal, 2 pounds superphosphate, 1 pound of sulfate of potash and 1 pound of chalk (calcium carbonate)". I used this mix in some early studies and it worked fair, but, again, only in a greenhouse.
During the 1940’s and 50’s, scientists at the University of California began searching for a more productive medium and one that could be used in containers out of doors. This work was summarized in Manual 23, The U.C. System for Producing Healthy Container-Grown Plants published in 1957. The primary U.C. mix consisted of 50% fine sand and 50% peat moss, plus there were pages of chemical additives described for specific crops. There was also a notation that redwood sawdust could be substituted for part of the peat. The success of this growth medium was directly related to the fact that in most areas of the near-desert west coast and desert southwest, it rains only when the irrigation is turned on, -- like being in a greenhouse. But the other practical problem was the weight, which added a great deal of shipping cost.
When I joined the faculty at the University of Florida in 1967, much of the plant production in containers throughout Florida was in a U.C. type mix. And with hand watering in greenhouses it was working fairly well. But, out of doors with the frequent rains common in Florida it was a disaster. Plant growth was poor; root rot diseases were rampant and seldom were roots found in the bottom half of the container.
Serendipity is a wonderful thing. In early 1968, I visited a number of nurseries in south Florida. It was mostly a get acquainted / find out what nurseries were doing kind of trip. At that point in time my experience with growing plants in containers consisted of lots of reading but growing only a modest number of plants while a student at Kansas State and Iowa State. But to the nurserymen I visited, I was viewed as an expert and they had lots of problems and needed answers. I tactfully tried to avoid answering the first few questions, and then quickly shifted to the correct answer ---- I don’t know, but will try to find out!
One particularly frustrated and outspoken nurseryman was George Behrens. He had spent considerable dollars over a number of years trying to grow Carissa grandiflora in containers. Carissa is a beautiful evergreen, low growing shrub with dark green leaves, white flowers and edible bright red fruits the size of a plum. It is native to a few Caribbean islands where it grows in deep sand and develops a deep taproot. I had heard from field growers that they could grow the plant but it would not survive transplanting. George was convinced that the plant could be best grown in containers and that the problem was with drainage. Wooden benches had been built on which plants in containers were placed, but that did not help. The containers he was using had drain holes only in the flat bottom, so he theorized that the wood against the plastic bottom sealed off water escape. His latest try consisted of using heavy welded wire panels suspended about 20 inches above ground. Wire spacing allowed containers to be placed and held securely and nothing touched the container bottom. No improvement.
By the time I left Mr. Behrens, I had 40 Carissa plants in one gallon containers, all showing about the same level of symptoms. My plan was to divide the plants into groups and try drenching with several concentrations of the new systemic fungicide called Benlate. When I got back to Gainesville, it was nearly dark. As I unloaded plants from the old station wagon, some were placed on an empty corner of a greenhouse bench, but there was not enough room so nine plants got placed on the floor. The nine plants were apparently in someone’s way so got pushed back under the bench and out of site. All plants in all greenhouses got watered by hand every day by the greenhouse crew under strict supervision of an old English gardener.
The study had six treatments: a zero fungicide control and five levels of Benlate applied as a drench and five replications. The one extra plant was about to crash and was set to one side. There were no detectable benefits from any fungicide treatment after two weeks, and after three weeks all of the plants looked worse than when they arrived. I took two plants to the disease diagnostic lab to look for pathogens. I was taking notes and photographs when I remembered that I could only account for 31 of the original 40 plants. When I located the nine plants under the bench, they were very dry, but all looked great as they had not been watered in three weeks. I moved all 40 plants to an empty greenhouse and placed a big sign --- Do Not Water! Within a week there was a dramatic improvement in the 31 plants I had considered throwing away. Mr. Behrens was right; drainage was the problem, but drainage from within the container, not drainage around the outside.
Clearly the Carissa plants needed a more porous mix, but since they were in a mix of about 50% peat and 50% sand, what could be added to provide even better drainage? I was teaching a class called Nursery Management and Production at the time and shared what had happened with a very inquisitive group of about 20 students. I mentioned that the U.C. manual had noted that redwood sawdust could be used for at least a portion of the peat, but getting redwood sawdust to Florida was not practical. Adding ground pine bark to the mix became part of the class discussion. There were reports that pine bark was toxic due to the high levels of phenol compounds and tannic acids. But there was no supporting evidence of this problem, just speculation. One student said his dad worked for a mill near Jacksonville and he could get bark if I wanted to do a study. The pulp mill at that time burned huge quantities of pine bark to get rid of it. Arrangements were made and a pickup load was hauled to Gainesville. Coarse particles were screened out and the rest used as part of several mixes for containers. Plants in mixes with pine bark grew better than those with just peat and concrete sand and far better than those that contained sandy field soil. In addition, only those containers with pine bark had white roots all the way to the bottom. Clearly plants grew much far better with the addition of pine bark (Figure 1), but some species developed chlorosis and other signs of micronutrient deficiencies. A possible solution to one piece of the puzzle of growing plants in container had been identified, but much work with improved nutritional additives was clearly needed.
We published our findings in an Ag. Experiment Station Report in 1971 and a second report in 1972. We also shared our findings with nurserymen during an open house in 1971 and with variations in 1972. One look at the plant response and the interest by nurserymen in adding ground pine bark as part of the container growth medium skyrocketed. Over the years, pine bark would go from being burned as an unwanted byproduct to being in short supply due to the high use. Scientists and nurserymen elsewhere may have been studying using ground pine bark as part of container growth media at this same time, but these two studies were where it began in Florida.
Figure 1. Growth of Carissa grandiflora with a container growth medium of 50% peat and 50% concrete sand (left), versus a mix with 40% ground pine bark, 30% peat and 30% sand (right). Immediately upon sharing this plant response with nursery owners, pine bark went from unwanted to where can I get it!
1. Whitcomb, Carl E. 1971. Effects of Container Sidewall Porosity, Growth Media and Presence or Absence of Micronutrient Fertilizer on Root and Top growth of Carissa grandiflora, var. Boxwood Beauty.Univ. of Florida, Institute of Food and Agricultural Sciences, Research Report. Pages 23-25.
2. Whitcomb, Carl E. 1972. Effects of Watering Frequency, Growth Media and Nutritional Conditions of Stock Plants on Growth and Quality of Carissa grandiflora var. Boxwood Beauty. Univ. of Florida, Institute of Food and Agricultural Sciences, Research Report. Pages 30-31.