Most of the focus on mixed containers has been on their attractiveness at the time of sale. How the combination looks at retail often overshadows concern over how the combination will look two months from then. In other words, how well does your mixed container design endure in the long term?
When preparing mixed containers, we put together the right combinations of plants, balancing size, shape and color. They look great when they leave our greenhouses or garden centers. Customer satisfaction is — and should be — top priority. However, how will the mixed container look after it has been in the buyer’s garden for months? While it’s important to consider aesthetics at the moment of designing mixed container comb-inations, other factors regarding plant mix compatibility should also be taken into account.
At the Learning Gardens of the Chadwick Arboretum at The Ohio State University (OSU), we are working to answer some of these questions with trials. We launched our first trial in spring 2003. In 2006, we conducted our fourth mixed container trial and evaluated a series of combinations throughout the summer and fall.
We evaluate each species/cultivar as it grows in the combination cont-ainer and also evaluate each species/cultivar growing as a single species container (called a monoculture container). By conducting this trial over time, we aim for a database of information that will be used by growers in designing combinations.
The participating companies (see sidebar, below) provided the combination designs. The OSU Custom Combinations used plant material from the participating companies. Individual cultivars (components of the combinations) were grown as monocultures in separate containers.
Varieties were transplanted May 30, 2006. Monocultures were placed in 12-inch pots; combination plantings were placed in 16-inch containers. The containers were located in an outdoor, full-sun location. Varieties were planted in Metro-Mix 300 growing mix.
Rooted cuttings were treated with a Plantshield drench just prior to transplanting; there were up to three reapplications for monocultures and three for combination plantings. Containers were watered as needed with a drip irrigation system. The 16-inch mixed containers were given 4.23 oz. and the 12-inch monoculture containers were given 3.17 oz. of Osmocote 16-9-12.
The geraniums in the monoculture pots were deadheaded once. No pruning or deadheading was performed on any of the other combinations. Lower temperatures in the beginning of the season slowed plant growth; however, higher temperatures increased growth mid season. Rainfall was moderately above normal.
As far as pest and disease occurrences, aphids were found on calendula in design OSU-4 and Japanese beetles were on var-ious plants. Some powdery mildew was found, mainly on verbena. Some calibrachoa, petunia, leucanthemum and ivy geranium experienced iron deficiency. The deficient calibrachoa, petunia, leucan- themum and ivy geranium were treated twice at 1-week intervals with iron chelate foliar spray. All plants were fertilized with Greencare 20-20-20 at a rate of 300-ppm nitrogen on June 29, July 5 and July 18, 2006.
The trials director and trials manager evaluated plants on a monthly basis July 19, Aug. 11 and Sept. 27, 2006. A 14-member team of Master Gardeners conducted monthly consumer preference evaluations. Consumer preference evaluated overall appearance and aesthetics of the containers on a personal preference basis.
The OSU performance evaluations considered the balance/dominance of the containers as a whole and each individual plant’s contribution to the design. Balance/dominance is an index used to describe the dominance of a particular component of the mix (one plant may be “taking over”). This index is not related to aesthetics: A very balanced combination may not look appealing and vice versa. Ratings were based on a 1-5 scale: 1 = poor/not acceptable, 2 = fair, 3 = good, 4 = very good, 5 = excellent.
A complete record of past and present trial results, tables and photoscan be seen at http://flori  culture.osu.edu/trials/MixedPage.html. The top combinations in the 2006 OSU Mixed Container Trial are listed here:
OSU Evaluations. The best-performing combinations with an overall balance/dominance season average in the range of 4.67-3.75 (on a 5-point scale) were Ecke-6, Ecke-10, Bodger-4, OSU-4, Dummen-10, Ecke-11 and Ecke-7. Also performing very well with ratings in the 3.67-3.50 ranges were Dummen-14, Ecke-5, Bodger-7, OSU-7, Dummen-5, Dummen-9, OSU-1 and OSU-13.
Consumer preference. The best-performing combinations with an overall season average in the range of 4.12-3.77 (on a 5-point scale) were OSU-16, OSU-7, OSU-17, OSU-1 and Ecke-9.
The monoculture pots were trialed separately to the mixed combinations. All the plants that were part of the mixed container designs were also separately trialed in 12-inch monoculture cont-ainers. Here are the top cultivars in the monoculture containers:
OSU evaluations monoculture containers. The best-performing monocultures with an overall season average in the range of 5-4.58 (on a 5-point scale) were agastache ‘Acapulco Orange’, coleus ‘Burg-undy Wedding Train’, coleus ‘Fright Night’, ipomoea ‘Sweet Caroline Red’, agastache ‘Acapulco Salmon Pink’, ipomoea ‘Sweet Heart Purple’, ipomoea ‘Sweet Heart Red’, geranium ‘Pinnacle Dark Red Improved’, coleus ‘Molten Lava’, osteospermum ‘Crescendo Primrose’ and ipomoea ‘Sweet Caroline Bronze’.
Also performing very well with ratings in the 4.50-4.25 range were bracteantha ‘Brilliance Yellow’, ipomoea ‘Sweet Caroline Light Green’, begonia ‘Gumdrop White’, petunia ‘Surprise White’, coleus ‘Big Blond’, petunia ‘Sweet Surprise Purple’, diascia ‘Miracle Pink’, ipomoea ‘Sweet Heart Light Green’, petunia ‘Tiny Tunia Pink’, salvia ‘Stampede Cherry’, geranium ‘Pinnacle Violet Rose’, geranium ‘Survivor Blue’, pentas ‘Bahamas Pink’, petunia ‘Sweet Surprise Blue Sky’, pentas Á ‘Bahamas Lavender’, scaevola ‘Purple Fan/Fan Dancer’ and impa tiens ‘SunPatiens White’.
Consumer preference monoculture evaluations. The best-performing monocultures in the consumer evaluation with an overall average score of 4.75-4.17 were scaevola ‘Purple Fan/Fan Dancer’, petunia ‘Sweet Surprise Purple’, diascia ‘Miracle Pink’, coleus ‘Burgundy Wedding Train’, ipomoea ‘Sweet Heart Purple’, coleus ‘Molten Lava’, agastache ‘Acapulco Salmon Pink’, impatiens ‘SunPatiens Orange’, begonia ‘Gumdrop Rose’, verbena ‘Tropical Breeze Pink’ and impatiens ‘SunPatiens White’.
Also performing well with a score of 4.16-4.02 were petunia ‘Sweet Surprise Blue Sky’, impatiens ‘Little Lizzy Orchid Butterfly’, impatiens ‘SunPatiens Magenta’, petunia ‘Sweet Surprise Purple Vein’, petunia ‘Tiny Tunia Plum Ice’, petunia ‘Surprise Kardinal Vein’, petunia ‘Tiny Tunia Pink’, pentas ‘Bahamas Lavender’, begonia ‘Gumdrop Mandarin’ and osteospermum ‘Summertime Sun Pink’.