There has been a beautiful explosion in new coreopsis varieties lately. Flash back 10 years and the color offerings would have been yellow, yellow or yellow.
Now, designers are delighted to have their artistic palettes loaded with garnets, oranges, corals, pinks and stunning bicolors. These new annual varieties are complex hybrids that have been placed in series, depending on their height and landscape use. These are great component plants, adding a new color range for the container market.
But different varieties require different culture. We have made an effort to produce compact plants that need minimal pinching, (once for full plants), that will please consumers with their easy care and self-cleaning habit. Terra Nova Nurseries’ new grower, Conor Carey, is on board to suggest the perfect tools to produce the perfect plants in our Punch, Lemonade and Pie series (see “Coreopsis To Consider” sidebar for descriptions of the three series).
Rooting of unrooted cuttings is relatively simple and will usually finish a 72-cell tray in two weeks, possibly three if under winter conditions. Because these are long-day plants, propagation is best accomplished under short days, whether they are provided by natural day length or with black cloth.
Mist is usually only required for the first five to seven days, depending on environmental conditions. Rooting hormone is not required, but is beneficial, and a rate of 500 ppm IBA works well. I prefer to use K-IBA because it is easy to prepare and store, not to mention a huge labor savings when sticking by using the spray-drip down method.
If it is not possible to give short days during propagation, Florel is beneficial. Apply at 200 parts per million (ppm) once during propagation to remove or abort flowers and promote vegetative growth. This is best done when the roots reach the edge of the cell, because Florel can inhibit rooting. Be careful not to get any into the soil.
Begin applying 100 ppm nitrogen after roots develop. Avoid using excess ammoniacal nitrogen, especially while growing under cool or dark conditions, as stretching can become an issue.
Finish time from liner to 4-inch pot is four to six weeks, or six to eight weeks for a 6-inch or gallon-sized pot. Coreopsis is an obligate long-day plant and, therefore, requires short nights in order to flower. This can be accomplished by using night interruption between 10 p.m. and 2 a.m. during natural short days.
However, it may be beneficial to bulk the plants under short days for the first one to two weeks before switching to long days. This is not necessary but helps keep plants compact and well branched.
Pinching is beneficial and will help give a full, rounded plant. Timing of the pinch is best around one to two weeks after planting, or once roots reach the edge of the pot. Florel is effective and can take the place of a pinch, but will slightly delay flowering. One application at 400 ppm or two at 200 ppm have proven effective to aid in branching. These rates are for growing conditions in the Pacific Northwest and may need adjusting depending on drying time, season or other factors. If growing in larger containers or if the plants get somewhat leggy, a second pinch may be needed.
Media, Pests & Diseases
Coreopsis prefer a well-drained media, and it is important to let them dry down between irrigations to maintain proper wet-dry cycles and avoid root and crown rot issues. Fertilize at a rate of 200 ppm nitrogen and maintain a target EC of 2.0 mS/cm, but alternate with 15-0-15, especially during winter months to prevent soft growth. A pH of 5.5 to 6.8 is ideal. A pH above 6.8 can cause iron deficiency symptoms.
The most common pest problems are aphids and thrips, especially while flowering. Use preventative control strategies for thrips, because they are more difficult to control once plants are flowering. Rust and powdery mildew are other possibilities, but with proper airflow and watering practices, it can be easily avoided. Preventative control for these two pathogens can be achieved by using a spray in the strobilurin class of fungicides, particularly Heritage at label recommended rates and intervals. This works well in preventing and combating the various fungal pathogens that can affect coreopsis.