Doronicum ‘Little Leo’ delivers an abundance of cheerful, semi-double, daisy-like, bright-yellow flowers to the early spring landscape. With its ease of production and compact habit, many growers use this cultivar in early spring perennial programs where there is typically not a lot of breathtaking color available.
Doronicum, commonly called leopard’s bane, is considered a cool-season perennial and does not tolerate the extreme summer heat found in much of the United States. In many locations, it will go dormant during hot summer weather. ‘Little Leo’ is most commonly produced in USDA Hardiness Zones 4-7 and AHS Heat Zones 12-5. When produced in warmer zones, it is often treated as a cool-season annual, as it succumbs to summer heat and humidity. This doronicum is commonly used in containers or patio pots, mass or border plantings, rock gardens, woodland plantings or as cut flowers.
Doronicum ‘Little Leo’ is easily propagated from seed. Growers commonly sow 2-3 seeds per cell in 288- or 220-cell plug trays and cover the seeds lightly with germination mix or medium-grade vermiculite. The covering is optional, but it helps maintain a suitable environment around the seed during this phase and will improve germination uniformity.
The seed flats should be moistened and moved to a warm environment where the temperatures can be maintained at 68-72º F for germination. Many growers utilize germination chambers during this stage to provide uniform moisture levels and temperatures. Seedlings will emerge 14-21 days after sowing.
Following germination, reduce moisture levels somewhat, allowing the growing medium to dry out slightly before watering to help promote rooting. Fertilizers are usually applied once true leaves are present; apply 100-ppm nitrogen every third irrigation or 50 ppm with every Á irrigation using a balanced, water-soluble source. When plugs are grown at 68-72º F, they are usually ready for transplanting in 6-8 weeks.
For container production, ‘Little Leo’ is suitable for 1-qt. to 1-gal. containers. When planting large containers, plant two plugs per container to properly fill out the pot. Doronicum performs best when grown in a moist, well-drained medium with a slightly acidic 5.5-6.2 pH. Most commercially available peat or bark-based growing mixes work well, provided there is adequate drainage. When planting, the plugs should be placed so the original soil line is even with the surface of the new container’s growing medium.
Doronicum can be grown using moderate fertility levels. Growers using water-soluble fertilizers should apply 150- to 200-ppm nitrogen as needed or feed with a constant liquid fertilization program using rates of 75- to 100-ppm nitrogen with every irrigation. Growers commonly apply time-release fertilizers as a top dress onto the media surface using the medium labeled rate or incorporate fertilizers into the growing medium prior to planting at a rate equivalent to 1 lb. of elemental nitrogen per yard of growing medium.
Doronicum require an average amount of irrigation, as they do not tolerate overly wet or dry conditions. Root zones that remain waterlogged tend to get root-rot pathogens, which can quickly lead to crop losses. When irrigation is necessary, water plants thoroughly then allow the soil to dry slightly between waterings.
‘Little Leo’ has a naturally compact growth habit and will usually not require height control strategies. Under certain growing conditions or under high plant densities, it may be necessary, although not common, to use PGRs. In the northern parts of the country, I recommend applying a tank mixture of B-Nine (daminozide) at 2,000 ppm plus Sumagic (uniconazole) at 3 ppm. Apply PGRs as the flower stalks are just beginning to elongate above the foliage. One to two applications applied seven days apart should provide adequate height control.
‘Little Leo’ can generally be grown free of insects and plant pathogens. Occasionally, aphids, spider mites and thrips may appear and cause only a minimal amount of crop injury. These infestations rarely require control strategies. The primary diseases growers should watch for are Botrytis, powdery mildew and crown/root rot caused by the pathogens Pythium and Phytopthora. None of these insects or diseases requires preventative control strategies. Growers should have routine scouting programs to detect their presence early and determine if and when control strategies are necessary.
Doronicum ‘Little Leo’ is easy to force into bloom and is most commonly produced for early spring sales. Leopard’s bane has an obligate cold requirement to flower. I recommend vernalizing doronicum as large plugs (72 cell or larger) or in the final container for a minimum of nine weeks at 35-44° F. After the cold requirement is achieved, plants can be grown at any day length, as they are day-neutral plants. The length of the photoperiod does not have any effect on the time to flower or the number of blooms produced.
The time to bloom after vernalization is a function of temperature. Grown at 63° F, ‘Little Leo’ will take approximately seven weeks to reach flowering, while plants grown at 58° F will flower in nine weeks. Though producing doronicum at cooler temperatures increases the time to flower, it will improve the plants’ overall quality characteristics, such as the color intensity of the foliage and flowers.
To obtain full, flowering plants for spring sales, it is beneficial to plant them during late summer of the previous season. I recommend transplanting plugs into the desired container during mid to late August, bulking them up before winter, overwintering them and forcing them to bloom in early spring. Many growers successfully produce flowering doronicum by transplanting large, vernalized plugs in the late winter and forcing them at 60-65º F for approximately seven weeks.
Doronicum ‘Little Leo’ is available to the industry as seeds, plugs or finished containers. The seed is supplied by Ernst Benary of America, www.benary.com , and is available through many seed distributors. Plugs can be acquired from many perennial plug producers or plant brokers; finished containers may be purchased from many reputable companies across the country.