Culture Report: Rex Begonia Shadow King Series By Jim Devereux

The first true series of Rex begonias brings consistency, ease of care and vivid colors to the market for year-round sales — from spring to the holidays.

As the story goes, Rex begonias were introduced purely by accident as a stow away in the sheath of an orchid bound for England in the 1850s. The Shadow King series, however, is no accident. Bred over many years, the Shadow King is the first, and only, Rex series.

While there are many begonia Rex programs, they are collections of begonias rather than a true breeding program. A “series” nomenclature translates to uniformity throughout the growing process. Traditional Rex programs are made of selections from many different breeders or, more commonly, random sports from many different parent lines. The consistency of the Shadow Kings is what allows true commercial production on a predictable schedule.


The Shadow King series is a rhizomatous — storing water within their stalks — making them ideal for the negligent consumer. The predictable wet/dry cycle from a homeowner is quite acceptable to this versatile series. A shade plant that will thrive in the front porch container as well as the corner of a living room or as a festive table top decoration. Their strong basal branching keeps the overall height down, while pushing a well-rounded habit.

‘Shadow King Cherry Mint’

This seven-color series can easily be positioned for year-round sales with both spring and holiday finished containers. Shade combination components have become predictable and a bit stale. The crisp colored leaves of Black Cherry or Wintergreen promote interest and contrast to a spring container. Add value for the consumer by dropping the short term beauty of a poinsettia and adding the long-lived Lava Red to the holiday assortment. The bright red heart of Rose Frost or Cherry Mint shine brighter than a Valentine’s Day mini rose.


The Shadow King series is available as a leaf from our friends at Innova Plant, Costa Rica, or as a quality rooted liner from Pell Greenhouse, Michigan and Davis Floral, Georgia.

Leaf rooting requires high relative humidity above 70 percent. Leaves should be placed on the cell facing the same direction to avoid as much overlap as possible, reducing the occurrence of botrytis. A K-IBA foliar application of 250 ppm has proven to be effective in generating roots more quickly than without.

Additionally, K-IBA applications may be used on day one and day two from stick for increased benefit. Fungicidal application should also be provided within 48 hours of sticking. Pageant works well at 6 ounces per 100 gallons. It is imperative to maintain a media temperature of 74 to 76° F via bottom heat until root growth is apparent. Below these temperatures will cause additional crop time and probable loss. While rooting a Shadow King is not difficult, it is time consuming at nine to 10 weeks.

The Shadow King series is well suited for 1- to 2.5-quart production. EC levels should be maintained at 1.0 to 1.2 with a pH of 5.8 to 6.2. Temperatures post-transplant should remain on the warmer side, with 68° F day and 64° F night. Dropping below will not only lengthen production time, but much colder can initiate a state of dormancy within Rex begonias adding many
additional weeks to finish.

‘Shadow King Rose Frost’

The Shadow King series, like all Rex begonias, prefers lower light levels; ideally situate the pots in a shaded area under 1,500 foot-candles. High light may act
a growth regulator, stunting the crop. Plant growth regulators are very rarely required; if the plants are ready before the season is ready for them, cooling or dry downs will allow for long holding periods. For the Shadow King series, plan on total time from transplant to finish in 1 quart at nine weeks and 12 to 13 weeks for 2.5 quart.

More information on the Shadow King series and all other innovative genetics may be found at

Jim Devereux

Jim Devereux is vice president of Green Fuse Botanicals. He can be reached at