6/27/2013
Rex Begonias: King of the Shade
Randy Uhl
Few plants can provide dazzling color and intriguing leaf shapes in a seemingly endless array of combinations. Shadow King Rex Begonias from GreenFuse Botanicals, with their stunning array of colors and varying leaf forms, can brighten up any shady location, even flourishing in deep shade environments. These traits make Shadow King appealing to anyone looking for a colorful, low maintenance plant for indoor and outdoor shaded locations. For the greenhouse grower, their culture is less problematic than with many older types, and the crop time is more consistent and relatively uniform within the series.
pictured: Rex Begonia Shadow King Green-Pink Tips
The origins of modern Rex Begonias include multiple native species found across the globe in tropical and subtropical understory environments. As such, their primary requirements are warm temperatures, shade and humidity. The Rex Begonias of old were primarily suited as potted plants for indoor use, but newer hybrids such as Shadow King are equally at home in a shaded garden or patio setting, while still being well-adapted for houseplant use. The new 2013 introductions include Cool White, Green-Pink Tips, Pink and Red Lava.
Crop planning from cell packs
Pot size: Plants per pot (ppp) Crop Time (weeks)
4 in. (10 cm) 1 ppp 7 to 9
6 in. (15 cm) 1 ppp 10 to 13
Temperature requirement: The optimum growing temperature is 63 to 65F (17 to 18C) night temperature with a minimum of 68F (20C) days. Growing below this range will delay the finishing of the crop, adding weeks to the overall production time.
Media and pH requirement: The fine root system of begonias won’t thrive in continuously saturated soil. Allow the medium to dry slightly between irrigations during the low light winter months for best root development and to maximize plant growth.
When producing finished plants during the spring and summer, Rex Begonias require damp soil conditions. Don’t allow plants to wilt or leaves may become damaged, resulting in brown margins.
Rex Begonias grow well in a broad pH range, but prefer more acidic media; pH 5.7 to 6.2 is optimal in peat-lite soils.
Fertilizer requirements: Feed with a balanced fertilizer at 100 to 150 ppm Nitrogen. The optimal soil EC should be 0.8 to 1.2 milimhos in a peat-lite mix. Even when feeding at these low rates, make sure that salts don’t increase above 1.3 milimhos or damage may occur to roots and leaves.
Light level/shade level: Grow in a lower light level the first two weeks after transplant to allow for proper adjustment to the environment. Light levels of 800 to 1,000 foot candles are ideal. After the first two weeks, grow at 1,500 to 2,200 foot candles. No shading is required when producing Rex Begonias during the winter months or in regions with naturally occurring lower light levels. For most areas of the country, consider shading after April 1 at 30% to 50% and then at 65% to 75% from mid-June through the summer. Light levels higher than this will stunt the plant, even if you don’t see burn.
Growth regulators: PGRs shouldn’t be necessary. Strawberry Lime, Rothko and Moonlight may require some Cycocel applications at 750 ppm to tone plants for a high-quality finish. A Bonzi drench at 1 ppm would also hold plants and tone them for
shipping.
Disease and insects: Insect pests are an infrequent problem, but can include aphids, mites and mealybugs.
Botrytis and Pythium/Phytophthora—Provide good air movement around plants to help avert foliar diseases. Incorporate preventative fungicide applications. Spray on a regular schedule to guard against Botrytis and Powdery Mildew during damp/low light times of the year. Botrytis will show as small brown dots on leaves and will spread very quickly from affected plants. Powdery Mildew will appear as a fine white powder on the leaf surface.
Exercise care in transplanting rooted liners so as to keep them even with (not below) the new soil line, as the crown of the plant shouldn’t be covered with soil. A single fungicide drench targeting water molds is suggested at one week after transplant and will suffice for the duration of the crop.
GT
Randy Uhl is technical sales support for Green Fuse Botanicals in Santa Monica, California and Henry F. Michell, Co. in King of Prussia, Pennsylvania.