October 2002

Recycling the Rex Begonia By Rick Schoellhorn

There is always a strange sense of déjà vu inworking with new crops, remembering an earlier time where you worked with aplant and then seeing it resurface on the market again. That’s the way it iswith rex begonias. When I was first studying horticulture at Cal Poly San LuisObispo in California, one of my class reports was written on “RadiationMutation Breeding in Rex Begonias.” I remember being fascinated by theidea that mutation could give these plants their vivid leaves of silver andpurple and red. This was right around the time the first microwave ovens werecoming out, and popular opinion held that they would cook your brains if youstood near one while it was in operation. While that fear was apparentlyunfounded (I live in Florida now anyway, where UFO’s and ballot counts are agreater concern than microwaves), it is true that the diversity of leaf colorsand shapes in the rex begonia owe a lot to being irradiated with X-rays. (As aside note, this same kind of “mutation breeding” is what gives us somany poinsettia cultivars to choose from. Radiation mutation is a commonplant-breeding tool that helps in some cases to jumpstart new cultivars morequickly than traditional breeding techniques).

Rex begonias are not new by any stretch; however, they arebeing re-marketed and with some really nice results. In the past, the marketfor these plants was primarily as houseplants, but now we are thinking biggerthan that and rex begonias are surfacing as an annual shade groundcover or asthe foliage accent in shade mixed containers. There are also some new cultivarswith better tolerance of high heat and humidity, and conversely, tolerance oflow humidity. So there’s lots of potential for marketing these plants ashigh-dollar annuals in the gardening season and carrying them over into thewinter houseplant market as well for novelty sales and arrangements withseasonal plants.

Rex Cultivation

While the extremely patient grower can produce rex begoniasfrom seed, they are produced as vegetative liners so that color forms remainstable in production. In general, the rex group of begonias, prefers cool,moist conditions with high relative humidity. If you have good luck withtuberous begonias or reiger begonias then you’ll probably do okay with rextypes as well. The humidity seems to be a key factor in getting good leaf sizeon plants. Like a lot of begonias, rex hybrids do poorly in heavy, cold, soilmixes, so avoid both heavy soils and too much water while getting plugsestablished. They prefer lower light levels in production, as their leavesscorch in bright sun very quickly.

Rex begonias are sold in all pot sizes from 2 1?4-inchto specimen hanging baskets and color bowls. Since the growth habit for rexbegonias is mounding, they are generally pretty compact and don’t require anygrowth regulators in production. Some growers are producing these plants in 8-and 10-inch hanging baskets for value-added patio sales, and hanging basketsseem to suit the plant’s requirement for good air circulation as well. Whenusing rex begonias in mixed containers, it is probably best to start with a4-inch plant, as this size begonia stands a better chance of competing withmore vigorous annuals in mixed containers. Remember that lower light and coolertemperatures will really bring out the color in rex begonia leaves, and highlight will cause all colors to fade.

Trial Results

We have been trialing rex begonias to evaluate them for heattolerance, and while the majority of plants simply cannot take our heat, thereare some cultivars that showed much better quality under Southern summerproduction. What we are hoping for is something to fill the niche of hosta inthe Deep-South landscape, as hostas have notoriously poor performance underhigh temperatures. We have seen great winter hardiness in a lot of begoniaspecies, and for us, it is finding heat tolerance that is the key to a goodperennial begonia.

The results of our trials showed that outdoor production isrisky, the leaves of these begonias are very fragile, and a hard rain can tearthrough the foliage. Also, our evening rain patterns increased bacterial leafspot on all cultivars, but the plants that still did well under theseconditions should show additional vigor under optimal production Áregimes. In this research, we trialed 37 cultivars. Our top selections based onsummer trialing in Florida were:

‘Chocolate Man’, Milestone Agriculture. Silver and brown foliage withbright pink flowers in fall. A great fall combination of colors and exceptionalvigor and leaf spot resistance.

‘Maui Mist’, Proven Winners. Striking pink-purple and silver-tonedleaves with deep, blackish green edges, vigorous.

‘Snow Queen’, Milestone Agriculture. Leaves are predominantly brightsilver, strong growth, disease-tolerant.

‘Fairy’,Milestone Agriculture. Predominantly silver-toned foliage.

‘Chicago Fire’, Proven Winners. Purple and green with silver markings inthe centers of the leaf.

‘Boston Cherries and Chocolate’, Proven Winners. Reds, purples andsilvers spotted over the dark leaves.

‘Silver Queen’, Milestone Agriculture. Another predominantly silverfoliage type with a darker green edge on the leaf.

‘Tita’, Milestone Agriculture. A predominantly red-brown foliagewith fewer highlights of any kind. In comparison to other hybrids, a bit drab,but these plants really performed well and would be a great addition to mixedcontainers.

This trial was continuing throughout the summer, and as wefinally got some cool nights, all the cultivars began to look better. If therewere a general observation to be made out of this trial, it would be thatsilver- or brown-toned leaves seem to hold up under high heat and humiditybetter than red-toned leaves and those leaves with lots of different colorspresent on each leaf. We will continue testing begonias in 2003, but underspring and fall season conditions and in comparison with some species ofbegonias that exhibit good heat tolerance.

I think the main thing that “makes” the rexbegonias (in fact all the foliage interest types) is that they are salable fromthe time they begin to fill a 4-inch pot through all later phases inproduction, so you have some freedom in what sizes you grow and how you usethem to best exploit the high dollar niche they offer growers and retailers.

There are many little-known begonia species that haveincredible potential in our expanding market; most of these are rhizomatic,meaning the stem creeps along at soil level, just like the rex begonias, butmay have leaves up to 18 inches in diameter. Some examples of other promisingbegonia species are:

B. gigantea. Solid green foliage, leaf stalks may reach five feet inheight with 18-inch leaves, white winter flowers.

B. nelumbiifolia.The water lily begonia, also solid green, but leaves are nearlycircular, glossy green, and 12-16 inches around. Plants reach 3-4 feet inheight.

B. heracleifolia. Star begonia is a Florida Nursery GrowersAssociation plant of the year. Brown-purple and silver-toned palmate leaves upto 12 inches across, mounding habit and masses of pink flower stalks inwinter.

B. benito-chiba. This is actually a rex-type foliage on an upright,cane-type plant. Very strong, good landscape performance in the South, but trulystriking in containers and mixed plantings.

B. bowerii. The eyelash begonia, another foliage type, not as flashy asthe rex, but a very strong, vigorous plant that does well in mixed containersand shade gardens.