Recycling the Rex Begonia

November 5, 2002 - 12:54

The rex begonia is back as a niche crop that can bring great benefits in cool, moist conditions with a high relative humidity.

There is always a strange sense of déjà vu in
working with new crops, remembering an earlier time where you worked with a
plant and then seeing it resurface on the market again. That's the way it is
with rex begonias. When I was first studying horticulture at Cal Poly San Luis
Obispo in California, one of my class reports was written on "Radiation
Mutation Breeding in Rex Begonias." I remember being fascinated by the
idea that mutation could give these plants their vivid leaves of silver and
purple and red. This was right around the time the first microwave ovens were
coming out, and popular opinion held that they would cook your brains if you
stood near one while it was in operation. While that fear was apparently
unfounded (I live in Florida now anyway, where UFO's and ballot counts are a
greater concern than microwaves), it is true that the diversity of leaf colors
and shapes in the rex begonia owe a lot to being irradiated with X-rays. (As a
side note, this same kind of "mutation breeding" is what gives us so
many poinsettia cultivars to choose from. Radiation mutation is a common
plant-breeding tool that helps in some cases to jumpstart new cultivars more
quickly than traditional breeding techniques).

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

Rex Cultivation

While the extremely patient grower can produce rex begonias
from seed, they are produced as vegetative liners so that color forms remain
stable in production. In general, the rex group of begonias, prefers cool,
moist conditions with high relative humidity. If you have good luck with
tuberous begonias or reiger begonias then you'll probably do okay with rex
types as well. The humidity seems to be a key factor in getting good leaf size
on plants. Like a lot of begonias, rex hybrids do poorly in heavy, cold, soil
mixes, so avoid both heavy soils and too much water while getting plugs
established. They prefer lower light levels in production, as their leaves
scorch in bright sun very quickly.

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

Trial Results

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

The results of our trials showed that outdoor production is
risky, the leaves of these begonias are very fragile, and a hard rain can tear
through the foliage. Also, our evening rain patterns increased bacterial leaf
spot on all cultivars, but the plants that still did well under these
conditions should show additional vigor under optimal production Á
regimes. In this research, we trialed 37 cultivars. Our top selections based on
summer trialing in Florida were:

'Chocolate Man', Milestone Agriculture. Silver and brown foliage with
bright pink flowers in fall. A great fall combination of colors and exceptional
vigor and leaf spot resistance.

'Maui Mist', Proven Winners. Striking pink-purple and silver-toned
leaves with deep, blackish green edges, vigorous.

'Snow Queen', Milestone Agriculture. Leaves are predominantly bright
silver, strong growth, disease-tolerant.

Milestone Agriculture. Predominantly silver-toned foliage.

'Chicago Fire', Proven Winners. Purple and green with silver markings in
the centers of the leaf.

'Boston Cherries and Chocolate', style='font-weight:normal;font-style:normal'> Proven Winners. Reds, purples and
silvers spotted over the dark leaves.

'Silver Queen', Milestone Agriculture. Another predominantly silver
foliage type with a darker green edge on the leaf.

'Tita', Milestone Agriculture. A predominantly red-brown foliage
with 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 mixed

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

I think the main thing that "makes" the rex
begonias (in fact all the foliage interest types) is that they are salable from
the time they begin to fill a 4-inch pot through all later phases in
production, so you have some freedom in what sizes you grow and how you use
them to best exploit the high dollar niche they offer growers and retailers.

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

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

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

B. heracleifolia. Star begonia is a Florida Nursery Growers
Association plant of the year. Brown-purple and silver-toned palmate leaves up
to 12 inches across, mounding habit and masses of pink flower stalks in

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 truly
striking in containers and mixed plantings.

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

About The Author

Rick Schoellhorn is assistant professor of floriculture at the University of Florida, Gainesville, Fla. He can be reached by phone at (352) 392-1831 or E-mail at

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