January 2003

Nemesia and Diascia

Getting an early start on spring sales is critical to
growers around the United States. The problem is finding plant material that
can be grown under cool conditions, will flower under early spring short-day
photoperiod, and has some tolerance of early spring outdoor conditions so that
homeowners have a success to fuel the rest of their spring purchases. The two
crops we are covering this month are perfect for just this portion of the
season and also extending into summer for Northern production. Both nemesia and
diascia are in the same family as snapdragons. So cool temperatures are fine
for production, photoperiod doesn’t appear to be an issue, and both groups of
plants appear to be fairly frost-tolerant once hardened off. So here are a
couple of easy-to-grow crops you may want to fit into your production and early
spring retail orders to give spring sales a boost. Like calibrachoa, these
crops are changing quickly and have a diverse genetic background, so consider
this a primer on succeeding with two strong spring crops.

Nemesia

Many years ago (dang, but I love being old enough to say
that!), I used to grow a lot of nemesia from seed. We grew hybrids of Nemesia
strumosa, a great cool-season annual with vivid and varied colors. This species
was not frost-hardy, so it was used mostly in Southern California, where I grew
up, as a winter annual. The color range in N. strumosa hybrids was and remains
impressive, almost every color in the rainbow and a few bicolor forms only
Maxfield Parrish might appreciate.

While I definitely encourage you to try Nemesia strumosa as
a seed annual (Check out Thompson & Morgan’s hybrids ‘KLM’, ‘Mello
Red/White’ and also Pan American’s ‘Sundrop Mix’), this month, I wanted to talk
about some vegetatively produced nemesia species that are a lot more tolerant
of temperature extremes. These are the relatively new nemesia cultivars sold as
hybrids of Nemesia foetans, N. pallida, N. capensis, N. fruticans and N.
caerulea (even the taxonomists are confused about some of these names so don’t
feel bad if you are too). The plants are sturdier, frost-tolerant and much more
forgiving of warmer temperatures than the old-fashioned N. strumosa types.

There are a lot of excellent vegetative nemesia cultivars on
the market, and under spring production conditions, they are all superior
flowering plants for our spring market. The major differences between cultivars
seem to be flower and plant size. I think you will also see a lot more
development of these groups as their potential for early sales and their ease
of production in minimally heated greenhouses becomes better-known.

Currently, the color range of these plants goes from white
to pink, into lavender and deep or sky blue. While that color range is not bad,
I’m hoping to see more happening with expanded colors in this great plant (it
is all part of a plot to replace pansies as the premier winter annual). Some
cultivars are sweetly fragrant, but more on that when our trials are completed.

Nemesia are cool-season crops here in the South, although
their season expands into summer in the Northern states. I was surprised to see
‘Blue Bird’ flowering in July in North Florida and surviving through an entire
year in the Deep South, so there is potential for a longer season here as well.
Main requirements for a good crop are: 150-200 ppm (low-ammonium nitrogen)
fertilization, high light and some additional calcium and magnesium in early
production. A micronutrient application can also improve crop quality. Avoid
high temperatures and low light as these problems will reduce quality of the
crop quickly. In early production, the plants can grow quite quickly; try
B-Nine (2,500 ppm) to control growth.

Diascia

Diascia is a close relative of nemesia; both are members of
the snapdragon family Scrophulariaceae. Diascia offers larger flowers, larger
plants with a more open growth habit and colors ranging from scarlet through
salmon and coral into pink.

Producing quality diascia follows the same guidelines as
nemesia: Keep light levels high, calcium levels high and ammonium nitrogen
levels low and apply micronutrients. Flowering on diascia is continuous, so an
application of Florel (500 ppm) at planting can help even out the crop and
improve plant size and uniformity before flowering begins. Some growers are
still doing manual pinches to get the same results.

With diascia, you may want to bump fertility levels up to
between 200-250 ppm to keep foliage color dark and to keep up with a generally
faster crop. There is a lot of variability between cultivars on the market, from
very compact "dwarf" forms to some very large and vigorous basket
types. Check with your distributor to get the growth habit that matches your
production.

Trialing Results

The University of Florida is currently trialing 26
vegetative nemesia and diascia releases as winter landscape materials in
Florida (see Figure 1, below). The trial is conducted in Florida, but you can
see pictures and explanatory notes of the different cultivars every two weeks
at www.hort.ifas.ufl.edu. So far, the trial has had 12 nights below 32º F,
and all entries are still doing well, though some show a bit of frost burn.
Flowering is reduced due to the frosts, but there are definite differences in
foliage quantity and quality, especially in the diascia.

You may ask what value this has for Northern growers. My
answer would be that this type of winter trialing gives growers across the
United States the opportunity to learn about low-temperature risks for winter
crops and also tells us a lot Á about photoperiodic responses during the
short days of the winter season. As critical as photoperiod is turning out to
be for specialty annuals in early-season production, this type of trialing can
tell a grower a lot about how the plant will perform in the early spring
greenhouse.

For the future

So in general, these two crops can be grown pretty much the
same, they offer an early-season jump-start to your flowering programs, and an
extension of fall flowering programs in many areas of the United States. If you
aren’t growing them, you should be–they are easy, high-dollar alternative to
some of the traditional annuals grown in these seasons. Another plus to both
nemesia and diascia is that they are also excellent for the mixed container and
work well with a variety of component plants.

There are some blue-lavender forms of diascia available in
Europe, so be on the lookout for some new colors in the next few years. Also, a
lot of new variegated varieties are showing up in Europe. Variegated nemesia is
also out there, so soon we’ll be able to combine the cool-season color of these
two crops with some foliage interest as well. I think we are only scratching
the surface of the genetic potential of these plants and will be seeing a lot
of development in the next few years.