Ready, Set, Go with Winter Osteospermum Production

August 21, 2003 - 12:19

If your conditions are right, you can produce this high-margin crop throughout the winter.

Over the past few years, we at the University of Connecticut
have been cropping osteospermum as a novelty winter crop, and results have been
good in both crop quality and customer acceptance and satisfaction. Since
year-round cuttings are now widely available and with the recent introduction
of dwarf cultivars in a widening array of colors, the possibilities for winter
pot production are better than ever!

The success of an osteospermum pot program or schedule
depends on a number of key visual indicators that are easily measured and
observed during various crop stages. Our ongoing research indicates that by
meeting these targets, a great osteospermum crop can be produced almost by the
numbers.

The Production Regime

For winter production, cropping usually starts October 1 and
runs through March. This works well in Connecticut since outside temperatures
are low enough to allow for the low greenhouse day/night temperatures needed
for bud initiation and development.

In our experiments, plants were established using three or
four plugs per 61/2-inch azalea pot (with three plugs per pot producing a
good mass market item and four plugs per pot making an excellent retail florist
product). Containers were filled with a coarse, well-drained bag mix such as
Metro mix 510 or Fafard 3-B, and the planted pots were maintained at a night
temperature of 62-65° F. The initial watering included a preventive
fungicidal drench, since root and crown rots may be a problem early in the
crop.

We fertilized the crop with 3- to 4-month slow-release
pellets by top dressing each pot with 1/2 teaspoon of 13-13-13 after
planting. After watering in, the plants were fertigated weekly. The first week
we used 150 ppm nitrogen and 300 ppm nitrogen every week thereafter. All
fertigation was derived from a stock of six parts calcium nitrate and four
parts potassium nitrate (equivalent to a 14.5-0-17.6 fertilizer with 120-0
calcium). As an alternative, a peat lite fertilizer special of 20-10-20 at the
above weekly rates (150 ppm nitrogen the first week and 300 ppm each week
thereafter) will do the trick as well.

Monitoring of pH and soluble salts was done monthly using
the pour thru method, and we determined that the best crop performance was
achieved at a pH of 5.5-6.5 with soluble salts at levels of 25-100 ppm
(equivalent to Spurway extractable).

All plants were pinched to induce better branching. Pinching
was accomplished when plants were approximately 2-3 inches tall, usually one
week after potting, leaving 8-12 leaves per plant. After pinching, lateral
shoot development requires about 21/2 weeks to reach a length of
approximately 1-11/2 inches. When most breaks reach 1-11/2 inches
in length, the plants were moved to a 50° F (night temperature) greenhouse
for bud initiation and development. During this growth stage, the daytime
venting set point in the greenhouse should be 60° F, which will allow for
an inside air temperature of 60-66° F, depending Á

on outside air temperature. High day temperatures (70° F
or greater) during early bud initiation will delay bud development and increase
crop time. To avoid this delay, try to have bud initiation complete by the
first week of March; this will allow you to take advantage of naturally cool
temperatures without cooling your greenhouse.

Following 6-8 weeks at the 50° F regime, flower buds are
typically 1/8-1/4 inches in diameter. (This is variety dependent,
with dwarf types requiring less time and some varieties producing larger or
smaller flowers.) At this point, evaluate the need for a PGR application. I find
that when plants reach 6 inches in height, or close to it, they should be
treated with PGRs. Plants 4 inches or smaller will finish at a reasonable
height without PGR application. Our PGR of choice has been a tank mix of 1,500
ppm of both Cycocel and B-Nine applied as a foliar spray to the point of
run-off (approximately 1 gal. of solution per 200 sq.ft. of bench area). This
mix has proven extremely effective in controlling late stretch of both stem
internodes and flower peduncles, especially for crops produced during late
March when inside temperatures can reach or surpass 70° F on bright spring
days.

Finishing the crop can proceed once the terminal flower buds
have reached the 1/8- to 1/4-inch size. Two options are available.
Option 1: Continue to grow the plants at 50° F night and 60° F day
temperatures; thereafter, the first flowers will open in approximately four
weeks with one half of the flowers open within five weeks. Option 2: Raise the
night temperature to 60-62° F and the day venting set point to 70-75°
F. Using the second scenario, first flowers will open in approximately two
weeks, with one half of the flowers open within three weeks. This latter option
results in a savings of two weeks in crop time compared to option 1. Regardless
of the option followed, crop quality was comparable.

About The Author

Bob Shabot is a horticulturist in the floriculture greenhouse at the University of Connecticut, Storrs, Conn. He can be reached by phone at (860) 486-2042.

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