August 2003

Ready, Set, Go with Winter Osteospermum Production By Bob Shabot

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

The success of an osteospermum pot program or scheduledepends on a number of key visual indicators that are easily measured andobserved during various crop stages. Our ongoing research indicates that bymeeting these targets, a great osteospermum crop can be produced almost by thenumbers.

The Production Regime

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

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

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

Monitoring of pH and soluble salts was done monthly usingthe pour thru method, and we determined that the best crop performance wasachieved 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. Pinchingwas accomplished when plants were approximately 2-3 inches tall, usually oneweek after potting, leaving 8-12 leaves per plant. After pinching, lateralshoot development requires about 21/2 weeks to reach a length ofapproximately 1-11/2 inches. When most breaks reach 1-11/2 inchesin length, the plants were moved to a 50° F (night temperature) greenhousefor bud initiation and development. During this growth stage, the daytimeventing set point in the greenhouse should be 60° F, which will allow foran inside air temperature of 60-66° F, depending Á

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

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

Finishing the crop can proceed once the terminal flower budshave 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 daytemperatures; thereafter, the first flowers will open in approximately fourweeks with one half of the flowers open within five weeks. Option 2: Raise thenight 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 twoweeks, with one half of the flowers open within three weeks. This latter optionresults in a savings of two weeks in crop time compared to option 1. Regardlessof the option followed, crop quality was comparable.