Flower Bud Initiation On Regal Geraniums - Knowledgebase Question

Springfield, NJ
Question by jmatpatlaw
February 28, 2001
I carry over my regal geraniums during the winter by taking cuttings, rooting them and growing the rooted cuttings in my basement under cool white fluorescent lights. Even though I expose the plants to maximum day temperatures of about 65 degrees in my basement and night time temperatures of about 52 degrees in my unheated garage, I still am unable to get the plants to intiate buds. Is it possible to do so with such lighting? If not, is there any other type of fluorescent light bulbs which will do the job for me? I don't want to use HID halide or sodium bulbs. If necessary, I'll wait until daytime temperatures are in the low 50s and place the plants in the sun after hardening them off (starting in the shade and gradually exposing the plants to sunlight).
In conclusion, am I beating my head against the wall in trying to get my regal geraniums to come into flower without the use of a greenhouse (or cold frame) or HID lamps?




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Answer from NGA
February 28, 2001

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According to cultural instructions to growers from Oglevee's, one of the largest suppliers of geraniums, non-budded Regals (Martha Washington) such as yours would need a four week cooling/bud initiation period when temperatures are kept at or below 56F at night and in the sixties (max 68F) during the day, followed by 8 to 10 weeks of growing on.

According to Penn State, however, while all varieties can be initiated by four weeks at 48 to 50 degrees, some varieties may only require two weeks at that temperature.

Oglevee's indicates that the Regals require an extended day length of 18 hours of light at 10 or more footcandles. In the greenhouse, they suggest using incandescent lighting to provide at least 10 f.c. of light at plant level by stringing 100 w bulbs at 4 foot centers 6 feet above the bench.

According to Penn State, "Regals need mum type lighting from planting until color shows" and Penn State uses 5 watts/sq. ft. of incandescent lighting.

Oglevee's notes that Regals flower better when slightly stressed for moisture starting about 3 to 4 weeks after transplant (although not to the point of wilting -- excess dryness would damage roots and cause leaf scorch)and that when kept too wet or in a high humidity environment, the plants tend to revert to vegetative growth and abort any initiated buds.

Finally, Regals seem to need slighly higher levels of fertilization than typical geraniums, some sources indicating as much as 30% more, so make sure you are fertilizing enough.

You might want to check your foot candle reading and see if you are close to the recommended amount of light. You should also be aware that lower light levels can add about two weeks to the forcing process. I hope this helps you trouble shoot.


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