QBARS - v24n4 Gibbing Rhododendron for Fall Bloom

Gibbing Rhododendron for Fall Bloom
by J. R. Todd, Jr., Lenoir, North Carolina

For the past several years, I have experimented in a general way with gibbing buds of rhododendron to see whether or not fall blooming could be obtained, as has been done successfully with camellias, Gibberellic acid was obtained from Hastings Garden center, as prepared for the American Camellia Society.

The largest and most well-developed buds were selected, and usually the largest upper new growth terminal under the bud was carefully pinched out, and one drop of gibbing acid was placed where the terminal was pinched out, in the same manner as camellias are gibbed.

Gibbing was done on three different dates, August 11, August 27, and September 11, 1969. Results varied considerably, with some varieties blooming within three weeks from date of gibbing, some as late as 90 days, and some failed to bloom at all. Out of approximately 50 budded plants gibbed, approximately 25 failed to respond satisfactorily. Approximately 25 others did respond and bloomed. Listed below is a summary of the varieties which did bloom in the fall as the result of gibbing with some degree of success. Shown is the date gibbed; the date of blooming; and comments as to the results on the basis of poor, fair, good, very good, or excellent.

Observations and Summary
It should be made clear that usually only one or two buds on each plant were gibbed, and this experiment did not include anything like a sufficient quantity to arrive at any definite or scientific conclusions; however, the following comments may be of interest:

1. It would appear that plants with the largest and most well-developed buds responded better than plants with less well-developed buds.
2. It would appear that early blooming varieties, such as 'Christmas Cheer', 'Scarlet Wonder', and vernicosum 18139', responded better than late blooming varieties.
3. With some varieties, flower size appears to have been increased.
4. It would appear that buds gibbed in early August provided better bloom than those gibbed later. Many buds gibbed in mid-September failed to open at all.
5. Three or four trusses were cut and placed in water indoors, and some lasted for as long as two weeks.
6. It would be interesting to see what develops when all buds of a plant are gibbed whereby the entire rhododendron would be in full bloom in the fall.
7. It is suggested that more scientific controls and experiments be made in order to determine accurately which varieties perform best with gibbing, and that such information could be of interest to nurserymen and florists who wish to provide rhododendron plants in full bloom out of season.