Hedge trimmers are for HEDGES. To many, shrub maintenance means shearing with hedge trimmers. This is from ignorance, historically. Proper ornamental maintenance is done mainly by pruning, using hand pruners, loppers, handsaws, small chainsaws, etc. Hedge trimming, or shearing, properly only belongs on a hedge, in a formal garden, or in maintaining topiary.
If the rhodedendron in question is in drastic need of pruning, it can be done any time, but fall or winter pruning will reduce the number of flowers next spring. Have to balance the need with the consequences.
Mr powerreel's suggestion that the plants can determine day length is valid, but this is not used by most plants in determining flowering. Temperature sequences are more important to the plant. I have a Mohican viburnum that has flowered three times this year, last time 10 days ago because of unusual temperature fluctuations. Also this year saw henbit (a winter annual) germinating in August and then flowering in late Sept when temp increased.
[Edited by GroundKprs on 11-10-2000 at 06:36 PM]