Fresh plant material should be cut in late afternoon or early evening when plant sugars and moisture are at their highest levels. Early morning is an alternate time, but not as good. If, however, plant material will be dried, the ideal time is midday. All fresh material should be conditioned overnight before use. 

Use very sharp clippers or a sharp knife (for dahlias a sharp knife is best; chrysanthemum stems should be broken not cut). Sharpness is the key with any cutting tool to prevent bruising and tearing of plant tissue, which may lead to early decay. Carry a deep container of water into the garden and place cut material into the water immediately. Recut stems at an angle below the surface of the water.

Flowers that unfold (iris, daylily, poppy) should be cut when color is showing in the bud and petals have begun to loosen. Blossoms that open and enlarge slowly, like roses, should be cut when they are beginning to open but before the center is expanded. Remove any foliage that would be underwater.

Put plant material in deep tepid water, with or without preservative, in a cool spot out of drafts. Condition overnight. Some plant material requires special treatment to condition well.

References

Belcher, B. Creative Flower Arranging. Timber Press, Portland OR.

Wood, J. and D.D. Smith. Table Settings for All Seasons. National

Garden Clubs, Inc.

Garden Club of NJ, Inc. Conditioning of Flowers and Foliage.

October 1996.

Philadelphia Committee of The Garden Club of America. Tips for

Exhibiting in Flower Shows. Revised and edited, January 2001.