Milkweed and Migration
The timing of milkweed emergence and monarch migration are closely synchronized. Monarchs sometimes seem to push the limit, arriving just as milkweed emerges. This spring 2011 image illustrates "egg-loading." Monarchs would not lay more than one egg per plant or leaf if milkweed were larger or more abundant.

Image: Debra Barnes, New Johnsonville, Tennessee, April 14, 2011