Asparagus In The Summer

I normally let the asparagus patch go to ferns after the shoots get the size of a pencil. Today, while weeding, I picked half a dozen tender asparagus spears that tasted just as good as the first shoots of spring. I also note the local stupidmarket is offering fresh asparagus from Mexico at an outrageous price. I live in Eastern Ontario in zone 3b. There must be a way of forcing asparagus to produce later in the year or special strains are used. My asparagus seed came from the University of Guelph and is called "Guelph Centennial", an all male variety. Anyone got an answer?
Farmer John
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