Escobaria vivipara var. kaibabensis

Escobaria vivipara var. kaibabensis or Kaibab Spiny-star cactus are powder white snowballs. Seed was collected on the east flank of the Kaibab plateau along Hwy 89a. The plants can get tennis ball sized and can offset. This species is one of the most cold hardy species of cactus. Plants have taken -22F in our garden and grow easily in most habitat zones within the area. In general this species grows from Canada to Mexico and from Wisconson to Arizona. 
 
I do not guarantee these in a zone 5 because everyones growing conditions are different but this would be a good trial plant to grow in your cold outdoor garden. Try to plant outdoor 90 days before 1st hard freeze.