- A mix of the heat tolerant cultivars Grand Rapids, Prizehead, Royal Oak, Bronse Arrow, and Merveille Des Quatre Saisons.
45-60 days. Non-GMO. Heirloom. Heatwave Lettuce Seed Mix. Lactuca. The Heatwave Lettuce Mix lettuces that thrive in the heat and remain productive. Our choice "slow-bolt" varieties feature Grand Rapids, Prizehead, Royal Oak, Bronze Arrow, and Merveille Des Quatre Saisons. These lettuce types texture range from green and red looseleaf to Bibbs.