Answer: Actually, it's too late to plant lettuce here now, as the temperatures are getting too warm, and lettuce is a cool-season vegetable. There are two distinct growing seasons in the low desert with different annuals thriving in each season. There's a cool season from approximately the end of September through April. Annuals can be installed from late September to February. Some gardeners prefer to wait until October, as cooler temperatures also help kill off whitefly populations which can quickly decimate plants.
The warm season starts with planting in mid to late February. Some plants will make it through the summer's heat; others will end their growth when the heat arrives in May or June.
It's a common misconception that vegetables should be planted in the shade here, but they need full sun to perform, especially the cool-season veggies. Warm season vegetables can benefit from protection from hot afternoon sun, but still need at least 6 hours of sun per day.
A good reference book that contains planting calendars for the low desert is called "Desert Gardening for Beginners: How to Grow Vegetables, Flowers and Herbs in an Arid Climate." ISBN 0-9651987-2-3. Good luck!
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