Answer: Zinnias do extremely well in the low desert, but they are considered warm season flowers. You can sow them from about March through early July and they will bloom until frost kills them. I have some blooming now that I sowed in July and they've been blooming wonderfully since about early August. They take full sun, but mine are in a northern exposure that protects them from hot afternoon sun in the summer, which seems to help. They bloom profusely if deadheaded regularly.
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. 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.
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