California Poppy needs full sun during cool-to-warm weather. It is perennial, but also grows as an annual in gardens and in wild areas where summer temperatures exceed about 90°F for long periods or where winter temperatures drop below about 15° to 20°F. It grows and yields best at daytime temperatures of about 55° to 80°F.
Established plants may die back or go dormant during summer heat. In hot-summer areas, California Poppy suffers and may be killed by prolonged periods at temperatures of 90°F or higher. In areas where plants might survive the summer, they are often cut back severely, to stubs of about 1 inch, after going dormant.
California Poppy tolerates frost to about 20°F or below. Established perennial plants may tolerate cold snaps to 15°F or below.
Good drainage is essential for growing California Poppy. It is sensitive to overwatering and wet soils; also to coarse or sandy soils that dry quickly. It prefers well-drained clay and loamy soils but tolerates and often thrives in poor or infertile soils provided that they drain well (such as clay soil on hillsides), and tolerates a wide range of soil pH from about 5.2 to 8.3, with an ideal pH of about 6.5 to 7.5. It may germinate poorly, underperform, and need more-frequent watering in coarse and sandy soils.
Many California native landscape plants don’t tolerate soil fertility, and suffer or die in the rich, microbially active soils needed for vegetable gardens. California Poppy is partially an exception; it makes a reasonable companion in garden borders that receive less water, or interplanted with established non-native plants in well-drained soils where watering is infrequent. While normally best kept to drier soils, it can be grown among or beside vegetables and perennials, especially in raised beds and soils that drain well. When grown in rich soils that remain constantly wet or moist, California Poppy tends to suffer from root rots and other diseases. It may produce more vegetative growth and fewer or no flowers in fertile soils, especially those that are high in nitrogen.
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