Coreopsis gigantea aka Giant Coreopsis

Giant coreopsis is straightforward to grow within its narrow climate niche — coastal California and similar mediterranean regions — but unforgiving outside it. The non-negotiables are full sun, sharp drainage, and dry summers; established plants are reliably drought-tolerant, but waterlogged winter soils and hard frosts (below about −4 °C / 25 °F) will quickly kill it. In cool, wet climates such as the UK, Plants For A Future notes it is "not very cold hardy" and recommends greenhouse cultivation.

The species is restricted to nearly frost-free habitats and is cold-tolerant only to roughly −4 °C (25 °F), which corresponds to USDA hardiness zones 10–11 and UK zone 8. It thrives in the cool, foggy summers and mild winters of the California and Baja California coast.

Giant coreopsis is summer-deciduous: it leafs out and flowers during the cool, wet winter and spring, then drops its leaves and goes dormant through the dry summer, leaving sculptural bare branches. During the dormant period it should be kept dry — Wikipedia warns that the plant is "not tolerant of excess moisture, needing minimal watering during the summer." Resume normal rainfall or light irrigation only when cooler weather returns in autumn.

The flower heads are bright yellow, daisy-like, and 6–20 cm (about 2.5–8 inches) in diameter, produced in showy clusters at the branch tips. Bloom time runs from late winter through early summer, peaking in spring during California's rainy season.

Outdoors, plant in full sun in lean, sharply drained sandy or loamy soil; the species cannot grow in shade. It succeeds in ordinary garden soil as long as drainage is excellent. It is a star of native-plant, drought-tolerant, wildlife, and coastal restoration gardens in California, and is grown for its sculptural form as much as its flowers. In wetter or colder climates, plant under glass or in a sheltered, very well-drained position.

Propagation methods recorded by Plants For A Future are: seed sown in March in a cold frame; division of established clumps in spring or autumn; and basal shoot cuttings taken in May or June.

The large yellow flower heads attract bees and other insect pollinators; PFAF lists giant coreopsis as a pollinator- and wildlife-attracting plant.

There are no documented edible uses for giant coreopsis. Plants For A Future assigns it an edibility rating of 0 out of 5.

No medicinal uses are documented for giant coreopsis; Plants For A Future assigns it a medicinal rating of 0 out of 5.

Plants For A Future records that an orange to red-orange dye can be obtained from the flowers and stems, and that the species attracts wildlife and pollinators.

Giant Coreopsis grows vertically and new growth emerges from the top of the plant.

Giant Coreopsis’s native range is South-western N. America.

Giant Coreopsis does best in dry soil and should only be watered sparingly.

Giant Coreopsis loves a well-draining soil. Perlite and vermiculite help with drainage, while coco coir adds organic matter, so a good potting soil mix will have all three. You can improve store-bought soil by adding some perlite to it.

Giant Coreopsis thrives in bright and direct sunlight. To ensure your plant receives enough light to survive, place it less than one foot from a window. The current weather in your area may affect the placement in your home. For example, if you live in a region that has longer and more intense periods of sunlight, then you may want to place the plant farther away from the window to avoid direct sunlight and reduce the risk of sunburn. Alternatively, if you live in a region with relatively milder temperatures and less intense sunlight, then you may be able to place the plant closer to the window for increased exposure. Ultimately, the current weather in your area should be taken into consideration when determining the best placement for your Giant Coreopsis.

Repotting the Giant Coreopsis is necessary either when it has doubled in size or once every year, whichever happens first. With fresh potting soil replenished annually, the plant will receive all the necessary nutrients, rendering the use of fertilizer unnecessary. Keep in mind that the source of a plant's energy is the sun, not fertilizer.

Giant Coreopsis is not known to cause harm to humans or pets.