The best time for planting most daffodil (Narcissus spp.) bulbs is fall so cold winter temperatures chill the bulbs and trigger them into developing flower buds, but some daffodils exist that don't need chilling, and they can be planted at other times of year. A large family of flowers hardy in U.S. Department of Agriculture plant hardiness zones 3B through 10, depending on the variety, daffodils can grow 1 to 2 feet tall and 1/2 to feet wide.
When the soil temperature drops to 60 degrees Fahrenheit 6 inches below the surface in fall, it's time to plant most daffodils. In cold areas of the United States the soil reaches this temperature in late summer or early fall, and in warm USDA zones the soil temperature doesn't reach 60 F until early winter.
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To measure the soil temperature, push a screwdriver 6 inches deep into the soil, then remove it. Insert a thermometer into the hole and wait two or three minutes before removing it and checking the reading.
Test the soil temperature in a shady area or cover the thermometer if it's in direct sun to prevent the sun's warmth from affecting the reading.
In cold USDA zones, plant daffodils before the ground freezes in winter. Daffodil bulbs need one or two months to grow their roots into the soil before becoming dormant over winter. Planting daffodil bulbs in frozen ground is also hard or impossible. Plant daffodil bulbs that day if an early, hard frost is forecast. Cover the planting area with a layer of shredded leaves, straw or hay 3 to 4 inches thick.
Only certain daffodil varieties grow well in warm USDA zones, no matter when their bulbs are planted. Most daffodil varieties form flower buds when they experience temperatures between 35 and 45 F for eight to 10 weeks. If the soil temperature is rarely so low for the required length of time, plant jonquil or tazetta daffodils, which need less chilling to form flowers.
Tazetta daffodil 'Minnow' (Narcissus 'Minnow') grows 6 to 8 inches tall and offers creamy white flowers with buttercup yellow cups, and jonquilla daffodil 'Quail' (Narcissus 'Quail') features deep golden yellow, highly fragrant blooms, and grows 12 to 14 inches tall.
'Minnow' is hardy in USDA zones 5 through 9 and 'Quail' is hardy in USDA zones 4 through 9.
Paperwhite narcissus (Narcissus papyraceus) doesn't need a period of chilling to trigger flower development. Originally from the Western Mediterranean, paperwhite narcissus bulbs begin to grow when they receive water, and four to six weeks later blooms appear. Between two and 20 small, white fragrant flowers will appear on each stem.
Paperwhite narcissus is often grown as a houseplant, but it can be planted outdoors during frost-free seasons within its hardiness range, which is USDA zones 8 through 11. In colder zones the bulbs can be planted after the final frost in spring.