Planting jonquils (Narcissus jonquilla) at the right time means they'll bloom as expected in spring. They grow in U.S. Department of Agriculture plant hardiness zones 4 through 9. Plant them in fall when the temperature of the soil drops below 60 degrees Fahrenheit. In USDA zones 8 and 9, this could be as late as December. In most climates, plan to get them in the ground in September or October.
Choose a Spot
Prepare the planting site in the spring or summer. A good spot for jonquils will get four to five hours of direct sunlight in the morning with dappled shade in the afternoon. They thrive in full sun but the flowers fade more quickly.
Soil pH Requirements
Test the soil pH. Jonquils grow best in soil with a pH of 6 to 6.5, although a pH of 6.5 to 7 is OK. If the soil pH is above 7 or below 6, use lime to raise the pH or sulfur to lower it. You can buy soil test kits and meters from garden centers. Take the soil samples at a depth of 3 to 4 inches. The amount of lime or sulfur required to change the pH depends on the soil texture. To raise the pH of 50 square feet of sandy soil by 0.5 pH unit or from a pH of 5.5 to 6 it will take 1 1/4 pounds of lime but, if the soil is loamy, it will take 2 1/2 pounds. To lower the pH from 7 to 6.5 in sandy soil it will take 1/4 pound of aluminum sulfate but in loamy soil it will take 1/2 pound. Turn the soil to a depth of 10 to 12 inches, spread the lime or aluminum sulfate then till it into the soil.
Checking Soil Drainage
Jonquils must have fast-draining soil. Test how quickly the soil drains by digging a 1-foot-deep by 1-foot-wide hole where you'd like to put the jonquils. Fill the hole with water. Wait until it drains, then fill it again. If the water soaks into the surrounding soil in two hours or less, it drains quickly enough.
If there is water in the hole after two hours, mix a 2- to 3-inch layer of organic matter, like composted pine bark mulch, well-aged manure or compost, into the soil to improve drainage. Mix it into the top 10 to 12 inches of soil thoroughly. You can mix in lime or sulfur and organic matter into the soil at the same time.
If water is still standing in the hole after 4 hours, the soil drains too slowly for jonquils. Consider building a raised bed for the jonquils or choose another planting site. Do not add fertilizer until planting time.
Planting Jonquil Bulbs
Use a soil thermometer to check that the temperature of the soil is below 60 F. Soil temperature is often different than air temperature.
Mix 5-10-10 or 5-10-5 fertilizer into the soil to a depth of 4 to 6 inches just before planting the bulbs. Use 1/2 pound for each 50 square feet of soil.
Dig 6-inch-deep planting holes in average soil or 8-inch-deep holes in sandy soil with 6 to 12 inches between each hole. Jonquils planted more closely together will have to be divided sooner than those spaced farther apart. You can also plant jonquils in groups of six or more for a classic planting pattern. Drop one bulb in each hole with the pointed end up and cover the bulb with garden soil.
Care After Planting
Water the area with the newly planted bulbs well to settle soil. Spread a 2- to 3-inch layer of organic mulch over the area. If the weather is dry, water the bulbs when the top 1 inch of soil begins to dry. The jonquil bulbs are growing roots and need uniformly moist soil until temperatures drop below freezing.