It’s not too late to plant bulbs such as tulips, daffodils, and alliums this fall for beauty next spring.
When we plant bulbs in autumn, they’re in a dormant stage of their life cycle, according to Doris Taylor, Plant Clinic manager at The Morton Arboretum. Each bulb already contains a small plant and flower bud. Once the bulb is in the soil, it will start to grow roots. In spring, the plant packed inside the bulb will sprout to grow and bloom.
The bulbs need to spend the winter in cold soil, Taylor says. Because they evolved in places with cold winters, such as Afghanistan and Iran, they’re genetically programmed not to flower unless they’ve spent 10 to 14 weeks chilling.
“Bulbs need well-drained soil,” she says. Most bulbs, including tulips, daffodils, alliums, and hyacinths, need full sun.
If you are planting bulbs around trees, choose those that will bloom early, before the tree leaves unfurl to shade the bulb plants. Taylor suggests crocuses, Siberian squill (Scilla siberica), glory of the snow (Chionodoxa forbesii), snowdrops (Galanthus nivalis), or tiny early irises such as Iris reticulata or I. danfordiae.
“Plant plenty of them,” she says. “It takes a lot of small bulbs to make a good show.”
The rule of thumb for bulb planting is to dig a hole that is three times as deep as the bulb is wide—so if a bulb is 1 inch wide, its bottom should sit 3 inches deep. Use a narrow trowel or garden knife to dig carefully, avoiding major tree roots. Or use a dibble, a pointed tool made to poke holes in soil. Water well after planting, and spread a layer of mulch.
Plant the bulbs with the pointed (stem) end up and the flat (root) end down. If you can’t tell which is which, set the bulb on its side; the plant will find its way to the surface.
Most flowering bulbs look best in groups, Taylor says. Plant at least five to seven bulbs in one area. Rather than planting them individually, you can dig one large, wide hole for a group of bulbs.
Since Chicago-area soil generally has plenty of phosphorus, there’s no need to add bone meal or other fertilizer at planting, she said. The time to fertilize bulb plants is after flowering, when they need nutrients to build the next year’s flowers into their bulbs.
If you don’t get dormant bulbs into the ground before it freezes, you can overwinter them in containers, Taylor says. They still will need to chill for 10 to 14 weeks, but you also will need to protect them from harsh cold and from freeze-thaw cycles.
Use large containers and good potting mix. Keep the containers over the winter in an unheated but protected place, such as a window well or unheated garage. In early spring, move the containers out into the sunshine so the bulbs can sprout and bloom right in the pot.