The approach of autumn makes it time to think about which bulbs to plant for spring bloom. That’s because spring-blooming bulbs are planted in the fall. In order to flower, they must go through a period of chilling in cold, winter soil.
Many spring-blooming bulbs can be planted to brighten the space beneath tree branches, said Julie Janoski, Plant Clinic manager at The Morton Arboretum in Lisle. “It’s important to choose the right species and plant them carefully, to avoid damaging the tree,” she said.
The best bulbs to plant beneath or around deciduous trees bloom early in the spring, so they will finish flowering before the tree opens its leaves to block the sun. Don’t bother planting bulbs beneath evergreen trees; no bulb plant can survive in that year-round shade.
Species that are good companions for trees will have small bulbs. That means you won’t have to dig a large hole for them and damage many of the roots of an established tree. And they will be long-lived, so you only have to plant them once and won’t need to damage the tree’s roots by replanting year after year.
Tulips are not the best choice in the Chicago area. Most hybrid tulips struggle to rebloom a second year in our region’s weather and soils.
“They’re basically annuals in our climate,” Janoski said. Tulips also usually have large bulbs, as big as 2 inches in diameter, and need a very well-drained, full-sun site. It’s best to find another place for tulips, as well as giant Dutch hyacinths and daffodil species with large bulbs.
However, daffodil species with smaller bulbs — an inch or less in diameter — can do well around trees. Although they thrive best in full sun, most daffodil cultivars can tolerate partal shade, and they will live and flower for many years with no fuss.
“Just be sure to choose early-flowering varieties,” Janoski said. “Late daffodils, which bloom toward the end of April or in May after the tree has leafed out, won’t get enough sunlight to create another flower for next year.”
A tree that is small or has a more open canopy of branches, such as a redbud, may allow you to get away with later-blooming varieties. A more open canopy will allow some sun to reach the bulb plants after they bloom, when they need it to form flowers in next year’s bulbs.
If you’re planting a tree this fall, you have a special opportunity to establish a garden around it, including bulbs. “You can plant shade-loving perennials and bulbs around the root ball in the same fall that you plant the tree,” Janoski said.
Since you’re planting them around the newly planted root ball, you don’t risk damaging any tree roots. That means you can plant daffodils with larger bulbs. Over time, the tree roots will grow out and intertwine with the other plants’ roots.
Miniature or dwarf daffodils, such as Narcissus Tete a Tete or Little Gem, can be charming beneath a tree or shrub. “To have an effect with small bulbs, you need to plant plenty of them and plant them close together,” Janoski said. “If you just sprinkle them around, they’ll get lost.”
Here are some other spring bulbs that are effective when planted under established trees and around shrubs:
Species crocus. Often called snow crocus, these plants bloom earlier and are smaller and more delicate than the popular giant crocus (Crocus vernus). The small bulbs are planted just an inch or two deep, so they are unlikely to interfere with tree roots. Snow crocus species include Crocus tommasiniana, Crocus chrysanthus and Crocus sieberi.
Siberian squill (Scilla siberica). Scilla prefers dappled sunlight or part shade and often will reseed if it is planted in suitable conditions, forming large swaths of low, dangling bright-blue flowers in late March or early April. It often spreads in lawns. Scilla siberica Spring Beauty is a popular cultivar.
Striped squill (Puschkinia scilloides var. libanotica). This flower is similar to scilla, but its blooms are pearly white, often with a faint blue stripe down each petal.
Checkered fritillary (Fritillaria meleagris). The flowers, in shades of white or purple, are shaped almost like nodding tulips, with tiny spots that make them look like checked gingham cloth. Just a few inches high, the plants prefer partial shade.
Snowdrops (Galanthus nivalis or Galanthus elwesii). The very earliest bloomers, snowdrops may have nodding white flowers as early as February, depending on the winter weather. Over time, they grow into dense clumps.
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (mortonarb.org/plantadvice or [email protected]). Beth Botts is a staff writer at the Arboretum.