Autumn, when trees take on sunset colors and nights are growing cold, is the time to invest in next spring by planting flower bulbs.
“They’ll pay you back by blooming in April and May,” said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle.
Even if your garden already includes tulips and daffodils, there are always spots where you could tuck in a few more bulbs. For example, consider the area around the base of a tree or shrub.
“Sunlight reaches those spots in early spring, before the trees open their leaves to create shade,” Campbell said. “That’s an opportunity for bulbs to bloom.”
For spots under and around trees and shrubs, choose bulb species that bloom early and are somewhat shade-tolerant. For example, snowdrops (Galanthus nivalis) have white nodding flowers that may bloom as early as February, depending on the weather. Several species of crocus, such as Crocus chrysanthus, Crocus sieberi and Crocus tommasinianus, flower a couple of weeks earlier than the popular Dutch crocuses (Crocus vernus).
The blue nodding flowers of Siberian squill (Scilla siberica) usually open in early April. Glory-of-the-snow (Chionodoxa forbesii) also has blue blooms, but with white centers that almost make them seem to twinkle. Striped squill (Puschkinia scilloides) bears its small white flowers in loose clusters; look closely, and you’ll see a pale blue streak down the middle of each petal.
Beyond beauty, there’s an extra advantage to planting these early bulbs: They will provide nectar and pollen for bees and other pollinating insects early in the season when few other flowers are blooming.
Be sure to plant enough. “These are all small plants with small flowers, so you have to plant a bunch of them together to make much of an impact,” Campbell said. For that reason, they are often sold in packs of 25 or 50 bulbs.
The bulbs themselves are mostly small and don’t need to go too deep, so you can plant them without doing too much damage to tree roots.
Later-blooming bulb plants and those with larger bulbs, such as daffodils, tulips, hyacinths, alliums and bluebells, should be planted in full-sun sites, not under trees. They can be planted among compatible perennial plants in well-drained soil.
What is a bulb? This dry, brown thing is actually a package containing a partly-developed flower with its leaves and a food supply. The plant is dormant in the fall, but once the bulb is planted and watered, it will wake up enough to grow some roots. Then it will go back to sleep and wait out the winter until springtime brings sprout-and-bloom time.
Generally, the best time to plant bulbs is between late September and late October. The soil will be cooling down, but the bulbs still will have time to grow roots before it freezes.
Planting them is easy. Using a trowel or soil knife, dig a deep hole, two to three times as deep as the bulb is tall. That will protect the bulb against fluctuations in the weather.
Place the root end of the bulb down. On tulips and daffodils, that’s the wide, flat end; the pointy part, where the stem will grow, goes up. On other bulbs, the root end may be harder to discern. Look for little dots where roots were attached. “If you really can’t tell, plant the bulb on its side,” Campbell said. “The sprout will find its way up.”
You can also dig a wide hole and plant a whole cluster of bulbs in it. “Just make sure that the depth of the hole is right for the kind of bulbs you’re planting,” Campbell said.
There’s no need to fertilize bulbs when you plant them; they come with a food supply. Good soil that is rich in organic matter will supply all the further nutrients they need.
After you plant the bulbs, water the area thoroughly and spread a 1- to 2-inch layer of mulch on the soil. It will insulate the bulbs against their biggest danger: coming out of dormancy too early and sprouting during brief winter warm spells.
“Tuck them in under that blanket of mulch so they’ll stay asleep until they are safe from a freeze,” Campbell said. “They’ll know when it’s time to sprout and flower.”
For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.