Two Kinds of Flower Bulbs, Two Planting Seasons
“Flower bulb” is a loose umbrella term that covers true bulbs, corms, rhizomes, and tuberous roots — different underground structures that all store food for the plant and behave similarly enough for planting purposes. The more useful distinction for timing your garden is usually when a bulb goes in the ground, which generally falls into two groups:
- Fall-planted, spring-blooming bulbs — tulips, daffodils, crocus, and similar bulbs that need a cold period over winter to bloom the following spring. These are typically considered hardy and, in many regions, can stay in the ground year-round.
- Spring-planted, summer-or-fall-blooming bulbs — dahlias, gladiolus, canna, calla lily, and tuberous begonias. Many of these are tender and not reliably winter-hardy in colder zones, so they’re usually planted after the frost risk has passed and, in some cases, dug up again in fall for winter storage.
Knowing which group a bulb belongs to is the first step in deciding when to plant it. The sections below look at each group in more detail, with general timing guidance for a mid-range zone such as USDA zone 6.
Fall-Planted Bulbs for Spring Blooms (Zone 6 and Similar)
When to Plant in Fall
A common rule of thumb for fall-planted bulbs is to get them in the ground roughly six to eight weeks before the ground is expected to freeze solid, which in a zone 6 climate often lands somewhere in the October-to-November window. Soil temperature matters more than the calendar date — many gardeners wait until the soil has cooled to around the mid-50s°F before planting, since bulbs planted too early in warm soil may sprout prematurely.
If you’ve missed that window, it may still be worth planting as long as the ground remains workable and hasn’t frozen. Bulbs planted later than ideal sometimes bloom slightly later or less vigorously the first spring, but many still establish reasonably well. Our January garden to-do list also covers forcing a few of these same bulbs indoors in pots for earlier color, and checking on dahlias or gladiolus stored over winter.
Reliable Perennial Choices (Daffodils, Crocus, Allium)
A few fall-planted bulbs tend to come back reliably year after year in zone 6 and similar climates, without needing to be dug up:
- Daffodils (Narcissus): Generally considered one of the more dependable perennial spring bulbs, and typically left alone by deer and rodents.
- Crocus: Among the earliest bulbs to bloom in late winter or very early spring, and known for naturalizing (spreading slowly on their own) over time in many gardens.
- Grape hyacinth (Muscari): Small, early-blooming, and also prone to naturalizing in favorable conditions.
- Allium: Produces round, architectural flower heads and is often described as relatively deer- and rodent-resistant.
- Tulips: A classic choice, though many hybrid tulips tend to decline in vigor after a few years and may need replanting more often than daffodils or crocus. Species and Darwin hybrid tulips are generally considered somewhat longer-lived.
Spring-Planted Bulbs for Summer and Fall Color
When to Plant After Last Frost
Tender, spring-planted bulbs are usually put in the ground after the danger of frost has passed and the soil has warmed, since cold, wet soil can cause them to rot before they sprout. For many zone 6 gardens, this often falls sometime in May, though it’s worth checking your specific area’s typical last frost date rather than relying on a fixed calendar date.
Bulbs That Can Bloom Most of the Summer
Several spring-planted bulbs are known for extended bloom periods when deadheaded (spent flowers removed) regularly:
- Dahlias: Bloom from mid-to-late summer into fall in many climates, with flower sizes ranging from under an inch to large “dinner plate” varieties. They generally prefer full sun and well-drained, rich soil.
- Gladiolus: Often staggered — planted in batches roughly every one to two weeks — to spread out the bloom window rather than having everything flower at once.
- Canna: Grown from rhizomes and valued as much for bold, tropical-looking foliage as for its flowers, which can continue through summer if faded blooms are removed.
- Calla lily: Also grown from rhizomes; note that calla lily is considered toxic if ingested, so it’s worth keeping it away from pets and children and wearing gloves when handling the rhizomes, since they can cause skin irritation in some people.
Most of these tender bulbs are not reliably winter-hardy in zone 6 and are commonly dug up after the first frost, dried, and stored indoors over winter in a cool spot (often cited as somewhere in the 40–50°F range) before replanting the following spring.
Planting Depth and Spacing Basics
Exact depth and spacing vary by bulb type and size, so it’s worth checking the specific guidance for whatever you’re planting, but a few general patterns show up across sources:
- A commonly cited rule is to plant a bulb roughly two to three times as deep as the bulb itself is tall, which for larger bulbs like daffodils and tulips often works out to somewhere around 6 to 8 inches deep.
- Rhizomes such as canna and calla lily are typically planted shallower, often in the 3-to-4-inch range, with the “eyes” or growing points facing upward.
- Smaller bulbs like crocus and grape hyacinth are generally planted shallower than large bulbs, often just a few inches deep.
- Spacing is usually a few inches apart for small bulbs and closer to a foot or more for larger, spreading types like canna or calla lily, though this varies by variety.
Bulbs in Containers vs. in the Ground
Both options can work, and the better choice often depends on your climate and goals rather than one approach being universally better:
- In the ground generally offers more natural insulation over winter for hardy bulbs and tends to need less frequent watering, since container soil dries out faster.
- In containers, drainage is easier to control, and pots can be moved — which is useful for tender bulbs in colder zones, since a container can sometimes be shifted to a sheltered spot or indoors rather than digging the bulbs up.
- Containers do typically require more attentive watering and may offer less insulation against extreme cold, so hardy bulbs left in pots over winter in colder zones are sometimes at greater risk of frost damage than those planted directly in garden beds.
Where to Buy Bulbs
Bulbs are commonly available from local garden centers and nurseries, as well as online specialty retailers that ship seasonally — many online bulb sellers time their shipments to arrive close to the ideal planting window for your region. Buying from a retailer with zone-specific collections can be a reasonably convenient way to avoid ordering summer bulbs too early or fall bulbs too late, though it’s still worth double-checking the bulb size, firmness, and any care notes before planting, since quality can vary between suppliers.
FAQ
Is it too late to plant bulbs in zone 6? It depends on the type of bulb and the current ground conditions. Fall-planted bulbs like tulips and daffodils can generally still be planted as long as the soil hasn’t frozen, even if it’s later than the ideal window — though blooming the first year may be somewhat less reliable the later they go in. Spring-planted tender bulbs are a different question and are mainly about waiting until after frost risk has passed, not about running out of time.
What flowers come back every year in zone 6? Many fall-planted bulbs, including daffodils, crocus, grape hyacinth, and allium, are generally considered reliable perennials in zone 6 and are often left in the ground rather than dug up. Tulips can also come back for several years but may decline in vigor over time for some hybrid varieties.
Are there any bulb flowers that bloom all summer? Dahlias, gladiolus (when planted in staggered batches), and canna are often cited as bulbs that can provide color through much of the summer, especially with regular deadheading. “All summer” is a generalization, though — actual bloom length varies by variety, climate, and care.
What flower bulbs can I plant right now? That depends heavily on your local frost dates and soil temperature at the time of reading, so it’s worth checking current regional guidance rather than relying on a general answer. As a rough pattern, fall tends to be the window for spring-blooming bulbs, and late spring (after last frost) tends to be the window for summer-blooming tender bulbs.