Planting a bulb garden is a great way to highlight your landscape and gardens, but the key to success lies in how you plant them in the fall. If you’re new to gardening, understanding when to plant bulbs can seem a little tricky, especially if you live in a region with varying temperatures. Timing depends largely on your location and the climate you experience in the fall and winter; of course, in New York where I'm located, it may be snowing by Halloween or 70 degrees in December, but there's still firm logic behind planting in the dormant season. To learn more, we tapped Amy Yarger, the Senior Director of Horticulture at Butterfly Pavilion, a leader in invertebrate research, conservation, and education.
When to Plant Flowering Bulbs in Cooler Climates
If you live in a cooler climate, such as the northern U.S. or Canada, you’ll need to plant your flower bulbs early enough to give them a cold period. "The chilly temperatures of winter in northern climes trigger chemical cues in the plant so that it can produce flowers at the right time," explains Yarger. This is true for most spring-flowering bulbs, including tulip bulbs, early-blooming daffodils, and grape hyacinth bulbs.
- Cold period required: Bulbs need exposure to temperatures between 35-45°F for about 10-14 weeks to bloom in the spring.
- Best time for planting: Aim to plant bulbs after the first frost but before the ground freezes solid. This is usually in mid-October to late November for colder climates like USDA Zone 6a, such as in Westminster, Colorado. Timing your bulb planting before the harsh winter temperatures strike allows for fall root growth.
- Earlier planting for northern regions: If you’re in the northernmost parts of the U.S. or Canada, you may need to plant as early as late September. This gives the bulbs enough time to settle in before winter fully sets in. If you wait until the late winter, you likely won't have the cold temperatures necessary to make the magic happen.
When to Plant Flowering Bulbs in Warmer Climates
In warmer climates, the process is slightly different because you don’t have the same cold winters that cooler regions experience; however, you can still enjoy beautiful spring blooms by adjusting your planting schedule.
- Later planting time: Plan to plant your tender bulbs in late fall, typically in November or even December, once the average nighttime temperatures drop to 40-50°F. Begin to monitor the even temperatures in the fall as you wait for the right time to get the bulbs into soil.
- Soil temperature matters: "Soil around 55 degrees Fahrenheit helps the bulbs establish roots before the winter freeze," notes Yarger. "This allows the bulbs to establish roots before any cold spells."
- Importance of fall precipitation: Cooler fall temperatures bring much-needed rain, which helps bulbs establish strong roots. Soil moisture is important for fall-planted bulbs.
How to Tell When It’s Time to Plant
Whether you live in a cooler or warmer climate, keeping an eye on the weather and evening temperatures is one of the best ways to determine when to plant your bulbs.
Nighttime temperatures around 40-50 degrees Fahrenheit are a good indicator that it’s time to plant. When the soil has cooled to around 55 degrees Fahrenheit, the bulbs can start establishing roots before the ground freezes (in cooler areas) or before winter sets in (in warmer areas). Bulbs need time to adjust to their new environment before the weather gets too cold, so don’t wait too long to get them in the ground once temperatures start to drop.
What to Do if You Miss the Fall Planting Window
Life happens, and sometimes you might miss the perfect fall planting window. If this happens, there’s still a way to enjoy your bulbs—though it’s not ideal for long-term success. You can chill your bulbs in a refrigerator for 10-14 weeks to mimic the cold period they need. Once they've been chilled, you can plant them in the spring when the soil is workable; however, as Yarger advises, don't store your bulbs with any produce! "Fruit, especially apples, gives off ethylene gas which will interfere with blooming. Consider this pre-chilling time for bulbs a stop-gap measure rather than a long-term solution. It's much better for the long term success of the bulb to plant in the fall."
Bulbs That Don’t Require a Cold Winter
If you live in a region that doesn’t experience a cold winter, don’t worry—there are bulb varieties that don’t need a lengthy cold period to bloom. Some great options for warm climates include freesias, Peruvian squill, and certain species of alliums. These bulbs are well-suited to climates with warm winters, and will still bring beautiful blooms to your garden.
FAQ
Do bulbs need to be mulched?
Yes, especially in cooler climates. Adding a few inches of mulch helps protect your bulbs from extreme temperature fluctuations and protects the moist soil. Spread a layer of mulch, such as shredded leaves or straw, over the garden beds once the ground cools to insulate the bulbs over winter.
Should bulbs be watered often?
Bulbs should be watered after planting to help them settle into the soil. Watering once is important whether you have sandy soil or heavy clay soil. After that, they generally don’t need much water during the fall and winter. Overwatering hardy bulbs can cause rot, especially in spots without well-draining soil.
Do I need a special bulb fertilizer?
While additives aren't always necessary, fertile soil helps improve the growth and bloom quality of your flowering bulbs. Organic fertilizer for bulbs is typically rich in phosphorus, which supports root development, and potassium, which aids in overall plant health. Applying fertilizer at planting time gives bulbs an extra boost as they are established in the soil. That said, if your soil is already rich in nutrients, especially organic matter, bulbs will probably be fine without it. Make sure to avoid high-nitrogen fertilizers, as that mixture will encourage leaf growth over flowers. Always follow the instructions on the fertilizer packaging for best results.
