How Deep Should You Plant Tulips?
Tulips are easygoing bulbs, both in planting and care, given a few best-growing requirements. With the proper planting this fall, their graceful blooms happily color the spring landscape. Enjoy future rewards with easy planting this month. Follow a few tips, including how deep to plant tulip bulbs, with gardening expert Katherine Rowe.
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Tulips and their elegant cupped blooms, stately on slender stems, give a happy welcome to spring. Their single, double, and frilly forms bring waves of early, mid, and late-season color. Proper planting in the fall ensures the best flowering. Planting tulips perfectly deep protects the dormant and developing bulbs against temperature fluctuations and moisture issues. It also allows a necessary chill time.
In many growing areas, November is the optimal time to plant tulips for their spring show. Whether in the ground, potted arrangements, or forcing blooms indoors, be sure you know how deep to plant your tulips so they can bring big garden rewards as temperatures warm in the spring.
Tulip Overview
Native to Europe and Asia, tulips grow naturally in mountainous regions from the Balkans to the Himalayas, where cold, wet winters give way to warm, dry summers. As true bulbs, they grow during the cool season and flower in spring, entering dormancy during the summer. Flowers decline when soil temperatures warm above 70°F (21°C).
Tulips are short-lived spring-flowering bulbs, often grown as annuals for their strong display in their first growing year. In subsequent years, their vigor declines. Some tulips last one to two years, while others average three to four years, depending on climate, cultural conditions, and variety. They may perennialize in USDA zones 3-8 with varying results, lasting for a few years.
Best Siting and Growing
The best foundation for growing tulips is the proper planting location in full sun to partial shade. Full sun (six or more hours daily) promotes the best flowering and health. The easy-going bloomers also do well in the dappled light of a tree canopy, with four or so hours of sun exposure.
Well-draining soils are essential, especially during the bulbs’ dormant period prior to and after flowering. Prolonged periods of soggy conditions in the summer or winter make plants susceptible to bulb and root rot. Evenly moist soils with good drainage are best during the growing season, while drier conditions in the warm season promote perennializing.
When to Plant
Tulips do best with fall planting to allow a necessary winter chill period, or vernalization. The fall placement assists with reaching temperatures of around 35-45°F (2-7°C). Tulips need about 12 to 16 weeks of restorative chill.
Wait until hot spells pass for a fall planting, best when temperatures are in the 60s (~16°C) and lower. For many areas, this is in October and November. Planting is easiest when the soil is workable, and the ground isn’t yet frozen, but fine if you’ve already had a heavy frost.
In warm climates like zones 8 and 9, you can plant through December and January and into the spring. Opt for pre-cooled bulbs from the grower to ensure they’ve met the necessary chill time for flowering. Or, give them 14 weeks in the refrigerator before they go in the ground.
In-Ground Depth
Depending on the variety, the average planting depth for tulips is five to six inches deep. The average spacing is four to six inches apart. But, there’s a handy trick to use in the field: because varieties and bulb sizes differ, a good rule of thumb is to place the bulbs three times as deep as their size. A two-inch bulb, then, benefits from six inches of depth.
Tulips, like other spring-flowering bulbs, look best in a mass or grouping. Cluster them closely with a spacing of twice the size of the bulb. Space the same two-inch specimen four inches apart. Err on the side of nearer rather than distant spacing for these plants. They’ll even grow shoulder to shoulder.
Orient them tapered side up (root base down) for ease of growth. If planting in bulk, dig a trench or plot at the proper depth to fill and situate the bulbs before covering them with soil. Tailormade to the job are handheld bulb planters and augers, helpful for large displays.
In Containers
Tulips grow beautifully when planted dense and deep in containers. Pots allow for a closer spacing than in-ground situations. For an abundant look, completely fill the pot with bulbs. Underplant cool season annuals and perennials for a spring surprise to transform the design.
Start with a well-draining potting media and partially fill the pots three-quarters full. Tuck the bulbs shoulder to shoulder and cover them with soil. Leave an inch or two of space beneath the pot’s rim before the soil level. Water well until it runs through the container and drainage holes.
For bulbs that need a winter chill period to grow, place the pots outside this month. An unheated cold frame or greenhouse works well, too. Nestle them close to a building or wall under a layer of leaves or mulch the tops for insulation. Outdoors, they’ll receive adequate seasonal moisture without additional watering. If indoors or undercover, keep the soil moist but not waterlogged.
After about 10 to 14 weeks, as temperatures warm and new growth begins, uncover the containers and move them to their display location for budding.
After blooming, stop watering and lift the bulbs for storage or composting.
Forcing Blooms
Many spring-flowering selections bloom indoors any time of year through forcing. You can force tulips into flowering after adequate cold exposure to bring their cheer to the interiorscape or create a lovely gift.
To make bulb growing easy, purchase pre-chilled bulbs. Or, bring in containers overwintered outside as they show new growth.
Forced tulips grow in a variety of interesting ways, from mossy terrarium displays to rooting in water. Place them atop a bulb vase, jar, or dish, making sure only the root end (base) of the bulb is submerged. More water coverage leads to rot. Adding gravel can help situate the bulb.
To prolong the interior display, keep the blooms out of direct sunlight and away drafts from heater vents and fireplaces. Keeping them cool at night helps flowers last longer.
Mulch and Winter Protection
At planting, add a layer of compost and mulch to help regulate soil temperatures, retain moisture, and suppress weeds. Mulch helps keep the soil cool during warm spells to keep leaves from popping up too early.
A three-inch layer of leaf litter, clean straw, or bark provides added insulation. The insulation protects against winter freeze/thaw cycles, which may cause frost heaving. Soils naturally freeze and thaw with temperature fluctuations.
In early spring, lighten the layer if it’s thick for the sun to warm the roots, and so new leaves can emerge.
Another element of protection for newly planted selections relates to wildlife. Carbohydrate-filled tulip bulbs are enticing to squirrels, chipmunks, raccoons, deer, and more. If your bulbs are prone to wildlife damage, keep an organic repellant handy. Some gardeners dip their bulbs in a bucketful of granular repellant at planting and reapply to soil surfaces regularly, particularly after rains.
An overlay of chicken wire fencing helps deter digging. You can also interplant with daffodils or snowdrops, which are poisonous to wildlife. Overall, planting in abundance is the best way to ensure a full display, even if some are lost to local foragers.
