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A Step-by-Step Guide: Growing Bulbs Successfully
by Katie Stannard
Gardeners are the most optimistic people on the planet. We dig holes in the ground, drop bulbs in, and wait—sometimes as long as six months—and may even forget along the way what we planted and where. But when the first cheery blooms of snowdrops (Galanthus), winter aconite (Eranthis hyemalis), or crocus begin to light up our gardens, we know we were right all along to be hopeful.
Great bulb gardeners are not only optimistic but also curious and adventurous. They balance their enthusiasm and experimental spirit with solid information about the cultural needs of different bulbs—the what, where, how, and when of bulb planting. Keep in mind that bulbs are easy to grow. They come with everything they need to bloom the very first year already packed inside them.
Selecting Bulbs
To succeed with bulbs, select varieties that are suited to the growing conditions in your yard. Most fritillaries, for example, prefer very well drained soil. Above is Fritillaria imperialis 'Lutea Maxima'.
Choosing the bulbs that will grow best in your garden is easier when you are familiar with the likes and dislikes of different bulbs and consider how well you'll be able to accommodate their needs. Here are some tips to help you choose the right bulbs for your garden.
Do your homework. Find out which bulbs grow well in your area. Check with local experts, such as your county extension office, who often can recommend bulbs and other plants well suited to the area. Other great resources include gardening groups, plant societies, good garden centers or nurseries, and neighbors.
Know your zone. Selecting bulbs that are well suited to your climate is critical. If you don't know it already, find out your hardiness zone, and make sure the bulbs you want to grow are hardy in your area. Books and good mail-order catalogs note specific zone recommendations for different bulbs, and most bulb packages you buy in garden centers will provide the same information. Bear in mind that vendors can be overly optimistic about zone recommendations, but this will encourage you to experiment by pushing the zone limits of various plants.
Know the growing conditions in your garden. Proper soil moisture is vital for bulb health. The most important piece of information I can share is this: Most bulbs do best in loose, fertile, well-drained soil. Most spring-blooming bulbs also prefer soil that stays pretty dry during the summer when they are dormant. The number-one cause of early bulb decline is soil that stays too damp for too long, which may be due to poor drainage, too much moisture, or a combination of both. Bulbs are often planted in beds with moisture-loving annuals and perennials. But tulips and hyacinths, native to dry-summer central Asia, do not take kindly to the frequent summer waterings these other plants require. If tulips and hyacinths don't return and rebloom year after year, too much summer moisture may be to blame.
Then again, there are some bulbs that require regular moisture in the summer. Snowdrops, winter aconite, snake's-head fritillary (Fritillaria meleagris), and camassias prefer humus-rich, well-drained soil that never goes bone-dry in the summer. Generally, these bulbs are smaller or fleshier and need the summer moisture to ensure good growth and basic survival. These are the bulbs to plant with your moisture-loving perennials.
As you peruse catalogs or garden-center selections, it's important to determine whether the bulbs you like will actually perform well in your garden's growing conditions, or if you need to set aside time for the important work of improving the soil and drainage.
Know where the sun shines in your garden. Most bulbs do best year after year when planted in full sun. Daffodils (Narcissus), snowflakes (Leucojum), and small early-blooming bulbs like crocuses and Siberian squill (Scilla siberica) tolerate some shade. In the South these bulbs actually seem to prefer it, especially when they are planted under deciduous trees that leaf out after the bulbs have completed much of their growth cycle. Snowdrops, snake's-head fritillaries, and winter aconite prefer light shade, where the soil is somewhat cooler. Consult the cultural instructions that accompany your bulbs for specifics on which bulbs need warm or cool soil, full sun, or light shade in your area.
Know what a healthy bulb looks like. When making bulb selections it helps to know what is considered "normal" for a particular type of bulb in terms of size, shape, and firmness. Size is a complicated issue. Most online or mail-order catalogs list the approximate sizes of their bulbs, such as "15 to 17 cm," which is the circumference measured in centimeters. Comparing prices and sizes is important because what looks like a bargain may get you smaller, immature bulbs. To further muddy the waters, species or antique varieties often are genetically smaller than modern hybrids, both in bulb and overall plant size. For example, compare the gorgeous red and white species tulip Tulipa clusiana or lady tulip with the modern Darwin tulip 'Golden Apeldoorn'. The bulb of the former is the size of a macadamia nut, and the plant grows to 21 inches, while the latter bulb is the size of a plum and grows to 24 inches. Many gardeners are discovering that heirloom and species bulbs add an important dimension of tradition and wildflowerlike grace to their gardens.
That being said, within a specific variety, bigger is better: A larger bulb will likely produce more or taller foliage and more robust blooms. Just be sure to check sizes listed in various catalogs, and look for language such as "all of our bulbs are blooming size."
When you buy bulbs, pick firm and solid ones, unless you're purchasing naturally fleshy bulbs, such as fritillaries, Spanish bluebells (Hyacinthoides hispanica), or camassias. Small blemishes or bits of mold generally won't affect bulb performance, though it's wise to make sure there's not a larger soft or rotting spot underneath a patch of mold.
Preparing the Soil
Since good drainage and the right moisture level are critical for bulb health, what should you do if you don't have that ideal friable, humus-rich, well-drained soil? The task of turning a sand or clay bed into bulb paradise may be a bit daunting, but the long-term benefits for bulbs and other plants will be well worth the effort.
As most bulbs should be planted no deeper than about 8 inches, you should loosen and amend the soil to a depth of 12 inches. If you are working in clay soil, adding compost and chunky organic matter while turning over the bed will greatly aid in loosening the soil. A great way to improve drainage in clay soils is to create raised beds on top of the existing soil, using good organic amendments and keeping in mind that a 12-inch-deep bed is better for bulb health than a 4-inch-deep bed.
Happily for those of us with unrelenting clay, there are several bulb varieties that actually thrive in clay soils and soggy spots, including the larger snowflakes, campernelle daffodils (Narcissus x odorus) and the tazetta daffodil 'Grand Primo'.
If your soil is quite sandy, add compost, coir, or other water-holding organic materials. Compost also provides nutrients to the soil, encourages beneficial insects and bacteria, and discourages harmful pests. Check with local resources such as your county extension office for more specific advice on addressing your particular soil needs. In order to determine precisely what your soil requires, have your soil tested through your county extension service. For a nominal fee, the soil will be analyzed for nutrient content, and based on the soil and nutrient requirements of the plants you want to grow, the extension service will make suggestions for soil amendments.
For the rare occasion when the number of bulbs purchased and hours available for preparing the bed and planting exceed the reality of the time-space continuum, here's a tip for planting quickly in soil that's not suited to your bulbs' needs. Buy a large bag of compost to use as your ready-made "amended" soil, and dig a wide hole or a trench to accommodate your bulbs. Space the bulbs a little closer than recommended, setting tulips, daffodils, and hyacinths near the bottom of the hole, filling in with a layer of compost, and planting smaller bulbs in successive layers. Use the remaining compost to fill the hole, water well, and mulch with leaves, straw, or pine needles. Then vow to do better next year!
When to Plant
Small bulbs, such as grape hyacinth, Muscari armeniacum, shown here with yellow and purple pansies, are prone to dry out quickly in storage and should be planted as soon as the soil cools off in early fall.
If you've ever been to a garden center in August, I bet you've seen the signs proclaiming Now Is the Time to Plant Bulbs. The public might be better served if they instead said Buy Now, Plant Later. Generally, you can plant most spring-blooming bulbs in the fall when soil temperatures in your area drop to about 60°F.
Don't panic if there's an early-season frost or frosts. The ground stays warmer much longer than the surrounding air, so you should still have plenty of time for planting. In my Zone 5b garden, I've planted tulips at Thanksgiving and, snow permitting, into December as well, and I've heard tales of other Michigan gardeners who plant tulips in January!
In most zones, small bulbs should be planted as soon as the soil is cool enough. They dry out more easily in storage than larger bulbs, and as they are planted more shallowly, they are subject to freezing earlier. What's more, if planted early, they have enough time to develop good root systems before the ground freezes. This group of "small bulbs" includes crocuses, snowdrops (Galanthus), and grape hyacinths (Muscari). Any of the fleshy bulbs that prefer more moisture should also be planted earlier, including fritillaries, Spanish bluebells, and camassias. Next, plant hyacinths and daffodils, which root better if the soil is not too cool, and finally tulips, which prefer the coolest soil.
Planting Techniques
Use the "three times rule" for setting out bulbs: Plant at a depth three times the height of the bulb and space them three times their width apart.
The "three times" rule is a good rule of thumb to use when planting spring bulbs: Plant the bulbs at a depth three times the height of the bulb, and space them three times their width apart. Plant 2-inch bulbs 6 inches deep—that is, 6 inches from the soil level to the bottom of the planting hole. Plant with the pointy side of the bulb facing up. If you can't tell which is the rooting side and which is the sprouting side, plant the bulb on its side. It will figure out which way is up! Other basic guidelines: Plant larger bulbs deeper, smaller bulbs less so. Plant deeper in sandy soils, less so in heavy soils. Plant deeper in the North, less so in the South. Planting deeper helps protect the bulbs against cold and is also said to help enhance the longevity of bulbs and keep them from dividing into so many smaller bulbs that blooming suffers.
Plant larger bulbs, such as full-size tulips, hyacinths, and daffodils, at a depth of about 8 inches, and install smaller-size daffodils, such as 'W.P. Milner' or jonquils (Narcissus jonquilla), 5 to 6 inches deep. Plant crocuses and snowdrops 2 to 3 inches deep.
The "three times" rule should help to produce a nicely spaced look; plant closer together for a lusher look. Spacing bulbs farther apart—6 to 8 inches for larger bulbs and 4 to 5 inches for smaller ones—will give them a bit more room to increase over the long run, which is especially important in a naturalized setting. Again, be sure to consult the cultural instructions for your bulbs.
One other handy tip for planting: Carry a ruler with your planting tools or a trowel with measurements marked on the handle or shaft in permanent pen. This is a fast and easy way to check proper depth and spacing for new bulbs.
Watering and Fertilizing
Most bulbs do better with regular fertilizing, and bulb fertilizer is one good choice. Some gardeners prefer to use bone meal (though the way it is processed today saps most of its nutrients) or rock phosphate. Even better is a healthy dose of compost—in fact, if you regularly improve the overall quality of your soil with compost and other organic amendments, you won't have to provide much fertilizer for most bulbs. Mix compost or fertilizer into the soil when you're planting or top-dress, following label directions. To help boost the bulbs for next year's bloom you can also top-dress the soil in the spring after blooming. Remember to work any fertilizers well into the soil, and avoid high-nitrogen fertilizers (like lawn fertilizer).
Water the soil well after you've planted your bulbs, and maintain good soil moisture from fall through spring (when the soil isn't frozen) to help with good rooting and bulb growth. If the winter is especially dry and mild, you may want to check periodically to make sure that the soil is moist enough.
Spring and Summer Bulb Care
It's essential that you let all bulb foliage and stems mature and fade to yellow before you remove them, as the nutrients they store during this period feed the bulbs for next spring's flowering. Wait at least six weeks after blooming before you cut or mow. As soon as the foliage yellows you can remove it, then cover any holes left in the ground from the flower stalks lightly with soil to keep pests out. Feel free to cut off spent flower heads to prevent seed formation, except for those bulbs you want to self-sow, such as Crocus tommasinianus, snowdrops, winter aconite, grape hyacinths, and squills. Then ensure that the bulbs stay as dry as possible during the summer months, except for those noted above. If you want to provide the driest possible summer conditions, consider the age-old technique of lifting out tulips or hyacinths after the foliage has yellowed and storing them dry in a cool basement or storage area over the summer. Then simply replant the bulbs again in the fall and fertilize. Using bulb-planting baskets will help you to locate these bulbs when it's time to dig them up.
You may also want to consider planting companions that will help camouflage aging bulb foliage, combining self-seeding, old-fashioned annuals like nicotianas, larkspurs (Consolida), johnny jump-ups (Viola tricolor), corn poppies (Papaver rhoeas), or forget-me-nots (Myosotis) with early-summer perennials, native plants, or hostas. Also, planting bulbs in narrow, foot-wide drifts or swaths helps make the maturing foliage seem to disappear among the other growing plants, a marvelous recommendation from Gertrude Jekyll.
With just a little effort, bulbs will provide much enjoyment in your garden. In today's rush-rush world, bulb planting—which makes us slow down and wait through the cold and rain and snow of winter—is one of gardening's greatest gifts of optimism and hope.
Katie Stannard is vice president for bulbs at Old House Gardens. She is a master gardener and holds a B.A. from Carleton College and an M.A. from Carnegie Mellon University. She confesses to a small addiction to hyacinths, double daffodils, and cannas.
Photos: Alan & Linda Detrick, David Cavagnaro, Scott Kunst