CORVALLIS, Ore. – Paperwhite narcissus bulbs, because of their fragrance, are popular to grow in pots indoors, but nearly all bulbs sold in the fall work well in pots that stay outdoors.
"It's easy to create a stunning display that begins to grow in the fall or middle of winter, then bursts into bloom in the spring or early summer," said Linda McMahan, Oregon State University Extension horticulturist. "In fact, if you choose the right plants, you can create a bulb display that extends through the seasons.
“Although you can put each kind of bulb in a different pot, mixing them up provides an extravagant display."
Bulbs often do better in pots than in the ground because pots provide better drainage, critical for their long-term survival. Also, gophers and other underground creatures won't find them. McMahan has a number of tips for growing bulbs in pots.
Don’t be afraid to pack the pot full of bulbs, she said. Plant a lot of bulbs at different, overlapping levels. You can easily put 20-30 bulbs, sometimes even more, into a pot that is 14–20 inches across. Use bulbs of many different sizes for an interesting display and longer seasonal appeal.
For longest bloom, look first for crocus. Tulips of all kinds work well. Some of McMahan's favorites are the “species tulips” and their cultivars. Species tulips, often available in garden centers, are sometimes shorter than the taller bedding tulips and tend to come back year after year.
Narcissus and daffodils also are stellar pot bulbs. Choose both early and later blooming varieties for continued bloom. The taller Allium also works well, but shorter alliums can sometimes take over. "I avoid grape hyacinth, which also tends to dominate," McMahan said.
Branch out a bit, McMahan advises, and try Brodiea, hyacinths, Fritillaria, dwarf iris or other bulbs. Dwarf iris, like tulips, often do better in pots than in the ground because of their high drainage requirements.
Plant bulbs with their tips pointing upward and, generally, follow directions for planting depth on the package. Use regular planting or potting soil, recently purchased if possible. "If you reuse older planting mix, be sure to add bulb fertilizer," McMahan advised.
"Fill the container a little more than halfway full of soil, then add a layer of large bulbs such as narcissus (daffodil). Leave only a little space between them; about half an inch is OK. Add more soil and plant the next larger bulb, such as tulip. Repeat adding soil and bulbs alternatively, placing the smallest bulbs like crocus at the top, covered with another inch of soil. Water well and place in a protected spot out of the rain.”
It is best to leave the pot outside so that the bulbs get a cold period, which stimulates growth and flowering. Be sure to bring the pot inside temporarily when temperatures dip below about 28-30 degrees overnight. Bigger pots are safer than smaller ones because it takes longer for the soil mass to freeze all the way through.
Once green spikes of foliage being to poke through the soil, make sure the plants get plenty of light. A good time to add fertilizer is when plants are blooming; preferably a slow-release type.
After the flowers have bloomed, leave the foliage to die back on its own. Then remove the bulbs and plant them in the garden in the fall, or simply leave them in the pot for the next year. The bulbs will remain dormant and need water only when the autumn cycle begins anew.