You, too, can multiply your bulb-type plants

By Mary Fran McClure
WSU Chelan/Douglas County Master Gardener

Large Tropicana canna leaf.
A Tropicanna canna flaunts its tropical looks all summer. Although it can’t survive our winters outdoors, read how to overwinter it and add additional plants. – Provided photo/Mary Fran McClure
Mary Fran McClure
Mary Fran McClure – WSU Extension Chelan/Douglas County Master Gardener – photo by Don Seabrook, Wenatchee World

Our garden writers’ enthusiasm about propagating plants is obvious if you’ve been reading our recent weekly columns.

First was how to successfully root geranium cuttings, next came tips on starting vegetable seeds, and last week the column focused on the fun of trying those challenging exotic seeds.

Today, I’m writing about how to multiply those wondrous little packages of underground potential: Bulbs and bulb-like plants. Given their needs of water, soil, sunlight and soil temperatures, most of these plants easily multiply and provide plenty of additional plants.

First, it’s probably best for a quick explanation of the different types of these compact storage units.
Bulbs hold their nutrients in layers called scales — easy to think of an onion and how you can see its layers. True bulbs include tulips, narcissus (daffodils), Dutch iris, camas, scilla and more.

Some bulbs are more prolific at producing new bulblets, while others produce fewer. If allowed to go to seed, many will germinate and slowly grow into producing bulbs, but deadheading those old blooms encourages replenishing the bulb and pushing out new bulblets.

Tulips were planted years ago in our raised beds and multiply each year. Crowded bulbs bloom less or not at all.

Two years ago, I dug them in late summer, dividing bulbs and then replanting them by spreading around the perimeters inside the beds. Fortunately, we have great drainage in our raised beds where we also grow vegetables, or the tulips might rot with summer irrigation. They prefer drier soil once mature.

Corms are hard, little nubs with nutrients held in their centers. Examples include gladiolas, crocus and crocosmia. After blooming, the corm shrinks as new ones grow on top of the old. After top leaves have yellowed, dig down and remove the old corm and replant new ones.

There are two types of tubers; the most usual have large tuberous roots. These include Irish potatoes, dahlias and daylilies.

New roots grow outward from the mother tuber and thicken to become new tubers, developing their individual large, fleshy storage areas. When dividing, be sure to include growth buds at the base of each tuber, not just the swollen tuber itself.

The second type of tuber remains as one enlarged base, and roots grow outward from it.
Tuberous begonias, cyclamen and caladiums fall in this group. Be aware that some of these are annuals. As perennial ones enlarge, they can be cut into sections, each with a growing bud.

Lastly, rhizomes are like tubers but longer, with branching fingers. These include bearded iris, rex begonias, sweet potatoes, lily of the valley, Oriental lilies and cannas. Some can’t survive our colder climate unless stored in above-freezing temperatures.

For example, cannas are hot-weather favorites, but can’t take our cold winters without protection. Some gardeners are satisfied treating them as annuals, while I treat them as tender perennials.

During summer, I grow them in containers or out in the landscape, then allow them to mature until after our first light frost. I cut off their tops then dig the rhizomes without dividing clumps, then pack them closely in large containers of soil to overwinter in the garage.

It is important when digging them to realize how widespread those newly grown rhizomes are and not mistakenly cut some in half.

Cannas in storage need very little water and care; in fact, less is better than none.

One year, a large container of cannas was neglected for four months, and the center ones still survived! I check mine about once a month, adding a little water when needed.

Spring comes and a little new growth may start appearing in those containers. I carefully separate plants, dividing those new healthy rhizomes and giving each an individual pot or grouping some in large containers. It’s still too cool for planting outside, so I keep them in a sunny, protected location; after the soil has warmed, plant them in a sunny spot where they’ll show off their dramatic tropical leaves and blossoms all summer.