Plant cannas in warm soil

Bob Dluzen
The Detroit News

Many longtime gardeners consider canna lilies the workhorse of the flower garden. That’s because they are available in such a wide range of flower colors, sizes and foliage color.

Canna lilies — or just cannas since they are not actually lilies —  are loosely classified as tender bulbs or summer flowering bulbs as opposed to spring flowering bulbs like tulips, hyacinths and daffodils.

Even though they are commonly called bulbs, they are not true bulbs rather they are specialized underground stems called rhizomes.  In cannas rhizomes store food; are a way for the plant to reproduce asexually; and help anchor the plant.  

This size of rhizome may be planted as is or divided. The light-colored shoots are growing points that have already started growing in storage, others are still dormant.

They are tropical plants so they can't survive our cold winter temperatures. In tropical regions they are perennial plants, but here in our climate we have to plant rhizomes every year. 

Many gardeners dig their bulbs every fall and store them over winter. It’s a relatively easy way to build up the number of bulbs over time.

Canna rhizomes are easy to overwinter. In the storage container under the straw, the canna bulbs looked in fine condition this spring.

Because they are tropical plants, cannas require warm soil, so we need to wait until the soil is warm enough to plant in the spring, generally around 60 degrees Fahrenheit. We are approaching those conditions now.

If you are unsure of your soil temperature, dig down a few inches and use a soil thermometer to determine how warm the soil is. If you don't have a soil thermometer, a kitchen thermometer works just as well. By the time we reach Memorial Day however, you can count on the soil temperatures being pretty stable in the 60s and warm enough to plant.

Check the soil temperature at planting depth. Cover the rhizomes with an inch or two of soil.

Cannas are very versatile in the garden. They can be used in a number of ways  to enhance your garden landscape. They can be an integral part of the design especially if you want a lush, tropical look. 

The plants themselves range in size from under 2 feet to some varieties that grow to 6 or 8 feet tall. Most common varieties are about 4 to 5 feet tall at maturity.

The taller ones make a perfect backdrop. Those with red leaves provide a wonderful contrasting color to other yellow and orange flowers.

They are very adaptable and do very well in pots as long as the container they’re growing in is large enough.

Tall varieties can be used as a temporary screen during the summer to hide such things as trash cans and compost bins that you don't want to look at.

There is some discussion on how deep to plant canna bulbs. You see numbers anywhere from 3 to 6 inches deep. But generally when you see those kinds of numbers, it refers to the depth of the hole.

Since canna bulbs vary in size, the hole depth is not an accurate measurement. Instead, match the hole to the size of the rhizome. Make it big enough so you are able to cover the growing points with an inch or two of soil.

If you received a clump of canna bulbs from a gardener friend you may have to divide the clump before planting. They are usually quite easy to separate. Just grab each end of the clump and start twisting and bending. Soon they will pull apart at a natural separation point. 

Two to three growing points per rhizome is a good size to plant. 

I like to add some compost to the hole before planting to help feed the plants through the summer. 

Cover the growing points with about 1 to 2 inches of soil. 

Space the according to size, the smallest ones can be as close as a foot apart while the tallest may need to be three feet apart.

Once the flowers have faded, remove them to stimulate new flowers. 

Fertilize your cannas with a general garden fertilizer once or twice during the summer if your garden soil is less than optimum.

At the end of summer you'll be able to dig canna rhizomes of your own to store through winter  starting the whole cycle over again. 

After the summer has ended, I'll discuss how to overwinter cannas in this blog.