Monday, March 29, 2010

Bulbs, Tubers, Rhyzomes & Corms, Oh My.

Science has never drummed up quite as effective a tranquilizing agent as a sunny spring day. ~W. Earl Hall

Many of us are still patiently waiting for our fall planted bulbs to bloom. While we wait, it's time to plan spring planting of summer blooming flowers. Many of these flowers are not hardy, which means they don't survive the cold winters under normal circumstances. It's also time to determine whether you want to divide or add to your supply of hardy bulbs, corms, tubers or rhizomes this year. What is the difference between bulbs and these other plant types?

Why aren't they all just called bulbs? A "bulb" is what a tulip or daffodil grows from. It's the rounded thing (for lack of a better word) that stores the flower which will eventually bloom. The pointy part is what the stem grows out of, and the flat bottom is where the roots will form. This is a simple definition for the others:

A corm is what a gladiola grows from each season. It looks like a bulb but has an indentation at the top, and a flattened part with roots at the bottom like a bulb.

A tuber is thinner and looks kind of like a carrot in some ways. The roots are at the bottom again, and the stem grows out of the top. If you've pulled up Queen Anne's lace it looks like this as do daylilies, both wild and cultivated.

A rhizome is what we plant to obtain the Iris. It's an ugly, long, thick root that lays sideways with one end bending upwards, which is where the stem appears. Rhizomes should always be planted fairly close the surface, unlike bulbs or corms which need to be planted fairly deep.

You don't really need to know these definitions to grow these type of flowers, but it helps to know the terms if you are reading articles or books on landscaping or planting instructions. Below are some of the most common type of summer blooming flowers that grow from bulbs, tubers, rhizomes or corms.

Tuberous Begonias
Elephant's ear (Colocasia esculenta)

Lilies (Lilium spp.)
Rhizomatous Iris
Lily of the-valley (Convallaria)
Blazing Star (Liatris)

You'll notice that most stores have large displays of these out for purchase already. I have planted and divided daylilies as early as April in my Zone 5 landscape, but most of the others should be planted AFTER the last frost in your area. Even if you can work the soil, the tender varieties should be planted after the frosts have finished. It's hard to be patient, but it is important to do so.

Next Monday I'll post more on planting and selecting the summer blooming flowers I've mentioned today.

On OFL we have an article on growing gladiolas.


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