What Is a Culm? The Jointed Stem of Grasses
A culm is the upright stem of a grass plant. University of Illinois Extension calls the stem, also known as the culm, the main backbone of the grass.
The short answer
The culm is the vertical stem of a grass. The Florida Department of Agriculture and Consumer Services says culms are usually hollow except at the nodes. Leaves grow there. Montana State University Extension says the culm grows like nested tubes. The innermost becomes the flowering stem holding the seed head.
What is a culm?
It is the stem aboveground. The Florida circular defines it as the vertical, above ground stem of a grass plant. Illinois says stems can be smooth or hairy. Some have a whitish, glaucous powder. Plant structure is covered in cannabis leaf anatomy.
Are grass culms hollow?
Most are between joints. The Florida circular says culms are usually hollow except at the nodes. A node is the area where leaves attach. Each leaf sheath wraps the stem from its node. Water flow inside stems is covered in cannabis xylem and phloem.
How do culms differ between grasses?
Growth habit differs.
| Habit | What it means | Source |
|---|---|---|
| Bunchgrass | Clumps with tillers next to the bunch | Montana State |
| Rhizomatous | Spreads by underground stems | Montana State |
| Running | Spreads by stems along the soil surface | Florida circular |
The Florida circular notes corn can grow prop roots high on the stem. Montana says growth in most of its grasses occurs close to the ground.
How to: step by step
- Pick a fresh tall grass or grain stem.
- Run your fingers down it to feel the joints.
- Use a hand lens to check for hairs or powder.
- Cut one stem between two joints to look inside.
- Compare two or three grasses.
- Note the plant name and date.
Troubleshooting
Cannot see joints: pick a taller stem.
Leaf sheath hides the stem: peel the sheath back gently.
White film on the stem: Illinois calls that a glaucous stem. It is a normal trait.
Kind Seed Co shares these plant notes for growers of all kinds. Seed parts are covered in cannabis seed anatomy and planting plans in planning an outdoor cannabis garden layout.
Sources
- Grass identification, University of Illinois Extension
- Identifying grasses, Florida Department of Agriculture and Consumer Services
- Grass identification basics (MT201402AG), Montana State University Extension
FAQ
Is a culm the same as a stem?
Yes. Illinois says the stem of a grass is also known as the culm. The Florida circular calls it the vertical, above ground stem.
Do all grasses have hollow culms?
Not always. The Florida circular says culms are usually hollow except at the nodes.
What is a tiller?
Montana State defines tillers as erect or upwardly ascending shoots growing from the base of a bunchgrass.
What is a rhizome?
Montana State calls it a horizontal underground stem that usually sprouts new shoots at the nodes.
What are prop roots?
The Florida circular says some grasses like corn grow roots high on the stem that prop up the plant.
