Heard these terms but not quite sure what the difference between them is? So a bit of Botany first.
They all belong to a group collectively known as ‘cryptophytes‘. Simple plants that produce buds underground. It includes:-
- Geophytes – those that grow in dry soil
- Helophytes – those that grow in marshy soil
- Hydrophytes – those that grow underwater, such as waterlilies
Its not a well know term and instead we refer to Bulbs, Corms, Rhizomes & Tubers. So, a basic description of each?
- Bulb – a type of underground bud with a short, thick stem and tightly packed leaf scales. An onion is a typical bulb.
- Corm – swollen underground stem, without scales, that acts as a food store. A Crocus has a corm
- Rhizome – horizontally creeping underground stems, just below the surface. Like an aerial stem, it contains buds from which new stems sprout. Iris are typical rhizomes
- Tuber – underground storage organs. Like rhizomes, it contains buds from which new stems sprout. Can be separated to produce new plants. Dahlia & Potatoes are tubers.
They all perform a similar function, a specialised food storage organ that ensure the plant survives for many years – a perennial. Plant dies back to these structures during dormancy, to survive adverse environmental conditions, cold wet winters and hot dry summers.
Plants also use these structures as a way to spread and multiple. We gardeners also use this ability to propagate and increase our stock of plants.
- Rhizomes and Tubers – you can cut off individual bits containing a bud to produce a new plant. – Japanese Knotweed uses this property to spread and is hence so difficult to eradicate.
- Bulbs & Corms – cannot be split, but form new offsets or cormlets around the mother plant. These are what produce next years growth and increase the size of the plant clump.
Bulbs & Corms are often confused and look similar. Corms are solid structures where bulbs are made up of layers of fleshy leaf scales. Corms have a shorter lifespan, being replaced each year by new cormlets.
Did you know: a Stolon is similar to a rhizome, but is an overground root, called a runner. It takes root at points along the stolon to form new plants.