A rhizome is a swollen stem of a plant that grows horizontally – normally just under the surface of the soil, or as in the case of many Irises, on the surface.
The basic difference between a root and a rhizome is that rhizomes have buds, from which new shoots emerge. Roots do not have buds, but simply anchor the plant into the ground and absorb moisture and chemicals from the soil for the plant’s nutrition.
Two typical examples of plants that have rhizomes as their main stem are irises and Ginger. The rhizome of the Iris is a little different to most rhizomes in that it grows on the surface of the soil instead of under the soil. This is because the rhizome of the Iris needs to be baked by the sun in order to provide flowering shoots.
Rhizomes are normally fleshy in appearance - such as with the two examples - with strands of roots attached.
An Iris is a good example of a rhizome because it lives on the surface of the soil. This enables close inspection without having to dig it up!
You will see that the rhizome has roots growing out of it – downwards into the soil in order to carry on normal functions of roots. It will also have visible buds which are close together along the ‘stem’. If you are inspecting in the growing season, you will see that at least one of those shoots have developed into the spear-like leaves of the Iris plant. The leaves and flower stalks grow directly from the stem of the plant which is the rhizome.
Leaf scales will be noticed if you look carefully. These are not the true leaves of the Iris, but protective scales for the rhizome stem.
If left for a few years, the rhizome of the Iris will continue to grow outwards from its central starting point – in search of new soil and new food supplies. This will lead to an ever increasing branched structure with new shoots emerging only at the tips of the rhizomes. In gardening terms, this will lead to an unsightly clump of rhizomes with a bare centre and a ‘ring’ of irises at the perimeter.
The Rhizome is the basic food storage organ of the plant, as with other plants which grow a conventional branched, upright stem.
Because rhizomes have a dormant or otherwise bud structure along their length, they can be cut into sections – each section containing at least one bud, and ‘rooted’ to produce new plans. This is best carried out in autumn or winter. The fact that your rhizome cutting has to ‘root’ - the same as any other type of stem cutting accentuates the fact that the rhizome is a stem.
The image shows the stem segments or 'nodes', the shoots, and the roots. Each of the stem segments will have modified - sometimes scale-like - leaves, and most importantly, a bud from which a new shoot can be tempted to emerge. As with most plants, the stem is 'anchored' to the ground by the root system.
Each section will (should) e-grow as a plant the following year, providing that the sections are large enough to each have a bud. The buds are easy to see with lily of the valley also – another plant that has a rhizome as a main stem.
Garden Plants that have rhizomes as their main stem include… Canna, Convallaria or Lily of the Valley, Flag Iris, Several Ferns, Alstroemeria and Zantedeschia.
Several herbs and spices also have rhizomes – in this case being the main ingredient for the pot and include …. Ginger, Turmeric, Galangal.
Vegetables include… Rhubarb,
There are also several weeds that grow from rhizomes…