Nodes and Internodes

Plant stems are divided into nodes and internodes. 

​Nodes are small knobby areas found on stems. You need to know about nodes when pruning and tree training. Internodes are the spaces between nodes and the length of internodes can tell you secrets about your plants

Stem showing internodes, nodes, leaves, and petioles (Knulclunk) Public Domain

Nodes and leaves

Nodes produce buds, tendrils, and leaves. Sometimes those leaves have stems, called petioles. When identifying a plant, it helps to note if the leaves are arranged opposite each other, alternate up the stem, or are in a whorled pattern. Even if there are no leaves present, you can use the nodes and leaf scars to find the same information. Leaf scars are where petioles used to be attached. They look like tiny crescents. Whorled arrangements are a little trickier to identify without leaves because nodes can produce multiple leaves.

Modified stems

Aside from the normal stems we see coming out of the ground, there are also stems that run along the soil surface and underground stems. Aboveground modified stems can be crowns, spurs, or stolons. Stolons are often called runners, which is only partly true. All runners are stolons, but not all stolons are runners. Strawberries use runners to send out daughter plantlets that appear at each node.

Underground modified stems are bulbs, corms, rhizomes, and tubers. These underground stems are often mistaken for roots. If you can see buds, leaf scars, or nodes, it an underground stem. And each of those nodes can produce several buds. The eyes of a potato are nodes.

Pruning

Nodes are important when it comes to pruning. It is just above a node where most cuts are made. To keep your plants healthy and productive, you want pruning cuts to be clean, smooth, and at a 45° angle, just above a node. You will also want to make sure that the node is pointing in the direction you want the new growth to go because it will. When you make this cut, all of the plant nutrients and hormones that had been directed toward continued stem growth will now be directed to the node, which will produce new growth. The same principles are applied when notching.

Notching

If you have a young fruit tree that isn’t putting out as many lateral branches as you would like, you can use notching. Notching is a method used two to three weeks before flowers appear to create a better structure. To notch a tree, first identify where branches are needed. Then, find nodes in those areas. Cut shallow notches one-third of the way around each branch, just above those nodes. By cutting through the phloem, the flow of auxins (growth hormones) will be redirected into the node, encouraging stem growth. Do not cut into the structural part of the branch. You should only notch a few nodes at a time, in case something goes wrong.

Nodes, cuttings, and grafting

If you are propagating plants using cuttings, you will want to be sure to identify the nodes because that is where all the new growth will appear. To take a cutting, make sure the stem has at least two nodes. Cut just below one node. This is where roots will form. Then cut above the second node, which is where new leaves and stems will form. Grafting relies on pairing the internodes of two different stems to create a new plant.

Internode length

Most plants have average internode lengths that are longer in the early part the growing season and become shorter, later in the season. Generally speaking, healthy plants have longer internodes than unhealthy plants.

Solomon’s Seal stem with adventitious roots at the nodes (Matt Lavin) CC BY-SA 2.0

Plants use hormones, called gibberellins, to promote internode elongation, increase cell division, stimulate flower production, and regulate seed enzymes. Commercial growers apply gibberellins to plants to increase the size of Thompson seedless grapes, to end dormancy earlier than normal, and to force camellias to bloom out of season, among other things.

If you see internodes that are longer or shorter than normal for a plant at a specific stage of its growth, it can provide you with clues about its health. Shorter internodes can indicate low soil fertility. Longer internodes can mean the plant isn’t getting enough sunlight. This is called etiolation.

Take a closer look at the plants in your garden to see where the nodes are and how the length of the internodes change.