In the science of plant biology, a plant's stem consists of nodes and internodes. A plant stem's nodes are those critical areas from which leaves, branches, and aerial roots grow out from the stem, while the internodes are those intervals between the nodes. Locating the nodes of a plant is important when you are doing regular maintenance, such as pruning, and also when you are trying to propagate plants from stem cuttings or grafts.
The base of a bud, leaf, twig, or branch is always attached to a node, so this is one easy way to find them. Even without visible buds or leaves, you can tell where the node of a twig is by some signs that are visible only at a node:
- A scar in the wood where a leaf has fallen away
- A knob-like, slight fattening of the wood (such as the rings on a bamboo cane)
- Solid sections of the stem in plants with hollow stems such as forsythia, smooth hydrangea, and bamboos
By contrast, internodes are the sections of stem between nodes. If the nodes are the crucial “organs” of the plant, the internodes are the blood vessels carrying water, hormones, and food from node to node.
Usually, internodes are lengthy and provide several inches of spacing between adjacent nodes. However, some plants are notable for how close together with their leaves, and thus their nodes, always are. Dwarf conifers, for example, have closely spaced nodes. Yews and boxwoods, with their dense leaves, also always have short internodes. This fact is why these plants can be sheared or pruned into any shape, including the special sculpted forms of topiaries.
Whether you are new to pruning, or just intimidated by it, locating the node is an important step in the pruning process.
- Always prune just above a node on a stem. In this way, the dormant buds in the node itself will grow out into new stems. If you cut below a node, you leave a section of stem (the internode) that cannot grow new stems. This section will be prone to rotting and becoming susceptible to diseases that can kill your plant.
- Prune above nodes that have buds facing away from the center of the plant. The new growth will grow in that direction, leaving the center of the plant open to air and light. This prevents diseases and pest infestations. This also works well when you are shaping a plant. For example, when pruning roses, you can prune back to nodes with buds facing outward, because this will promote outward growth, creating a nice open shape to the plant.
Many types of plants, both woody and herbaceous, can be propagated by stem cuttings, a process that yields a plant identical to its parent. A 6-inch or longer cutting is taken from the parent plant for rooting in the soil. For successful rooting, cut immediately below a node, because this is the area that will produce the roots. The cutting also needs a terminal bud or another node above the soil line where the new stem and branch growth can occur.
In contrast to pruning, when you want to make cuts for grafting—joining a branch tissue segment of one plant to the stem tissue of another host plant—you make these cuts in the host plant not near the nodes, but right through the center of an internode. In the whip and tongue graft, for example, careful cuts need to be made along the grain of the wood in the internode space. If you were to make these cuts through the thick, knobby nodes, they would not be straight, and the graft union would be likely to fail.