Look at the stem of a plant and you will notice there are little junctions called nodes. Here, the older growth creates new growth, as this is where a new axillary bud or petiole may emerge. In fact, it seems all the above-ground action on a plant happens at the nodes. It is a very important place to access if you plan to do any grafting. Also, it is at the nodes that you can discover if your dioecious plant is male or female.
Similarly, the space between nodes, known as the internode, can be of great interest. That’s because the length of the internode can tell you a lot about the conditions the plant is growing in.
When a plant is overcrowded and needs to get additional sunlight, it will produce extra gibberellins and auxin in the upper growth regions. These hormones cause the plant to grow more rapidly, which in many cases will allow the plant to better compete for the available sunlight.
This more rapid growth is what makes the internode spacing longer. When the plant can photosynthesize at its desired rate, the hormones will decrease and the growth rate will return to normal.
However, if light levels continue to be low at the taller heights, the plant will continue to exhibit long internodes. This spindly, weakened condition obviously leads to a general lack of vigor and, often, failure to bud or bloom.
Heat is another reason that a plant may develop longer internodal spacing. In this case, the plant is trying to cool itself off by stretching upward. Often, winter crops like broccoli will “bolt,” or produce longer stems and flower, as a response to excessive heat.
There is a general understanding that short internodal spacing is a sign of plant vigor. That’s because one goal of every grower is to maximize their plants’ rate of photosynthesis and thus maximize the entire crop’s yield.
More intense sunlight will typically cause a plant to have higher rates of photosynthesis and thus produce shorter internodal spacing.
Of course, not all plants respond the same way to light stimulation, so some plants can photosynthesize properly and produce short internode regions in dimly lit locations. As such, knowing your crop is important.
Being able to recognize what the normal internode spacing should be for healthy specimens of your plants allows you to react accordingly to deviations from this.
Wind can also cause the stimulation and release of plant hormones that affect growth, causing the production of shorter internodal spacing and a thicker stem. A minimal amount of modest wind is usually all that is needed to be beneficial for strengthening a plant.
Problems with Short Internodal Spacing
Short internodal spacing is not always an indicator of plant vigor and health. The macronutrient nitrogen is responsible for both leaf and stem growth on a plant. Along with the yellowing and premature dropping of older leaves, insufficient nitrogen will also produce shorter internodal spacing on many plant types.
Cold temperatures, particularly during specific growth stages, can also cause shorter internodal spacing. Similarly, intense light radiation will cause the photodestruction of auxin, leading to shorter internodes and small plant height.
Zinc is an important nutrient in the regulation of auxin production, so insufficient zinc levels can cause short internodal spacing too.
Most perennials, like the deciduous and woody grape vine, produce and store carbohydrates in their roots to produce shoots the following year. If these carbohydrate levels are low, the plant will subsequently show poor growth and closer internodal spacing. Even infestations of certain mites can cause shortened internodal spacing.
Most plants under normal conditions will respond to strong, long hours of sunlight by increasing photosynthesis and producing nodes on their stems more frequently. As such, growers are typically pleased to see their crop have shorter internodal spacing.
It should be remembered, however, that this response is not universal for all types of plants and that short internodal space can actually be signal of a potential problem with some varieties. Knowing the normal characteristics for your crop is pertinent towards the ultimate success you obtain.