Ask Erik

The final vertical height of your crop will have a lot to do with genetics (genotype) of the crop. Some varieties are better suited to growing indoors under lights than others. As you have stated, using the same genetics indoors the plants have become taller versus the same variety you grew outdoors. What you are witnessing is the plants genetic make-up (genotype) being influenced by the physical environment to create a different physical expression of the same genes. This is often referred to as the phenotype; the physical expression of the genes as dictated by environment. Tomatoes are often classified as “determinate” or “indeterminate” varieties. Determinate means they will get to a certain height and mature, while “indeterminate” varieties will continue to grow upwards until they run out of room or as long as the climate allows for.

Indoors, plants may not have to work as hard in some areas, like water and nutrient absorption, while they may have to worker harder in others, such as capturing solar energy from the lighting levels provided by artificial light sources. With this increased level of water and nutrient availability, but less “sun,” the plants are searching for light, fueled by abundant nutrients; ultimately creating more of a “stretch” in their growth pattern.

If you are running out of room before the plants hit the lights, you can bend, train and even prune the branches and vines back. A trellis support system or six square inch grid screens can be suspended and secured at the top of the crop canopy. You may have some luck training the branches and vines to grow along more horizontally rather than vertically in the trellis netting, reducing the overall height of the crop. Once the grid is filled, and fruits or flowers have formed, you may choose to remove the main growing point of the tomato plants, so they can concentrate their energy into the fruits and flowers rather than growth.

Most growers find that having more and stronger sources of “blue” light in their artificial light sources helps to keep internodal distances tighter. Lower humidity levels (40 to 50 per cent relative humidity) and more even light to dark cycle temperatures will also promote closer, squatter growth habits in your crop.

An abundance of nitrogen or not in the correct ratio with potassium will encourage more elongated and softer growth in plants, often making them more susceptible to insects and diseases.

Plants produce naturally occurring growth hormones called “cytokinins” that help make them stockier and bushier. There are also naturally occurring soil bacteria that help to release these hormones to plants. Some great 100 per cent organic bloom stimulants are available that will help to supplement these levels, resulting in tighter and bushier plants for growing under lights. You can also inoculate the growing medium and root system with bacterial inoculants designed for use with hydroponics gardens.

Good luck and good growing.
Cheers, Erik Biksa