Low stress training

What is LST?

What is LST?

Buck

LST, short for low stress training, is a technique used to keep plants at a low height and to fill out the canopy. It can be used indoors or out.

Auxin is a growth hormone produced by the growing tip that inhibits the growth of side branches. A common way of stopping its production is to cut off the top of the growing tip, Then the side branches, now uninhibited, grow in a rosette around the cut tip.

LST inhibits auxin production by bending the main branch, including the growing tip, so it is in a sideways position. As it continues to grow it is trained to continue horizontal growth. The side branches exhibit gravitropism; they orient themselves based on gravity. Since the stem is horizontal the branches start growing vertically. Each branch becomes a vertical stem.

Keeping the main stem horizontal saves a lot of vertical space so it is convenient to use when it is at a premium. This is not its only advantage. It is an excellent way to grow large plants. Each of the side branches off the main stem becomes the equivalent of a vertical main stem. The single plant can spread out and become much larger than it would have if the main stem had been growing vertically.

There are many ways to keep the stem horizontal. Stakes, screens, and ties are often used. Indoors, the stem is often bent in a spiral within the container to conserve space within the canopy. However, in some circumstances it may be more convenient to keep the stem horizontal and straight. The advantage of that is that the new vertical stems line up in a straight row. Other advantages are that the plant does not grow as tall as it would have untrained, and does not have the stereotypical symmetrical canopy found in both top pruned and unpruned plants.

Outdoors, to grow the largest plant possible, start it early, perhaps under lights indoors. Use supplemental lighting to prevent flowering. Set the light cycle so it breaks up the dark period for a few minutes several times each evening. Give the plant LST so it has a lot of vertical "stems", each ready to produce side branches. Then let it grow out.

A similar technique is grow a plant in a container without pruning its top until it reaches a certain height, then turning it sideways so the main stem is horizontal. The container has to be modified so the roots can be watered from the new top and drained from the new bottom. The new side, which was the open top, must be sealed. The branches that were growing sideways will reorient themselves vertically and grow their own side branches.