Is geotropism a myth? How cannabis roots actually grow.

For a long time plants were believed to possess geotropism — the ability to orient themselves towards the centre of the Earth. It turned out to work differently. Let us look at what actually drives root growth and how to apply it in the grow room.

What was believed before.

Geotropism is the supposed ability of a plant to grow along the pull of gravity. The main evidence was root behaviour: a root cannot see light, yet it always grows strictly downwards, and after hitting a stone it goes around and continues down. It seemed logical to assume gravity was in charge.

What NASA research showed.

Experiments in space changed everything. Without gravity a plant still developed its roots directionally — but orienting towards the light source (phototropism). Move the lamp to the side and the roots start developing the opposite way. Indoors, where the lamp hangs directly overhead, roots grow predominantly downwards.

Other tropisms.

• Hydrotropism: positive — roots move towards water; negative — they leave an oversaturated zone in search of drier ground.
• Chemotropism: positive — towards a fertilised patch of substrate; negative — away into less fertilised soil.
• There are others too — thermotropism, for example, orientation by temperature.

What this gives the grower.

Knowing that roots follow light and water, you can place irrigation deliberately and build a schedule that pushes roots to spread out rather than rot in a permanently wet substrate. Chemotropism explains why an even distribution of nutrients encourages a healthier root system.