Gravitropism and root growth: how roots find their way, and how biostimulants can help

Roots grow downward because of gravitropism: cells in the root tip sense gravity and shift the plant hormone auxin, so the root bends toward the soil. Biostimulants do not switch this on. Selected seaweed, amino acid and humic products can support root growth, nutrient uptake and stress tolerance, but only after you find out why the roots are weak.

Part 1 of 6 in the Plant Science Series by Gafar Laiya: plant physiology and biostimulant science, in plain language. Published 30 October 2026.

Weak roots are usually a soil or stress problem first

• Hard or compacted soil that roots cannot push through.
• Waterlogging that leaves roots without oxygen.
• Salty soil or salty irrigation water that burns root tips.
• Low organic matter, so the soil holds little water and few nutrients.
• Transplanting shock, when roots are damaged or dry out at planting.
• Nutrient imbalance, such as too much nitrogen and too little phosphorus or potash.
• Root diseases and nematodes.

How to check the roots in your own field

• Pick three or four plants that look weak and three or four that look healthy. Dig them up with a spade; do not pull them.
• Healthy roots are mostly pale or white at the tips, with plenty of fine root hairs. Brown, black, slimy or stunted roots point to waterlogging, disease or salt.
• Look for roots that turn sideways or stop at a hard layer. That points to compaction.
• Compare the depth: weak plants usually have a shallow, short root system.
• Take a soil sample and test for salinity (EC), pH and nutrients before spending money on any product. See how to take a soil sample.

What gravitropism is, in simple words

Plants have no eyes or muscles, yet a root knows which way is down. Cells in the root tip contain small starch-filled grains called amyloplasts. They settle to the lower side of the cell, and that tells the plant which way gravity points.

The signal changes how the growth hormone auxin is spread. In a root, more auxin on the lower side slows growth there, so the root bends downward. In a shoot, more auxin on the lower side speeds growth there, so the shoot bends upward. That is why a seed sown at any angle still sends its root down and its shoot up.

Side roots grow at an angle, not straight down, so the plant can search a wider volume of soil. Gravity is also not the only cue. Roots respond to water, oxygen and nutrient-rich patches as well, which is why moisture and soil condition shape the root system as much as gravity does.

Gravitropism in the first three crop stages

Illustration of the first three crop stages: the root grows down (positive gravitropism) and the shoot grows up (negative gravitropism).

What roots need at each crop stage

What biostimulants can and cannot do

A biostimulant is not a fertilizer and not a pesticide. It helps the plant use nutrients better and cope with stress. It does not replace gravity sensing, and it does not fix a hard, salty or waterlogged soil by itself. Effects depend on the active ingredient, the formulation, the crop, the soil and the weather.

The main types and what they are used for

• Seaweed extracts: contain a mixture of natural plant-growth substances. They are used to support root and shoot growth and to help crops handle stress.
• Amino acids and protein hydrolysates: building blocks that support plant metabolism, and are used to help crops recover from stress and take up nutrients.
• Humic and fulvic acid: work through the soil. They are used to support root growth and to help roots reach nutrients. See compost and humic acid.
• Microbial products: beneficial microorganisms that live around the roots and can help release nutrients.

Match the problem to the approach

No single product solves every problem. Start with the cause, then choose the product.

How to choose and use a biostimulant

• In India, only biostimulants listed in Schedule VI of the Fertiliser Control Order can be sold. Ask your supplier for proof.
• Pick the product for the problem and the crop stage, not for the name on the pack.
• Keep balanced fertilizer and soil care going. A biostimulant works alongside nutrition, not instead of it.
• Test on a small strip first and leave a strip untreated. Compare roots and plants after two to three weeks.
• Follow the label for dose and timing, and check that the product mixes with what you spray.
• Write down what you applied and when, so you can judge the result honestly.

From more inputs to better processes

Farming has long asked only how much fertilizer to apply. A better question is whether the roots can use what is already in the soil. Is the root system growing well? Is the plant under salt or water stress? Is the soil alive and rich in organic matter? Biostimulants have a place in this thinking, when they are properly formulated, matched to the problem and tested in the field.

How we work with farmers at Gujarat Bio Organics

• Understand the plant: what the crop needs at each stage.
• Understand the soil: what limits the roots and nutrient uptake.
• Choose the right solution: a suitable product, tested in the field, with an honest expectation of results.

Tell us your crop, stage and what you see in the roots, and we will suggest a programme. Send an enquiry or see the Immunity range.

Written by Gafar Laiya, founder of Gujarat Bio Organics, working with farmers since 2006. Results differ from farm to farm with soil, weather, crop and management. Farmer experiences on this site are their own reports, not a promise of results.