The Root System: The Foundation of Plant Performance

Roots do much more than absorb water and nutrients. They explore the growing medium, influence its chemistry and interact with microorganisms. When a plant grows poorly, the problem may therefore lie in the root environment rather than the amount of fertilizer supplied.

Before changing the nutrient recipe, look at water distribution, oxygen availability, substrate structure, pH and EC. These conditions influence root growth and the uptake of water and nutrients.

In my experience in professional horticulture, growers can be highly skilled in climate, irrigation and fertilizer management, while detailed knowledge of the rhizosphere is often concentrated among just a few people. Understanding what happens immediately around the roots adds an important biological dimension to those familiar cultivation measurements.

How roots grow and acquire nutrients

A root system develops throughout the plant's life. Primary roots extend, lateral roots branch and root hairs increase contact with the surrounding medium. Plants propagated from cuttings form adventitious roots rather than a seed-derived primary root, so their architecture can differ from seed-grown plants.

Root growth responds to local conditions. Nutrient-rich zones can encourage branching, while poor aeration or physical resistance can restrict development. Total root mass tells only part of the story: the distribution of roots, active growing tips and root hairs also matters. The root tip is especially important for exploring new parts of the growing medium.

Nutrients reach roots through water movement, diffusion and contact with new parts of the substrate as roots grow. Once nutrients reach the root surface, transport proteins regulate their entry into cells. Roots can also influence local pH through ion uptake and the release of protons and organic compounds.

This explains why fertilizer concentration and actual nutrient uptake are not the same thing. Poor aeration, excessive salinity or unsuitable pH can restrict uptake even when sufficient nutrients are present. See More Fertilizer, Less Uptake? The Roots Decide.

The rhizosphere: where roots change their environment

The rhizosphere is the narrow zone directly influenced by root activity. Roots remove water and nutrients while releasing ions, organic compounds and other materials. As a result, the conditions immediately beside a root can differ from those in the surrounding soil or substrate.

Roots release compounds known as root exudates, including sugars, amino acids, organic acids, phenolic compounds and other metabolites. Their composition changes with plant species, developmental stage, nutrient status and environmental conditions (Robert et al., 2025).

Some exudates influence nutrient availability. Organic acids can help mobilize phosphorus or iron under particular conditions, while certain root-secreted enzymes contribute to nutrient release from organic compounds. Other exudates provide nutrients or chemical signals for microorganisms.

The rhizosphere is therefore not simply a nutrient solution surrounding the roots. It is a changing chemical and biological environment, and one of the plant-associated spheres.

How microorganisms influence the root zone

Root exudates influence which microorganisms can grow near roots. In turn, microorganisms release metabolites, compete for nutrients and can change the availability of minerals. Fan et al. (2025) describe how root exudates and microbial metabolites act as nutrients and signals in plant–microbe interactions.

Some bacteria can mobilize phosphorus or influence root development. Other microorganisms mineralize organic nutrients, while arbuscular mycorrhizal fungi can extend nutrient acquisition beyond the immediate root surface in compatible plant–fungus associations. These are different mechanisms, not interchangeable benefits of every microbe.

The outcome depends on the organisms present and their environment. Interactions may be beneficial, neutral or harmful. Adding a microbial product does not replace the need for suitable oxygen, moisture, temperature and nutrient conditions. The article How Do Bacillus Bacteria Help Plants? explores several bacterial functions in more detail.

Root biology in soilless cultivation

Roots also release exudates and interact with microorganisms in coco, peat-based substrates, rockwool and hydroponic systems. However, these environments differ considerably in water retention, aeration, nutrient buffering and microbial activity.

In mineral-fed systems, many nutrients are supplied in readily available forms. Microbial nutrient mobilisation may therefore play a different role than it does in soil, where nutrients can be bound to minerals or organic matter.

De Haas, Dhooghe and Geelen (2025) reviewed root exudation in soilless cultivation. Their work shows that substrate and growing conditions influence this process, while important questions remain about the effects of nutrient-solution composition, EC and pH.

What about Cannabis roots?

Cannabis roots have received considerably less research attention than the plant's aboveground organs. Libik-Konieczny et al. (2026) review their metabolism, associated microorganisms and possible roles in whole-plant signalling.

The research provides useful directions for understanding Cannabis physiology. These findings do not establish that manipulating root-associated microorganisms or exudates will reliably increase cannabinoid or terpene production.

What growers can do

Healthy roots need a suitable balance of moisture and oxygen, enough physical space and an appropriate nutrient environment. When growth slows, examine these conditions before increasing fertilizer.

Start with irrigation patterns, substrate moisture and changes in water use. If the substrate stays wet longer while water use and growth decline, check irrigation frequency and drainage before adding more fertilizer. Check pH and EC using a measurement appropriate to the growing medium, remembering that the freshly mixed nutrient solution may differ from conditions within the root zone. The practical plant monitoring guide explains how to choose and record these checks in different growing systems. Where roots can be inspected, their development and visible condition provide additional information.

If microbial products are part of the cultivation strategy, the root environment remains important for their establishment and activity. The aim is not simply to have more microorganisms, but to support a functioning root system and the biological processes that contribute to plant performance.

References

Robert, C. A. M., Himmighofen, P., McLaughlin, S., Cofer, T. M., Khan, S. A., Siffert, A., & Sasse, J. (2025). Environmental and Biological Drivers of Root Exudation. Annual Review of Plant Biology, 76, 317–339. DOI: 10.1146/annurev-arplant-083123-082752

Fan, X., Ge, A.-H., Qi, S., Guan, Y., Wang, R., Yu, N., & Wang, E. (2025). Root exudates and microbial metabolites: signals and nutrients in plant-microbe interactions. Science China Life Sciences, 68(8), 2290–2302. DOI: 10.1007/s11427-024-2876-0

de Haas, B., Dhooghe, E., & Geelen, D. (2025). Root Exudates in Soilless Culture Conditions. Plants, 14(3), 479. DOI: 10.3390/plants14030479

Libik-Konieczny, M., Hordyńska-Tomsia, N., Mazur, Z., Zieliński, K., Bibro, M., Kurczab, J., Gerszberg, A., Hnatuszko-Konka, K., Supel, P., Waligórski, P., & Rodziewicz, P. A. (2026). Back to the roots: Cannabis sativa L. root metabolism, microbiomes, and biotechnological potential. Applied Microbiology and Biotechnology, 110, 301. DOI: 10.1007/s00253-026-13955-2