When people talk about hydroponics, they immediately think of water, nutrients and light. But there is one key element that is often underestimated: the substrate.
The substrate does not feed the plant, but it is crucial for stability, oxygenation, water retention and rooting. To choose it poorly is to start with a handicap.

In this guide we look at the main substrates used in hydroponics, with advantages, disadvantages and practical tips, including what changes with automated systems such as Tomato+.

1. Perlite

An expanded volcanic material that is lightweight and very porous.

Pros

• Excellent root oxygenation

• Very high drainage

• Does not compact

Cons

• Retains little water → requires frequent watering

• Can generate dust (irritant)

• Unstable for large plants

When to use it

Perfect for propagation, sowing and fast-growing crops.

2. Vermiculite

Expanded mineral similar to perlite, but much more absorbent.

Pros

• Very high water retention

• Maintains constant moisture

• Excellent for germination

Cons

• Too "wet" for many crops

• Risk of stagnation and poorly oxygenated roots

• Less stable

When to use it

Ideal when mixed with perlite or fiber to improve hydration.

3. Coconut fiber.

One of the most widely used substrates in the world.

Pros

• Excellent balance of water and oxygen

• 100% natural and renewable

• Stable pH

• Easy to handle even for beginners

Cons

• May contain salts if not washed

• Requires initial swabbing

• Not always sterile

When to use it

Excellent all-purpose substrate for lettuces, herbs and various indoor crops.

4. Rock wool

Classic of professional vertical farming.

Pros

• Inert and completely sterile

• Total control over water and nutrients

• Very physically stable

• Standard formats for NFT, DWC, ebb&flow systems

Cons

• Not biodegradable

• Problematic disposal

• Can irritate skin and respiratory tract

• Requires pH stabilization

When to use it

Perfect for large automated plants and constant production.

5. Expanded clay

High-porosity clay pellets.

Pros

• Reusable many times

• Good oxygenation

• Highly draining

• Perfect for DWC, ebb&flow, hybrid systems

Cons

• Requires thorough cleaning

• Tends to accumulate salts

• Does not retain much water

• Unsuitable for initial stages

When to use it

Good as a structural substrate or in support of rooted blocks.

6. Innovative organic substrates (peat, wood fiber, biodegradable mixes).

Increasingly used for sustainability and recyclability.

Pro

• Natural and biodegradable

• Good moisture management

• Environmentally friendly

Cons

• High variability

• Less suitable for high-precision systems

• Possible biological contamination

What Tomato+ uses: a different solution from traditional substrates

While many hydroponic systems require the use of complex substrates to manage, Tomato+ has developed Compostable Pods with structure and fibers designed to ensure:

• Optimal waterabsorption during germination

• Evenly distributed seeds (stable germination)

• 100% biodegradable materials

• Zero contamination because everything is sealed and standardized

• Compatibility with the AI reading of the plant and its root state.

This eliminates the problem of substrate choice, reduces complexity for the user, and ensures software-controlled growth conditions.

What is the absolute best substrate?

There is no "best" in an absolute sense. It depends on:

• type of planting (manual, automatic, professional)

• species grown

• ability of the user

• frequency of irrigation possible

• goal: productivity, simplicity, sustainability

In summary:

• Rock wool → precision and professional productivity

• Coconut fiber → versatility and simplicity

• Perlite + Vermiculite → great mix for seeding

• Expanded clay → recirculated or structural systems

• Tomato+ pods → best balance of performance, cleanliness, and automation

Conclusion

Substrate is the basis for growth, and is as crucial as nutrients and light. Understanding the differences allows you to choose the best solution for your hydroponic system.

With Tomato+, complexity disappears: everything is already optimized, standardized, and biodegradable, ensuring stable and predictable growth through integration with software and AI.

Thank you for reading this article. Keep following us to discover new content on hydroponics, vertical farming and smart agriculture.
Tomato+ Team