Pros and Cons – an Experienced Agronomist’s Perspective

Sowing cacti and succulents is always a process with elevated risk. High humidity, warmth, fine substrates, and the weak immune systems of young seedlings create ideal conditions not only for germination, but also for fungal diseases.

For this reason, the use of fungicides at sowing is one of the most debated topics among collectors and professional growers.

As an agronomist with many years of hands-on experience, I will say this clearly from the start:
there is no universal “yes” or “no” answer.
Everything depends on conditions, goals, and cultivation philosophy.

Why are fungicides used at sowing at all?

The most common problems during early germination are:

• seed rot before emergence;

• damping-off (“black leg”) in seedlings;

• surface mold on the substrate;

• outbreaks of Fusarium, Pythium, Rhizoctonia;

• mass loss of seedlings during the first 2–6 weeks.

Fungicides are used primarily as a preventive measure, not as a cure — once seedlings are affected, treatment is usually too late.

✅ Advantages of using fungicides

1. Reduced losses at the earliest stage

The most obvious benefit is lower mortality of seeds and seedlings, especially with:

• rare and expensive seeds;

• slow-germinating species;

• collector forms (variegated, crested, genetically unstable lines).

2. More stable and predictable results

Fungicides allow growers to:

• keep sowings closed for longer periods;

• tolerate minor mistakes in moisture control;

• achieve more uniform germination.

This is particularly important in commercial or semi-professional production.

3. Control in sterile substrates

When using sterile or mineral substrates (pumice, perlite, coconut fiber), fungicides:

• compensate for the lack of beneficial microflora;

• prevent rapid colonization by aggressive pathogenic fungi.

4. Reduced stress for the grower

Not a scientific term — but very real 🙂
Fungicides reduce the number of situations where “everything was fine yesterday, and everything is gone today.”

❌ Disadvantages and risks

This is where the most important considerations begin.

1. Suppression of beneficial microflora

Fungicides do not distinguish between “good” and “bad” fungi.
They suppress:

• mycorrhizal fungi;

• saprophytic organisms;

• microorganisms involved in building long-term plant immunity.

As a result, seedlings may:

• adapt more slowly after ventilation begins;

• become more sensitive to stress later in life.

2. Reduced germination due to overdose

This point is critical and often underestimated.

Excess fungicide directly reduces seed germination.
When overdosed:

• some seeds fail to germinate at all;

• germination becomes delayed or uneven;

• overall germination can be worse than in sowings where no fungicides were used at all.

This is especially noticeable in sensitive genera such as:

• Ariocarpus

• Aztekium

• Blossfeldia

• many mesembs, Haworthia, Gasteria.

In this case, “more protection” clearly means a worse outcome.

3. “Sterile dependency”

Seedlings grown in completely sterile conditions may:

• struggle to adapt after pricking out;

• develop weaker root systems;

• react more sharply to changes in environment.

4. False sense of security

Fungicides do not compensate for:

• poor substrate choice;

• excessive organic content;

• stagnant moisture;

• unclean containers.

If cultivation practices are flawed, fungicides merely postpone the problem.

When is fungicide use justified?

✔ rare and valuable seeds
✔ large or mass sowings
✔ high humidity and closed-sowing methods
✔ unstable or cool climatic periods
✔ situations where substrate sterilization is not possible

When can fungicides be avoided?

✔ small hobby sowings
✔ good air circulation
✔ fully mineral substrates
✔ gradual ventilation from an early stage
✔ when the goal is resilient, naturally adapted plants