It is a common question among growers: why do microorganisms mainly work preventively, not curatively? Microbiologist Marco Breekweg has a simple answer for us in response to his earlier articles that were published: microbes need healthy roots to do their job.
In this article, the owner of microbial solution company Biomicrobes explains why timing is everything, and how microbes can support crops during different growth stages.
© Microbac
Everything starts in the root zone
When you walk through a greenhouse, your attention usually goes to what's happening above ground: the leaves, the fruits, the growth. But the real foundation is below, in the root zone.
There, plants and microorganisms live in a quiet partnership, constantly exchanging nutrients and signals.
More and more growers are taking advantage of this by adding beneficial bacteria or fungi to their crops. The key takeaway? Microbes need to be there on time to make a difference.
Why healthy roots matter
Microbes can't cure a sick plant, Marco explains. "They only work with roots that are actively growing and excreting substances. Plants constantly release sugars, amino acids, and organic acids. That's food for microbes. A strong, healthy root system attracts and feeds them. But when a plant is weak or diseased, it releases very little, so microbes simply have nothing to work with."
Microbes choose the easy way
Bacteria adapt quickly to their environment. "If there's plenty of sugar, they'll focus on that and spend less energy on other functions like producing enzymes or growth hormones. It might sound like they're being lazy, but it's actually a smart survival strategy," Marco says.
For growers, this means it's important to reapply microbes regularly so the root zone stays diverse and active.
Familiar helpers in the greenhouse
Several groups of microorganisms play important roles in horticulture. Bacillus species are fast colonizers that make nutrients available to plants. Trichoderma are fungi that establish around roots and utilize organic material. Streptomyces are bacteria that produce enzymes and influence the root environment. Azotobacter are capable of fixing nitrogen from the air, while Rhizobium, known mainly for its role in legumes, can also benefit other crops. Mycorrhizae are fungi that extend the root's reach through their thread-like structures, and Pseudomonas are versatile bacteria that quickly colonize roots and produce organic acids.
"No single species can do it alone. The strength lies precisely in collaboration," Marco explains.
Colonization takes time
After application, microbes need time to activate and establish themselves around the roots. This process can take anywhere from several days to a few weeks. "If you wait until problems appear, you're often too late. The microbes simply don't have time to build a strong population."
What can still be done later – and what cannot
Microorganisms work best when they're present from the start, but they can still offer benefits later on, as long as the plant is healthy enough. Active roots continue to release food for them to use.
"With problem plants, think of severe root damage or disease, microorganisms no longer work," the experienced microbiologist explains. "The roots aren't active enough to feed the microbes, so their contribution is minimal or even zero."
Building a preventative buffer
When microbes establish themselves early, they form a natural buffer around the roots. "They take up space, which makes it harder for harmful organisms to settle in. By topping up regularly, you keep that protective layer in place."
Microbes when sowing
Applying microbes early during sowing or planting is a smart move, says Marco. "The sooner they come into contact with the young root, the better they can attach."
This can be done through seed coating, substrate treatment, or a drench after sowing.
With seed coating, a thin layer of microbes is applied to the seed so they become active as soon as germination begins. A light drench after sowing helps bring microbes close to the emerging root.
"In all cases," Marco advises, "use low doses and spread them evenly. Young roots are sensitive, and even colonization works better than one big peak."
Common mistakes
Although more and more growers are using microbes, things still sometimes go wrong. Marco points out a few common pitfalls.
Microbes shouldn't be combined with aggressive substances like hydrogen peroxide (H₂O₂) or chlorine, and they must be stored cool and dark until just before use. Always dissolve them in water only right before application.
He also emphasizes applying them preventively and on time, just like biological control agents, and maintaining the population afterward. "Especially in recirculating systems or when disinfection is frequent, you'll need to reapply."
When drain water is reused, microbes travel along with it. That can be both a risk by inviting unwanted spread, or an opportunity: beneficial microbes can establish themselves throughout the system. In organic substrates this often happens naturally, but in sterile media like rockwool or perlite, topping up is especially important.
Growers who avoid these pitfalls will see clear results: a more stable root environment, stronger and finer root branching, greater resilience under stress (such as drought or salinity), and more efficient nutrient uptake.
The future: microbial management
The demand for microbial products is growing. With new fertilizer regulations and sustainability goals, growers are being pushed to use inputs more efficiently. The next step, Marco says, is microbial management, actively steering the root zone with the right combinations of microbes, organic inputs, and irrigation strategies.
"Microorganisms aren't a miracle cure for sick plants," he concludes. "Their power lies in their partnership with healthy roots. Start early, reapply regularly, and create good conditions. With strong plants, microbes can help at every stage of cultivation. With problem plants, their effect is much smaller. Think of them as a living insurance policy: when they're in place on time, they're ready to support your crop in an increasingly complex growing environment."
Biomicrobes will be present at the Canadian Greenhouse Conference, October 8 and 9 at booth number 1131.
Want to read more about Marco Breekweg's vision and the functioning of microorganisms in horticulture?
How microorganisms help a crop grow
Bacillus in the root zone: how microbial cooperation leads to stronger plants
Bacillus as living insurance of the root zone
For more information:
Biomicrobes
[email protected]
www.biomicrobes.com
