Germination in hydroponics: how to successfully germinate your seeds?

Germination in hydroponics: how to successfully germinate your seeds?

You are setting up your vegetable garden.

You carefully place your seeds in the germination sponges.

You wait.

Then, a few days later, some start to emerge… while others show no signs of life at all.

Is this normal?

Very often, yes.

A seed is not a light switch that you flip on with water. Germination is a biological process that depends on several conditions and whose speed varies according to the species, the variety, and even from one seed to another.

The good news is that in hydroponics, the main parameters are relatively simple to understand.

What does a seed need to germinate?

Before thinking about nutrients or the harvest, let’s go back to the beginning.

To start germination, a seed mainly needs three things: water, oxygen, and a suitable temperature. Light can also play a role in triggering germination for certain species.

Water allows the dry seed to rehydrate.

It swells gradually, and the mechanisms necessary for the development of the young plant are set in motion.

But this does not mean that the seed should be drowned.

It also needs oxygen to ensure its respiration. A medium that is constantly saturated and poorly oxygenated can therefore become counterproductive.

This is precisely the role of the germination sponge: to maintain a humid environment around the seed while preserving a sufficiently aerated structure.

How to use a germination sponge?

The hydroponic sponge here replaces the potting soil used for a classic sowing.

Its role is not to feed the plant.

It serves primarily as support for the seed and then for the first roots.

Start by moistening the germination sponge. It should be damp throughout, without trying to artificially saturate it with water.

Then place the seed in the provided opening.

The depth depends in part on the species and the size of the seed. In traditional sowing, a general rule of thumb is to cover seeds that do not need light with about twice their diameter. Some seeds, on the other hand, need light to promote their germination.

With a preformed hydroponic sponge, avoid at all costs pushing a small seed too deep into the support.

It must remain in a humid environment while being able to easily develop its young shoot upwards.

Then install the sponge in its cultivation basket.

One or several seeds per sponge?

The temptation is understandable:

“If a seed might not germinate, I’ll put in five and I won’t worry.”

The problem arises a few days later when all five germinate.

You then end up with several young plants sharing the same small space, and their roots quickly begin to intertwine.

For seeds with good germination rates, one seed can be enough.

For some small seeds or when a batch is older and you want to secure the emergence, sowing two seeds can be relevant. If several plants appear, you can then keep the most vigorous one rather than letting several large plants compete for the same growing spot.

The goal is not to germinate as many seeds as possible.

It is to obtain one healthy plant per spot when the species needs that space to grow.

What is the growing dome used for?

The small transparent domes provided with some vegetable gardens have a very simple function: to limit drying out around the seed during germination.

The principle is comparable to that used for classic sowing under a transparent cover. The University of Missouri recommends covering the medium after moistening to maintain humidity until germination occurs.

This creates a small, humid environment around the seed.

But the dome is not intended to be the permanent home of your basil.

When the young shoot has emerged and begins to develop, the need changes.

The University of Missouri recommends removing the cover and providing plenty of light once germination is well underway.

On a hydroponic vegetable garden equipped with domes, the principle is therefore simple:

dome during germination, then removal when the young plant has truly emerged and begins to lack space.

Do you need light to germinate a seed?

This is a slightly more subtle question than it seems.

Not all seeds react exactly the same way to light during germination.

Some can germinate in the dark, others are influenced by light.

However, one thing quickly becomes essential after emergence: light.

The young shoot then begins to develop its first leaves and must gradually ensure its growth through photosynthesis.

This is when insufficient lighting can produce long, thin, and fragile plants.

The University of Missouri recommends placing young plants under high light as soon as they emerge. Illinois Extension also recommends keeping the lighting close to the young plants and suggests a duration of 12 to 16 hours per day for seedlings grown under artificial light.

On an indoor vegetable garden with integrated horticultural lighting, this transition is much easier to manage: the seed germinates directly where the young plant will continue its growth.

What temperature for germination?

There is no perfect temperature for all seeds.

Each species has its own range.

The University of Missouri indicates, however, that a temperature of about 18 to 24°C is suitable for the germination of many plants commonly sown at home, while noting that some species prefer cooler temperatures.

In practice, a normally heated living room is often a good starting point for many aromatic herbs and vegetables.

Above all, avoid extremes.

A vegetable garden placed right against a very cold window in winter or in the immediate vicinity of a radiator can suffer from conditions that are much less regular than the rest of the room.

And remember: a temperature that suits a lettuce is not necessarily optimal for a tomato or a pepper.

If a specific variety is slow to germinate, check its needs before changing the whole vegetable garden.

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How long should you wait before worrying?

This is probably the most frustrating question.

You have two sponges side by side.

One shoot has already come out.

The other seems completely empty.

It is tempting to immediately conclude that the second seed is dead.

However, germination times vary enormously depending on the species and conditions.

Temperature, the age of the seeds, their quality, humidity, and variety can all change the speed of emergence.

So avoid a rule like “no shoot after three days = failed seed.”

Look instead at the indicative duration provided for the variety you have sown.

This is particularly important when you are mixing several crops in the same vegetable garden: a basil and a pepper can perfectly well start at different paces.

Why aren't my seeds germinating?

If you have well exceeded the normal timeframe announced for the variety, a few simple checks often allow you to identify the problem.

The sponge has dried out

During germination, the seed must be able to absorb water.

A medium that dries out completely can interrupt the process. The University of Missouri points out that seeds in the process of germinating can be quickly damaged when they dry out.

So check that the sponge remains properly damp.

The sponge is constantly drowned

The opposite excess is no better.

A seed also needs oxygen.

If the medium is constantly totally saturated and the environment lacks air, germination can be disrupted.

Damp does not mean submerged without oxygen.

The temperature is not suitable

A seed can have water and oxygen and still remain inactive if the temperature is too far from its germination range.

Before throwing away the seeds, research the needs of the species in question.

The seeds are old or have been poorly stored

Germination capacity decreases over time, more or less quickly depending on the species and storage conditions.

A seed that does not germinate therefore does not necessarily indicate a problem with the vegetable garden.

If several seeds from the same packet fail while other varieties germinate normally under the same conditions, the seed lot itself becomes a lead to investigate.

The seed is placed too deep

A very small seed buried deep in a sponge may have more difficulty reaching the light after germination.

Respect the recommendations specific to the species and avoid systematically pushing all seeds to the bottom of the sponge.

Should you add nutrients from day one?

A seed contains reserves that allow the young plant to start its development.

Its first structures are therefore set in place before it is capable of functioning as an adult plant.

This does not mean, however, that there is a universal rule to grow all seeds for several weeks in pure water.

In a hydroponic vegetable garden, follow the protocol and dosage of the system and nutrients you are using, rather than improvising an additional concentration in the hope of accelerating germination.

Adding more nutrients does not turn a slow seed into a fast one.

The best reflex remains to provide it with good conditions of humidity, temperature, and, at the right moment, light.

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Can you use any seeds in a hydroponic vegetable garden?

Hydroponics does not require a mysterious category of “hydroponic seeds.”

A basil seed remains a basil seed.

The real choice focuses instead on the plant you want to obtain and the space it will need once adult.

A small lettuce, a mint, or a basil are naturally easier to integrate into a compact vegetable garden than a plant that becomes very large.

That is also where the freedom to choose your seeds becomes interesting.

On Belverdia vegetable gardens, the seeds are not locked into a proprietary consumable: the Verdia One, for example, is currently delivered with 14 cultivation baskets, 14 germination sponges, and 14 domes, while the seeds remain the user's choice. The product sheet indicates compatibility with most vegetable and herb seeds.

You can therefore select a variety from Belverdia or from another seed supplier, then sow it in a sponge compatible with your installation.

Just be careful not to confuse freedom of choosing one's seeds with universal compatibility of all accessories: the size of the sponges and baskets must remain adapted to the vegetable garden used.

A successful germination starts above all by not intervening too much

When a seed does not move, our first reflex is often to want to do something.

Add water.

Add nutrients.

Move the sponge.

Dig up the seed to check.

Then put it back.

In reality, a successful germination requires above all consistent conditions and a little patience.

A damp sponge.

A suitable temperature.

Oxygen.

Then enough light as soon as the young shoot appears.

And a good quality seed.

The rest is largely played out inside the seed.

Your role is not to force it to grow.

It is simply to give it an environment in which it can start.

→ Read also: The 7 most frequent mistakes with a hydroponic vegetable garden