How To Germinate Seeds For Hydroponics Without Rockwool (7 Better Alternatives)

Hydroponics is an excellent indoor farming technique, but how do we germinate seeds for hydroponics without rockwool or soil? Let’s find out. 

Hydroponic seeds are not germinated as typical soil seeds, where you just sow them, and they magically appear as plants. Here, you have to germinate them under your own supervision before moving them to the hydroponic system. 

There are a lot of different mediums used to germinate seeds for hydroponics, but first, let’s understand why we don’t simply use the soil as we always have.

Why Do We Need A Medium To Germinate Hydroponic Seeds?

A medium other than soil is used to germinate hydroponic seeds due to the following reasons 

Soil has a lot of inorganic and organic factors that habituate the seed. When such soil-grown seeds are shifted to hydroponic conditions, they behave oddly due to transplant shock.

Since the soil is not involved, some other medium is required where the seeds can germinate and grow their roots and develop a seedling.

Hydroponic seed germination mediums provide space for water retention and root enlargement to the seeds.

Being inorganic, these media do not decompose; hence do not disturb or cause any complications in the biological process. 

Why Rockwool Is Commonly Used To Germinate Hydroponic Seeds

The most commonly used medium to germinate hydroponic seed is rockwool. This is due to its ability to retain moisture for a longer time and make it accessible to the germinating seed throughout the period of sprouting. 

Also, being made of completely inorganic material, it does not rot or become home to pests and microbes that might harm the seedlings. 

Disadvantages of Rockwool

However, there are a few disadvantages of rockwool that cannot be ignored.

  • It is made of nonbiodegradable material that does not degrade even after long-term usage. And as time passes, it just clusters into itself, making it unusable for germination and harmful to the environment as well.
  • It is more costly when compared to other alternatives that can be used to germinate seeds for hydroponics. 
  • Another disadvantage is that manual supervision is needed due to high water retention, which can cause waterlogging to the roots, which may hinder their growth and nutrient uptake ability.

How To Germinate Seeds For Hydroponics Without Rockwool

Rockwool is basically just a seed starter. The purpose is to provide a space for the seed to absorb oxygen and an adequate amount of water under optimum temperature and pH. This can be done by many alternative seed starters like jigsaw foam, clay pellets, rice hulls, coco coir, net cups, vermiculite and perlite. 

Just like you would germinate the seed in the rockwool, the other alternatives work the same way except for little differences which we’ll see in detail. 

Alternatives to Rockwool

Rockwool has many alternatives which are better in different aspects.

When talking about a seed germination medium, some factors that should be taken into consideration are air spaces, water retention, nutrient uptake, and most importantly, their cost.

Now, let’s have a look at all the alternatives.

Polyurethane Foam

This is one of the simplest alternatives to rockwool for germinating hydroponic seeds. It comes it large sheets and is generally very cheap. This is made from the same material from which the exercise mats are made.

Actually, you can even use those mats to germinate the seeds. However, polyurethane foam has some other benefits too. 

Polyurethane Foam to be used as a cheap alternative to rockwool to Germinate Seeds For Hydroponics
Polyurethane Foam

The sheets are cut in 1×1 inch sizes and a little hole is made in the center. Then water the foam and let it soak in water until it is filled with it. Then place the seed in it, put it on the tray, and place the setup in a place with optimum conditions of air and temperature for seed germination. Once you see the stem coming out of the seeds, you can place them in the hydroponic system. 

The most favorable quality of polyurethane foam is that it minimizes transplant stress. However, the foam is not biodegradable and hence might not be the best choice for you if you are an eco-conscious person. 

Vermiculite and Perlite

These are small pebbles of volcanic origin. Both vermiculite and perlite are always used hand in hand due to their characteristics. 

Vermiculite is a brown rock that has high water retention capability. However, these rocks do not provide aeration if they are used alone. Therefore, they are often used in a 1:1 ratio with perlite rocks.

Little popcorn-shaped pebbles of perlite
Little popcorn-like pebbles of vermiculite

Perlite is a white-colored rock that has little to no water-holding capacity but has high aeration capability due to its shape, which is like popcorn. All the pebbles are randomly shaped, which makes a lot of airspace when they are used in abundance or with other media. 

The proportion of both rocks can be changed to meet the specific requirements of the plant as well, as some seeds require more water than others and vice versa. 

Rice Hulls

Rice hulls are a little covering of rice before they are extracted as grains. They are very lightweight and hence float on the water’s surface. They have high water retention capability and provide good aeration.

These characteristics make them a favorable choice to germinate seeds for hydroponic plants.

Since they float on water, the water levels in the container in which the seed is sowed to germinate are kept very low, 3–4 inches from the base.

Rice Hulls to be used as an alternative to rockwool to Germinate Seeds For Hydroponics
Rice Hulls

The standard procedure is to water the rice hull until they are fully hydrated and then add further water until the water rises 1–2 inches higher from the top of the medium.

Also, being very lightweight, they retain warmth for a long time, making ideal conditions for the seed to germinate.

Rice hulls are actually the byproduct of rice processing factories and plants. So, they are of little to no use of them and are usually discarded as a waste product, making them a very cheap medium to germinate seeds for hydroponics without rockwool. 

Moreover, experiments show that the same seed germination rate in rice hulls was 10 times greater than in soil. 

Coco Peat

This is something that you can make at your home too. Just take the coconut husk, cut it into small pieces, and then grind it in a grinder until it turns to a dust-like appearance.

The resultant product is called coco coir, more commonly known as coco peat. 

Coco peat is basically ground cellulose, the same material that makes up wood.

Now wood cannot be taken up as a nutrient by seed or plant, is it? The same is the case with coco peat.

Therefore, synthetic or organic fertilizers are added to the water, which is then given to the medium for seed germination. 

Coco Peat to be used to Germinate Seeds For Hydroponics Without Rockwool
Coco peat

Its pH is 5.2-6.8, and hence can be used to germinate seeds of almost all kinds of hydroponic plants. Neutral pH, combined with high water holding capacity, makes it a very effective seed starter. 

Moreover, it is completely biodegradable. You can germinate all the seeds you want without worrying about the environment. Yet, it can be kept for years without going bad. 

Since it resembles dust, it can also be mixed with soil or other seed starters and still works ideally as a growing medium. 

Net Cups And Clay Pellets

Net cups are little plastic cups with a lot of empty spaces in between their wall to let the airflow through them.

Since they’re hollow like a simple cup, germinating seeds in them alone is not possible. This is why clay pellets or hydroton pellets are added to them to give the seeds something to hold on to. 

They’re like spherical-shaped little beads; now you can imagine how many air spaces there would be between them.

This way, they provide excellent aeration to the germinating seed. However, clay pellets are not all good, as they have some serious drawbacks too.

Picture of a lot of clay pellets to be used as an alternative to rockwool Germinate Seeds For Hydroponics
Clay Pellets

As the name suggests, they are made of clay. Since clay absorbs a lot of water, so do they.

After absorbing a lot of water, they get much heavier than their original weight. If there are a lot of watered clay pellets in the pot, it makes the pot too heavy to be carried easily.

This might not be a problem for you if you consider it as just a little muscle exercise. 

However, another drawback that cannot be taken positively is that clay pellets absorb water excessively and then dry out similarly; very quickly.

Due to this low water-holding capacity, you need to keep your eyes on it and water the medium whenever you see them drying.

Comparison chart of different media's factors that aids to germinate seeds for hydroponics
Comparison Chart Of Different Growth Media


There are a number of alternatives to rockwool that work equally well or better in different aspects. The final decision as to which seed starter to use depends upon your specific needs and the seeds you are germinating. Also, let’s not forget that seeds need care as human babies before they become strong enough to take care of themselves. Whatever medium you use, in the end, it comes down to your interest and attentiveness to your plants.

4 thoughts on “How To Germinate Seeds For Hydroponics Without Rockwool (7 Better Alternatives)”

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