Starting Seeds for Hydroponics – An Easy Step By Step Guide

Growing your own hydroponic plants can be a very rewarding experience. Not only does it save you money, but it allows you to customize the types of plants and vegetables that are grown in your system.

However, getting started with seed germination involves some knowledge and technique – something as simple as the wrong temperature or humidity can mean the difference between success and failure.

This blog post will provide an overview of why it’s better to start your own seeds rather than purchase seedlings from a store, what accessories you need for successful germination, step-by-step instructions on how to do so, how to transplant those seedlings into hydroponic systems, and finally tips on what things not do when attempting this process.

We hope this guide will help you succeed in your seed starting journey.

Now that we’ve established the basics let’s dive into the details of how to start hydroponic seeds!

Why Are Seeds Better Than Seedlings From A Store?

seeds vs seedling

The biggest advantage for you to germinate seeds is the cost savings. Purchasing seedlings can become quite expensive, and not all stores carry a large variety of plants and vegetables. Seed starting also allows you to customize the type of plant or vegetable you’re growing – which may be difficult to do when purchasing pre-grown seedlings.

On top of this, starting seeds yourself gives you control over how they are grown, allowing for better results in hydroponic systems.

What Equipment Do You Need To Start Seeds For Hydroponics?

When you start seeds hydroponically, there are several accessories you’ll need in order to ensure success.

To get started, the following equipment is needed:

1. Growing medium

When you start seeds hydroponically, there are several accessories you’ll need in order to ensure success.

To get started, the following equipment is needed:

1. Growing medium

rockwool cubes with holes

Your choice of growing medium will depend on how long you plan to keep your seeds in the germination stage. Some people prefer to do seed starting with rockwool cubes and moving them directly into hydroponic systems, while others may use net pots, coco coir, starter plugs, or other types of media.

There are other alternatives for starting medium, which you can check out here.

2. A container/railway

Since you can start an immense number of seeds, it is better to look for trays and boxes that can fit these individual cups and hold water. Look for containers whose depth is between 4 and 6 inches for the best results!

3. Humidity Dome 

humidity dome for plants

The dome or tray traps moisture around the seedlings so they don’t dry out too quickly while also providing air circulation. It should be kept lightly damp until your plants start to emerge.

Another option is to use a humidifier for plants.

4. Heating Mat

Heating mats provide warmth and moisture during germination, ensuring good, healthy young seedlings start! Heating mats will help offset the cold temperature from your winter air conditioner while providing a warm environment for plants on top!

5. Grow Lights

Grow lights help ensure that your young seedlings are getting enough light as they grow into mature plants more suitable for hydroponic systems. Make sure you choose a grow light specifically designed for the type of your growing plants.

6. pH Meter:

A pH meter is necessary to ensure that the water you use for your hydroponic system has the correct acidity – usually between a range of about five and six.

7. Chemicals for raising or lowering pH levels

Adjusting your PH is the only way to control your nutrient balance. When starting seeds for hydroponics in an environment with high pH levels, adding an acid such as phosphoric or nitric acid (in tiny amounts) may be necessary to balance the PH.

Adding too many chemicals will cause a buildup of salts, so it is essential to use only what you need and not over-apply your solution.

8. Seeds:

Lastly, make sure when buying seeds that you pick quality seed varieties that are suitable for hydroponics.

Germinating Seeds Using Rockwool

Rockwool is a popular substrate for hydroponic growers because it provides optimal conditions for the seed and helps keep your seeds moist while they are sprouting.

To start with, you will need to purchase cubes from any gardening store or online shop that sells hydroponics supplies. They usually come in packs of 50-100 cubes per pack, so make sure you have enough to cover all the seeds you want to germinate at once.

Step 1: Soak the Rockwool Cubes

Take the rockwool cubes and place them in a bowl or container filled with water and let it soak for an hour to absorb. Make sure to use lukewarm water, as this will help speed up germination. Let the cubes soak for at least an hour before you start planting your seeds.

Cubes are great for hydroponic planting because they can retain moisture and air. But, if you squeeze them too much, they will deform. The cubes can stay wet for a few days without the need to add water, so just be careful.

Pro Tip: Once you have your water in the container for germination, it is absolutely essential that you test to make sure the pH levels are within a specific range. A few growers recommend adding a half-strength solution or a lower nutrient solution to seeds at this stage. Test the pH of your water using a pH level test and drop it to 5.5 – 6 with a liquid solution. If it’s higher than this, never go below 5.5, as this can damage the Rockwool.

Step 2: Plant Seeds

Once the rockwool cubes are soaked, it’s time to plant your seeds. Carefully take out a cube and make a small hole in the center with your finger or a pencil to depths up to but not more than ¼ inch deep. Alternatively, you can buy cubes that come with holes in them.

Take one seed and place it in the hole, making sure that it is firmly embedded in the cube. Do this for all of your seeds until you have planted them all. The seed needs to be at a height where the water can wick up the cube to the seed while also allowing air circulation from above.

The first thing you should do is cover the container. This can be done with an upturned tray of the same size or something that can sit across the tray without pushing on the cubes. It will create a dark environment that’s vital for successful hydroponic germination.

Step 3: caring for your seeds

It is best to check the water level every day once you have started growing your seeds in Rockwool, even though seeds planted in that medium do not require any watering during the hydroponic germination period.

It is advised not to add any nutrient solution at this stage because seeds sprout are becoming stronger and only need them once they are in your hydroponic system.

The container where you will be seed starting should have an area temperature of 68 degrees Fahrenheit. If growing conditions in the nursery are below this, a heating mat can help keep your trays warm.

After 3-4 days, the first true leaves will emerge. When this happens, carefully select the smaller of the two growing shoots, and cut off the smaller one shoot right above the cube.

Step 4: Transplanting Your Seedlings

Seeds germinate between 2-3 weeks until they can be planted into your hydroponic system.

To avoid waiting, you may check at the bottom of Rockwool starter cubes and transplant when the plants develop healthy root growth that begins to protrude through the bottom. This is a good sign because plants can become root bound in their already moist cubes if left too long.

Now you can move them into larger containers such as air-pots or net pots filled with hydroton rocks to give them more space to grow.

Make sure each seedling has plenty of room so that its roots can spread out without getting tangled up with other plants. If multiple seeds germinate inside a single cube, look for the healthiest one and remove the others. 

When transplanting, be sure to handle the seedlings gently and avoid damaging their fragile roots.

This might seem like a simple task, but plants are vulnerable to transplant shock at this stage. This isn’t only because of the pressures of being removed from the grow tray but also from transitioning into a new environment. The initial shock will take some time for them to recover from.

Step 5: Final Care for Your Seedlings

Once you have transplanted your seedlings, it is important to provide them with the necessary nutrient solution and care that they need in order to thrive in a hydroponic system. Make sure to keep an eye on water levels, pH balance, and other nutrient levels such as calcium and magnesium. You should also monitor temperature levels as some plants may require cooler temperatures during germination while others prefer warmer temperatures once they begin growing.

Why Haven’t All My Seedlings Survived?

There are numerous reasons why not all seedlings will survive, and not all can be explained. But, depending on plants, there are temperature differences that must be accounted for. If you have cool and warm weather plants as seedlings in the same environment, this could be too much of a temperature swing for either type of plant.

Other things you need to be wary of are as follows:

  • Set up everything you need for planting before taking out seeds or plantings from cold storage
  • Media drying out – seeds germinate when placed in a warm moist environment. If they dry out between watering, this can kill them or prevent them from sprouting.
  • Keeping the humidity high is essential. A humidifier or just an upturned tray on top of your grow tray will help maintain the water and dampness. A transparent dome while under lighting can be beneficial too.
  • Don’t overwater or let your Rockwool cubes become too wet as this can lead to seeds rotting before they have a chance to germinate properly. As soon as seeds germinate, you can spray inside your grow tray rather than pouring water.
  • Don’t overfeed – when you start feeding with nutrients, this should only be when you see the first sets of true leaves. The EC of your water should be at a maximum of 0.8 – 1.2. During the early stages of life, plants will obtain all their nutrients from the cotyledons. Only when these first true leaves show they become dependent on external sources of nutrients or fertilizers.
  • Proper feeding – It is important to feed only when you see the first set of true leaves or until a final EC of the water between 0.8 and 1.2.


Starting seeds hydroponically is an excellent way for anyone, even beginners, to start out with little money or space to grow their own food and save some cash in the process!

In this blog post, we have shown you all the steps necessary to start your own plants hydroponically. If you’re still not convinced that this gardening method is suitable for you, check out our article on how to get started with seedlings at home.

Share the knowledge by posting on social media or sending us an email. 

Happy Planting!

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Daniel Buckner is an indoor gardening enthusiast and hydroponic expert with years of experience cultivating a variety of plants. Passionate about sustainable living and urban gardening, Daniel shares his knowledge through engaging content to inspire and educate fellow gardeners. Discover the joys of indoor gardening with Daniel's practical tips and valuable insights.

3 thoughts on “Starting Seeds for Hydroponics – An Easy Step By Step Guide”

  1. Can you please help me and tell me the ideal mixing ratio for A&B fertiliser and the and the best pH needed for growing plants.

    Thanks in advance from a beginner.


    • Hi Tim, a common mixing ratio for A & B fertilizer is 1:1, which means that equal amounts of parts A and B are mixed together to make the nutrient solution. As for the second question, the ideal pH range for plants in hydroponics can vary depending on the specific type of plant being grown but generally falls between 5.5 and 6.5. Good Luck 🙂


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