HOME: A beginners guide to seed starting for hydroponics

HOME: A beginners guide to seed starting for hydroponics

We’ve received questions from aspiring vertical farmers and home-growers about seedlings for hydroponics. Questions like; do I need to grow from seeds in a hydroponic system? Should I use young plants from a local supplier? How can I shorten the time to harvest? And can I grow the whole year-round in a vertical farm?

If you are having the same questions please read on. This blog is for you. 

Seeds are better than seedlings
  1. Grow what you like, and when you like
  2. Seeds are clean and don’t come with bugs, but young plants might
  3. Seeds are inexpensive
  4. It's more fun
Things you need to start with seeds
  1. Purchasing seeds
  2. Types of seeds
  3. Media
  4. Seedling tray
  5. Heating mat
  6. Grow lights
  7. Nutrients
Step-by-Step Instructions - Germinating seeds for hydroponics
  1. Prepare the growing medium
  2. Place the seeds
  3. Add water and nutrients
  4. Grow lights and hardening
  5. Ventilation
  6. Cutting small seedlings
  7. Transplanting the seeds

One of the amazing things about vertical farming and hydroponics is that you have complete control over the whole environment like air, water, light and nutrients. So you will be able to create optimum conditions for a plant to grow.
You may have had some success with your grow shelf or you might be making one right now. It is exciting to grow your own and you will enjoy eating from your produce. But where do you get the first plants from? Perhaps you bought some young seedlings from a store in your neighborhood. Buying pre-grown seedlings help you to get started fast and get growing. However, if you would want to optimize your harvest and your growing system it is a smart idea to germinate seeds as well.
In this blog, we’ll look at why seeds are better than seedlings. In the second part, we’ll go over the things that you need to start with seeds. And in the third part, we’ll help you with a step-by-step guide, so you can germinate seeds for hydroponics yourselves as well.


Seeds are better than seedlings

Buying seedlings are an amazing option if you’re in a hurry and new to vertical farming.
If you’ve been growing for a while and you’ve got a grow shelf or system you should consider germinating seeds at your location. The quality of the seed or young plant has a very large influence on your harvest and possible issues that you can encounter.

Grow what you like, and when you like

Perhaps you want to grow a special herb or a Japanese vegetable that your local store does not have. When you buy seedlings from the store you’ll depend on what they have available. For example, when we were looking for strawberry plants, no store had them, because it wasn’t the season for regular growers. In addition, some young plants are difficult to get especially if you want exclusive (and high-value crops) that are normally imported from overseas. These plants may have a protected status and there must be some reason why they are imported. However, you can often buy seeds from all over the world and have them shipped to your home or farm.

Seeds are clean and don’t come with bugs, but young plants might

When you start from seed to young plant in your own space, you can germinate them in a clean and soil-less environment. But when you buy from a store you won’t know how clean the media or sponge is. For example, when we bought young kale plants it came with some kale bug eggs as well. We didn’t notice it until a hole appeared in the kale and it is too late. In another instance, I noticed some dirt around the lettuce plants. I didn’t know what it was until I watched the time-lapse. Apparently, at night some bugs came out and they stayed near the root zone area.
Another issue with young plants from the store is that they are often fitted in a net pot. That net pot might not fit your hydroponic system and you’ll have to replant. Replanting them in your pots might damage the roots and healthy roots will give you healthy plants. When you start from seeds in a soil-less system you can avoid issues with roots that are damaged during replanting.

Seeds are inexpensive

Buying seeds is always more affordable than buying seedlings of the same crop. And you won’t have to worry about transport from the store to your grow system. With seeds, you can grow at your location. 

It's more fun

It’s fun to watch something grow from seed. And are you a person who recognizes the leaf shapes? when we bought seedlings we want to buy beautifully shaped leaves, but nothing is more beautiful than the leaves from a seedling that grows in your own space.

Things you need to start with seeds

Seeds are relatively easy to germinate. You will need a seedling tray, water and some warmth, nutrients are often not required in large quantities.

Purchasing seeds

Your local garden store will have seeds, and there are many websites from which you can buy seeds. 
Try not to buy more seeds than you can use. If you are buying extra keep in mind that seeds are living organisms. Store them in a dark, cool and dry environment. If temperature and humidity fluctuate it will rapidly deteriorate the quality of your seeds. Also, make sure that rodents and insects can’t get to the seeds. You can refrigerate seeds. Place it in an enclosed or sealed box below 4 degrees Celsius and relative humidity of about 20-40%

Types of seeds

Organic seeds
Organic seeds are becoming more popular. The choice of whether you use organic or conventional seeds is up to you. Note that the definition of organic differs per country, so check out what organic means. The availability of organic seeds is increasing, but there are probably more conventional varieties available.

Heirloom seeds
Heirloom seeds are open-pollinated by wind or insects and with no human intervention. Heirloom seeds may have local characteristics and can be surprising. Yet they are less predictable than hybrid seeds and it can be a challenge to grow them successfully. They may be more prone to disease and insects.


Seed plugs
You can get seeding plugs that are made for seed germination. Often they are made from rock wool, coco coir, peat, or something similar. These cubes can hold water and air. Rockwool cubes are very good at absorbing water and are clean. Coco coir and peat plugs may also be optimized for a certain ph range and contain some nutrients to help the development of the seed into a plant. Each plug has a hole in which you can drop 1 to 3 seeds (depending on your preference). 

Perlite or vermiculite
In this case, you can drop seeds on the perlite or vermiculite. but transplanting the seeds will be difficult since the roots will grow into vermiculite. It can however be a very good option if you are growing microgreens or herbs that you would want to cut after a few days anyway.

Sponge cubes
This is one of the cleanest approaches for soilless germination. You can also find sponges that have some 3d shape so your seeds will fall right in the middle. Sometimes you can reuse these sponge cubes if you're able to recover the cubes during transplanting.

Seedling tray

A seedling tray holds the media, whether it is rock wool, coco peat, or sponge cubes. Often they have a tray in which you can pour water, a mesh on or pre-made plug holes in which you can insert your media and a cover to keep it humid.

Heating mat

If you are growing in colder regions, you could consider buying a heating mat to increase the temperate to 20degree Celsius. If it is too cold, seeds might not germinate. If you’re in a hot region, you could place the seedling tray for 2-5 days in a cooler darker place to stimulate germination.

Grow lights

In the first few days, you will be able to germinate at a window sill or with some natural light. Light plays an important role to trigger the seed to germinate and it will develop towards the light. As soon as it starts to sprout, grow lights can help the seedling to grow a thick meristem and develop better rooting. This will help the plant to develop and grow well and it is more likely that the plants will grow stronger and vigorously. Without grow lights, you might get spiny and thin seedlings. You don’t need too much light. Consider your seeds as a baby, baby’s cannot take solid food, so if you’re putting strong grow lights that are meant to drive photosynthesis in adult plants it would exhaust the seedlings. Use plant-centric lights that are made for plant nurseries and that can help you to get to more than 10 and less than 40 umol/m2/s on the plant leaves. Do not use high wattage lights above 40watt in a single fixture, most likely they will emit too much plant-centric light or unbalanced light. 


Seeds will have some nutrients within them, you can start with clean tap-water or a very diluted solution. Do not use nutrients at the same strength as you would with adult plants.

Step-by-Step Instructions - Germinating seeds for hydroponics

Prepare the growing medium

Rinse or soak your sponge or rock wool, make sure they are moist. You can treat rock wool with RO filtered water since rock wool has a high pH. 

Place the seeds

Not all seedlings will germinate, so you can use 1-3 seeds per tube. This is up to your preference.

Add water and nutrients

Fill the tray with RO treated water in case of rock-wool, coco-coir, or peat. Fill it with normal tap water in the case of sponge cubes. Make sure the cubes have about 1 cm of water but not more. the seeds should not be submerged in water. Add water if the water level goes down.

Grow lights and hardening

If you’re growing indoors some grow lights will help you to get healthy and strong seedlings. You can use grow lights up to 10-12 hours a day, maintaining a day/night rhythm. As seedlings grow the need for light increases. Especially when they develop true leaves. Seedlings grow towards the light so the light intensity on the leaf increase naturally. If you grow without or with weak natural daylight you need to use grow lights. With the Nurser 3 grow light set you can also opt to turn on 1 light and turn on both lights as the seedlings grow. Move the lights up if the leaves get too close to the light. You have to move the lights up to avoid leaf burn. This is particularly the case with fluorescent, incandescent, and HID lights. They will generate a lot of heat so you need to put them at a fairly large distance. In addition, these light sources are not optimized for plant-centric light. LEDs are much cooler so you’ll have fewer burn issues. Get lights with plant-centric light, since plants are receptive to different light than the human eye.


Air movement is helpful, especially indoors. it will make the seedling stronger and also supply co2 which is needed by the seedling for its photosynthesis. Airflow can also spread disease or insects problems, so if you can filter your air it would be helpful. Fresh outside air would be the best. 

Cutting small seedlings

If you’ve placed multiple seeds in a cube and they start to sprout together, cut the weakest one and keep the stronger ones.

Transplanting the seeds

Your seedlings are ready for transplantation when they develop one set or two sets of true leaves. A true leaf is a leaf that can conduct photosynthesis and this means the plant can grow. Baby leaves are the leaves that appear right after germination, they may even have the empty seed on top, but they are not leaves that can drive photosynthesis. this process from seed to seedling with some true leaves can take up to four weeks, but check the germination instruction on your seedling packaging. The seedling should also have plentiful, healthy, and white roots.
Handle seedlings with care, they are tender and easily damaged. Do not press the medium around the plant or on the roots, this will damage the roots. Once your seedling has enough leaves remove the sponge if possible, else place the seedling in your hydroponic system with its original cube. You could trim down the sponge if you’d like to. 

You’re now ready to grow like a pro. Let us know what you are growing. We’d love to hear from you.

Another process to prepare seedlings is through a process of plant tissue culture. If you are interested, we'll make a post about that later.

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