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Pre-germination: The essential guide to pre-germinating plants

Seed trays with plant sprouts

Plants play an important role in our everyday lives and can bring life and colour into our homes. How do you start growing your own plants from seed?

The best way to grow your own plants for the greenhouse or garden is to start their life by pre-germinating them indoors.

Pre-germination is a technique where you sow seeds in small containers or baker, with the aim of getting the plants to germinate and grow. Before repotting them to their final location in the garden or greenhouse.
The purpose of pre-germination is to give plants an early start and protect them from external influences, such as weather and pests, until they are strong enough to withstand these factors.

What does it take for plants to germinate?

It takes the right conditions for the tiny seed to germinate and grow - the temperature, timing, light, growing medium and humidity must be just right.
In addition, pre-germination of different seed types may require patience as they don't necessarily germinate at the same time.
With the right approach and equipment, you'll experience success with pre-germination.

The optimal germination conditions

To ensure optimal growth for the little sprouts, there are several factors to consider:

  • Light: Plants need sufficient light for photosynthesis, otherwise you will get spindly and spindly plants.
  • Temperature: Most plants germinate well at temperatures between 18-25°C.
  • Humidity: The plant sprouts need correct soil moisture, not too much and not too little.
  • Land: Sprouts need the right type of soil with the right amount of nutrients.
  • Air circulation: Plants need adequate air circulation to prevent mold and other diseases from destroying the sprouts.
Pre-sprout grow light mini greenhouse

What do I need for pre-germination?

Successful pre-germination requires preparation with the right materials and equipment, and of course the desired seeds.

Here's the key. When choosing sprouting equipment, you should invest in good quality that you can enjoy for many years to come.
This saves the environment a lot of waste and is also good for your wallet.

  1. Seed tray: Choosing the right one seed tray is of great importance for the development of your plants. A good and stable seed tray with good drainage at the bottom is essential to retain moisture in the growing medium and allow excess water to drain away.
    This way you provide the best possible conditions for the plant to develop into a healthy, solid and robust plant.
  2.  Mini greenhouse lid: Once you have sown the seeds, no more watering should be done, otherwise you risk the seeds rotting, so it is recommended to put a lid on the tray so that the soil does not dry out at any point during the sensitive germination process.
    A transparent mini greenhouse lid is recommended so that small plants can be monitored and receive light.
  3. Irrigation tray: A good and stable watering tray is recommended, as it makes it easy to water the plant sprouts from below. At no time should you water from above, as you risk the small plant sprouts rotting, or gnats entering the soil.
  4. Gromedie: Here there are countless possibilities, but the use of garden soil is not recommended, as it contains too many fungi, bacteria and viruses that can damage the sprouts. If you want to grow organically, there is really only one option at the moment, and that is to use coconut soil.

    Coconut flour does not normally contain any form of harmful fungi, bacteria and viruses, but does not contain any form of nutrition either, so it is therefore important to add a good quality fertiliser, preferably at half strength to begin with.

  5. Light: Without light, the small sprouts die quickly, so light is a crucial parameter for success with your plants. Here you can either try putting your seed trays in the window, which will result in plant sprouts stretching towards the daylight, which results in poor and weak plants. A better alternative is to use one grow light lamp that can provide the correct amount of light. For plant sprouts, between 120-180 uMol/m2 is recommended.
  6. Heat: A heating mat can promote germination, especially for seeds and roots that require extra heat to germinate.
  7. Fertilizer: If you choose to use coconut fiber as seed soil, it is recommended to add a good one liquid fertilizer at half strength. Then increase the amount of liquid fertilizer as plants grow. Remember to choose one that suits the Danish conditions with a lot of lime in the water!

3 good tips for a successful pre-germination

  1. Use a cool room with as much light as possible, for example by using LED grow lights, which have low electricity consumption.
    Until the seeds germinate, it can be beneficial to have extra heat, which you can achieve by using a heating mat.
    Once the plants have emerged, the temperature should be lowered to 18 degrees. If it gets too hot, for example from a radiator under a windowsill, the plants will become limp and weak.

  2. Find old flower pots, trays or similar and sow lettuce, spinach or peas.
    Seeds are relatively easy to germinate and can be planted out in late March or early April. March is also a good time to start pre-germinating tomato plants, which can later be planted in a covered raised bed or greenhouse.

  3. Always sow in coconut fibre in seed soil or prickly soil. Ordinary garden soil can harbour weeds, fungi and diseases. This can make it difficult for small plants to thrive.

Why does pre-germination go wrong?

There are many factors that can lead to pre-germination going wrong. Here are some of the most common reasons:

  1. Errors in the soil mix (Use seed soil or coconut fiber soil)
  2. Overwatering or drying out (Use sub-watering tray)
  3. Lack of light (Use a good glow light lamp)
  4. Temperature too high or too low (18-20gr C. is best)
  5. Too much fertilizer (Choose seed soil or coconut fiber soil)
  6. Lack of cleaning of seed trays (Bacteria - clean your tray thoroughly)

By paying attention to these factors, you can minimize the risk of pre-germination going wrong and ensure that your plants grow and thrive.

When do you pre-sprout?

When to start pre-sprouting depends on several factors. How long the sprouts take to develop, e.g. chilli is slow to develop. This is especially true for the hot flavours.

Mini cherry tomato

When to sprout tomatoes?

  • Tomato plants grow quickly and it usually takes less than a month for the seeds to grow 10-15 cm tall.
    Your windowsill or plant table can quickly become overcrowded with half-sized plants fighting for space and light.
    It's therefore a good idea to consider where you want to place your tomato plants as they grow.
    You may want to get a heavy-duty grow light lamp that can cover a large area. If you have a window with good light, you can use this to illuminate your tomato plants, or you can get a full-spectrum grow light.
    It's also a good idea to think about how you will water and prune your plants, as tomato plants need regular watering and pruning to grow healthy and strong.
    Remember, never cut the top shoots of the tomato plant, otherwise you'll end up with a bush of tomato plants that won't produce a good yield.
  • Pre-germinating tomato seeds is an exciting process. It allows you to grow your own fresh tomatoes.
    Follow the above guidance for pre-germination about 8 weeks before planting to mid-May for outdoor tomatoes or early June, and make sure you have a good plan for storing and caring for your tomato plants as they grow.
  • Read more in-depth about pre-germination of tomatoes from seed here.

Step-by-step guide to pre-germinating tomatoes

In this guide, you'll notice that we use seed trays from Danish and Quick pot. If you're curious about which seed trays are recommended, you can read more about it in our guide here.

Tomato plant with fruit

1. Find your seeds: Choose seeds by germination percentage. It would be a shame to spend a lot of time and energy on seeds that don't germinate.  

2. Select seed tray: We recommend choosing one of our seed trays from Danish or Quick Pot.

3. Fill your seed tray: Fill your seed tray with soil suitable for pre-germination of tomato plants, such as coconut fibre, seed soil or potting soil.  

4. Take your Pushplate: Place your pushplate over the cells in the seed tray. Apply pressure and make sure the entire surface is pressed down. Then place your seeds in the soil. If you don't have a push plate, you can use your finger to poke holes. Then place the seeds in the holes.

ATTENTION! Be careful not to press your pushplate down too hard as the soil becomes too compact. 
You also need to be careful not to make the holes too deep.

Last but not least, the type of Pushplate you choose should match your seed tray.

5. Distribute the seeds: Then distribute the seeds in the holes you've just made with your push plate or finger. It can be difficult to ensure that only one seed is placed in the soil at a time, as when growing tomato plants, the seeds can fight for space, so it can be important to be precise.  

6. Top with soil: Cover with soil and brush off to create an even surface.

7. Place your seed tray in the underwater tray: Place your seed tray in an underwater tray. The underwater tray serves its greatest purpose by collecting the water.
Drain from the seed tray. 
Later, when the plants have germinated, all watering is done from below in the watering tray. This prevents the plants from rotting from overwatering the soil up through the roots and prevents the tiny seedlings from being damaged by overwatering.

8. Water your seed tray: Until the seeds have germinated, we recommend top watering while adding a little water to the substrate.
You have now germinated your tomato seeds. 

  1. Use a cool room with as much light as possible, for example by using LED grow lights, which have low electricity consumption.
    Until the seeds germinate, it can be beneficial to have extra heat, which you can achieve by using a heating mat.
    Once the plants have emerged, the temperature should be lowered to 18 degrees. If it gets too hot, for example from a radiator under a windowsill, the plants will become limp and weak.

  2. Find old flower pots, trays or similar and sow lettuce, spinach or peas.
    Seeds are relatively easy to germinate and can be planted out in late March or early April. March is also a good time to start pre-germinating tomato plants, which can later be planted in a covered raised bed or greenhouse.

  3. Always sow in coconut fibre in seed soil or prickly soil. Ordinary garden soil can harbour weeds, fungi and diseases. This can make it difficult for small plants to thrive.

When do you pre-sprout chillies?

Hot pepper - for balcony

  • It's usually best to pre-sprout chilli plants indoors during the winter or spring months.
    They need a certain amount of heat to germinate.
    If you plan to grow chilli plants outdoors in the garden, you can pre-sprout them indoors for 4-8 weeks. Before the last frost date.
    For stronger versions of the chilli, you may need to start as early as December.

  • As chillies need to be pre-germinated very early, it is necessary to use grow light to support their growth over the winter.

Step-by-step guide to pre-germinating chilli

Hot pepper - for balcony
  1. Fill your pots/sprouting trays: Fill them with seed, topsoil and water in the soil. It should be moist, but be careful not to get it too wet.
    It's important that there are holes in the bottom of your pots so that water can drain away.

  2. Add a seed or two: Whether you need one or two seeds depends on the germination percentage.  
    Once you know the germination rate - add one or two seeds to your pot or germination tray. 
    Then cover with approx. 0.5 cm of seed or potting soil and water with an atomiser.

  3. Place them in a warm place: It should be 26-29 degrees. Remember to be patient as it can take some time. A couple of weeks to be more precise, before the seeds germinate. It is possible to achieve faster germination with a lid or some cover.

  4. When the seeds have germinated: Place them in a bright location, e.g. south/east-facing windows. It is important that you remove any lids or covers. For early germination, use grow lights 14 hours a day.

  5. Make sure you're always on the move: The soil should not dry out and you should also avoid overwatering. We recommend the first 4-6 leaves. 
    ATTENTION! This is where your plants are ready to be repotted into larger pots if you have used germination trays.

  6. Have you planted multiple seeds in the same pot: You can either remove the smallest one or repot them in separate pots once they have set the first 4-6 sets of leaves. This is also when your plants are ready to be repotted into larger pots if you've sown in small seed trays.

  7. Soil temperatures:When the soil temperature in the greenhouse is around 15-18 degrees, your plants can be planted out in a large pot, raised bed or directly in the ground.
    Make sure to slowly acclimatise your plants to direct sunlight by putting them outside for a few hours a day and bringing them back inside. The wind will also help make your small plants more robust.

  8. Water regularly: with fertiliser water, preferably every time you water. Look forward to harvesting your first fruits.
    If your plants become too dense, you may want to remove some of the lower branches. This is to provide air and avoid fungus and mould.

  9. Harvest: Take your seeds from a ripe fruit and leave them to dry so you have seeds for next year's cultivation. If you have more chillies than you can use, you can make them into chilli paste, chilli oil, dry them or freeze them so you have your own chillies all year round.

  10. Do you want to: Perennials need to be brought inside over the winter and watered regularly, so it can be beneficial to grow them in pots.

When to sprout cucumbers?

  • Cucumbers are a popular vegetable that can be grown in the garden or on a balcony.
    If you want a good harvest, it's important to start pre-sprouting your cucumbers at the right time.
    This will ensure that the cucumbers have the best possible start to the season.

  • The germination time of cucumber seeds depends on the climate.
    In general, you can start pre-sprouting cucumbers indoors in February or March. 
    When the weather is still cold. When the weather is warm enough, cucumbers can be planted outdoors in the garden or on the balcony.
Sweet peas

When do you pre-sprout peas?

  • Sow peas from late April to early May. This is often the best time as it ensures that the peas have the best opportunity to grow and develop in an environment with sufficient heat and moisture.
    By planting one to two weeks apart, you can also ensure a continuous harvest of fresh peas throughout the season, instead of having to harvest all the peas at once
sprouting peas

Pre-germination of pea seeds is done by the following:

  1. Lay the pea seeds soak for approx. 24 hours.
  2. Fill a seed tray with coconut fiber mulch or seed soil, it is recommended to use one QuickPot 150 R Sowing tray with 150 cells.
  3. Now a pea is sown in each of the 150 cells.
  4. The cells are then covered with coconut flour/ sowing soil.
  5. Place the tray in a warm and bright place, where the temperature is around 20-25 degrees Celsius.
  6. Keep the soil moist until the peas begin to germinate, usually within 7-10 days.
  7. Once the peas have germinated, they must be transplanted into a larger pot or planted in the ground in the garden.
  8. If you grow them as pea shoots, they must be harvested when they are approx. 10-15 cm high,

When to sprout potatoes?

  • Late February is the best time to pre-sprout potatoes. This gives them time to germinate and grow before they are planted in the ground in the spring.
  • Before you put the potatoes in the ground, fill pots or boxes with potting soil or another form of soil. Make sure there is a good amount of soil at the bottom of the container so the potatoes have a solid place to stand.
  • Once you've prepared the container, it's time to put the potatoes in the ground. Place them so that they are evenly distributed in the container. Then cover them with soil so that they are covered to approx. 1/3 of their height.
  • It is important to keep the soil slightly moist throughout pre-germination, spraying the soil regularly with water. Make sure the soil is always moist but not wet.
  • If you didn't get the potatoes to pre-germinate at the end of February, you can still get some pre-germination in the first half of March. Follow the same steps as described above to ensure successful pre-germination.
Fertilizer, growing medium and accessories

Pre-sprouting - Should we fertilize?

Fertilization is an important part of the process of pre-germination of plants. To ensure that your plants get the nutrients they need, you should fertilize them according to the following procedure:

  1. Use a good quality seed soil. The soil must contain nutrients to support the early growth of the plants. If you use coconut fibre, you should add a weak solution of liquid fertiliser from the start.

  2. You can fertilise the seeds with a weak solution of liquid fertiliser. Once they have germinated. This will give them the nutrients they need to grow strong.

  3. Continue to feed the plants with a weak solution of fertiliser every one or two weeks. It depends on their needs.

  4. Use liquid fertiliser. This is intended for germinating plants as it will give them the nutrients they need. To grow properly.

By following these steps, you can ensure your plants get the nutrients they need and will grow strong and healthy.
It's important to note that it's best to fertilise plants regularly with a weak solution of fertiliser, as an overdose of fertiliser can damage plants.

When is it time to repot and how do you repot?

It's not always the best strategy to sow plants individually in large pots from the start.
It will take up a lot of space on your windowsill and the plants will also have a harder time thriving. This is because they don't have enough root growth to hold the soil.
It's better to start with seed trays or mini greenhouses and gradually move the plants to larger pots when they're ready.

When should you repot?

Once the seeds have germinated, the plants grow bigger and bigger until they become too dense in their pot or seed tray.
This is where you should start thinking about repotting. Repotting will give your plants the space they need to continue growing while allowing their roots to reach into fresh soil to get the nutrients they need. Look to see if the roots have filled the cell they are in and if the roots can be seen at the bottom of the cell - lift the tray and take a look.

How to repot

Before you start repotting your plants, it's a good idea to put a newspaper or a piece of paper underneath, as it can be a bit difficult with soil. When the plants are ready to be transplanted, you first take them out of their pot or seed tray, then divide them by the roots if there are several plants in the cell. Since the roots of the plants are vulnerable in this process, it is important to be efficient and transplant each plant as soon as possible.

be aware that you do not dry out the plant's roots during the transplanting process. Therefore, it is a good idea to be efficient and transplant each individual plant as soon as possible. If you want to be extra on the safe side, you can fill the pots with a little water before planting, so that the soil mixture is slightly moist.

When the plants are ready to be put back in the ground, make a hole with your finger in the new potting soil and then carefully set the plant down. Then cover the roots with soil and lightly press around the plant with a finger so that it is firm. It is also important to remember that pot transplanting in larger flowerpot may be necessary several times during pre-sprouting, as the plants grow and take up more space.

Remember that the larger the plants, the more grow light you need, as the plants require more light as they get bigger. It is therefore recommended to use a grolys lamp which can be dimmed and raised/lowered above your plant table.

How to prevent cold shock in the cuttings

To ensure that the plants are in the best possible condition when they are to be planted in their final growing place, it is important to harden them so that they avoid cold shock or burning of the leaves. This can have a negative effect on growth and may even stop it temporarily or permanently. Therefore, it is a good idea to take some precautions to prevent the shock.

First step: Start the curing When the weather gets warmer, you can start curing your plants. You can start by putting them out in the morning in a sheltered place and no direct sun. Then you have to bring the plants back in in the evening. You can do this for a week to prepare the plants for their new life outside.

Second step: Gradual adaptation to the new environment By repeating this step day after day, the plants will gradually become accustomed to their new environment and the new weather conditions. In this way, you can ensure that they avoid cold shock and thus have the best opportunity to thrive and grow.

By following these steps, you can avoid cold shock in your cuttings and ensure they have the best possible start to their new life outside. So get started with the hardening and good luck with the pre-sprouting!