How do you start tomatoes indoors?
Tomatoes and other summer vegetables grow best when started indoors in a special seed-starting mix and breathable pots. This helps the seedlings grow into strong plants.
What does starting seeds indoors mean?
Most vegetables are sown directly in the raised bed, in the square where they will stay. The seeds germinate there, the seedlings emerge and the plants grow until they are ready to harvest.
When you start seeds indoors, the seedlings grow in a greenhouse or on a windowsill. You give them just the right amount of light, nutrients and warmth until they are large and strong enough to plant outside in your raised bed.
This page explains how to start them in small MM-Airpots with MM coconut seed-starting mix.
This works much better than ordinary pots filled with MM-Mix or potting compost, and it does not take long to set up.
When you start seeds indoors, the seedlings grow in a greenhouse or on a windowsill. You give them just the right amount of light, nutrients and warmth until they are large and strong enough to plant outside in your raised bed.
This page explains how to start them in small MM-Airpots with MM coconut seed-starting mix.
This works much better than ordinary pots filled with MM-Mix or potting compost, and it does not take long to set up.
Please note: Almost all the photographs show the older MM seed-starting mix, but the steps are nearly the same with MM coconut seed-starting mix. We will create a separate page once we have all the new photographs.
The older seed-starting mix is similar to MM-Mix, but contains half as much plant food and is sieved more finely. It contains compost, peat fibres, coconut coir and wood fibre. Each bag contains 5 litres of ready-to-use mix.
Moisten this mix thoroughly before sowing. Cover the pot with cling film secured by an elastic band to stop it drying out too quickly, then remove the film as soon as the seedling emerges.
Keep checking that the mix remains moist and add water from above. Once it dries out, it can be slow to absorb water again. Do not make it too wet either, as this drives the air out of the mix.
The newer seed-starting mix is made from pure coconut coir and comes as a compressed block. Add water to let it expand. Coconut coir contains no nutrients, so add one tablespoon of MM plant food as well. This makes 6 litres of seed-starting mix.
This mix does not need to be nearly as wet because its fibres hold moisture very well. There is no need to cover the pot with film after sowing. If it later becomes a little dry, add some water to the saucer; the fibres absorb it easily from below.
Another advantage is that the mix does not attract fungus gnats because it contains none of the organic material their larvae feed on, so they do not lay eggs in it.
Finally, coconut mix does not make your hands dirty. A small detail, but a pleasant one.
Moisten this mix thoroughly before sowing. Cover the pot with cling film secured by an elastic band to stop it drying out too quickly, then remove the film as soon as the seedling emerges.
Keep checking that the mix remains moist and add water from above. Once it dries out, it can be slow to absorb water again. Do not make it too wet either, as this drives the air out of the mix.
The newer seed-starting mix is made from pure coconut coir and comes as a compressed block. Add water to let it expand. Coconut coir contains no nutrients, so add one tablespoon of MM plant food as well. This makes 6 litres of seed-starting mix.
This mix does not need to be nearly as wet because its fibres hold moisture very well. There is no need to cover the pot with film after sowing. If it later becomes a little dry, add some water to the saucer; the fibres absorb it easily from below.
Another advantage is that the mix does not attract fungus gnats because it contains none of the organic material their larvae feed on, so they do not lay eggs in it.
Finally, coconut mix does not make your hands dirty. A small detail, but a pleasant one.
Many true summer plants, including tomatoes, take months to produce fruit and only do so when it is warm enough. They also need warmth to germinate and grow.
Here in the Netherlands, it is too cold until mid-May. If you only sow then, you are too late: four months later the days are shorter and temperatures fall quickly, leaving little chance of ripe tomatoes.
Start tomatoes indoors between late March and mid-April. Move the plants into your raised bed in late May and you can harvest the first tomatoes in late July, continuing until mid-October.
Courgettes, pumpkins and cucumbers grow faster, but they also need plenty of warmth at first. Start them indoors later, from late April to late May.
If this is your first time, begin as late as possible: tomatoes around mid-April and the others during the first half of May. This shortens the time you have to care for the plants indoors, which is not always easy for beginners.
Here in the Netherlands, it is too cold until mid-May. If you only sow then, you are too late: four months later the days are shorter and temperatures fall quickly, leaving little chance of ripe tomatoes.
Start tomatoes indoors between late March and mid-April. Move the plants into your raised bed in late May and you can harvest the first tomatoes in late July, continuing until mid-October.
Courgettes, pumpkins and cucumbers grow faster, but they also need plenty of warmth at first. Start them indoors later, from late April to late May.
If this is your first time, begin as late as possible: tomatoes around mid-April and the others during the first half of May. This shortens the time you have to care for the plants indoors, which is not always easy for beginners.
Besides summer vegetables, we start a few other varieties indoors. They stay inside for much less time and move outside quite soon.
We use this method for African marigolds, Bush basil and Liquorice mint. They germinate more reliably in warmth and are especially vulnerable while small, for example to slugs.
The same applies to sunflowers. Slugs love the young plants, but because sunflowers grow quickly, start them in a large Airpot straight away.
We also recommend this for pelleted seeds such as Crystal lettuce, Crispy, Green Batavia, Red Butterleaf and Oakleaf. These plants eventually fill a whole square, but you can use that square for another crop first.
If you only have a few squares, you can also raise many other vegetables in small Airpots. When space becomes available, plant them in the square and harvest earlier than if you only sowed then. This works well for Baby broccoli, Chinese chives and Dino kale.
Please note: Do not start varieties that dislike transplanting, such as carrots and beetroot, in pots.
Read the full short indoor-starting method here.
We use this method for African marigolds, Bush basil and Liquorice mint. They germinate more reliably in warmth and are especially vulnerable while small, for example to slugs.
The same applies to sunflowers. Slugs love the young plants, but because sunflowers grow quickly, start them in a large Airpot straight away.
We also recommend this for pelleted seeds such as Crystal lettuce, Crispy, Green Batavia, Red Butterleaf and Oakleaf. These plants eventually fill a whole square, but you can use that square for another crop first.
If you only have a few squares, you can also raise many other vegetables in small Airpots. When space becomes available, plant them in the square and harvest earlier than if you only sowed then. This works well for Baby broccoli, Chinese chives and Dino kale.
Please note: Do not start varieties that dislike transplanting, such as carrots and beetroot, in pots.
Read the full short indoor-starting method here.
What do you need to start tomatoes indoors?
Below, you can see how we start tomatoes. Cucumbers, courgettes and pumpkins need a slightly different approach, which I will explain too.
Besides the seeds, you will need:
Besides the seeds, you will need:
- small MM-Airpots
- MM coconut seed-starting mix
- cling film and elastic bands if you use traditional seed-starting mix; these are not needed for coconut mix
- one label for each pot
How to do it
Step 1: Gather everything you need.
Step 2: Fill the Airpots with MM seed-starting mix. Gently firm it with the back of a spoon, then moisten it thoroughly without making it too wet.
Step 3: Make a hole no more than 1 cm deep in the centre of each pot.
Step 4: Cut open the seed packet and put one seed in the hole, then gently close the hole.
Step 5:
If you use the older seed-starting mix, carefully add a little water, cover the pot with clear cling film and secure it with an elastic band. This prevents the mix drying out too quickly.
If you use coconut seed-starting mix, skip the watering and covering in this step.
If you use the older seed-starting mix, carefully add a little water, cover the pot with clear cling film and secure it with an elastic band. This prevents the mix drying out too quickly.
If you use coconut seed-starting mix, skip the watering and covering in this step.
Step 6: Put the pot in a small bowl or saucer and place it somewhere warm. If you are sowing different varieties, add a name label straight away.
The pot below contains coconut seed-starting mix. If the mix becomes a little dry, add some water to the saucer and the coconut fibres will absorb it from below.
The pot below contains coconut seed-starting mix. If the mix becomes a little dry, add some water to the saucer and the coconut fibres will absorb it from below.
I like to sow twice as many plants as I will eventually need. If I want one tall tomato beside the trellis in each of two raised beds, for example, I start four plants.
If one seed fails to germinate or something goes wrong while the plants are growing, I still have a spare.
Many Makkelijke Moestuin gardeners start a huge number at once, but I am not a fan. You have to keep every plant healthy until it can go outside, which is a lot of work, and every pot needs room on the windowsill. I do not know what your home is like, but my windowsills are not very large.
You also end up with far too many plants and have to give them away or throw them out. Almost nobody can bring themselves to do the latter.
If one seed fails to germinate or something goes wrong while the plants are growing, I still have a spare.
Many Makkelijke Moestuin gardeners start a huge number at once, but I am not a fan. You have to keep every plant healthy until it can go outside, which is a lot of work, and every pot needs room on the windowsill. I do not know what your home is like, but my windowsills are not very large.
You also end up with far too many plants and have to give them away or throw them out. Almost nobody can bring themselves to do the latter.
What happens next?
The first seedlings emerge after about a week. This happens by itself; you do not need to do anything.
As soon as you see them, remove the film from the pots:
As soon as you see them, remove the film from the pots:
Move the pots to the brightest place you have, but preferably somewhere that is not too warm.
Keep the mix moist and turn each pot a quarter turn every day. This stops the seedlings leaning towards the light.
Keep the mix moist and turn each pot a quarter turn every day. This stops the seedlings leaning towards the light.
Caring for plants on the windowsill
Keeping young plants healthy on a windowsill can be difficult. Plenty of light without too much warmth is important: full sun, but no warmer than 20°C, and preferably a little cooler. If you have a greenhouse, they can move there.
Continue turning the pots a quarter turn each day and keep the mix moist.
With the older MM seed-starting mix, water at the base of the plant. With MM coconut seed-starting mix, add water to the saucer so the fibres can absorb it from below.
Continue turning the pots a quarter turn each day and keep the mix moist.
With the older MM seed-starting mix, water at the base of the plant. With MM coconut seed-starting mix, add water to the saucer so the fibres can absorb it from below.
Repotting, hardening off and planting outside
Around late April, move the plants into large Airpots. They now need more nutrients, so fill the pots with MM-Mix or MM coconut mix with plant food added.
Repotting encourages the plants to form extra roots and helps them grow faster and stronger.
Repotting encourages the plants to form extra roots and helps them grow faster and stronger.
During the second half of May, gradually get the plants used to outdoor conditions by leaving them outside a little longer each day. This is called hardening off.
Once they are hardened off, plant the strongest plants outside in your raised bed.
Step-by-step help from the app
That was a lot of information, but you do not need to remember it all.
Every step is explained in the app, which gives you the right instructions at the right time.
The app guides you from the very beginning, when you start the seeds, to removing the plant at the end of the season, and through everything in between.
That makes it difficult to go wrong.
It is almost unbelievable, isn't it, that one tiny seed will eventually give you masses of tomatoes?
What about the other varieties?
Cucumbers, pumpkins and courgettes also need to be started indoors, but much later, from late April to late May.
Their seeds are much larger, so germinate them first and only then put them in seed-starting mix. Use a large Airpot straight away because these seedlings grow quickly.
Read the full method here.
Their seeds are much larger, so germinate them first and only then put them in seed-starting mix. Use a large Airpot straight away because these seedlings grow quickly.
Read the full method here.
For other vegetables, herbs and flowers, such as loose-leaf lettuce, Bush basil and African marigolds, you will usually use small pots. Read more about that method here.
Want to start seeds our way?
The seeds, air pots, MM-Mix, and pre-sow vermiculite are in the shop. The rest you've already got 🙂
Good luck!
PS: Why do seedlings grow better in Airpots than ordinary pots?
In ordinary pots, roots continue growing in endless circles along the sides. All that root growth leaves them less able to take up nutrients.
MM-Airpots are different because they also have openings in their sides:
MM-Airpots are different because they also have openings in their sides:
When a root approaches one of these openings, it stops growing. This is called air pruning. The plant responds by producing new roots again and again, creating a stronger root system with plenty of young, healthy roots that absorb air, nutrients and moisture.
This helps plants grow faster and sturdier.
They also need repotting less quickly and suffer less disturbance when moved to their final place in a raised bed or MM-mini.
They also need repotting less quickly and suffer less disturbance when moved to their final place in a raised bed or MM-mini.
We sell two sizes: small Airpots for the first stage and large Airpots for repotting tomatoes into ordinary mix. Start cucumbers, courgettes and pumpkins in the large size straight away.