Pre-Sowing with Vermiculite? Here's How

If you want to grow your own summer vegetables, pre-sowing is the way to go. That means you germinate the seeds indoors and move the plants outside later on.

You'll need some special pots, vermiculite, and MM-mix. Your plants will grow much faster and stronger than with the usual pots and potting soil.
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Pre-sowing my bush tomatoes

What is pre-sowing you ask?

Most seeds can be sown straight into your raised bed. They germinate, seedlings pop up, and your plants grow big and strong.

When you pre-sow, you start sowing indoors.

Your seedlings grow in a greenhouse or on the windowsill. You give them just the right amount of light, nutrients, and warmth. When they're ready, you'll transfer them to your garden.

This page gives you the scoop on pre-sowing using MM-Airpots and a mixture of fine vermiculite and MM-mix.

This works way better than using just soil or vermiculite in an ordinary pot. Also, it’s fast and easy to do.
Why do you need to pre-sow?
Many summer plants like tomatoes take months to produce fruit. And even then, only if the weather is warm enough.

They also need plenty of warmth to germinate and grow. Here in the Netherlands, it only gets hot enough the second half of May. But if you wait and only start then, you're too late. Four months later the days get shorter and cooler. You'll need a lot of luck to harvest ripe tomatoes.

So, pre-sow your tomatoes between late March and mid-April inside. If you move the plants into your raised beds at the end of May, you'll pick your first tomatoes by the end of July and continue through mid-October.

Zucchini, pumpkin, and cucumber grow faster, but they also need a lot of warmth early on. That's why you pre-sow them indoors too, but you can start later: from late April to late May. Their seeds are much larger, so the process is a bit different than with tomatoes. 
When do you sow summer vegetables?
Pre-sow tomatoes from March 25 to April 15.

For zucchini, pumpkin and cucumber you pre-sow later. The ideal time is late April to mid-May.

If you are pre-sowing for the first time, best to start as late as possible: tomatoes preferably around mid-April, the rest in the first half of May.

This way you don't have to take care of your plants for as long indoors. That's not always the easiest part for beginners.
How many seeds do you sow?
I like to sow 2x as many plants as I'll need later. So if I want to put two tall tomatoes, I'll germinate four.

If one doesn't sprout, or if something goes wrong during the process, then at least I have a backup.

Many gardeners germinate a whole bunch at once. I'm not into that. You have to keep them all safe and happy indoors until they're strong enough to be moved outside and you also have to find space for them on the windowsill. My windowsills aren't that big.

Afer all that, you'll end up with too many plants. You either have to give them away or throw them away. And no one wants to put good plants in the trash. 

What do you need to pre-sow?

Just these few thing: 

Here's how you do it:

Step 1: In the mixing bowl, combine one part vermiculite and one part MM-mix.
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Equal parts MM-mix and vermiculite
Step 2: Pour in just as enough water so the mixture sticks together.
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Add some water
Step 3: Fill the MM-airpots with your new concoction. Press it down gently with the rounded side of a spoon.
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Fill up the pots
Step 4: Poke a hole in the middle of the soil mix up to 1 cm deep. 
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Perfectly poked holes: max 1 cm deep
Step 5: Cut open the seed bag and place 1 seed in the hole. Then gently cover the holes.

(Our tomato seeds are expensive, so you only sow 1 seed per pot. For cheap seeds, you can use 2 or 3).
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Step 6: Put your MM-airpots in a bowl or dish and place it in a warm place.

If you are sowing different varieties, label them right away. 
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Nice and cozy on the windowsill

So, what's next?

After about a week the first seedlings will emerge. It's automatic, one day they're just there! You don't have to do anything except check if the mix is still moist. You should check regularly because seeds won't germinate without moisture.

As soon as you see the seedlings poking out, put the pots somewhere that gets the most light, but won't get too warm. 

Keep your mix moist and give the pots a quarter turn every day. This stops the seedlings from growing crooked. 
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Tomato seedlings on the windowsill

Windowsill care

Caring for your plants while they chill on the windowsill actually is kind of tricky. They want lots of light, but not too much warmth: that's important. So full sun, but not warmer than 20°C max, preferably a little cooler. 

Keep giving them a quarter turn every day and keep the mix moist. 
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The baby tomato. They grow up so fast.

Repotting, hardening off and moving them out

Toward the end of April, transfer your plants to a larger pot full of MM-mix. No vermiculite this time. In a bigger pot, your plant has more room for its roots so they'll continue to grow.

Once the end of May rolls around, let the plants get used to the outside. Start with an hour and then let them out a little longer every day. This is called hardening off.

After a few days, you'll move the most beautiful plant into its new home. 
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A freshly planted cherry tomato alongside the trellis

The app helps you step by step

Alright. So, that was a lot. But you don't have to remember it all.

Each step is fully written out with images in the app. It also gives you the right instructions at the right time.
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The app walks you through every step
From starting your seeds to removing the plant at the end of the season. And everything in between. 

That way, you pretty much can't go wrong. 

Crazy, right? I think it's kind of magical. You can make so many tomatoes from just one tiny seed.
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The Yellomato in an MM-mini

Ready to pre-sow?

The seeds, air pots, mix and pre-sow vermiculite are in the shop. The rest you've already got :-). 

Good luck!
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PS... Why do seedlings grow better in MM-Airpots than in regular pots?

Okay, so in regular pots, roots keep growing along the sides of the pot. They're so busy growing in endless circles, they don't absorb as many nutrients.

With the MM-Airpot it's different. These net pots have openings on the sides:
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MM-Airpots
If a root comes too close to the side, it stops growing. This is called air pruning. 

Instead of the roots getting longer and growing in circles, the plant will then produce new roots over and over again. The result is a strong root system with lots of young and healthy roots that absorb air, nutrients, and moisture.
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Left: A regular pot. Right: An MM-Airpot.

Your plants will grow faster and become sturdier.

On top of that, you don't need to repot them as often. You'll also have less trouble transferring to your outside garden raised bed or MM-mini.
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What's the diff? Left is an MM-Airpot, right a regular pot