Pre-sowing with Vermiculite? Here's How You Do It

If you want to grow your own summer vegetables, you first have to pre-sow them indoors. They need special pots and on a mixture of pre-sowing vermiculite and MM-mix.

They grow better and faster this way than with ordinary pots with potting soil.

What is pre-sowing you ask?

You sow most vegetables outdoors directly in your raised garden bed. The seeds germinate, the seedlings emerge, and the plants grow up big and strong, ready to harvest.

You pre-sow indoors.

The seedlings grow in a greenhouse or on the windowsill. You give them just enough light, nutrients, and warmth until they are strong and large enough to transfer to your raised bed outside.

This page is about the pre-sowing process using MM-Airpots with a mixture of fine pre-sowing vermiculite and MM-mix.

This works way better than using just soil or just 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, they only do so if it's warm enough.

But they also need warmth for germination and growth. Here in the Netherlands, it's too cold for that until mid-May.

If you only start sowing then, you're too late. Because 4 months, later the days are shorter and it cools down quickly. You'll need a lot of luck to harvest ripe tomatoes.

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

Zucchini, pumpkins, and cucumbers grow faster, but they also need a lot of warmth early on. That's why you also pre-sow them indoors, but can start later: from late April to late May.

Since those seeds are much larger, the process is a bit different than with tomatoes. You can read more about that here.

When do you sow summer vegetables?

What do you need to pre-sow

This is what you need:

How to do it

Step 1: In the mixing bowl, make a mixture of half vermiculite and half MM-soil mix.

Step 2: Pour in just as much water until the mixture sticks together.

Step 3: Fill the Airpots with the mixture. Press it a little with the rounded side of a spoon.

Step 4: Make a hole in the middle of the jar in the soil mix with a maximum depth of 1 cm.

Step 5: Cut open the seed bag and put one seed in the hole. Then press the holes closed again.

(Our tomato seeds are expensive, therefore you only sow 1 seed per pot. For cheap seeds, you can use 2 or 3).

Step 6: Put the jar in a bowl or dish and place it in a warm place.

If you are sowing different varieties, put a name label in it right away.

How many plants do you pre-sow?

Personally, I like to sow 2x as many plants as I will need later. So if I want to put a tall tomato in 2 raised beds near the trellis, I pre-sow 4.

If one does not emerge, or something goes wrong during growing, then at least I have a reserve.

Many Planty Gardeners pre-sow a whole load at once. I am not a fan of that. You have to keep them all in good condition until they can go outside - a lot of work - and you have to give them a place on the window sill. I don't know what kind of house you have, but my windowsills are not that big.

Moreover, you will soon have far too many plants. You either have to give them away or throw them away. Hardly anyone can do the latter.

How does it go?

After about a week the first seedlings come up. This happens automatically, you don't have to do anything. However, you must regularly check if the soil mix is still moist, because seeds cannot germinate without moisture.

As soon as you see the seedlings emerge, place the pots in the lightest spot you have, but preferably not too warm.

Keep the soil mix moist and turn the pots a quarter turn every day. This prevents the seedlings from growing crooked.

Taking care of plants on the windowsill

Keeping plants well on the window sill is quite difficult. Lots of light and not too warm: that is important. So full sun, but not warmer than 20 degrees, preferably a little cooler.

Keep turning them a quarter turn every day to prevent crooked growth, and keep the soil mix moist.

Repot, harden off and plant out

Towards the end of April, transfer the plants to a larger pot with only soil mix. This will allow them to create extra roots and they will grow even better.

In the second half of May let the plants get used to the outside air, a little longer every day. This is called hardening off.

Once you have done this, you can place the most beautiful plant outside in your raised bed.

Step by step help from the app

Well, that was quite a story. But you don't have to remember it all.

Because each step is written out in full in the app and gives you the right instructions at the right time.

From the very beginning - pre-sowing - to removing the plant at the end of the season. And of course everything in between.

That way, it can hardly go wrong.

Admit it: it's almost unimaginable right? That you can harvest masses of tomatoes from such a small seed?

Pre-sowing in my own way?

The seeds, air pots, soil mix and pre-sowing vermiculite can be found in the shop, the rest you probably have at home. 🙂

Good luck!

PS: Why do seedlings grow better in Airpots than in regular pots?

In ordinary pots roots keep growing: in endless circles along the wall of the pot. Because of all that growth they hardly get around to absorbing nutrients.

This is different in the Airpots because they have openings on the side:

If a root comes close, it stops growing. This is called airpruning. The plant will then produce new roots over and over again. The result is a strong root system with many young and healthy roots that absorb air, nutrients and moisture.

In this way your plants will grow faster and more sturdy.

Moreover, you need to repot them less often and they will have less trouble transferring to their final spot - your vegetable gardenraised bed or an MM-mini.