Heat Today will be hot in the south of the Netherlands: up to 30 degrees! Check whether your reservoir is still full, whether the mix is still moist, shade vulnerable plants around midday, and wait with sowing until it cools down.
Techniques
Sowing and starting indoors
How do you keep your pre-sown plants healthy?
Pre-sown plants need 4 things: lots of sunlight, the right temperature, moisture, and enough nutrients - but not too much. How to care for your windowsill plants.
Now I use large MM air pots for tomatoes and summer vegetables. They grow just as well as in the former larger pots I used, but take up less space. In most of the photos, you can still see the old pots.
Windowsill pre-sowing
Summer vegetables need to be pre-sown indoors. Then they have to get strong before they can survive the outdoors. That takes time. For tomatoes, it's 7 weeks or so.
Other than time, they need 4 things to grow well indoors:
Other than time, they need 4 things to grow well indoors:
- lots of light - sunlight direct overhead is best
- the right temperature - around 15°C
- enough nutrients - but not too much
- consistent watering
How do you make sure they get all these things?
Why do you raise summer vegetables indoors?
For tomatoes, it takes about 4 months to grow from a seed to a plant with ripe fruit. They need warmth and sunlight during this time.
If you start sowing seeds outdoors when it's warm enough - around late May - it's too late. By September, days are shorter and it cools down quickly, so you won't harvest much.
But if you sow seeds indoors in late March or better, mid-April, you'll have a nice tomato plant by late May. Then you'll harvest lots of tomatoes from late July to mid-October.
Other summer veggies like cucumbers, zucchini, and pumpkins also need warmth to germinate, so it's better to do that indoors. Since they grow fast, sow them indoors in late April or early May and plant them outside in your container by the end of May.
This also prevents birds from stealing seeds and slugs from eating the delicate seedlings.
This also prevents birds from stealing seeds and slugs from eating the delicate seedlings.
1. Seedlings want as much light as possible
Your plants need lots of sunlight. They even create their own nutrients from it. If they don't get enough light, they'll go looking for it. Then their stems grow long and get floppy.
So choose the spot with the most possible light. Place your plants as close to the window you can. And give the pots a quarter turn regularly, so they get light from all sides.
This is how Laura does it:
This is how Laura does it:
She puts them on a table that she can easily move. The table follows the sun during the day and the plants get as much light as possible.
A south-facing window is perfect for sunlight. But beware: temperature is also important. It can be tricky to get the balance right.
A south-facing window is perfect for sunlight. But beware: temperature is also important. It can be tricky to get the balance right.
2. Not too warm - around 15°C
In order to sprout, summer vegetables need a lot of warmth, around 20°C. But once the seeds become plants, that's too warm. Not because they can't handle it, but at lower temperatures, they grow slower and become stronger. And that's what we're going for.
So put your young pre-sown plants somewhere with direct sunlight, but not too warm. Experienced vegetable gardeners put their seedlings in a light, unheated bedroom or in a cold greenhouse after they've germinated.
Mochi puts them under a skylight in the spare room:
So put your young pre-sown plants somewhere with direct sunlight, but not too warm. Experienced vegetable gardeners put their seedlings in a light, unheated bedroom or in a cold greenhouse after they've germinated.
Mochi puts them under a skylight in the spare room:
Xanadu keeps seedlings in the stairwell under a skylight. When it gets too hot, they open the door to the roof terrace for a cross breeze:
If you don't have an ideal spot, or if it's endlessly sunny, there are a couple options.
Take your plants out of the window during the hottest part of the day. Or put something in between like a sheet of white paper or some netting for example.
Tinus uses gauzy curtains:
Take your plants out of the window during the hottest part of the day. Or put something in between like a sheet of white paper or some netting for example.
Tinus uses gauzy curtains:
For Silvia, it's very simple: she just places them in front of her sliding glass door.
Do you have a greenhouse or unheated conservatory?
You're lucky 😄
Because starting from early May, you can move your plants there. Just make sure to regularly check if the potting mix is still moist, as it can dry out quickly in sunny weather.
If it's going to freeze at night, bring the plants inside in the evening, just to be safe. 🙂
If it's going to freeze at night, bring the plants inside in the evening, just to be safe. 🙂
3. Enough nutrients, but not too much
When your seedlings are small they don't need a lot of nutrients. The MM-Mix is full of them, so your seedlings will grow too fast if you only use that. I use equal parts MM-Mix and vermiculite for just the right balance.
As the plants get bigger, they'll need more nutrients. At the end of April, transfer your tomato seedlings to a pot with just MM-Mix.
Traditional MM-Mix contains compost, peat fibres, coconut coir, wood fibre and nutrients, so the plant food is already included. This makes it suitable when you move tomatoes into a larger pot. Moisten the mix thoroughly first and keep it moist afterwards.
MM coconut mix is made from pure coconut coir and comes as a compressed block. Let it expand with water and add MM plant food. It is then ready for a square, an MM-mini or a larger pot. Keep this mix moist too; it absorbs water more easily than traditional MM-Mix.
MM coconut mix is made from pure coconut coir and comes as a compressed block. Let it expand with water and add MM plant food. It is then ready for a square, an MM-mini or a larger pot. Keep this mix moist too; it absorbs water more easily than traditional MM-Mix.
Pumpkins, cucumbers, and zucchinis have larger seeds and should be pre-sown later: from late April to half May. You sow those seeds in the same half-vermiculite-half-MM-Mix mixture in a pot or MM-Airpot.
Since these plants are inside for a much shorter time, you don't have to move them into a larger pot.
No, roots can poke out of the MM-Airpots. It doesn't matter, you can leave them be. The plant will produce new roots inside the pot and form a solid root system.
Since the pot is not very big, cucumber, zucchini, and pumpkin plants need to be moved to their final home outside within a month.
So, let's say you started too early and it's not time to transplant them outside. After 4 weeks or so, transfer your plants to a larger pot with just MM-Mix.
To skip all that, I start as late as possible: the end of April works best 😉
Since the pot is not very big, cucumber, zucchini, and pumpkin plants need to be moved to their final home outside within a month.
So, let's say you started too early and it's not time to transplant them outside. After 4 weeks or so, transfer your plants to a larger pot with just MM-Mix.
To skip all that, I start as late as possible: the end of April works best 😉
4. Water regularly
Keep the mix moist, from the very beginning until the moment they can go outside. The bigger the plants, the more water they need.
If they are in an MM air pot, it's best to water them from below. So, in the saucer or tray that the pots are placed in.
If they are in an MM air pot, it's best to water them from below. So, in the saucer or tray that the pots are placed in.
Getting them used to the outdoors
If you've done all this - and everything went well - by the second half of May, you'll have beautiful plants ready for the outdoors. There's little chance of a hard frost after that.
But before you can leave them outside day and night, you have to get them used to the fresh air first.
But before you can leave them outside day and night, you have to get them used to the fresh air first.
This is called hardening off: you put your plants outside a little longer every day. After about 5 days, you can leave them out all night. If the temperature will stay above 10°C for the next few days, you can transfer them to their permanent home in the garden box.
They need some time to get used to that too. But after a week, they'll start to grow again.
They need some time to get used to that too. But after a week, they'll start to grow again.
The rest is a piece of cake
Keeping the plants in good shape in the windowsill is the trickiest part of growing summer vegetables.
But once they're outside, nature takes over and you don't have to do too much. Just some extra attention once in a while. But more on that next time.
Happy pre-sowing!
But once they're outside, nature takes over and you don't have to do too much. Just some extra attention once in a while. But more on that next time.
Happy pre-sowing!
PS: Tips from experienced Makkelijke Moestuin gardeners
I once asked the community how Makkelijke Moestuin gardeners keep their indoor-raised plants healthy. Many of the photographs on this page came from their replies.
The best tip? Start as late as possible, so you shorten the time these plants need all this indoor care. Start tomatoes in the days before 15 April, and the other summer vegetables from early May.
The best tip? Start as late as possible, so you shorten the time these plants need all this indoor care. Start tomatoes in the days before 15 April, and the other summer vegetables from early May.