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How to grow petunias from seed

There is a bit of trepidation about growing petunias from seed, with most gardeners preferring to buy small plug plants and grow these on but with a little bit of knowledge and some patience, petunias are no more difficult to grow than any other flowers.

The main problem people find with growing petunias is in the size of the seeds. They are VERY tiny and can be difficult to control.

The fact that they are black, making them all the harder to sow into soil, well not to sow, but to see if you have sown them where you think you have. You can, however, make life easier by adding a little bit of sand to your seeds. Then mixing the small petunia seeds with the sand, you can then see how thinly and where you have sown them.

Let’s get sowing

You can sow petunias in pots but the past has taught me that it is much easier to sow in flat seed trays, this gives you more space to play with. That means you will be able to sow more thinly, reducing the need for thinning later on. It is also easier to monitor the flat seed trays, especially for the moisture level of the soil. And you guys know me, I don’t see the point in over complicating things.

I don’t use anything fancy in way of a seed tray, but a couple of good things to ensure are that there are drainage holes in the bottom and, if like me you have an unheated greenhouse, that the tray will fit inside a propagator.

I have a bundle of seed trays (in two different sizes) that I bought online (I’ll link them below for anyone who is in need of their first set up). They are sturdy and will last for ages, but I also use any old random bits and bobs we have lying around, like the plastic trays veggies are packed in in your local supermarket.

So, now you have your very glamourous trays, fill them with soil, it doesn’t have to be anything fancy, but you want a seedling soil or potting compost, something fine so that the wee root systems don’t have to fight to get going. Importantly too, with low nutrient content, so not your good stuff. The reason you use low nutrients is to prevent the delicate new seedlings from being “burnt”. They are incredibly delicate to start with.

OK, once you have filled your tray, use the base of another tray or pot or even your hand to press it down so that it’s level.

Hurrah! We are ready to go!

Right, now we have a nice level surface for our seeds so next we need to give that compost a really good water. We do this now rather than after we sow the seeds as the water will move the seeds around, no matter how fine you think your watering can rose is. Just trust me on this one, the seeds move sooooo easily. So we do it now to keep things neat and organised. So give it a really good soak.

Ok ma tha (right then), that’s us ready to go.

This is the bit that freaks some people out. Petunia seeds are tiny. Soooooo tiny and that makes them quite difficult to handle.

See what I mean? There are actually about 50 tiny seeds in the tip of that little tube.

So forget any ideas you had of sowing these seeds one by one, that just is not going to happen. Instead, we are going to sprinkle.

So like I said before, we sprinkle these as evenly as we can across the tray. If you are worried about not being able to see these, you can mix the seeds with some sand, that way you can see where you sprinkle the sand and know that you have roughly sprinkled the seeds to match.

OK so we have watered the compost, sprinkled the seeds… what now?

Well believe it or not that’s it. The trick with petunias is that they NEED light to germinate, so unlike with other seeds, we don’t add a layer of compost or grit over the top of the seeds. We leave them on top of the soil, letting the light get to them. Easier than you thought huh?

If like me you don’t have a heated greenhouse or live somewhere not particularly warm then you can put your seed tray into a propagator In a sunny spot to help keep the moisture and any warmth the sun generates in. I find this makes a big difference with my seedlings.

Sunflowers and Gazania in the propagators

Easy peasy huh?!

As promised, here are links to the trays, propagators etc I use.

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