The double cup method is a cheap way of starting
Another benefit of this method is that you can go a lot longer without having to re-pot your seedlings. Instead, you can add more compost to the cup as they grow.
You want to start by getting a regular plastic drinking cup and adding a small stone to the bottom, I will show you why soon.
Then make some drainage holes in a secondary cup. You can do this with a drill or by melting the holes with a hot object.
I melted mine by heating a screwdriver up over my oven top and then puncturing the holes.
Then place the cup with drainage holes inside the cup with the stone.
The stone then creates a gap which allows water to drain away and also acts as a little reservoir.
Add a small amount of compost to the cup and press it down firmly.
You can then sow your tomato seed into the cup.
Sprinkle a little more compost to lightly cover the seed. Then wait for germination.
As your tomato plant grows, you can keep adding more compost to the cup until you fill it.
All of the buried stem will develop roots, leading to a very strong plant. And because the volume of soil is always increasing you don’t need to re-pot your tomato seedling!
Here is a pepper plant, grown using the same method, for example.