Spending lots of money on gardening just does not make sense to me. Of course since I do not have lots of money to spend, not really a problem. This is my method of having seedling starter pots without having to spend hardly any money.
Step 1: Supplies & Tools
1. Toilet paper / paper towel cardboard tubes. ( How many you need will depend on the size of the pan, I needed 28)
2. Baking pan: This can be metal or glass. If you can find one at a sale for a few cents then that's even better. The one in the pictures was bought at a dollar shop. So I invested a whole dollar + tax so far.
3. Growth medium. If you have it then use a good, fine compost. If you do not have a medium you will have to buy one. Which costs more money. Or get creative (feel free to share your creative solution to getting soil)
Step 2: Flatten Tubes
I have found that by flattening the tubes and forcing them to become rectangular instead of cylindrical I can fit more tubes inside the pan. Also it seems to be slightly more stable.
To do this step flatten each tube so that it forms two distinct edges or creases. Next open back up the tube and center these creases on each other. Now flatten again forming another set of creases. After fully forming the creases open the tube again. The tube should be mostly rectangular now and have four distinct corners. Do this with all of the tubes you will need.
Step 3: Making Flaps
Now that you have your rectangular tubes you have to make flaps to close up one end. This will keep the soil in place and allow for easier transplanting into your garden.
You will need to make a cut at each corner. I find it is easier to cut the tubes while flat, cutting through opposite corners at the same time.
The length of the cut should be half the width of your rectangular tube. I found mine to be just under 3/4". This is where your pencil and ruler come in handy. If you want accuracy then use those to make sure you form your flaps just the right height.
Step 4: Folding Flaps
I use what I call the box fold (I have no clue if there's an official name for this fold) to close up the bottom of the tubes.
You start with one flap and fold it into the tube. Rotate the tube clockwise and fold the next flap. Continue this way for all four flaps. They should automatically overlap correctly except for the last flap. You will need to tuck one corner under the first flap you folded. This provides a decent closure to your tube without the need of tape, glue, etc. Also when you transplant into the garden you can pull open this fold to encourage deeper root growth.
Step 5: Place Pots in Pan
Now that you have folded all the pots (which does take a while. I would suggest this for a day during winter.) place them in the pan. If you lined up the tubes before you made them rectangular you will find you most likely need more pots. The rectangular pots fit tighter in the pan than the round tubes.
Once you have the pan full of pots simply take your growing medium and fill each pot to the brim. Some settling will occur so the soil will sink down a little after watering.
Now... plant seeds, be sure to label which seed goes in what pot.
Hopefully with a little care you can reuse the pan each year for many years. That little investment will go a long way. When not in use feel free to stack the pans (I'm assuming you will have more than one pan, right?) in a cabinet.
I keep a sack handy to collect the paper tubes. This way I have plenty for projects like this one whenever I need them.
To water these pots you can either sprinkle water from above or place a small amount into the pan. The cardboard and soil will wick up the moisture. I would suggest watering from above at least until the sprouts are decent sized.