There are many allotment holders that save and collect the cardboard loo rolls to use for starting off seeds in. I have tried leaving them round but they really bulk up and become a pain in the backside to store that way.
My solution is to find a cardboard box ideally the same depth or a little deeper than the loo roll and fold and flatten the rolls. As can be seen as I gradually filled the box I placed some at 90 degrees to make four rows that I'm gradually adding too.
My sister keeps hers for me, and by the time I get to use mine for pre germinated parsnips I will have a good quantity to play with.
A different sized cardboard box but the same idea a few years ago.
I normally start off the germination of parsnip seeds in Chinese's takeaway containers on a layer of damp kitchen roll, you can see a couple of roots on the seeds in the photo above.
When nearly ready to start transplanting germinated seeds, I fold the loo rolls in the other direction and place them in modules that then stack nicely, and add compost into the loo rolls.
I stuck a small coke bottle into a loo roll marked the bottle with a Sharpe and then cut just below the line so the bottle sits nice and snug on top of the roll. I then made another cut further up the bottle. It works so well as a funnel to get the compost into the toilet roll.
When I see the roots form I transplant the parsnip seeds into compost that I have added to the loo roll and because parsnips grow so fast once germinated, by the time I have a trays worth it's not unusual to see some seedlings poking their heads out
Using a bulb extractor I have that is slightly larger than the loo roll I extract a core and then pop the loo roll into the ground. I tend to use planting membrane and fill a whole bed with 105 parsnips in loo rolls.
One knows which seedling is the parsnip because its the one in the middle of the loo roll so weeding becomes easier as you know what not to weed.
Loo rolls also work well for other fast growing vegetables like runner or French Beans, and sweet peas.
I use small coke bottles with 1mm diameter holes drilled in the cap and mini watering cans, to make watering the loo rolls easier and not to saturate the loo rolls too much, because they can go mouldy if made too wet.
Historically until 2023 I have had great results growing parsnips this way, however last year there were so many slugs and snails that they ate all 105 transplanted parsnips