I've been saving empty soda bottles from work for next Spring. Two liter bottles will make big flowerpot with very straight sides, but that's not for seed-starting, that's for giving away plants. And they will be tippy! (I'll cut off the top and b urn or drill holes in the base.)
I'm also saving 20-ounce plastic soda bottles (2 3/4" diameter and 5 1/2" tall). These are still biggish for starting seeds, but good for potting up seedlings that I started in a 72-cell-tray of 6-pack inserts, or a 128-cell propagation tray.
The problem is that few soda bottles have straight sides. I save "Sobe" and "Vitamin Water" because they are mostly straight with small indentations. I'm hoping that root balls will still come out. They should, unless I let them get too root-bound. And if they are root-bound and circling , I need to spread those roots out anyway! That's what I'm telling myself, but I'll find out next spring.
Very rarely, someone at work will throw away a tall, narrow straight-sided water bottle. I forget the brand name, but they are cloest to your straight-sided lab-tubes.
My main design consideration is simple: the price is right.
I save paper coffee cups whenever I get one. My thoguht there was that, if I gave someone local a seedling in a PAPER cup, they will HAVE to plant it out or pot it up before the paper disintegrates. Is that too fiendish?
