This subject came up recently and I was going to suggest just buying plastic plant markers. Then searched for them in the places I used to buy them, and they seemed in rather short supply. And a lot more expensive than I remember. The availibility of old mini (or maxi?) blinds, plastic jugs, etc., plus the labor of slicing 'em up seemed like a lot more trouble than just buying pre-cut labels and and outdoor marking pen. When I was heavily into growing greenhouse veg plants, I got packs of 50 or 100 plastic labels for a very reasonable price. I *do* agree with "waste not; want not" but only of one's own labor (and materials and tools involved) are over-plentiful.