I used cardboard to plant seeds several times but it got too soggy! My new approach with my styrofoam boxes putting the 15 by 18 box into a white plastic bag is the answer! We throw cardboard away all the time. Some the the boxes are very strong and can be easily cut to form any size container like 4 inches deep and stapple the sides together to make a very storng container. Slidding this box into a white plastic garbage bag that only cost about 6 cents is the way to go.
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The plastic also makes the box stronger and a much better holder of moisture till your seeds sprout! Its very clean and the white plastic reflects lights back onto the seedlings so you can leave them in the boxes for weeks!
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At your grocery stores they throw hundreds of boxes that popcans come in that are the best size for planting and they will give you some free anytime! To make them even stronger put two together! If you ever see the wax coated boxes they are the best and much stronger. A box about 10 bt 15 is very strong and fits in many small bag nicely!
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Make two 6 inch by 12 boxes and put two together and both in one bag for a very strong box with two divided planting areas! What do you think? How about the very small box you can make like 6 by 6 even 6 inches deep. A whole new world of boxes is out there! The world of plastic is here make use of it! You can also get some thin wood slats and staple the box to the slats to make it very stong then put it in a bag
Ths is really a great way to make containers quick. Make a templet from one cut box and just draw on any piece of cardboard and cut it out. A minute a box! Lets hear about how it works for you. Plastic bags for 5 cents and cardboard free! I like bag at least .6 mils like the white garbage bags and they do work great and look nice in the greenhouse!