Egg cartons make eco-friendly, cheap seed starters to start your seeds indoors. Cardboard egg cartons have the added advantage of being biodegradable, allowing you to plant the seedling, pot and all, into the garden. Egg cartons are best used for seeds that have shallow roots (eg onions) or plants that do not like to have their roots disturbed (nasturtiums and cucumbers come to mind). For larger plants you can start them inside the egg cartons then transplant to a larger container when needed. Egg cartons are useful for growing seeds in ‘plugs’ or single form, which is gaining in popularity among large growers because of the huge advantages. Growing transplants in individual cells reduces competition among plants and improves uniformity. Transplant shock is also reduced because there is minimal disturbance to the roots during transplanting.
The downside of using egg cartons for seed trays is that they can become pretty flimsy. As I move my containers around under different heights of grow lights, handling the soggy containers can be tricky. In addition, because the water wicks through the cardboard container, I find that the soil dries out rather quickly, which can make germinating seed difficult and dry out young seedlings, stunting their growth.
What I needed was some form of holding tray for the base which would help hold in moisture and provide support. For plastic egg cartons I nest one set of egg cups inside the plastic lid (if using plastic egg cups don’t forget to poke extra holes in the bottom of the cups to drain water). My thoughts were I needed something similar for the cardboard cartons and the cardboard bottoms, even lined with plastic, just didn’t seem to do the job. My solution to this problem was to make by own free mini lids out of recycled salad containers to hold the egg carton bottoms.
What I used was the large (16oz) salad containers from purchased salad greens and spinach during the winter. I first cut the bottom off the height of an egg carton (about 1.5 inches). Place an egg carton inside and cut the plastic bottom lengthwise the width of the egg carton (about 4 inches). Now you have two sections. Place and tape the sections together, lengthwise, to create one 4 inch ‘tray’.
I also plan to use the discarded tops as mini-greenhouses. Placed over a tray of plants they will help hold in heat and protect them from bugs and critters, either indoors or out. (Read my post about Insect (or mice) Protection for Plant Starts)