This topic honestly can be confusing? I will take a culmination of a few I read and add something I do. Your container veggie garden did fabulous last year, and you are jazzed to start the season healthy. You wonder, should I throw out my old soil and start with new? Id recommend to re-vitalize it! After you have allowed your plant to grow in its potting soil for a year or two, I try to do this every year; you may want to rejuvenate the soil. This will add back nutrients that have been depleted over the years. This is a great way to recycle the soil you already have. Of course, if any of the plants that you were growing were infected with insects or any disease, you will have to get rid of the potting soil to avoid contaminating any new plants.
Put on a pair of garden gloves and remove any plants from your potting soil.
Lay a tarp outside and dump the contents of your flower pots in the middle of the tarp. Run your hands through the old potting soil and remove any plant roots, pieces of plant or stones. Crush up any soil clumps.
Weigh or eyeball how much old potting soil you have. Figure out what half of that is and add that much compost to the pile. You will end up with a ratio of 2:1 (old potting soil to compost). The compost will add new nutrients to your old soil. I have saved coffee grounds and eggshells all winter long so I add 10% off these ingredients to the pile.
Homemade Organic Fertilizer Recipe
To make your own balanced all natural fertilizer:
1/3 cup of green sand (potash and minerals)
1/3 cup of rock phosphate or bone meal (phosphorous and minerals)
1/3 cup of alfalfa or soybean meal (nitrogen)
1 tbsp Azomite (70 minerals and trace elements)
Add 25 percent of either peat moss or perlite to your old soil. This will keep your old potting soil draining well.
Use a shovel to mix the ingredients. Once they are combined, you can begin refilling your flower pots. This recipe has everything covered.