Use compost to perk up potting soil from a previous season and keep your container plants sitting pretty. If the past year’s mix doesn’t look too tired, take the quick-and-dirty approach and simply mix it with an equal amount of compost before putting it into your pots.
If more thorough rejuvenation seems in order, start by leaching the old potting mixture to remove excess salts that tend to build up in containers.
1. Put the used soil into a bucket with several small holes in the bottom and fill the bucket with water. Let the water drain out and then repeat this process. After the water has drained away a second time, spread the soil on a tarp in the sun to dry.
2.Mix the leached potting soil with an equal amount of rich, weed-free compost that has been sifted through a half-inch screen.
3.Toss in a light sprinkling of lime and gypsum, and about 1 tablespoon of slow-release or granular organic fertilizer per gallon (4.4 liters) of soil mix.
Add enough water to lightly moisten the mixture; then put it aside in a plastic storage bin or cardboard box to cure for 2 weeks. During this time, the microorganisms from the compost will spread throughout the mix.
When it’s finished, your container plants will have some first-rate potting mix to sink their roots into.
Adapted from The Complete Compost Gardening Guide, by Barbara Pleasant and Deborah L. Martin (Storey, 2008).