When your flowers fade, and the temperatures drop, it's time to empty your containers and put them away for the winter. It's tempting to keep and reuse the old potting soil, which can be pricey, especially when you have a lot of potted plants like I do. But this lightweight mix of compost, peat, perlite, and other materials doesn't last forever. Plants use up the nutrients in it as they grow, and the mix can become compacted and filled with roots. Sometimes pests, diseases, and weeds can take up residence, ready to pop back up when you replant in the mix. However, you can remedy each of these issues and get another use out of your potting soil with a little extra work.
It's generally fine to reuse potting soil if whatever you were growing in it was healthy. If you did notice pests or diseases on your plants, it's best to sterilize the mix to avoid infecting next year's plants. First, remove any roots, grubs, leaves, and other debris from the old potting soil. Then, decide on the best method for banishing microbes and insects.
One technique for sterilizing soil is called solarizing. It involves putting old potting soil in lidded, five-gallon buckets ($9, The Home Depot) or black plastic bags that are tightly tied shut and leaving them in the sun for 4-6 weeks. The heat builds up inside the buckets or bags just enough to kill bugs and pathogens.
You also can sterilize old potting soil in your oven. Place it in an oven-safe pan, cover with foil, and bake it at 180 to 200 degrees Fahrenheit for 30 minutes. (I tried this once, but didn't like the earthy smell it created.) It's also important to check the soil temperature with a candy or meat thermometer ($22, Williams Sonoma) to make sure it stays below 200 degrees. Higher temperatures can release toxins. When it's done, take the soil out of the oven and keep it covered until it cools.
Microwaving is another option. Put old, moistened potting soil in quart-size, microwavable containers. Cover them with microwavable lids—never use foil—that you can poke ventilation holes in or can leave cracked to allow steam to escape. Heat at full power for about 90 seconds per two pounds of soil. Remove the containers, cover the vent holes with tape, and let the soil cool completely before using it.
Once your old potting soil has been sterilized, you'll need to replenish its nutrients. You can do this by combining equal parts of new potting soil with the old and adding a dose of slow-release fertilizer pellets ($23, The Home Depot) according to package directions. Or, you can mix in one part compost to three or four parts of your old potting soil. Besides adding nutrients that plants need, both the fresh potting soil and compost will help keep the mix from compacting.
Reuse your clean potting soil in containers for vegetables, flowers, houseplants, or whatever you'd like to grow. If you're not up for sterilizing and refreshing old potting soil, you still can put it to use instead of throwing it out. It can be dumped directly out of your containers and into established beds and borders. I like to use mine in my raised beds or wherever I need to fill in holes or eroded areas in my yard. It can also be mixed into compost piles. The old potting soil you reuse can help you save money for what all gardeners want: more plants.
By reusing the soil, the plants will be susceptible to getting diseased and dying the next year. Second, the soil may be nutrient deficient. Many minerals and nutrients that fresh potting mix has will be depleted by the plants growing in the planters through the year.
Many gardeners simply mix used potting soil with new material, using about half of each, with a few handfuls of organic fertilizer added to boost plant nutrition. Or, you can place the old potting soil in the bottoms of very large containers, and fill the upper parts with a fresh mix.
Opened bags of new potting soil can retain quality for around 6 to 12 months. For unopened and unused potting soil, you can store it for about a year or two before it goes bad. Usually, potting soil lasts longer when stored in a dry and cool container.
You can still put dried-out potting soil to good use. As long as the soil has enough nutrients in it, you can rehydrate it and use it for growing plants. To rehydrate dried-out soil, place it in a shallow tray filled with water. It might take the soil a couple of hours to absorb the water.
The soil in your raised beds will break down over time; however, you don't need to replace all of the soil in your raised bed garden to have beautiful, vibrant, or bountiful plants. Before planting the following growing season, add Miracle-Gro® Refresh™ Soil Revitalizer to your old soil, following package directions.
Seal all of your bags with clear tape before placing the bags in the tub. You can also simply empty the potting soil straight into the storage tub itself, sans bags. After loading the potting soil, close the container with the lid, making sure it's completely snapped into place.
If the soil level has dropped, mix in potting soil or garden mix to fill the planter back up. Turn compost or fertilizer into the existing soil to add back in some much-needed nutrients.
How to Store Used Soil. Clean, airtight storage bins are the best friend to any potting mix you plan to keep in reserve. A sparkling interior is key—you don't want to put sterilized soil in a potentially contaminated container.
That potting soil is worn out because the peat moss has decomposed. That peat moss can decompose even if you never take it out of the bag. If your potting soil has been sitting in your shed since last year in an opened bag and it's gotten wet, toss it. If it somehow stayed bone dry, it should be OK to use.
Typically, changing the soil in your potted plants should happen every 12 to 18 months. There are some exceptions that may change this timing. These include if you're moving a plant into a bigger pot because it's outgrown its current pot or if the soil has become very hard.
Revitalize. Last year's potting soil may look ready to re-use, but odds are much of the nutritional value leached away on its first go around. Replenish lost nutrients by adding slow-release fertilizers, vermiculite or compost.
If you have an old bag of potting soil stored on your shelves, you can count on the opened bagged soil preserving itself for about 6 months before it starts degrading. Unopened bags can last one or two years. Check your bag for specifics – it may have a best by date.
Potting soil is any gardening media that is composed of dirt. It could be completely dirt or it is mixed with other soil-less materials. It is usually used for filling in low spots in a raised bed. Potting mix is an entirely soil-less garden medium.
Potting soil is sterile, which is good for indoor plants because it prohibits fungus. But outdoors, it won't retain any nutrients, in part because water leeches through it so quickly, taking what little nutrients there are with it. Grass will not thrive without rich nutrients in your garden soil.
Introduction: My name is Greg Kuvalis, I am a witty, spotless, beautiful, charming, delightful, thankful, beautiful person who loves writing and wants to share my knowledge and understanding with you.
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