Give Old Potting Soil New Life

Provided it's disease-free, freshen up this potting soil and reuse it in raised beds, planters, and other container gardens.

First, can I reuse potting soil?¹

Like many aspects of gardening — it depends.

If the potting soil has just been used for one season and all the plants were completely healthy, sure. However, if you know your plants ended up hit with downy mildew, or other plant disease, you'll want to either toss the soil or spend some time sterilizing it. Many fungi and viruses CAN overwinter in soil, making them especially hard to eradicate from year to year.

Sterilizing Potting Soil

Just a reminder — killing off the "bad" viruses will also kill off the "good" bacteria and microorganisms that are vital for soil and plant health. Soil sterilization can be done in the microwave or even in the oven, although this can make an indoor mess.

Or favorite method? Using the sun, called solarization.² Solarization leaves no chemical residue, is safe for organic crops, and is easy enough for home gardeners to complete.

1. Remove all the contaminated stems, leaves, and roots from your potting soil. Place the contaminated potting soil in a black plastic trash bag.
2. If your potting soil is completely dry, add a little bit of water; just enough to moisten the soil thoroughly.
3. Seal the bag and place it in the sunniest, brightest spot in your yard.
4. Solarization is both time and temperature dependent — depending on your gardening climate, your soil will take 4-12 weeks to be sterilized. Most weed seeds are killed off at lower temperatures, however more heat is needed for plant diseases. Soil solarization is effective against fungal pathogens such as wilt, Fusarium, and Phytophthora root rot, and bacterial pathogens such potato scab.

How to Reuse Potting Soil

Ok, you've determined your old potting soil is disease-free. Now with a little TLC, you can repurpose that potting soil for another batch of beautiful hanging baskets, perfect patio planters, or ravishing raised beds.

1. Top It Off

If the level of soil in your raised bed has dropped and you plan to garden in the same space, mix in some additional fresh potting mix to regain depth. Ideally, the soil level should be within an inch or so of the rim of the planter or raised bed. Use a fork or hand tool to blend the new soil into the old soil.

Blend new soil into the old soil.

Gardener's Supply Organic All-Purpose Fertilizer and Container Booster Mix

2. Recharge Soil Nutrients

Potting soil WILL become depleted of nutrients over time — it's important to put into your soil what you expect to get out of your garden beds. Compost and organic fertilizer will bring much-needed minerals and organic matter to your potting soil:

- A granular, organic fertilizer, like Gardener's Supply Organic Fertilizer, will slowly release nitrogen, potassium, and phosphorus into the soil over time.  Use 1/4 cup per square foot.

- No compost readily available at home? No problem. Try a compost-based amendment like Vermont Compost Container Booster Compost Mix. Use 3 cups per square foot. This is the secret sauce! This potent, all-organic formula includes concentrated plant and manure compost, washed granite, black rock phosphate, and other natural ingredients.

Sprinkle fertilizer and either compost, or a compost-based amendment, on to the surface of your old potting soil. Then blend with a trowel or cultivator.

Now plant! Direct seed, or transplant flowers, herbs, or your favorite edibles. Not getting the results you had hoped for? Consider testing your soil for nutrient deficiencies or pH shifts with an easy-to-use soil test kit.

Recharging older potting soil with compost and granular fertilizer sets future seedlings up for success.