How to Reuse Potting Soil Safely

Updated on February 3, 2018
The Dirt Farmer profile image

Jill volunteers at community gardens & learns about gardening through the MD Master Gardening Program & MD Master Naturalist Program.

How to Recycle Potting Soil

There's no need to buy potting soil every time you make a container garden. You can reuse the old stuff!

That unwieldy cart of potting soil seems like enough when you're at the garden center. (In fact, it often seems like more than enough when you're at the register). But once you start filling pots, it's often frustratingly inadequate.

“Did I really use an entire bag for one container?” you think. Then it’s back to the store and the checkout line — and back to shelling out more money on gardening supplies.

This year, it doesn't have to be that way. You can lower the cost of filling seasonal containers by reusing last year’s potting soil.

Fertilizer will keep plants looking good throughout the growing season, even if they're planted in old potting mix.
Fertilizer will keep plants looking good throughout the growing season, even if they're planted in old potting mix. | Source

Ways to Reuse Potting Soil

The easiest way to reuse old potting mix? Simply remove old plants from their containers, fluff up the soil and replant.

If you've reused the same soil for several years or it's developed a white surface crust, you may have to cut it with 50 percent new potting soil and/or apply fertilizer. (See "How to Reduce Risks" below.)

Of course, you don’t have to reuse potting soil solely in your flowerpots.

You can also

  • work old potting soil into flower beds,
  • work it into vegetable gardens,
  • use old potting soil to fill up holes in your yard,
  • add it to compost piles &
  • bury used potting soil in compost holes.

Before you start recycling old soil, however, be sure that you know the risks so that you can guard against them.

The Risks of Soil Recycling

Adding old potting soil to your vegetable garden is one way to reuse it.
Adding old potting soil to your vegetable garden is one way to reuse it. | Source

There are two main reasons reusing potting soil can put plants at risk.

  1. First, used soil sometimes contains pathogens--viruses, fungi, bacteria, nematodes and other organisms that carry disease. These pathogens can cause container plants to sicken and die.
  2. Used soil may also be deficient in the minerals that plants require. This, too, can cause plants to become diseased and die.

Reducing the Risks

How can you reuse potting soil without killing your plants? Try these simple strategies.

Source

1. Never reuse soil from a pot in which a diseased plant has grown.

The plant may be dead and gone, but the pathogens and other problems in the soil remain, making it likely that the next occupant will also sicken and die.

2. Pasteurize old potting soil before using it.

Soil that remains in pots exposed to the elements often harbors weed seeds, pathogens and/or insects, none of which are desirable in growing medium.

To kill off these harmful elements, bake the soil in the sun. First, empty the used soil into black plastic bags. Then place the bags in a sunny location.

The same pasteurization process that occurs during regular composting will occur inside the bags as temperatures within the mix rise, rendering the pathogens, weed seeds and other unwelcome elements in the soil harmless.

Although you can also put old soil in garbage cans or seal-able 5-gallon buckets, garbage bags are particularly easy to drag around, and the black plastic ones hold heat well.

Super-Safe Recycled Soil

Want to make extra sure that your used potting soil is safe? Don't just bake it in the sun--bake it in the oven or microwave! Laura Pottorff, Colorado State University Cooperative Extension Horticulturist and Plant Pathologist, recommends pasteurizing moistened batches of used soil at 180 to 200 degrees F for at least a half hour at a time.

3. Fertilize your containers after planting.

Exposure to the elements weathers the soil, leaching out nutrients. To counter this, apply fertilizer to assure that your container plants get the nutrients they need.

This is particularly important if you're using recycled potting soil, as many of its essential minerals may have been taken up by plants the previous year or leached out.

Use a slow-release fertilizer that lasts all growing season. Or, apply a liquid fertilizer (such as pee tea) every two weeks.)

Reusing old soil has risks, but you can limit them by following a few basic guidelines.
Reusing old soil has risks, but you can limit them by following a few basic guidelines. | Source

Will you try soil cycling?

See results

4. Mix some compost and/or new potting mix into the old, especially if you've used the same soil for several years.

Exposure to the elements also makes soil more compact. Adding new potting mix to the old will not only increase its fertility, but it will also make it more friable and improve its ability to retain moisture.

If you’ve used the same soil for several years, it’s probably wise to create a 50-50 mix of half old and half new potting soil.

5. Water with rain water to reduce salt buildup.

Does the soil in your planters have white crusting on the surface? Then it may be suffering from salt buildup, which can slow plant development.

To prevent this problem in the future, water your container plants with rain water. Rain water usually has a lower salt content than tap or well water. As for reusing salty soil in containers as is? Don't. Add it to your compost pile. Or, if you really want to use it in containers, cut it with 50 percent new potting mix.

6. Use less soil by adding old nursery pots into the mix.

Another way to keep costs down? Use less potting mix by adding an overturned plastic nursery pot to your container.
Another way to keep costs down? Use less potting mix by adding an overturned plastic nursery pot to your container. | Source
Source

Questions & Answers

  • What exactly is pee tea?

    Pee tea is diluted human urine that is used as fertilizer.

  • How long do I need to bake old soil in plastic bags in the sun for?

    Solarize the soil during the hottest time of year for four to six weeks.

  • How long does it take to kill harmful elements when baking soil outside in the sun?

    Bake the soil in plastic bags four to six weeks outside during the hottest time of your year.

© 2012 Jill Spencer

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    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      3 months ago from United States

      That shouldn't be a problem, Steven, if the tomato plant simply died from exposure to the cold. However, if it bit the dust due to a virus or some sort of infestation, you should not use the soil. Best to you! Jill

    • profile image

      steven hayes 

      3 months ago

      Thank you for the helpful article! I hope to recycle my soil from last year. I have only one question, I left a tomato plant in a 5 gallon pot all winter. Is that soil still healthy to use? Thank you!

    • vocalcoach profile image

      Audrey Hunt 

      4 months ago from Idyllwild Ca.

      Thanks, Jill, for this very helpful article on reusing potting soil. So glad to learn about pasteurizing old potting soil. Baking the soil in the sun couldn't be easier. I do a lot of gardening, so these handy hints will sure help me.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      4 months ago from United States

      Hi Jim. Washing with warm sudsy water should do the trick unless plants died in the containers from diseases, then . . . I don't know. My impulse would be to recycle them rather than reuse them, but your extension agent could give you better advice. Try Ask an Expert online at https://ask.extension.org/ask. The advice is free. Best, Jill

    • profile image

      Jim 

      4 months ago

      What about reusing the 5 gallon buckets I planted in last year - should I sterilize them some how?

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      4 months ago from United States

      Yes! See the gray box mid-article. It contains directions. Best, Jill

    • profile image

      4 months ago

      can i bake soil in the oven?

    • vocalcoach profile image

      Audrey Hunt 

      4 months ago from Idyllwild Ca.

      I love gardening and I love this helpful post. I'll be using your tips this spring. Thank you.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 months ago from United States

      No, Dolores, you can pasteurize the soil in the oven at 200 degrees for half an hour to kill harmful pathogens and insect eggs without losing the richness of the soil.

    • Dolores Monet profile image

      Dolores Monet 

      7 months ago from East Coast, United States

      I need to replant some of my container plants this Spring and was wondering about just this topic. I hate the idea of buying dirt, it just seems silly. When I was younger I used to make a mix that included outside dirt that I'd put in the oven on a low temperature for 20 minutes or so. Then I wondered if I'd cook out nutrients. Would it?

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      7 months ago from United States

      Hi Rose. The compostable material needs air in order to decompose, so . . . no, I don't think so.

      Taj, Thanks so much for stopping by!

    • profile image

      Taj Raza 

      7 months ago

      Thank you so much for providing such a useful information about Used Soil.

    • profile image

      Rose 

      10 months ago

      Can i make a compost bin out of a 5gal bucket with out putting holes in it i have no way of putting holes in the bucket

      ?

    • Peggy W profile image

      Peggy Woods 

      12 months ago from Houston, Texas

      That must be one huge moth! They can get large.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      12 months ago from United States

      Thanks, Peg. I like to pass on whatever I learn, and most of it is for newbies. There's so much to know! Every time I look into any subject, it quickly becomes complicated, and gardening is no exception. I just discovered, for instance, that the ugly hummingbird I've been seeing at our feeders is actually a moth!

    • Peggy W profile image

      Peggy Woods 

      12 months ago from Houston, Texas

      This is an excellent article for people to read who are new to gardening. I never discard potting soil and always reuse it in manners you mentioned.

    • Virginia Allain profile image

      Virginia Allain 

      13 months ago from Central Florida

      Very helpful info. I'm a thrifty gardener and reuse my container soil over and over. Now I'll do some treatment of it in a black plastic bag as you suggest. Good to know this technique.

    • rudyhiebert profile image

      rudyhiebert 

      17 months ago

      When Spring finally arrives, my soil enhancer preference will be the liquid organic concentrate that is fish extract and sea kelp based instead of with chemicals.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      2 years ago from United States

      Thanks for stopping by, Kappygirl. I've been working on my photography and am glad you noticed. (:

    • Kappygirl profile image

      Kappygirl 

      2 years ago

      This is a great hub with useful information. I often re-use soil but didn't know about pasteurizing it. I'll definitely have to do that in the future. By the way, you've got really nice pictures too!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      2 years ago from United States

      Thank you, Roberta. Appreciate it.

    • RTalloni profile image

      RTalloni 

      2 years ago from the short journey

      Congrats on your Hub of the Day award for this very useful info. Getting the most out of potting soil is a good thing!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      2 years ago from United States

      Hi, Kirsten. The weather shifting here too, and my summer flowers are fading away. Thanks for stopping by!

      MarleneB, baking soil in the oven is a little smelly, but well worth it! Glad you commented. All the best, Jill

    • MarleneB profile image

      Marlene Bertrand 

      2 years ago from USA

      Excellent tips! I absolutely love the idea of placing the soil in the oven. That is truly a clever solution to killing off harmful stuff in the soil. By the way, congratulations on receiving the Hub of the Day award.

    • Kristen Howe profile image

      Kristen Howe 

      2 years ago from Northeast Ohio

      Jill, great tips. I might have to do that next year for my summer plants---two of them have bit the dust, one's left for another week or so. Congrats on HOTD!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      2 years ago from United States

      Hi Donna. Yep, you want to be safe when reusing soil. I'm about to replace our tired summer flowers in pots for autumn ones. Will have to check out some of your hubs for ideas for an autumn door decoration. Our door looks best with a swag. I put up Indian corn, but it looks a little sad all by itself there. (: Thanks for dropping by and commenting. --Jill

    • purl3agony profile image

      Donna Herron 

      2 years ago from USA

      Great information, Jill! I never knew that I couldn't just reuse my potting soil so I'm grateful for your suggestions on how to safely recycle it. Pinning to my gardening board. Thanks and congratulations on your HOTD!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      2 years ago from United States

      Thanks, Patricia, for sharing the article, and for your kind comments. I'm delighted that the article brought up good memories for you.

      Thank you, too, Rebecca. I'm surprised but happy this is a HOTD.

    • rebeccamealey profile image

      Rebecca Mealey 

      2 years ago from Northeastern Georgia, USA

      Beautiful hub, Jill. And very useful. Congratulations!

    • pstraubie48 profile image

      Patricia Scott 

      2 years ago from sunny Florida

      Hi Jill

      this is so helpful...my Momma taught me so much about soil and plant care and much of what you say here she did.

      This has been a great refresher article for me to read because she has been gone from the planet for many years and I had forgotten some of what she said...so I am delighted to read this.

      Congrats on HOTD

      Angels are on the way to you this morning ps pinned shared G+ and tweeted

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      4 years ago from United States

      Hi sgbrown! Thanks for commenting. You sound like a real soil recycler! I do the same thing you do, plus throw old soil into the composter--and I bet you do that, too. Great to hear from you! All the best, Jill.

    • sgbrown profile image

      Sheila Brown 

      4 years ago from Southern Oklahoma

      Great information! I always reuse my old potting soil. I get a big bucket or pot and just start dumping the old soil inside as I clean out my pots for reuse. As I need mix for my new plants, I usually use 50/50 and add a little fertilizer. When I am planting in the ground, I will mix the old soil with the dirt I dig out and plant with that. Very good advice here, I've been doing the same thing for years and it works great! Up and useful!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      5 years ago from United States

      Hi Mike! Thanks for the feedback. I appreciate your comments & hope the ideas are useful to you this spring. Take care, Jill

    • Mike Robbers profile image

      Mike Robbers 

      5 years ago from London

      Nice hub! Some very useful tips! Thanks for sharing! Voted up & useful!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      5 years ago from United States

      @ Letitialicious -- I'm not sure about the plant, but you could save the soil by baking it in the oven a pot-full at a time to kill the pathogens in it, including fungal spores. You could also dump it into black plastic garbage bags and let it heat up on your deck or patio over the winter. Take care, Jill

    • Letitialicious profile image

      Letitialicious 

      5 years ago from Paris via San Diego

      I live in the city and recently inherited (literally) some pots with water logged soil, which I allowed to dry out, but I've planted one plant so far and it looks pretty droopy, several months down the line. Think there's any way I can save it/and or the soil?

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      5 years ago from United States

      @ aviannovice-- Hi Deb! Nice to hear from you. What a cool, unique memory. A woodstove. (: I reuse soil all the time, too, mostly when I change container plants outside with the seasons. Take care, Jill

    • aviannovice profile image

      Deb Hirt 

      5 years ago from Stillwater, OK

      I reused last year's soil and plan to do it again this year. My father used to bake soil in the over of the woodstove before he planted seedlings at a low temperature. It works, all right. An excellent piece, awesome and UP!

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      5 years ago from United States

      Buying dirt--it really does seem ridiculous, Mary--like driving to the track in order to walk, which I've also done. (: Thanks for commenting. Sounds like you're an old hand at reusing old potting soil! Take care, Jill

    • mary615 profile image

      Mary Hyatt 

      5 years ago from Florida

      My Mother would "turn over in her grave" if she knew I bought dirt! When I was growing up, we just went into the woods and got our potting soil. I live in S. Fl. where the soil is just sand, so I do a lot of container gardening. When a plant dies, I pull it out, and reuse the same soil for cuttings or another plant. I would never throw out potting soil, it's too expensive. Our Home Depot sells torn bags of soil cheap.

      I voted this Hub UP, etc.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      5 years ago from United States

      Hi Suzie HQ! Enjoyed your hub on unusual containers for plants & intend to read the one about free containers. I'd love to have my hub linked to yours. Thanks for commenting! Appreciate it. --Jill

    • Suzie HQ profile image

      Suzanne Ridgeway 

      5 years ago from Dublin, Ireland

      Hi Jill,

      What a great article and ideas on recycling soil! Loved the info and would like to link it in with one or two hubs of mine on recycled container gardening. Thanks for sharing and VU, Interesting, Useful and shared!!

    • Ben Zoltak profile image

      Ben Zoltak 

      5 years ago from Lake Mills, Jefferson County, Wisconsin USA

      Great article, I think I'm getting the idea. It sounds like, no matter what soil and compost from outdoors need to be processed or pasteurized as you say. I have three black walnut tress on my property too I was wondering if I should avoid composting their leaves?

      thanks!!!!

      Ben

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      Thanks for reading and commenting, Don. It's nice to meet you!

    • DON BALDERAS profile image

      DON BALDERAS 

      6 years ago

      This is enriching and Earth-friendly. Thanks for these ideas.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      Hey Q--Good to hear from you! Thanks for commenting. J

    • quester.ltd profile image

      quester.ltd 

      6 years ago

      As always, you are full of good information - look reading your Hubs and refreshing old ideas...:)

      q

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      Hey, Maren! Thanks. It is much less messy & stinky! Thanks for stopping by! Jill

    • Maren Morgan M-T profile image

      Maren Elizabeth Morgan 

      6 years ago from Pennsylvania

      I like your idea of baking in the sun rather thanmy cooking oven.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      Yep--sometimes you can't see what's killing your plants and must look at the "signs" of the problem, such as wilting, curled leaves, brown spots, etc. Glad you stopped by, Eileen! DF

    • Eileen Hughes profile image

      Eileen Hughes 

      6 years ago from Northam Western Australia

      Very helpful article. I had not thought about the nasties in the soil

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      Awesome, chefsref! Hope the "black bag" treatment works well for you. Take care, DF

    • chefsref profile image

      Lee Raynor 

      6 years ago from Citra Florida

      Hey Dirt Farmer

      I learned a new trick here today. The black plastic bag trick will come in handy. I have a lot of pots full of old soil that have been sitting for years

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      It's really cool how so many people are composting these days. Thanks for commenting, Shelly.

    • Shelly McRae profile image

      Shelly McRae 

      6 years ago from Phoenix, Arizona

      Good advice, Dirt Farmer. I almost always put last year's container soil in the compost, though I've occasionally mixed it with new. Thanks for sharing.

    • The Dirt Farmer profile imageAUTHOR

      Jill Spencer 

      6 years ago from United States

      Thanks for commenting, Robie! If you're placing the soil in bags at the end of summer, leave them there until spring. Take care, DF

    • Robie Benve profile image

      Robie Benve 

      6 years ago from Ohio

      Excellent advice on reusing potting soil! I sure dislike (for the sake of a kind word) the price tag on those soil bags. Thanks for sharing.

      Q: I never tried "baking in the sun" in the black bag. How long should I live it there to get rid of the unwanted guests?

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