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How to Reuse Potting Soil Safely

Jill likes cooking, writing, painting, & stewardship, and studies gardening through MD Master Gardener & Master Naturalist programs.

How to Recycle Potting Soil

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. But you need to be sure to do it right, or you may put your plants at risk. In this article, you will learn how to safely recycle 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.

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
  • or 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.

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.

The Risks of Soil Recycling

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.
you-can-recycle-potting-soil

Reducing the Risks

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

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.

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.

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 rainwater 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 rainwater. Rainwater 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.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: What exactly is pee tea?

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

Question: Are coffee grounds good for plants?

Answer: Coffee grounds can be used as a fertilizer for acid-loving plants like azaleas. They are also a good addition to your compost pile. I would not, however, pile up lots of coffee grounds on top of the soil unless you want maggots, which you might if you have chickens.

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

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

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

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

Question: Before I read this article, I baked used potting soil at 425 degrees F. Can I still use it?

Answer: Yes, you can. (Wow, at that temp, I bet the process really stunk! lol)

Question: What if my basil died, got gray fuzz, and wilted, but my parsley in the same pot is fine and survived the winter in zone 5? Is it okay to reuse the soil?

Answer: Basil is susceptible to downy mildew when the weather is hot and humid, and it sounds like your basil was infected with it. If you removed the infected basil and scraped up the top soil where it grew, you may have also removed the spores that cause downy mildew. If you didn't get all of it, the mildew will reappear when the weather turns. I would bake the soil before reusing it.

Question: Can you reuse soil to plant vegetables in a container?

Answer: Yes, you can reuse soil for a container vegetable garden. As with reusing soil for any plant, amend the soil as needed (see article) and don't use soil that has been home to a diseased plant. Also, select vegetables that grow well in pots, like lettuce and Swiss chard, and generally avoid vegetables that have long taproots.

Question: Is it okay to use soil from a petunia plant to plant herbs?

Answer: The soil should be fine from an edible aspect; however, it may not be the best for your purposes as petunias and some herbs, such as tarragon, rosemary, and lavender, have different soil and drainage requirements than petunias do.

Question: I'm using Foxfarm Happy Frog, can I add super soil amendments to the soil and use it again?

Answer: So long as the soil hasn't been contaminated by a diseased plant, you can add amendments or cut the old soil with new soil and reuse.

Question: Can I put used potting soil around mature trees?

Answer: Yes, you can. You could spread composted matter, too.

Question: Do you prepare the used potting garden soil by Schultz in the fall or early spring?

Answer: I am not familiar with used potting soil by Schultz. Perhaps the company could answer your question.

© 2012 Jill Spencer

Comments

Jill Spencer (author) from United States on August 31, 2020:

Hi, Terri. Soon I'm going to be faced with that same issue. Yes, you can move and reuse your soil so long as it was not home to diseased plants. Also, you may want to skim off and discard or compost the first inch or two of soil in the bed as they probably contain weed seeds, spores, and other things you might not want to take with you. Good luck to you! Jill

Terri on August 30, 2020:

Can I bag my raised bed soil and carry it with me when I move? I used Black Kow....hate to lose all of it.

Jill Spencer (author) from United States on March 15, 2020:

Hi, Lucas. The flower is a chrysanthemum. Best, Jill

Lucas on March 15, 2020:

Hi Jill, just wondering what the yellowish white flower in the pot with the gnome is called?

Jill Spencer (author) from United States on March 06, 2020:

Hi, Lamar. Thanks for commenting. You can store sterilized soil for later use rather than put it to immediate use. We put ours in cans in our shed. Also, some people ameliorate their soil by adding compost and potting soil in the fall. (That's when I do new flowerbeds and direct sow.) Also some people sow fall crops, create fall planters, and use old soil to fill in low spots or holes in their yards. The latter, of course, can be done anytime. Best, Jill

Lamar on March 06, 2020:

How can you place your potting soil in plastic bags in the sun to kill pathogens as the hottest time of year is June, July, Aug,. Too late then to plant as planting is April (zone 7)

Jill Spencer (author) from United States on January 17, 2020:

Hi, Mark. Perhaps you should write a hub about that.

Mark Brauer on January 17, 2020:

Please don't advise people to use Plastic Bags for Solarization! Instead a Hot House would be a much better option!

Jill Spencer (author) from United States on November 01, 2019:

Thanks for posting comments, Mary and April!

April on November 01, 2019:

Awesome! Thank YOU!

Mary Noriega on October 05, 2019:

I have used left over potting soil for years. My plants are healthy and growing.

Jill Spencer (author) from United States on July 20, 2019:

Thanks for the information, Karl. Appreciate it. Unfortunately, your link is not working for me, but I can probably find the article by shortening it. Thanks again. Jill

karl on July 19, 2019:

I saw someone asked about coffee grounds being used for acid loving plants. I followed this advice for years until I came across an article reporting that, "One researcher found that the pH of soil treated with coffee compost increased after 14 to 21 days of incubation, gradually decreasing thereafter. Obviously the pH of decomposing coffee grounds is not stable and one shouldn’t assume that it will always, or ever, be acidic" (https://s3.wp.wsu.edu/uploads/sites/403/2015/03/co... ...None the less, there appears to be other benefits in using coffee grounds that they cover in this article.

Rocklyn on June 03, 2019:

I have a resin whiskey barrel that had water sitting in it. I drilled holes, the dirt no longer stinks. Can it be re-used to grow vegies or flowers?

Jill Spencer (author) from United States on May 21, 2019:

Hi Vivian! If you live in a warm climate and the soil in your plastic bag has been in the sun and gotten hot over the winter, the soil should be pasteurized and ready to use. If not, place the bag in the sun now and leave it for a week or two. The point of the black bag is to get the temperature inside the bag up in order to kill harmful pathogens in the soil.

Vivian on May 21, 2019:

I have pots of soil in a black plastic bag all winter. can I use it.

Jill Spencer (author) from United States on April 29, 2019:

Hi Mary Ann, I have used ladybugs to control aphids but never white fly. Thanks for sharing your expertise. Best, Jill

Mary Ann Garcia on April 28, 2019:

Ladybugs Love Whitefly. I bought a container of ladybugs and released 1/3 of them every week, keeping them in the fridge. I have had no problem with Whitefly since.

Jill Spencer (author) from United States on April 23, 2019:

To each her own, Ann! Best to you. J

M Sharp, one way to control whiteflies is to rake up fallen leaves and destroy them then spray the underside of the leaves with insecticidal soap or oil. That may get them down to a level where natural predators will keep them at a low level. Good luck to you! Jill

Ann Favell on April 06, 2019:

No pee tea thank you. Disgusting!! With so many alternatives, absolutely not. Hope no one gives me anything edible that they have used that on. Animal manure is nasty enough. Human’s is worse.

M sharp on April 05, 2019:

How can I eliminate white fly, this is my third year fighting

Jill Spencer (author) from United States on February 24, 2019:

I've prepped several new flower beds since summer, adding compost as I dug the trenches. It's rained here a lot too, and the temperature has gone up and down; however, I've gotten only two small weeds. In other words, just because nothing's sprouting yet doesn't mean the soil is bad. When your area has had enough degree days to trigger seeds to germinate, you should see growth.

Dee Espo on February 24, 2019:

I bought 4 cubic yards of used cannabis bagged soil. I rototilled this into my front yard soil. It has rained like crazy. I deliberately have planted nothing and nothing has sprouted. Nothing is going in but yard plants. Did I kill my future plants with tainted soil before they even got planted?

Jill Spencer (author) from United States on March 30, 2018:

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

steven hayes on March 29, 2018:

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!

Audrey Hunt from Idyllwild Ca. on March 16, 2018:

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.

Jill Spencer (author) from United States on March 16, 2018:

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

Jim on March 15, 2018:

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

Jill Spencer (author) from United States on March 12, 2018:

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

v on March 12, 2018:

can i bake soil in the oven?

Audrey Hunt from Idyllwild Ca. on February 26, 2018:

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

Jill Spencer (author) from United States on December 02, 2017:

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 from East Coast, United States on December 02, 2017:

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?

Jill Spencer (author) from United States on November 25, 2017:

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!

Taj Raza on November 22, 2017:

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

Rose on September 22, 2017:

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 Woods from Houston, Texas on June 26, 2017:

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

Jill Spencer (author) from United States on June 26, 2017:

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 Woods from Houston, Texas on June 25, 2017:

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 from Central Florida on June 04, 2017:

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 on February 19, 2017:

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.

Jill Spencer (author) from United States on September 30, 2015:

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

Kappygirl on September 30, 2015:

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!

Jill Spencer (author) from United States on September 30, 2015:

Thank you, Roberta. Appreciate it.

RTalloni on September 30, 2015:

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

Jill Spencer (author) from United States on September 30, 2015:

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

Marlene Bertrand from USA on September 30, 2015:

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 from Northeast Ohio on September 30, 2015:

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!

Jill Spencer (author) from United States on September 30, 2015:

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

Donna Herron from USA on September 30, 2015:

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!

Jill Spencer (author) from United States on September 30, 2015:

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.

Rebecca Mealey from Northeastern Georgia, USA on September 30, 2015:

Beautiful hub, Jill. And very useful. Congratulations!

Patricia Scott from North Central Florida on September 30, 2015:

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

Jill Spencer (author) from United States on May 20, 2014:

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.

Sheila Brown from Southern Oklahoma on May 19, 2014:

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!

Jill Spencer (author) from United States on February 27, 2013:

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

Mike Robbers from London on February 26, 2013:

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

Jill Spencer (author) from United States on November 20, 2012:

@ 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 from Paris via San Diego on November 20, 2012:

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?

Jill Spencer (author) from United States on November 15, 2012:

@ 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

Deb Hirt from Stillwater, OK on November 15, 2012:

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!

Jill Spencer (author) from United States on October 12, 2012:

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

Mary Hyatt from Florida on October 12, 2012:

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.

Jill Spencer (author) from United States on October 12, 2012:

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

Suzanne Ridgeway from Dublin, Ireland on October 12, 2012:

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 from Lake Mills, Jefferson County, Wisconsin USA on October 01, 2012:

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

Jill Spencer (author) from United States on May 01, 2012:

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

DON BALDERAS on May 01, 2012:

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

Jill Spencer (author) from United States on March 22, 2012:

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

quester.ltd on March 21, 2012:

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

q

Jill Spencer (author) from United States on March 12, 2012:

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

Maren Elizabeth Morgan from Pennsylvania on March 12, 2012:

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

Jill Spencer (author) from United States on March 09, 2012:

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 from Northam Western Australia on March 08, 2012:

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

Jill Spencer (author) from United States on March 05, 2012:

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

Lee Raynor from Citra Florida on March 05, 2012:

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

Jill Spencer (author) from United States on March 05, 2012:

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

Shelly McRae from Phoenix, Arizona on March 05, 2012:

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.

Jill Spencer (author) from United States on March 04, 2012:

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 from Ohio on March 04, 2012:

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?