Is it Safe to Reuse Potting Soil or Should I Start Fresh?

Is it safe to reuse potting soil from our planters or is it better to start fresh each year? Find out the best options for your garden containers.

For creative ideas, also see 40 Unique Container Gardening Ideas.

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Can I Reuse Potting Mix?

Every new gardener who grows in containers has this question:

Is it safe to reuse my potting mix or do I need to start fresh?

Here are the short answers:

• Best Choice: Start fresh each year.
• Second Best: Replace half and add fertilizer.

But decide on a case-by-case basis.

Contents

• The Trouble With Potting Mix
  • The Half-New Solution
• How to Save Old Potting Mix
  • Potting Mix Tips
• End of Season Planter Care
• Resources

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The Trouble With Potting Mix

Yes, potting mix can be expensive, heavy to transport, and it seems wasteful to replace it after a single growing season but fresh really is best and sometimes safer.

Here’s why.

Potting mix degrades as plants use up nutrients. The good stuff is either used up or washed away.

Container plants can also develop various plant or soil diseases.

As summer goes on, you’ve probably seen how the potting mix in a hanging basket of flowering annuals changes.

The roots gradually fill the basket, nutrients are used up, and the potting mix becomes compacted.

In some cases, even if you wanted to reuse the soil you couldn’t because it’s basically a glorified root ball.

This asparagus fern was so rootbound there is no potting mix to recover.

On the other hand, a larger container of shallow-rooted herbs may still have some soil life left in it.

So, it also depends on what you grew, the condition of the soil, and if it’s disease-free. And, while some soil problems have visual clues, we’re really just guessing if the soil is problematic.

So, yes, we’ve all reused potting mix, often without any big problems but it always comes with some risk. It’s up to you to decide if it’s no big woop.

We never use soil straight from the garden in planters is because it lacks the traits needed for successful container growing.

How to Save Old Potting Mix

For me, the idea of sending potting mix or plastic pots to landfill just seems too wasteful and unnecessary.

If I am confident old potting mix is simply depleted and the plants grew fine in it, I just toss any leftover potting mix in my garden beds.

In rare cases, there may be a lot of loose soil leftover and I’ll remove any plant bits and keep it in a container with a lid (nice and dry) for next time.

If it’s mixed with plant matter (roots, stems, leaves, etc.), I chop the whole thing up and add it to the compost pile.

A proper compost pile naturally heats up. Once it reaches temperatures around 160°F (71°C), unwanted bacteria and pathogens are killed off.

Some gardeners bake old potting mix in the oven (180°F | 82°C for 30 minutes). This never seemed realistic to me due to the volumes of potting mix I use and the idea of breathing in hot potting mix in the house. So, I’ll leave that one for you to decide.

Related: How to Make Worm Tower for In-Ground Composting

End of Season Planter Care

What should I do with my planters at the end of the growing season?

If you keep containers filled over the winter—even weather-resistant ones—unwanted bacteria, viruses, fungi, and pathogens can grow in the soil and harm your plants next season.

So, you need to empty them in fall.

Yes, it’s more work. But, if you’ve ever had disease spread to new plants, you know what a heartbreak that is.

Tomato plants are infamous disease-carriers. Many annual flowers have fewer problems.

Fall Routine

• Empty containers, wash, then disinfect with 4 teaspoons bleach per quart of water for at least one minute, rinse and allow to dry thoroughly before stacking.
• Dispose of any diseased plants and their potting mix.
• Add remaining plant materials and organic potting mix to compost pile or store soil in dry containers.

Spring Routine

• Assuming they were cleaned and disinfected in fall, the pots should be good to go.
• When choosing new potting mix, get a type designed for the plants you are growing.
• I use an organic potting mix that is marked ‘food safe’ intended for edible plants (fruits, veggies, herbs) for all my container growing since everything is going in the compost pile later and I don’t want synthetic fertilizers or other soil additives ending up in there.

Organic Potting Mix | Amazon

• If you’ve set some old potting mix aside, and you’re sure it’s healthy (no signs of mold or other weird growth), use that too along with a serving of granular organic fertilizer (follow instructions on product label). This would be for outdoor use only to avoid bringing insects indoors.
• You can further improve your potting mix with the addition of good compost (decomposed organic matter) if it has been properly prepared. The natural heat of a compost pile can destroy unwanted bacteria and pathogens.
• Mix your potting mix ingredients thoroughly to provide a good growing medium.

Resources

Soil Calculator Tool

Use this free soil calculation tool to estimate how much potting mix you need to fill your containers.

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~Melissa the Empress of Dirt ♛