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The growing season, at least for us northern gardeners, is sadly coming to an end. Time to start winterizing gardens and yards, and emptying out containers and pots. Now the question becomes – what to do with the leftover soil? Tossing it out seems like such a waste, but is reusing soil a good idea?
The answer is yes… and no.
All container gardens require soil. Over time, the cost of that soil can add up. And I’m not just talking dollar-wise, I’m also talking time-wise. Because, if you’re anything like me anyway, once home, those soil bags never seem to go quite as far as hoped
Which, of course, means another trip to the garden center!
So, reusing soil can definitely be a money and time saver…if you keep safety in mind.
There are two main culprits that put your plants at risk when it comes to reused soil.
- First, used soil can contain pathogens, such as fungi, bacteria, or viruses.
- Second, this year’s plants may have depleted the soil of certain nutrients and minerals.
Either scenario, if not addressed, can cause next season’s blooms to sicken and even die.
With these concerns in mind, I’ve outlined some do’s and don’ts when reusing soil. By following this advice, you’ll give yourself the best chance of reusing your soil safely.
Where to Reuse Soil
Before we get into the do’s & don’ts, let’s take a look at where you can reuse soil next year.
1. Houseplants
2. Container gardens
3. Vegetable gardens
4. Flower beds
5. Backfill for trees and shrubs
6. Filling in holes in the yard
7. Top dressing for your yard when spreading seed
As you can see, reused soil has multiple applications. However, there are a couple of things I want you to keep in mind.
First, only reuse potting or container soil, not garden soil, with your houseplants and containers. Look here to learn more about the different soils.
Second, when backfilling, whether for trees or holes in your yard, make sure to mix in some native soil with your reused soil.
Reused soil tends to be lighter. By mixing it in with heavier ground soil, you’ll help prevent sinkholes from forming.
The Do’s of Reusing Soil
Check Your Soil Over
Over the growing season, debris such as leaves, weeds, or seeds can blow into your soil. And chances are, once you remove that plant, you’ll find roots clinging to the leftover soil and sides of the pot.
Not only that, it’s possible insects may have taken up residence in the soil.
So, the first thing you want to do is comb through your soil, removing any visible materials that shouldn’t be there.
Sterilize Your Soil
One of the biggest concerns with reusing soil is whether or not that soil is harboring any pathogens.
Unlike debris, pathogens such as viruses or bacteria aren’t readily visible to the naked eye. As a result, you only find out there is a problem when your plant starts to die. Also, you can’t always spot insects. So, even though you comb through your soil, you may miss some tiny bugs.
For these reasons, it’s always a good idea to sterilize your soil before reusing it. This will help kill off these harmful elements. Sterilizing soil involves heating the soil, and luckily, there are several ways you can do this.
The easiest way to sterilize soil is to put your soil into black plastic bags. Once done, place those bags in a sunny location. This allows the bags to heat up. And similar to composting, those high temperatures will kill off lingering pathogens or insects.
Other methods of sterilizing soil include steaming, baking, or microwaving. Read here to find out more about these methods and how to use them.
Amend the Soil
As your plants grow, they’ll use up the soil’s nutrients and minerals that help with growth. What they use and how much, will depend on the plant. Failing to amend your soil by adding nutrients back in may mean a poorer crop next year.
And, just like with sterilizing, there are also several ways to amend your soil.
First, it’s always a good idea to add in fresh potting or container soil, or a mixture of potting soil and compost. In general, aim for roughly 50% of reused soil coupled with 50% of new soil or a soil/compost mix.
Compost tends to be heavier, so if you’re finding the soil is too heavy after mixing in compost, add a little peat moss, coir, or perlite to fluff it up a bit. This will be especially important if you’re reusing soil for a container or houseplant.
Adding a slow-release fertilizer is another way to amend your soil and help replenish those lost nutrients.
If you’d like to get a little more specific and target certain nutrients, then test your soil to determine which minerals are depleted. After which, you can amend your soil with deficient minerals.
Lastly, always make sure to amend your soil after you sanitize it. If you don’t, you chance killing the good bacteria you’ve just added in with your amendments.
If you want to know more about the mechanics of amending your soil, then check out this article from SFGate.
Rotate Your Crop
Whether reusing soil or planting in the same in-ground garden, you want to keep your soil in top condition.
One key component of good soil management is crop rotation. The concept is simple – the same crop should not be planted in the same soil year after year.
Plants use up certain nutrients. They may also attract certain pests. If you consistently use the same soil for the same crop each year, those problems are going to compound.
Tip: Tomatoes are especially prone to pathogens if you keep planting them in the same soil.
And don’t limit this practice to edibles. For the same reasons as above, rotate your annuals as well. Your plants and soil will be much happier.
Keep Your Soil Dry
No one wants bone dry, dessert-like soil, but it’s important that when reusing soil, you keep the soil stored where it won’t be subjected to rains or snow.
Soil that becomes overly wet can invite fungus and mold.
A good way to store your soil is in large plastic tubs or containers. Ideally, if you’re reusing soil from both veggie and flower gardens, keep the two soils separated in their own respective containers. This way, next year you can use the flower soil for your veggies and the veggie soil for your flowers, effortlessly rotating your crop.
The Don’ts of Reusing Soil
Assume It’s Okay
If you’ve given your soil a cursory glance and nothing immediate is popping out, don’t assume it’s okay to use. Weed seeds and roots can be buried deep.
At a minimum, you need to comb through your soil thoroughly to ensure you’re removing any debris, roots, and weeds. And don’t forget to inspect closely for insects.
Reuse a Problem Soil
Although you can sterilize your soil, if you’ve had a crop this year that clearly had a pathogen or even a severe insect infestation, you’re better off just tossing that soil, rather than chance reusing it.
Similarly, if you’re just not sure about the soil, such as the plant’s heavily root bound, the soil smells a bit funky, or it’s setting off your radar in some way, it’s best to throw the soil out.
Some gardeners automatically toss out soils that held plants known to harbor pathogens, such as tomatoes.
Reusing soil can be a great way to save money. But the key is to be smart about its reuse. Take every precaution to ensure the soil is clean and nutritional. And any questionable soil, don’t hesitate to toss!
In the comments below, let me know if you reuse your soil and what you do to get it back into tip-top shape.
And if you enjoyed this article on the do’s and don’ts of reusing soil, feel free to share it!
