When growing houseplants, using the right potting soil is everything. Even if you water your indoor plants perfectly, if the soil can’t drain, then all your good care habits are for naught. What makes for well-draining potting soil?
Well-draining potting soil drains water sufficiently yet not quickly. The roots can still get the hydration they need but water does not remain in the soil long enough to trigger issues such as root rot.
This article will serve as your definitive guide to understanding well-draining soil. I’ll touch on all your biggest soil concerns and questions, such as how to make well-draining soil, if you can use old soil and for how long, and how to sterilize soil. I’ll also recommend many of my favorite soil mixes along the way.
Let’s get into it!
What Is Well-Draining Soil?
First, I want to ensure clarity when I talk about well-draining soil, so I figured a definition was in order.
Every indoor gardener should strive for well-draining soil, as it’s what most plants appreciate. When soil drains well, it means the soil will retain moisture but that the water within the dirt won’t overstay its welcome.
The rate at which the water drains is moderate, which is just right. Should the water drain too quickly, then a situation would transpire like what I touched on in the intro.
Your plant’s roots would barely get any water. Although you’re watering your plant about as often as you should, your houseplant could begin manifesting symptoms of being underwatered. Its leaves might dry out and turn yellow or brown. The plant would also wilt.
You’d be confused, especially if you’re following my highly-recommended fingertip test. If you need a reminder, the fingertip test reliably tells you how often to water your plant. You dip a clean finger an inch to three inches deep into the plant’s soil and feel how much moisture is currently in the soil.
If the soil felt dry because the water drained too fast, then you’d begin overwatering your plant. Instead of the plant’s roots getting barely a taste of water, now the roots are saturated in the stuff.
They’d remain in a pool of standing water until the water can make its way through the soil and out of the pot’s drainage holes. If your soil doesn’t drain well, this can take a while.
The longer the water soaks the roots like this, the higher the risk of root rot is. This plant disease is caused by excess water.
Root rot kills your houseplant from the roots up, making the roots soft, flimsy, and black. Healthy roots are white and firm. As more and more roots die, the plant begins to degrade as well until the whole thing is dead.
While some cases of root rot are treatable, the best treatment is prevention, which is what you can do by using well-draining potting soil for your houseplant.
How Do You Make Well-Draining Soil?
Now that you’re clearer on what well-draining soil is, how do you make your own? Well, above all else, you want to avoid materials like clay in the soil. Clay is too heavy and can prevent the water absorption speed your indoor plant needs to stay free of root rot.
Here are some soil ingredients you’ll want to prioritize instead.
Twigs make a fantastic ingredient as part of a compost pile, but you can always use them on their own to make well draining soil too. Break the twigs into small pieces, but don’t shred them or anything like that.
The structure of the twigs provides aeration to the soil, creating passageways for water to reach the roots. Since twigs are so skinny, you shouldn’t have to worry about them obstructing the pot’s drainage holes.
If you have some sand available, add it to your houseplant’s soil. The particles are tiny enough that the sand can mix into the soil and do all sorts of helpful things. For one, the sand aerates the soil for better drainage. On top of that, sand can also break up clumps of soil. Compaction is a natural result of using the same soil for a while, so sand might help you get a slightly longer life out of your current batch of soil.
I would caution you this: don’t have a heavy hand when mixing sand with potting soil. Too much sand can dry out the soil!
You definitely can’t go wrong with some compost in your plant’s soil. If your soil is on the drier side, maybe because you added too much sand, compost will increase moisture.
You also have exemplary drainage through compost, and the compost ingredients will make the quality of your soil lighter-weight as well. It’s a win-win all around.
To make your own compost at home here’s a list of common ingredients you can use:
- shredded newspaper
- dry leaves
- plant clippings
- coffee grounds
- most fruit and vegetable scraps.
The composting process entails earthworms and other microorganisms naturally breaking down the ingredients so you end up with organic materials. Compost is a friend of many types of indoor and outdoor plants, from fruit trees to perennials, garden beds, lawns, and more.
Just make sure you don’t toss anything and everything into the compost pile. Dairy is a no-no, as is pet feces, grease, fat, garlic, onions, and citrus peels. If you have clippings and shavings from wood that was pressure-treated, skip that as well.
Coco peat or coconut coir as sourced from the outer husks of coconuts makes a fantastic base for well-draining soil. As the coir gets into the soil, it develops air pockets for more air and moisture so the soil can drain efficiently. Another benefit of coconut coir is it degrades gradually so you get a longer shelf life out of it.
The phyllosilicate mineral known as vermiculite is available in a fine powder, medium-grain particles, and large particles. For most indoor gardens, I would say medium-grain or fine-grain vermiculite is just fine. The large particles can get caught up in your pot’s drainage holes depending on how large these are (which should be pretty sizable!).
I wouldn’t suggest vermiculite for every houseplant’s soil. If your plant prefers moist soil, then vermiculite is a great choice. For succulents and other plants that need dry conditions such as rhododendrons, you’re better off making potting soil with a different set of ingredients.
Pumicite or pumice starts as volcanic glass before hardening into volcanic rock. It’s broken down into dust or powder and then commercially sold to gardeners like you. Despite that it’s rock, pumice is naturally lightweight, making it the perfect amendment for your houseplant’s well-draining soil.
Even better than its aeration and water drainage is that pumice fosters mycorrhizae growth. This fungus species is helpful to houseplants, allowing them to absorb nutrients and moisture in greater quantities.
Pumice isn’t the only volcanic rock that’s a good addition to houseplant soil. So too is perlite. This soil aerator starts as glass before it’s heated to high temperatures of 1,600 degrees Fahrenheit. Then the perlite forms little white balls that you pour into your potting soil. You’ll have softer, aerated soil with awesome draining capacity.
The last ingredient to make well-draining potting soil at home is sphagnum or peat moss. I would especially recommend peat moss if your soil is very sandy or if it’s old and compacted.
The moss retains moisture quite well and also shifts chunks of sand for exceptional aeration and draining.
A few words of caution about peat moss. For one, it’s rather acidic on the pH scale. If your plant isn’t an acid-loving one, then I’d advise using the above ingredients for making well-draining soil. Peat moss also expires, sometimes in six months and in other cases in a year or two.
I would also think twice about using these ingredients to make well-draining soil:
- Sawdust: At first glance, sawdust seems like a good alternative to sand. It’s cheap and readily available as well. Yet sawdust sucks up soil nitrogen like no one’s business so you have to fertilize your plant sooner than its schedule requires. While sawdust is great for compost, it’s not so great in its original state, when it comes to well-draining soil.
- Brick powder: Using brick powder on one’s indoor garden has worked for some gardeners, but not often enough that I would say doing so is warranted.
Best Well-Draining Potting Soil for Indoor Plants
If you’d rather buy well-draining potting soil than make it, there’s nothing wrong with that! This section will act as a mini buyer’s guide. I’ll share my favorite well-draining potting soil mixes for succulents, flowering houseplants, and even very young plants that you’re starting from seed. All soil mixes are courtesy of Amazon.
The Best Well-Draining Potting Soil for Succulents
The Next Gardener Professional Grower Mix Coarse Blend
Your succulents will love this professional grower mix from The Next Gardener. This stuff is fairly priced and I’ve loved it from the first time I ever used it. It’s also in stock most of the time so I love being able to count on it.
This lightweight bonsai-based soil mix with optimal drainage has a pH of 5.5. That’s slightly acidic, so The Next Gardener recommends using their coarse blend on bonsai and cacti especially. The ingredients include 25 percent perlite and 75 percent substrate with some fertilizer, but not much.
Superfly Bonsai Succulent & Cactus Soil Mix
I’m also quite a fan of this succulent and cactus mix from Superfly Bonsai. So too is Amazon considering this well-draining potting soil is an Amazon’s Choice product.
It’s a little costlier than the soil mix from The Next Gardener, but I think it’s worth the money. Here’s why.
The soil comes premixed with ingredients like haydite, New Zealand pine bark, US-produced pumice, and hard Japanese akadama. You can hardly call this soil since it has no dirt. The substrate mix will improve your succulent’s drainage, especially if you’re growing a cactus.
The bag is resealable to keep the ingredients fresher longer. If you want more soil mix from Superfly Bonsai, they also sell 2.5-quart, six-quart, and 12-quart bags.
Ramsey Organic Succulent and Cactus Soil Mix
My last well-draining soil recommendation for succulents is this one from Ramsey. The blend boasts perlite and sand for soil drainage as well as one other interesting ingredient: seaweed. Yes, that’s right, seaweed!
There are up to 60 different trace minerals in seaweed, so your plant will get a healthy dose of magnesium, phosphate, potassium, and nitrogen.
The Best Well-Draining Potting Soil When Starting from Seed
The Next Gardener Organic Seed Starting Potting Mix
For those plants that are starting from seed, I like to use their Organic Seed Starting Potting Mix which is another pick from The Next Gardener.
Whether you want to grow fruits, indoor ornamentals, flowers, herbs, or vegetables from seed, this is a suitable soil mix for the job. It’s lightweight and formulated with frost gold and blonde peat moss as well as some organic fertilizer. According to The Next Gardener, using their potting soil helps roots develop quickly for more plant growth.
Miracle-Gro Indoor Potting Mix
For the gardener on a budget, try this indoor potting mix from Miracle-Gro, as it’s another Amazon’s Choice product. Made for container houseplants, Miracle-Gro’s potting mix includes coconut coir for aeration and water drainage.
Loaded with nutrients for up to six months, Miracle-Gro states that their formula attracts fewer gnats since it’s made without bark or compost.
The Best Well-Draining Potting Soil for Flowering Houseplants
Miracle-Gro Expand ‘n Gro Concentrated Planting Mix
See more blooms with well-draining soil like Miracle-Gro Expand ‘n Gro. Recommended for bigger containers and raised beds, this soil mix has six months worth of nutrients for feeding your flowering houseplants.
Just add water and the mix will grow to three times its size compared to native soil. Miracle-Gro says this formula allows the soil to retain 90 percent more aeration. The mix will also keep at least 50 percent more water.
Espoma Organic Potting Mix
Yet a third Amazon’s Choice product on this list, I think you’ll quite like this potting mix from Espoma. Their soil mix is intended for greater moisture retention thanks to Espoma’s myco-tone water-saving formula so your houseplants aren’t stressed from dry conditions.
You can even use Espoma Organic Potting Mix on your outdoor plants!
How to Revive Used Potting Soil
Whether you bought yours or you worked hard to make well-draining soil from scratch, it’s still only good for about a year, maybe two years. About six months in, the quality of the soil has already started going downhill.
Does this mean you have to get rid of it? Perhaps, but perhaps not! Here are some questions to ask yourself before deciding whether to revitalize your potting soil.
What is your soil’s pH? You’ll need a pH soil testing kit to know for sure. Most houseplants prefer a pH of around 6.5, maybe as high as 7.0. The exception is those plant species that enjoy acidity such as azaleas and blueberries among others. Alkaline or basic-pH plants such as asparagus and many species of fern might also need a slightly different pH balance than 6.5.
Does your plant have enough soil? Soil doesn’t stay light and loamy forever, as I’ve mentioned. Time and watering will make the soil collapse on itself, becoming compact. If you don’t even have enough soil to fill to your pot’s lip, then you’re better off replacing your soil or mixing some new stuff with the old soil.
Is the soil nutrient-rich? Nutrients drain out of the soil, so the older your soil is, the fewer nutrients are in there. However, if you’ve fertilized your plant, then you’ve reintroduced nutrients to the soil. This means you have to proceed carefully. Indoor vegetables like garden peas don’t like a lot of nutrients to start while carrots, cauliflower, and onion plants don’t mind as much.
Is the soil healthy? This is the most important question of all. Has the soil become moldy or mildewy in the past year or two? Did you have any infestations? Was your plant afflicted by fungal or bacterial diseases? If you answered yes to those questions, then you’re probably better off starting afresh with your soil. You also can try sterilizing it, which I’ll talk about a little later.
Steps to Follow to Revive Used Potting Soil
If you’ve decided to proceed with reusing your old soil because it’s healthy, relatively nutrient-rich, and its pH is decent, here’s how you revive the soil.
Step 1: Prime the Soil
Take your soil out into the garage or the yard and lay out a clean tarp. Pour your soil on the tarp and spread it out. Look for anything that shouldn’t be in the soil, including rocks, dead plant bits, weeds, and the like.
With a gardening rake, comb through the soil to break down soil clumps.
Step 2: Clean the Soil
If you used fertilizer on your plant and you’re reusing that soil, then the soil will have more than nutrients, but excess salts as well. You can remove these by cleaning the soil. To do so, transfer your soil from the tarp to a bucket. Make sure the bucket has a few drainage holes. Pour water in the bucket to the top and then let the water naturally drain out. Repeat the process again.
Take the soil and dump it back onto your tarp, spreading it so it can dry faster.
Step 3: Add Fresh Soil or Compost
If your soil is still relatively loamy and full, you can mix in compost. For soil that’s compacted and needs a lift, use fresh soil. I’d recommend a mix that’s half new soil and half old stuff. You can run the new soil through a sieve and then rake it through so the new and old soil evenly integrate.
If you’re incorporating compost into your old soil, you should also use a sieve. Like with the new potting soil, you want a mix that’s half old potting soil and half compost.
Step 4: Test the Soil’s pH
Now that your soil has a different composition, it’s not a bad time to use your pH tester to determine the new pH level of the soil. If the pH is too low, lime can increase it. Aluminum sulfate can reduce pH.
Step 5: Apply a Slow-Release Fertilizer
The new soil needs nutrients, but not all at once. Use your favorite slow-release fertilizer. Measure how many gallons of soil you have and then apply a tablespoon of the fertilizer per gallon.
Step 6: Allow the Soil to Cure
You can’t use your newly invigorated soil right away, so please plan for that. It takes upwards of two weeks for the ingredients in the soil to cure. The soil will cure best in moisture-free, dark conditions. Put the soil in a box or a plastic storage container and close the lid.
Here Are 3 Ways to Sterilize Your Indoor Potting Soil
I mentioned in the last section that if your plant was infested by bugs or disease that you can try sterilizing it. This could remove pathogens, weed seeds, and unwanted organisms from the soil.
Try any of these sterilization methods.
If you don’t mind a drawn-out process, then you can use your kitchen microwave as a sterilization instrument for old potting soil.
Fill microwave-safe containers with potting soil, as many as it takes. I would recommend labeling the containers so you can tell which ones you’ve microwaved versus which you haven’t. Oh, and make sure the lid has ventilation holes, which you can poke with a knife or fork.
Run your microwave on full power in 90-second bursts. I told you this can take a while!
If you have a larger microwave, you can save some time by pouring about two pounds of old potting soil into a bag made of polypropylene. Leave the bag open so it can ventilate and then microwave it for about two minutes, maybe two and a half minutes on full power.
It’s probably more convenient to sterilize your soil in the oven, as it’s far larger than a microwave. You’ll need a large oven-safe container with a depth of around four inches for making this process expedient. Pour the soil in and put foil over the top.
You should have a food thermometer like one for candy-making or cooking meat. The temperature of the soil should be between 180 and 200 degrees.
It should take about 30 minutes for the soil to reach these temps, but use the temperature as your litmus test rather than the clock. If the soil bakes too long or gets too hot, it can release toxins, so please be careful.
Your third soil sterilization option is to use steam. If you have a pressure cooker, this is the perfect instrument for heating your soil.
Put the soil in the pressure cooker and let it go until the temperature gets to 180 degrees or after 30 minutes, whatever happens first. You’ll need to add water to your pressure cooker, at least a few cups.
Have a few four-inch pans ready to put the soil on. Each pan should be covered in foil.
When you run the pressure cooker, don’t close the steam valve. It is okay to put the lid on. If your soil has manure or a lot of nitrates in it, pressure-cooking it could cause it to explode. You’ll want to proceed with extreme caution using this method!
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