A lot of people think that soil is pretty much the same thing whether it comes from your yard, a bag of potting mix, or an outdoor garden. It’s important to know which type of soil your indoor plants will thrive in or most likely die in. That said, is it ok to use outdoor soil for indoor plants?
No, you cannot use outdoor soil for indoor plants for these reasons:
- It’s heavier than potting soil so air can’t travel well
- Retains water longer, which can lead to root rot
- Lacks vermiculite, perlite, etc. so it’s less aerated
- Contains different nutrients than what indoor plants need
In this article, I’ll explain in further detail why using topsoil or outdoor soil for your houseplants is not advisable. I’ll even delve into whether digging up your backyard as a soil source is worth doing, so keep reading!
Why Using Outdoor Gardening Soil for Indoor Plants Is a Bad Idea
Outdoor gardening soil is also known as topsoil. As the name suggests, this is the topmost layer of soil and can be anywhere from five to 10 inches deep depending on whether the plant is out in nature or if it’s part of an outdoor garden.
Topsoil has lots of microorganisms and organic matter from compost, so the soil is very active. It has concentrations of air, water, organic materials, and minerals as well.
To you, this sounds great! If you have a few outdoor plants that thrive with outdoor gardening soil, then surely transferring some of this soil to your container plants in your home will be fine.
Yet that’s not the case. The following issues are why topsoil is a terrible choice for houseplants.
Outdoor Gardening Soil is Too Heavy for Indoor Plants
I know outdoor gardening soil and potting mix might look the same if you do a side-by-side comparison, but the soil types behave differently. Namely, topsoil is a lot heavier.
Large outdoor plants don’t mind heavier soil, but when it comes to your houseplants, it’s a different story. Heavy soil will compact on itself.
When the soil gets hard and immovable, the air pockets that were spread throughout disappear.
Plants, whether you grow them outdoors or indoors, need two things to live: oxygen and water. With less aeration, your houseplant doesn’t get as much oxygen.
In addition, the water that you pour into the plant’s soil will have a much harder time reaching the roots and nurturing the plant. Compacted soil can even stop water from reaching the roots even when you’re bottom watering.
One of two things will then happen:
- The water will evaporate in the soil before your roots get to drink it
- The roots will be oversaturated with water that will not be able to drain.
If it’s the former situation, and the water is evaporating before reaching the roots, then your plant will seem underwatered with symptoms like wilting, leaf yellowing, and a crispy texture.
If your houseplant is saturated in water, its roots could begin dying, which is known as root rot. When the roots die, the rest of your plant will as well.
Heavy soil can also make it hard for young roots to spread out, which can inhibit the growth of your houseplant. All around, it’s just a bad situation.
Outdoor Gardening Soil Retains Water for Too Long
There’s another factor working against your houseplants when you use outdoor soil. Outside of the soil compaction, topsoil is known for its great water retention. Is this such a bad thing if you’re growing plants like: coleus, arrowhead plants, spider plants, Chinese evergreen, pothos, or philodendron? Admittedly, no, because these plants are thirsty drinkers.
For all your other houseplants that need water far less often, using topsoil is practically a guaranteed death sentence. You can expect that much sooner than later, your plant will come down with a bad case of root rot.
I just touched on root rot in the paragraphs above, but I want to describe it in more detail now in case you need the refresher. Root rot occurs from overwatering or otherwise leaving your plants in standing water (aka water that doesn’t drain).
The roots of a healthy plant are white and firm, but a plant’s roots will begin to turn black and become mushy when the plant is developing root rot. The roots that have succumbed to root rot will also take on a distinct odor, a smell that will signify that something has died. In this case it’s the houseplant attached to the roots.
In the meantime, your plant’s leaves have become brown or yellow, at least at first. As root rot progresses, the leaves could turn black. The leaves will wilt and maybe even fall off your plant. Growth will stop since your plant is drowning.
Even if you water your indoor plant as regularly as you always do and it’s never been a problem before, since outdoor soil will be moister by nature, root rot is practically a surety for your plant.
Outdoor Gardening Soil Has Less Aeration
The ingredients in many indoor potting soils are sphagnum moss or peat moss, vermiculite, and perlite. Peat moss uses cation exchange capacity for increased nutrition holding.
It’s also able to keep lots of water per its weight. Vermiculite increases nutrient and water retention while helping to aerate the soil. Perlite prevents soil compaction and makes soil looser and airy.
Topsoil has none of those ingredients, which means its aeration is naturally lesser. Remember also that outdoor gardening soil is more compacted. That’s not a great combo for indoor plants.
Imagine wearing a shirt that’s a few sizes too small for you. It’s hard to breathe and you feel a lot of pressure, right? That’s kind of what your houseplant is going through when it has top soil or outdoor soil pushed up against the roots of the houseplant.
If your plant doesn’t have enough oxygen, it can’t do aerobic respiration where it takes plant sugars from photosynthesis and converts them to energy. When your plant is depleted of energy, it can’t dedicate the resources to new growth, so your plant stagnates. If the oxygen loss is especially pronounced, then your plant may not be able to sustain itself anymore.
Outdoor Gardening Soil Doesn’t Necessarily Contain plant essential nutrients.
Yes, I know it sounded especially promising before when I mentioned that topsoil is full of compost and microorganisms. Outdoor gardening soil is indeed nutrient-rich, but that doesn’t mean it has the right nutrients for your houseplant?
According to Texas A&M AgriLife Extension, as many as 16 plant nutrients exist. Here’s the full list:
Houseplants are picky. Some love nitrogen, others need far less. Actually, you can say that about any of the above nutrients, that some indoor plant species require more of the nutrients than others.
So sure, topsoil has lots of nutrients, but if it’s not the nutrients that your houseplants need or if the concentration of nutrients is all wrong, bad things will happen. Your plant could develop nutrient deficiencies.
The symptoms of a nutrient deficiency can vary but may include leaf tip and edge burning, leaf browning, and leaf curling or wilting. Growth will stop, including the production of fresh buds and foliage. Under the surface, the roots aren’t growing anymore either.
Overdoing it on the nutrients is just as bad, as what can result is a condition called fertilizer burn. Your houseplant’s leaves will wilt and turn brown or black. The plant can also take on a burnt appearance like it’s been sitting in the sun for too long.
Why Digging up Your Backyard to Use the Soil for Your Indoor Plants Is a Bad Idea
Alright, so you won’t use outdoor gardening soil for your indoor plants. That’s okay. What you’re thinking of doing instead is digging up a corner of your backyard and putting that soil in your houseplant’s pot.
Once again, all soil is not the same. Here is why you’re better off leaving your backyard undug.
Backyard Soil Bad Soil Structure
Your yard is more than soil, but also clay, silt, and sand, or maybe only some of those. Certain plant species such as succulents are fans of sand in their soil, but not other plants. As for clay, it lacks organic materials and sticks especially well to itself. In other words, if there’s clay in your soil, it won’t drain well.
The structure of your backyard soil is not strong enough to support plant growth. It’s just not worth using.
Backyard Soil is Nutritionally Poor
Unlike topsoil, backyard soil doesn’t contain nearly as many nutrients. What nutrients are in the soil could be sparse or perhaps the wrong kinds for your houseplant. I already talked about what a nutrient deficiency can do to your plant. It’s not something you willingly want to put your plants through.
Backyard Soil Has a Much Higher Risk of Pests
Even if your backyard soil was somehow structurally beneficial for your plants and full of the nutrients they needed, I would still caution you not to use it. Topsoil is commercially packaged and goes through some quality control standards, the same cannot be said for the soil in your yard.
If you just scoop and scoop and scoop, you might miss the pests hidden within the soil. Even if you do keep a closer eye on what you’re digging up, some plant pests are so microscopic that seeing them with the naked eye can be difficult.
Pests are, to an extent, inevitable when growing an indoor garden. That doesn’t mean you have to invite the whole insect kingdom into your apartment or office though. Many bugs are more than just nuisances, after all, but can kill your houseplant.
Using Backyard Soil Could Spread Disease
Soilborne diseases can be fungal, bacterial, or viral. The scary thing is that, even when the host plant dies, these diseases will remain in the soil waiting to infect their next victim.
Using chemicals on the soil can work to an extent, but this is often a pricy measure. Your best option is to get rid of the infected soil and start from scratch.
You have no idea if the soil in your yard contains the pathogens that can start a soilborne disease once you add a host like your houseplant. If that’s not unnerving enough, let me quote this 2012 report from the Journal of the American Board of Family Medicine.
The journal said this: “A variety of classic and emerging soil-related bacterial and fungal pathogens can cause serious human disease that frequently presents in primary care settings.”
Those diseases? They include respiratory tract diseases, gastrointestinal tract diseases, skin conditions, botulism, anthrax, and tetanus.
Leave your yard alone!
How Do You Know Whether You’re Buying Potting Soil or Topsoil?
Okay, you definitely want to start using potting soil formulated for indoor plants from now on. How do you know whether what you’re shopping for is potting soil or topsoil?
Here are three easy ways to tell the difference between Potting Soil and Topsoil:
First, I’d say to check the label. If that didn’t clear things up, then do a quick Internet search for the product and read through the description.
That should tell you whether your soil is intended for indoor or outdoor use. Some indoor soils are usable for outdoor plants as well, but you’ll probably want to avoid the product if it says vice-versa.
If you don’t see any mosses, perlite, or other aerating products like coconut coir on the ingredients list of the soil, then the chances are good that it’s topsoil instead of potting soil.
The exclusion of the above ingredients makes topsoil the cheaper gardening product of the two. However, if you buy a big bag of topsoil, it could be just as costly as a bag of potting soil, so don’t use price as your only indicator.