Seeing a flower growing out of a crack in the sidewalk may give you the optimistic impression that plants can survive under even the hard conditions (literally), but that isn’t the case for houseplants. Most popular houseplants are reasonably resilient, but only when they’re grown in a suitable environment, and that includes healthy, fertile, aerated soil.
It’s common to think of soil compaction as a problem limited to grassy lawns, but compaction can also create major problems for your indoor and outdoor potted plants. Read on to learn more about how soil compaction may be undermining your houseplants and how to aerate the soil in potted plants.
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What Causes The Soil In Potted Plants To Get Compacted?
Many factors can affect the soil density of your potted plants. One of the most obvious ways is if you compact and tamp the soil into the pot too hard. It also tends to naturally develop if you leave a plant in the same soil for years at a time without repotting. However, there are a variety of other causes that may be less obvious.
Incorrect soil Choice
You should never use garden soil or topsoil for indoor or outdoor potted plants because it lacks the aerating elements found in potting soil (such as perlite).
Without any natural elements like worms allowing air and water flow, potted garden soil will quickly become compacted. Garden soil also tends to be heavy in clay, which compacts when it dries out.
You can either buy or make well-draining potting soil for your plants.
If you prefer the latter, here is a simple DIY potting soil mix recipe:
- Mix two parts coconut coir or peat moss with one part sifted compost and one part perlite.
The coir and perlite are excellent for keeping your potting mix loose and aerated.
When your potted plants are in the appropriate soil, they make a great addition to your backyard. You can integrate them with other garden plants or use them to make an urban deck greener. For more ideas about how to turn your backyard into an oasis, check out these five tips to make your dream garden.
Garden soil doesn’t need perlite because worms, insect activity, and beneficial soil microbes aerate it. For potted plants, the soil will need perlite and beneficial microbes to create pathways for oxygen.
It’s easy to accidentally kill off your beneficial microbes in a potted plant, which will cause compaction, but it is also an easy problem to avoid or fix.
If your potted plants are outside, baking in the hot summer sun, the soil can dry so badly that the microbes go dormant or die. This scenario is prevalent when people fill their pots with garden soil (or a mix including garden soil) that is heavy in clay.
You can avoid this by avoiding dark-colored pots, placing the pots in areas with partial shade, and keeping them well-watered during the hot season.
Repeated under-watering can also cause the soil to harden. More so if your potting mix includes peat moss because it is extremely absorbent. If you let peat moss dry out, it can become hydrophobic (meaning it repels water).
Instead of absorbing water into the soil, dry peat moss will cause the water to roll off and spill over the sides or down edges of the pot.
This can worsen compaction, kill off your soil microbes, and ultimately kill your plants.
If you’re having compaction problems indoors, you might have killed your microbes by overwatering poorly-draining soil.
Standing water creates anaerobic conditions that can drown roots and beneficial microbes. This can also happen with outdoor potted plants if the drainage holes get clogged up, and a rainstorm fills the pot with water that can’t escape.
Overwatering can also contribute to compaction by causing the potting mix’s aerating materials (such as perlite) to drain out the bottom of the pot along with the excess water. Over time this will contribute to compaction.
Chemically treated water
Watering with city water that is treated with chlorine and ammonia can kill microbes. Using rainwater or filtered water is a good idea if you have highly treated tap water.
How To Test For Soil Compaction
Compacted soil is easy to identify in potted plants. You may tell by sight, but the best way is simply to feel the soil.
Can you run a finger through the potting mix quickly?
Is the soil soft and flaky, or is it hard and clumpy?
If the soil feels substantially different from how you’d expect fresh potting mix to feel, you may have a compaction problem.
How To Aerate Compacted Soil In Pots
When most people think about soil compaction, they picture grassy fields, where soil compaction results from walking or driving on the soil (in addition to some of the factors that apply to potted plants). If you’re dealing with soil compaction in the ground, check out our guides to aerating a compacted lawn and the five best tools for that job. For the best methods for eliminating compaction in potted plants, read on.
Replace Your Potting Soil
The best way to fix compacted soil in potted plants is to replace it with healthy, well-draining soil. Repotting your plants at least once every few years is an easy step that will have many other positive impacts on your plants. It restores aerating materials (like perlite), prevents excessive mineral or salt buildup, and allows you to remove any diseased roots.
When you replace the potting mix, make sure to use a well-draining variety so the problem will be less likely to recur. You want organic matter in your potting soil, but you also want to make sure it contains a healthy amount of these sorts of additives:
- Perlite is a lightweight volcanic rock commonly used to aerate the soil.
- Pumice is a lightweight, roughly textured volcanic glass often used for exfoliating devices you use in the shower, but it also adds aeration and weight to the potting mix.
- Horticultural sand (also known as coarse sand or sharp sand) is a rough grit made from quartz, granite, or sandstone, improving drainage in a potted plant.
- Peat moss is an acidic fibrous material made from moss from peat bogs, which is commonly used to improve the aeration of potting soil.
- Coconut coir is a well-draining material made from the fiber under coconut shells and is used as a more sustainable alternative to peat moss.
When you repot your plant with well-draining soil, consider switching to an unglazed clay or terracotta pot. These materials are ideal for encouraging oxygen and water movement throughout the pot and can absorb excess water, protecting the plant.
You may want a temporary solution to compaction, for example, if you want to wait until the preferred season for repotting your plant. You can manually aerate your potting mix quickly and easily. All you need is a long thin object, such as a chopstick, ballpoint pen, or a sturdy stick.
Before watering your plant, you should poke a chopstick into different areas of the soil. Push it down into the depth of the pot to break up clumps and create spaces for air.
You may run into roots. If they’re little roots, don’t worry about it, the plant likely has plenty and can spare a few. If you run into a larger root, wiggle the chopstick a little until you’ve maneuvered around the root. Then continue to press it into the pot.
After aerating, water the plant. You want to see the water draining easily out of the bottom of the pot. If you still have poor drainage after your first attempt, you can use the chopstick method a second time.
Replace soil microbes
Most people know you can eat probiotic foods like yogurt to restore healthy gut bacteria; the same principle applies to your plants. By adding beneficial microbes into the potting mix, you can bring your soil back to life.
The least expensive way to reintroduce microbes to the soil is by adding in a bit of compost.
If the soil is compacted, the soil level has probably fallen to well below the rim. You can aerate the pot and then add as much compost as needed to fill the pot. Mix it up with the existing soil to the extent possible without disturbing the roots too much.
If you don’t have room in the pot to add compost, you can use compost tea, worm castings, or commercially available plant probiotics. It will take time, but eventually, these beneficial microbes will help restore a healthy ecosystem for your plant.
Problems Caused By Compacted Soil
Compacted soil endangers your plant in several ways. The most obvious is that it is harder for a plant to form long roots in compacted soil than in loose, aerated soil. At the same time, compacted soil can cause more subtle problems, like creating a protective environment for sub-soil pests. All in all, it is a situation worth avoiding if you love your plants.
Here are some problems caused by compacted soil:
- Compacted soil in the bottom of the pot can stop drainage, resulting in drowned roots and root rot.
- Compacted soil in the middle (around the roots) can cause the water to absorb only around the edges of the pot, not at the center where the roots can access it.
- Compacted soil stops roots from accessing nutrients in the soil.
- Compacted soil can be hospitable to negative anaerobic microbes and inhospitable to beneficial microbes.
The Hard Truth About Hard Soil
It would be nice if you didn’t have to worry about compaction in potted plants, given that you aren’t walking or driving on them. But this is a problem you shouldn’t ignore because the life of your plants is on the line.
Fortunately, fixing soil compaction is as easy as being observant and repotting periodically. Keep your potting mix soft and loose, and you will have happier healthier houseplants.