I was there myself when I first started learning about container gardening. I was standing in the garden center looking at big ol’ bags of cheap topsoil. My brain kept saying, “Why should I pay an arm and a leg for potting mix when dirt is dirt?” What a silly idea. I didn’t learn until later that assumption cost me a headache.
As soon as I began planting herbs and flowers in pots, I decided to use nothing but plain old topsoil. Everything looked great for a couple of weeks. And then it rained. Water started collecting on top of the soil. And my patio container turned into a mud puddle after a stormy weekend. That’s when I figured out containers act much differently than garden beds.
So, to summarize, yes, you can put topsoil in your planters, but don’t expect topsoil to be the best option by itself. More importantly, there are other factors involved such as drainage, root development, airflow, and even the weight of your planter.
Can you put topsoil in your planters?
You betcha. Yes, you can use topsoil in your planters. The problem is that topsoil is created for planting directly into the earth versus for planting in containers.
When you’re planting in a garden bed, you don’t worry about where the excess water will go. Containers are totally different. Containers have limited drainage and little to no airflow surrounding the roots of the plants. This makes a world of difference.
Plain old topsoil tends to get too dense in containers, especially when it gets wet multiple times. Once topsoil gets saturated, it starts to pack together and holds way too much water. Depending upon the type of plants you’re growing, they might live for a while, especially outdoor tough plants, but ultimately long-term growth is going to suffer.
Again, trust me on this one, ignoring soil texture can hurt you in terms of container gardening. Roots need oxygen just as much as they need water.
Topsoil works better in the ground than it does in containers
In summary, topsoil doesn’t tend to perform well in containers compared to potting mix.
What happens when you just use topsoil in your planters?
Poor drainage
Without a doubt, poor drainage is the number one issue. Topsoil generally retains moisture longer than container gardening soils. When you have excess moisture trapped in small or medium-sized pots, it has nowhere to escape.
When roots remain consistently moist, root rot is likely. I experienced this personally with my basil plants last summer. Even though I thought I was watering them right, the leaves were turning yellow. The reason why is the soil remained consistently moist for far too long.
Containers dry out differently than raised beds and gardens
Sunlight exposure, wind exposure, and the actual size of your containers impact moisture content. As such, potting mix is designed to deal with these issues much better.
Compacted soil
Plain topsoil settles over time and compacts down. Compacted soil impacts root expansion. Additionally, water may collect on the surface as opposed to absorbing into the soil evenly. I’ve seen many people water their potted plants only to watch the water collect on top for several seconds due to compacted soil.
Loose soil is better
Fluffy loose soil is far superior to tight packed soil in allowing healthy root growth and providing adequate oxygen.
Heavy containers
Topsoil is extremely heavy. Wet topsoil is even heavier.
Using topsoil in large containers can be downright cumbersome for moving them around on your patio, balcony, or deck. I once purchased a decorative planter and filled it with cheap topsoil. Later I was shocked to find out that I could barely lift and move it around due to its massive weight.
While this may seem insignificant at first, if you frequently move your containers due to seasonal placement or bad weather, weight becomes an enormous factor.
Debris, weeds, and pests
Unfortunately, some lower-end topsoils may contain weed seeds, bugs, or debris. While not all cheaper topsoils will contain debris, it happens enough that it should be mentioned.
Prior to buying a lot of budget topsoils, I’ve discovered fungal gnats, sticks, and clumps within the soil. Most potting mixes are produced with significantly higher quality control standards for container production.
Instead, what we recommend
Honestly, most planters benefit greatly from using potting mix instead of topsoil. Specifically, potting mix is formulated to work perfectly with confined spaces like containers.
Quality potting mixes provide excellent drainage and allow for maximum root development, which equates to a healthier overall plant. Most commercial potting mixes include peat moss, compost, coconut coir, perlite, etc., which retain moisture while preventing the formation of dense, muddy soils.
Once you start comparing topsoil and potting mix head-to-head, you’ll notice the vast differences instantly, namely that potting mix dries out faster, weighs less, provides more oxygen, and promotes greater root development.
If you ask me today what’s the absolute best soil for planters, 9 out of 10 times I’m recommending starting off with a high-end potting mix. That being said, “premium” doesn’t necessarily mean “best.” I’ve purchased premium mixes that dry out too rapidly and subpar mixes that functioned remarkably well. Trial and error will always be part of container gardening.
Can you mix topsoil and potting mix together?
You can, and quite frankly mixing topsoil and potting mix is probably the cheapest way to fill larger raised planters or oversized pots. To do this effectively, you’ll want to use moderation.
Typically, I shoot for approximately 30% topsoil and 70% potting mix. That ratio will keep your container fairly light while providing stability and nutrients to your plants.
Based on personal testing, I’d highly recommend keeping the amount of topsoil under 50%, particularly if using clay-heavy topsoil. Topsoil based heavily on clay can cause serious drainage issues quickly.
Blending topsoil into potting mix seems to produce far better results than using pure topsoil. For some reason this mixture works best for large outdoor planters rather than smaller indoor containers.
Additional tips before you fill your planters
Always ensure your planters have drainage holes before adding soil. Regardless of how good your soil for container gardening is, without proper drainage, it will turn into mush.
Don’t pack down your soil! Keeping your soil loose will help maintain airflow and promote healthy root development.
Whether or not you choose to add fertilizers to your potting mix, consider adding a slow-release fertilizer for optimal nutrient supply throughout the season.
Treat your containers differently than garden beds. Containers tend to evaporate faster, especially during extreme heat.
Additionally, refreshing your container soil annually will be beneficial in ways you never imagined. Old soil loses nutritional value and structural integrity with age.
If you have large decorative planters that weigh excessively, consider placing light material at the base to lighten the load and conserve the new soil..
