Believe me, I’ve been there. You just got home from the nursery with tons of gorgeous flowers to plant up your containers, and…
Crap… you forgot to buy potting soil.
Using garden soil in your containers can’t be all that bad… right? So you head for the shovel to dig up a couple scoops of soil from your garden bed to fill it up.
As tempting as it may be, you should not use straight garden soil in pots. When used in containers, garden soil gets very compacted. Garden soil also lacks the drainage & nutrients necessary to grow healthy, potted plants.
Types of Garden Soils
There are many types of soil used in the home garden, each with distinct differences.
- Dirt from your own garden beds at home
- Bagged garden soil purchased at the store
- Potting soil or potting mix
- Seed starting mix
Garden Soil from Your Yard
The soil in your own yard consists of all sorts of goodness. But when you scoop garden soil or topsoil into a container, it doesn’t translate into a healthy container garden. Garden soil from your yard is very heavy and depending on your location will contain various amounts of sand, clay and/or silt. When it’s on the ground, it’s aerated by the worms, bugs and microorganisms that live in your soil. But, when used in containers, garden soil from your yard is too dense. It will get very compacted, causing poor drainage in your container which ultimately will rot the roots of your plants.
Bags of topsoil purchased from a store is comparable to what you’d actually find in the ground. The amounts of sand, clay and silt will vary depending on where the topsoil is harvested. The only difference between bagged topsoil and the soil from your yard is that bagged topsoil is shredded and screened to remove any large particles then processed to a looser consistency.
Both garden soil and topsoil are too dense/heavy and lack the nutrients needed for container plants.
Bagged Garden Soil
Bagged garden soil consists of natural topsoil or sand blended with bulky organic/woody material (like pine bark). Most garden soils are too dense to allow for good air and water movement when added to a container garden. Soils hold water very well in their small pore spaces and can drown roots—especially in shallow containers.
Many websites will tell you that yes you can use 100% compost when planting containers. However, I have tried this in the past with bagged compost and it did not work out so well. If you make your compost from leaf mold, this may work out to be a lighter mix that will be suitable for containers. But, if using regular compost or bagged compost, I would recommend combining it with at least 50% soilless potting mix so it doesn’t get compacted.
Many gardeners will use compost as a replacement for peat in their homemade potting mix recipes— it holds moisture well, but not nearly as well as the peat.
Potting mix or potting soil is the preferred option for growing plants, flowers and even vegetables inside pots.
Vendors might call their product a potting mix or a potting soil, but there is usually no distinguishing ingredient between them. The ingredients will be listed on the back of the bag.
Typical Potting Mix Contains:
- decomposed/woody material (around 50-65%)
- spaghnum peat moss (or equivalent)
- perlite and/or vermiculite
- a wetting agent
Seed Starting Mix
It’s also important to note that potting mix is different than seed starting mix. Seed starting mix is used to germinate and grow plants from seed. There’s actually no “soil” in seed starting mix. Because of this, you really wouldn’t use garden soil or potting soil to make seed starting mix.
Can garden soil be used in outdoor pots?
Garden soil can be used as the base of a homemade potting mix, but it should never be used straight in outdoor pots. Using any soil in a potting mix is not ideal, though. You are much better off using potting mix to make sure that you have the right balance of aeration, drainage, moisture retention and nutrition.
What happens if you use garden soil in pots?
If you use garden soil, such as Miracle Gro Garden soil or Vigoro Garden soil you may run into some problems. Garden soil is simply too heavy, making containers much harder to move around than if you used potting mix. That extra weight will lead to compaction from watering. The compaction will not allow the pot to drain and there will be no air in the soil for your plants. Additionally, garden soil will lack the nutrients your plants would usually gain from the ground that a soilless potting mix puts in right in the bag for you.
If you are hell-bent on using garden soil, I would recommend amending the soil to improve the moisture retention, drainage, aeration and nutrient levels. Scroll down to the heading “What can I use in containers instead of potting soil?” to get some ideas.
I accidentally used garden soil in pots — Will it kill my potted plants?
If you used soil from your yard, yes this can potentially kill your potted plants. But don’t worry, you can fix it! First, you’ll have to un-pot your plant. Instead of throwing away the soil that you put into your container, you can dump it into a bucket and amend the soil.
In the next section, I provide several amendment options.
Can you mix potting soil with garden soil?
Potting soil can be mixed with garden soil for particular cases such as raised beds, but it’s not a good mix for containers. You will still need to amend the mixture.
What can I use in containers instead of potting soil?
You can actually make your own potting soil by combining various ingredients together. Most gardeners will use perlite or vermiculite with peat or sphagnum moss. The important thing to remember is that to make potting mix, you will need “ingredients” to retain moisture, promote drainage and aeration and nutrients.
I like to use the ratio of 1 part moisture retention material to 1 part drainage and aeration materials plus the appropriate amount of nutrients, which will depend on the fertilizer you use and the size of your container.
If you are wondering what materials to use and you just need a recipe, try this:
- 1 part woody material, garden soil or topsoil
- 1 part perlite (for drainage)
- 1 part coco coir (for moisture retention)
- bone meal (balanced fertilizer)
If you want to get creative, here are more options!
1. Aeration & Drainage
What can you use for aeration & drainage in your mix?
- Perlite: Perlite is a volcanic glass that’s heated at high temperatures. The heat causes the glass to expand, resulting in an odorless mixture that feels like tiny little balls of Styrofoam. It’s great for drainage.
- PBH rice hulls: Available at a lower basic cost than perlite, PBH rice hulls dramatically reduce dust in the greenhouse mixing environment. Sterilized rice hulls are not a substitute for peat moss but replace perlite and vermiculite, the production of which requires fossil fuels.
- Horticultural sand: Horticultural sand is very gritty sand made from crushed granite, quartz or sandstone. It’s also called sharp sand, coarse sand or quartz sand. Because there’s a mix of gritty components, horticultural sand promotes drainage.
2. Moisture Retention
Moisture retention is another important component of soil used in potting mixes. Make sure that you always add a component for aeration & drainage along with a moisture retention component. If you don’t, your soil will become brick-like and so compacted that it can’t drain. This is not good news for your plants.
What can you use for moisture retention in your mix?
- Peat moss: Peat moss is the go-to for moisture retention in seed starting and potting mixes, but it’s not the most sustainable or eco-friendly option.
- Vermiculite: Vermiculite is natural mineral (magnesium-aluminum-iron) silicate, which basically means minerals compressed and dried into flakes, or pellets. It absorbs water and aids in moisture retention. Vermiculate is found in so many seed-starting mixes because it can protect seedlings from fungus. Vermiculite also has some drainage and aeration qualities, but not nearly as much as perlite.
- Coconut coir: Coconut coir (also known as coconut fiber, coco peat or coco coir), is my favorite alternative to peat moss. It has excellent water-holding capabilities and a pH level of 6 which will is good for most garden plants.
- Compost: Many gardeners recommend compost as an alternative to peat moss, but if you are using it in containers it will eventually become compacted in your containers and cause drainage issues.
- Leaf mold: Leaf mold is easy to make and can condition the soil and greatly improve moisture retention.
- Woody materials: Non-chemically processed woody byproducts of locally-sourced wood (such as wood fiber, sawdust or composted bark) can be a decent alternative to peat moss. But, it’s usually a less-than-ideal alternative because most wood isn’t locally sourced and can be chemically treated.
- PittMoss: Created by an inventor in Pittsburgh, PittMoss consists of reconstituted paper fibers with added proprietary ingredients.
- Worm castings: Worm castings are the waste from farmed earthworms, rich in nutrients and beneficial microbes. They can also hold 2-3x their weight (p35) in moisture.
For these reasons, I would recommend finding alternatives to use in your own garden.
Plants in pots need fertilizer if you want to them to thrive. Because they are in a contained space, they only have access to the nutrients that you put into the container. That’s why it’s important to add fertilizer to your DIY potting mix and make sure that you replenish the fertilizer often.
When you purchase fertilizer you’ll typically see 3 numbers on the label. These numbers represent the nitrogen (N), phosphorous (P) and potassium (K) or the N-P-K ratio. A fertilizer with the numbers 10-5-10 on the label means that the fertilizer contains 10% N, 5% P and 10% K. The remaining 75% of the bag’s weight is carrier product.
Nitrogen promotes optimum shoot and leaf growth, often at the expense of flower and fruit production. Phosphorous promotes strong roots and encourages fruiting and flowering. Potassium levels influence a plant’s heartiness and vigor. Learn more about fertilizer numbers. It’s best to find a balanced fertilizer that contains around equal parts of all 3 nutrients.
Here are some fertilizer recommendations for creating your own potting soil from garden soil:
- Miracle Grow All-Purpose Plant Food: This is an affordable and long-lasting fertilizer option that works well on most plant types. This is not an organic solution and contains chemicals so I’m also providing some alternatives.
- Osmocote: A common fertilizer used in container gardening, Osmocote contains 11 nutrients, slow-release feeding container plants for 6 months.
- Worm castings: Worm castings are the waste from farmed earthworms, rich in nutrients and beneficial microbes. In addition to moisture-retention qualities, the nutrients found in worm castings can last 6x longer (p35) than basic potting mixes.
- Bone Meal: Bone meal is made from steamed and then crushed animal bones. It’s high in Phosphorous, important for root development and flower blooms and calcium and nitrogen, which are also very beneficial to plant growth.
- Blood Meal: Blood meal is dried and powdered animal blood. It’s used as a fertilizer to increase soil nitrogen levels — and without nitrogen plants simply cannot grow. Blood meal is one of the richest non-synthetic sources of nitrogen, which is a crucial component of plant cells and one of the basic components of chlorophyll, the substance that helps plants convert sunlight into sugars.
- Liquid Kelp: Liquid kelp, seaweed, or fish-based fertilizers provide a range of benefits for plant health and growth.
Using straight garden soil in your containers is not a good idea. Garden soil on its own lacks the drainage, aeration, moisture control and nutrients necessary to successfully grow plants in containers. When used by itself, garden soil or topsoil in containers becomes so compacted that water cannot drain.
In other words: the roots of your plant drown in the water and your plants die.
But the good news is that you can amend your garden soil in order to use it in containers. Is the effort worth it? I’m not so sure… but it is possible! Use a 1-1-1 ratio: 1 part garden soil, 1 part moisture retention component (like coco coir) and 1 part drainage & aeration component (like perlite) and a well-balanced fertilizer (like bone meal or osmocote). Once mixed, your garden soil is now suitable for your containers!If you have a go-to DIY potting mix recipe that you love, be sure to head over to the Facebook page to share it.
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