Most gardeners rave over compost and its benefits for gardens. From amending poor-quality soil to feeding vigorously growing plants, compost is an excellent way to give your garden a helping hand. Given its lengthy list of attributes, can you skip potting soil and just use compost?
After all, it provides all sorts of benefits to plants, so why not? While we understand where the logic comes from, it’s not a good idea to skip potting soil altogether and replace it with compost. Why? It comes down to the composition of each type and its intended uses, but we’ll explain the answer more in the following sections.
Is Compost The Same As Potting Soil?
Compost and potting soil aren’t the same things, and while they’re both used in similar settings, they have entirely different purposes. To better explain our answer, let’s take a look at compost and potting soil separately.
Compost is considered a soil amendment, often used to improve the soil’s texture and incorporate missing nutrients. Many avid gardeners have their own composting setup, generally with an indoor bin to collect scraps and an outdoor container where all the scraps decompose.
Compost can consist of various scraps and ‘waste’ ingredients. Depending on the home, it could contain:
- Grass clippings
- Animal manure
- Kitchen scraps – such as fruit and veggie scraps, coffee grounds, etc.
Composting is a great way to repurpose kitchen scraps and other waste products that would otherwise be disposed of. It’s held in high regard, with some gardeners referring to it as “black gold.”
It can amend some of the trickiest soils, like clayish soils with drainage issues and sandy soils that are unable to retain water. While it’s an excellent way to improve soil quality, it isn’t ideal as a standalone soil replacement. It’s an irreplaceable amendment, but that’s as far as it goes. It’s just an amendment.
On the flip side, potting soil looks a bit different. Also known as potting mix, potting soil contains varying components to benefit plants, including:
- Sphagnum moss
As the name implies, potting soil is intended for use with potted plants. However, the name is somewhat misleading because even though it suggests it’s a type of soil, it doesn’t contain any soil!
The reasoning behind the lack of soil is the result of potential faults soil may have. Soil can carry certain fungi and other plant pathogens that inhibit growth and harm your plants. So, potting mix is created as a sterile alternative to the soil mixes available.
While the specific ingredients and the amounts of each component can vary, most potting mixes are relatively balanced to promote plant health. The organic material in the mixture (usually compost or moss) feeds the plants, while the perlite or vermiculite provides adequate drainage by keeping the mix loose and aerated.
This prevents the mix from compacting around the plant roots or soaking up too much water, which could harm or kill the plant since it prevents the roots from breathing. Some mixes feature other additions, like water-retaining crystals or chemical fertilizers, while others are specifically designed for certain plants.
So, when should you use potting soil? The best scenario to use potting soil is when you’re growing plants in a container or starting seeds. After you transfer the plants to flower beds or raised beds (if applicable), avoid using potting soil to continue feeding the plants.
Potting soil tends to be quite pricey, so adding pounds of it to your yard or garden beds will be expensive. On top of that, it doesn’t contain enough nutrients to feed your new plants after the season comes to a close.
Can You Use Compost As Potting Mix?
Although you might think compost would be the ideal way to grow plants, it’s not as suitable as you might think. It’s important to remember that compost isn’t supposed to be a standalone soil mixture. You’re supposed to use it as an addition to existing soil, as it works wonders to improve the overall quality of the soil.
However, let’s say you decide to use compost instead of potting mix. You don’t use any soil or potting mix; you choose to stick with compost and compost only. There’s a good chance your plants won’t thrive, and they might even die.
While composting is a good thing, you don’t want too much of it, or you might deal with issues. For example, ammonia toxicity and excessive salinity can become issues that plague your plants, causing them to struggle. On top of that, some compost piles are teeming with nutrients and minerals, while others are lacking in certain areas (it all depends on what goes into the compost pile).
Is It Beneficial To Plant In Pure Compost?
If you’re considering planting your seeds or flowers in pure compost, chances are you have some reasoning behind the decision. Maybe you want your plants to reap the benefits of pure compost, like easy access to nutrients or better water retention.
However, it’s essential to understand that all compost is different. As we mentioned earlier, some compost piles can lack particular nutrients because of what you put in the pile. Or, even though compost can help improve soil drainage with clay soils, it doesn’t do well on its own.
In many cases, plants grown in pure compost have stability and water retention issues. However, if you mix your compost with topsoil, you get the perfect combination of water retention, as it promotes good drainage but doesn’t get too dried out. On its own, though, compost quickly dries out once the water drains.
Compost is considerably lighter than most soils and soil mixes, so it can’t offer adequate stability to support robust root systems. While this is a problem initially, compost tends to compact over time, causing it to sink into the container. This means your potted plants will seem emptier after a few weeks as the compost settles.
So, while you might think planting in pure compost is an excellent idea, it might not be the best approach for healthy plants. That said, this doesn’t mean you shouldn’t use compost at all. It’s an exceptional additive as a way to amend poor-quality soil. All you’ll need is an inch or two of rich compost combined with existing topsoil to give your plants what they need.
What Should I Add To My Garden Compost Pile?
Creating a beautiful, rich compost pile to add to the plants in your garden isn’t a complex process. Microorganisms and various types of bugs do the hard work for you, breaking down the organic matter you add to the pile. However, for a successful composting pile, you need to have four essential ingredients: nitrogen, carbon, water, and air.
Without these four ingredients, your compost pile won’t break down as it should. Here are a few materials that contain these ingredients:
- Kitchen scraps: Various food scraps can go into compost piles and help create a nice, rich compost. Toss in fruit and vegetable trimmings, eggshells, coffee grounds, and filters. Avoid adding animal products, such as fat, meat trimmings, grease, or dairy products, as they don’t break down very fast and attract unwanted rodents and pests.
- Manure: While it isn’t the most pleasant-smelling addition, animal manures are an excellent nitrogen source. Horse, chicken, and cow manures are suitable for the compost pile, but dog and cat feces are not, as they can carry disease organisms.
- Dry leaves: Instead of bagging up the beautiful red, orange, brown, and yellow leaves in the fall, add them to your compost pile. To speed up their decomposition process, shred them before you add them to the pile.
- Grass clippings: If your lawnmower has a bag attached, consider adding the clippings to your compost pile. Grass clippings are beneficial for your lawn, so you don’t have to add them to your compost pile if you’d prefer to leave them on your lawn. If you decide to add the clippings to your compost pile, mix them with soil or dry plant materials, as the clippings are prone to compacting over time. This prevents air from entering the pile and slows down decomposition.
- Sawdust: Another great addition is sawdust, although you should always compost sawdust before adding it to your garden. If you don’t compost it before incorporating it into your garden, it can tie up the nitrogen in the soil. So, once you add it to your compost pile, add an extra nitrogen source to speed up decomposition.
- Miscellaneous: Aside from the above materials, you can also add things like hay, non-noxious weeds, hedge clippings, shredded newspaper, and sod from your lawn. Avoid adding large sticks and twigs, as these break down slowly.