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When choosing the best soil for outdoor potted plants, it is helpful to know what kinds of soil are available and how each one interacts with your plants. Knowing this will help you make a better decision when answering what soil to use with your outdoor potted plants.
Before getting into the best soil for outdoor potted plants, you must first understand the needs of a potted plant. Potted plants act differently than in-ground plantings in that they are restricted to the soil that you put in the pot. In contrast, in-ground plants can, in theory, go searching for nutrients and water in the ground. So, much like the old garden adage goes, your plants are only as healthy as their soil. That goes for potted plants too!
When selecting the best soil for outdoor potted plants, consider that your potted plants need these essential items:
- Soil that retains moisture
- Soil that allows for oxygen to reach roots
- Fertilizer or plant food
- Organic matter
Choose the best soil for your outdoor potted plants by ensuring the soil mix you fill your pots with provides the following necessary growing conditions for the plant.
Most potting mixes contain a high amount of peat moss, coconut coir, or both. These ingredients are added to the soil mixture because they hold on to tons of moisture. Many potting mixes on the market contain these ingredients as their primary component. When filling smaller containers up to five gallons in size, a bagged potting mix will be economical and sufficient for your needs. But when filling a larger container like a wine barrel or raised bed, you may need to add ingredients from our supplemental list below to help fill the volume of soil required.
When choosing the best soil for your outdoor potted plants, keep in mind that the soil must allow oxygen to reach the plants’ roots. In potting soils and other container mixes sold in stores, you will find that all have perlite, vermiculite, or both. These aggregates help provide air pockets allowing oxygen to remain in the soil so that roots can access it. Just like us, plants need oxygen to live. Any soil that becomes so waterlogged or compacted that oxygen pockets are eliminated will not be an ideal growing environment for a plant.
When growing a plant in the ground, it has access to minerals and plant food found deep within the soil. But when growing a plant in a container, it is limited to food resources only available in that vessel. Although most potting mixes contain some plant food, we recommend adding organic granular fertilizer to the container. The quantity of the fertilizer depends on the brand you choose. Read the instructions from the manufacturer for the best results.
Organic matter is essential for all plants and is another consideration when choosing the best soil for your outdoor potted plants. Organic matter in the form of compost is a great way to improve soil structure, add organic matter, and inoculate the soil with beneficial microbes. Compost can be added to any potted plant but should not exceed 30–40% of the soil volume. You cannot happily grow a plant only in compost. Compost is an amendment that will improve both potted and in-ground soil.
Additional Soil Ingredients
Filling an entire large container or raised bed with potting mix is impractical and expensive. Instead, you will need to add additional ingredients that can help fill the space and positively improve the soil structure. Here is a list of some of our favorite additives.
|Compost||Improves soil structure, adds organic matter||Add to any pot size, not to exceed 30-40% of fill volume|
|Raised Bed Mix||Inexpensive, sold in bulk||Use to fill large containers, raised beds|
|Fill Dirt||Fills large, raised beds||Typically, is poor in quality and should not exceed more than 10% of fill volume|
|Manure (horse is our favorite)||Adds low levels of fertilizer and improves soil structure||Best if composted and added to large container or raised beds, no more than 10% of fill volume|
Buying Bagged Soil Products
When buying bagged soil products, remember that the best quality soil will have a wide range of ingredients. We always look for a product with peat moss, perlite, compost, and a small amount of organic fertilizer. There are many quality brands out there that meet these requirements. If you want to buy ingredients separately and mix them yourself, keep in mind that peat moss is naturally acidic. You will want to buy a potting mix instead as it is already PH balanced. Add compost, fertilizer, and other products you need to reach your desired soil volume.
Do not fret about getting the exact formula when choosing the best soil for your outdoor potted plants. A more important step is to ensure that your plants have all the necessary items they need to thrive in the soil you are providing them. Questions to ask yourself: Do my plants have access to moisture, and does my soil hold in moisture? Do my plants have access to plant food necessary to grow and thrive? Is there organic matter in the soil? Does the soil retain oxygen for the plants’ roots? You can accomplish all this by mixing your own outdoor potted plant soil mixture or buying a high-quality mix with all these key items.