Soil is essential to plant growth, especially in container gardening. Not only does it provide anchorage for root systems but it also provides oxygen, water, and nutrients for your plants. Plus, it insulates roots from temperature fluctuations which helps keep the temperature at an optimal level for your plants.
One of the most common questions that newbie gardeners have when it comes to container gardening is how much soil does a plant need to grow healthy and strong.
Remember a container is not just a pot, it can be a raised bed, a bag, an old purse, a tea pot, or anything that can hold soil above the ground. It’s often a task just figuring out how much soil a 4’x8′ bed needs, or a 5 gallon bucket, or a 12 inch pot.
To help you out, we’ll be talking about how much soil should be in a pot or container plus additional tips for using potting soils and mixes. Let’s get started!
What is Potting Soil and Potting Mix?
Potting soil is a growing medium used for container gardening that contains dirt. It contains decaying organic matter and minerals that provide a steady supply of nutrition, especially for indoor plants.
It is also a long-lasting medium that won’t break down over time and become unusable. All you need is to amend it with fertilizer or organic manure.
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Meanwhile, potting mix is a soil-less medium designed specifically for container gardening. It contains materials designed to promote healthy growth in plants such as compostable organic matter, peat moss, vermiculite, and minerals.
Potting mix is less dense that potting soil which makes it ideal for seed starting. It also allows for better air circulation while preventing waterlogging and compaction.
Should I Use Potting Soil or Potting Mix?
Potting soil and potting mix are two different growing mediums each with very specific benefits for your plants. While they work well for growing plants in a container like pots, plant boxes, and raised beds, the quality of the soil and even the ingredients they contain can affect your plants’ progress and growth.
As a general rule, however, potting soil is best used for raised beds or filling bald spots in your lawn. The organic matter in this type of growing medium helps supply nutrients to plants especially if you’re growing edible crops.
Meanwhile, potting mix is ideal for containers and pots. The structure of potting mix is lighter and fluffier than ordinary garden soil. It is also less dense than potting soil which allows for better aeration, drainage, and root extension.
If you’re still unsure what to use, read the label of your plant project. Some plants like succulents are better suited for well-draining potting mix.
How Much Potting Soil Do I Need?
Now on to the big question, how much soil do plants need to grow in raised garden beds. To determine how much potting soil you need you’ll first need to measure your boxes.
If you’ve purchased a planter from the store, then they’re likely to have a tag listing the dimensions of the container. However, if you’ve chosen to build your own raised beds, you’ll need to take the measurements yourself.
Determine the length, width, and depth in inches of the box and then multiply those values to get the volume in cubic inches.
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For example, if a planter box measures 20 inches long by 12 inches wide by 6 inches deep, it has a volume of 1,440 cubic inches. Since most bagged potting soils are sold in cubic feet, you’ll need to know the box’s volume in cubic feet.
Divide your box measurements by 1,728, which is the number of inches in a cubic foot, to determine the cubic foot volume of your box. In this case, the planter box would be 0.83 cubic feet, or just over three-quarters of a cubic foot.
How Much Potting Mix Do I Need
When filling pots and other containers with soil, a general rule to follow is to fill them and stop when you reach 1 to 2 inches below the rim. When it comes to volume measurement, you can allocate the following for different sized pots and baskets:
- 4 inch pot (10 cm) = 1 pint (0.5L)
- 5-6 inch pot (13-15 cm) = 1 quart (1L) = 0.03 cu. ft.
- 7-8 inch pot (18-20 cm) = 1 gallon (4L) = 0.15 cu. ft.
- 24 inch pot (61 cm) = 25 gallon (95L) = 3.8 cu. ft.
- 30 inch pot (76 cm) = 30 gallon (114L) = 4.6 cu. ft.
- 10 inch hanging basket (25 cm) = 5.5 dry quarts (6L) = 0.21 cu. ft.
- 12 inch hanging basket (30 cm) = 7.9 dry quarts (8.4L) = 0.3 cu. ft.
- 14 inch hanging basket (36 cm) = 13.9 dry quarts (15.3L) = 0.5 cu. Ft.
Alternatively, you can use our soil calculator to know how much soil you need for your project.
How Much Soil Do I Need?
Simply determine the area that you need to fill in square feet and how many inches deep you need the soil to be.
If you need to know how much mulch you’ll need, just use our mulch calculator below:
Try our Mulch Calculator to determine how much mulch you’ll need for any area:
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