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 can be used for vegetable gardens or flower beds alike. 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 width of the area as well as the length 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, pull out your tape measure for this because in math class we remember that length times width gives us the area, but we’ll need the volume for this: 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. You might even need to know the cubic yards of mulch if you have large garden areas. Don’t worry we’ll help you find out the number of bags of mulch and soil you’ll need for any project. Just keep reading.
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 (you’ll need to pull out your measuring tape again):
- 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 total square footage of the area and how many inches deep you need the soil to be.
How Much Mulch Do I Need?
Don’t neglect mulch in the garden either. Using mulch can help your garden in the following ways:
- limiting weed growth
- prevents water loss
- helps keep plant roots from burning in the heat of the day
- encourages moisture retention
- aids in grass suppression and weed control
You don’t need to purchase premium products to use in your vegetable and flower gardens. There are many choices for mulch. You can buy rubber mulch from a garden center, or hardwood mulch, wood chips, organic mulch, pine needles, pine bark, and even straw. Just be sure to choose the right product for your needs. For my beds I use a mix of hardwood mulch and shredded cardboard and paper from my office shredder, that’s an inexpensive way to go
Just make sure that the thickness of the mulch is the right amount of mulch to reach your desired depth.
If you’re asking how much mulch do I need, just use our mulch calculator below to find out how much cubic feet of mulch or bulk mulch you’ll need:
Try our Mulch Calculator to determine how much you’ll need for any area:
For both calculators you can just round up to the nearest whole number to make it easier. For mulching beds and for containers a nice 3″ layer of mulch works well, if you’re using it as a pathway between beds and containers 6 inches of mulch is a good base.
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