Garden Soil vs Potting Soil: Where Each Goes and Why Pots Drown

The garden soil vs potting soil choice gets muddled because “garden soil” names two things. One is your yard: mineral soil at about 82.9 lb per cubic foot dry at the ideal 50 percent pore space (SDSU Extension, citing USDA NRCS). The other is the bag at the store: Miracle-Gro Garden Soil All Purpose prints 15 lb for 0.75 cubic foot, 20 lb per cubic foot, made from peat, forest products and compost. Miracle-Gro Potting Mix prints 12.6 lb for 25 dry quarts, about 13 lb per cubic foot, and adds perlite.

Both bags carry little or no mineral soil; our label-by-label comparison of topsoil and garden soil reads 9 of them, and potting soil vs potting mix covers the container labels. What changes the answer is the container. A 1980 paper in the Journal of Arboriculture by L. Art Spomer found that a little sand or perlite stirred into soil in a pot lowers its porosity until the amendment reaches about 10 volumes per 2.5 to 3 volumes of soil.

Where does each soil go?

Match the bag to what is under the roots: a drainage hole or pavement calls for potting mix; native ground calls for garden soil or topsoil blended into it. Rates come from 2 labels and 3 extension services.

Planting	Use	Rate or recipe	Source
Pots, window boxes, hanging baskets	Potting mix	Fill the container; one 25 qt bag fills three 10 in pots	Miracle-Gro Potting Mix label
Large houseplant repotted rarely	Potting soil that contains some mineral soil	Keep pH 6.0 to 6.5 (soilless mixes: 5.5 to 6.0)	UConn Home & Garden Education
Raised bed on a driveway or patio	Compost plus soilless mix, 1:1	Topsoil up to 20 percent by volume, only in beds 16 in or deeper	University of Maryland Extension
Raised bed on soil, poor or clay ground	Compost plus topsoil, 1:2 or 1:1	Or compost plus soilless mix, 1:1	University of Maryland Extension
Raised bed on soil, general	Topsoil plus compost	About 70 percent topsoil, 30 percent compost	Iowa State Extension
Raised bed with bagged garden soil	Garden soil plus topsoil or native soil	Equal parts	Miracle-Gro Garden Soil label
Existing in-ground bed	Garden soil or compost	Spread 2 to 3 in, mix into the top 6 to 8 in	Miracle-Gro Garden Soil label
Shrub or perennial planting hole	Garden soil	Hole 2 times the root ball width; backfill 50:50 with native soil	Miracle-Gro Garden Soil label
Seed trays	Seed starting mix	Finer than potting soil; peat, perlite or vermiculite, coir	UC Cooperative Extension Colusa County

1. 1Is it a pot, window box, hanging basket or other container with a drainage hole?

   YesPotting mix. Yard soil stays saturated near the bottom and compacts (Purdue HO-287-W, Spomer 1980, UConn).

   NoGo to the next question

2. 2Is it a raised bed sitting on concrete, pavers or a deck?

   YesCompost and soilless mix 1:1; add topsoil only up to 20 percent, and only if the bed is 16 in or deeper (University of Maryland).

   NoGo to the next question

3. 3Is it a raised bed on open ground?

   YesTopsoil and compost, about 70/30 or 2:1, worked into the soil below (Iowa State, University of Maryland); bagged garden soil goes in 1:1 with topsoil (Miracle-Gro label).

   NoGo to the next question

4. 4Are you starting seeds in trays or cells?

   YesSeed starting mix, finer than potting soil (UC Cooperative Extension).

   NoIn-ground bed: spread 2 to 3 in of garden soil or compost and mix it into the top 6 to 8 in of native soil (Miracle-Gro Garden Soil label).

Source: Purdue HO-287-W, University of Maryland Extension, Iowa State Extension, UC Cooperative Extension, Miracle-Gro label

The 60 percent topsoil, 30 percent compost, 10 percent potting soil blend that circulates on garden sites does not appear in the Maryland, Iowa State or label recipes above; Iowa State’s nearest is 70/30 topsoil and compost. Before buying any soil for an in-ground bed, a soil test from a land-grant lab shows whether the real limit is pH or nutrients, which more soil will not fix.

Why does yard soil stay wet in a pot?

Gravity cannot pull all the water out of a short column of soil. Purdue Extension publication HO-287-W explains that, in spite of drainage holes, some soil at the bottom of every container never drains; that perched water zone has virtually no air space, and it takes up a larger share of the pot as the container gets shorter.

How tall that wet zone is depends on pore size. Spomer charted a silty clay loam in a 10 in (25 cm) deep container and found it essentially saturated through its entire depth after watering and drainage, while very coarse sand drained too far. Roots in that soil run short of oxygen.

Potting mixes fix this with big pores. Purdue puts the target at 20 to 25 percent air space after drainage. Its peat and perlite mix held air in about 23 percent of the pot’s volume; a peat, bark, perlite and vermiculite mix, about 17 percent. UConn adds the second problem: mineral soils do not hold up under repeated watering and will rapidly become very compacted in a container.

Material	Weight, lb per cu ft	Total pore space	Air after watering, share of volume	Source
Potting mix (Miracle-Gro, as sold)	13.0	Not printed	Not printed	label: 12.6 lb per 25 dry qt
Peat and perlite mix	Not stated	61.4%	23.3% (38% of pores)	Purdue HO-287-W, Table 1
Peat, bark, perlite and vermiculite	Not stated	59.1%	16.5% (28% of pores)	Purdue HO-287-W, Table 1
Bagged garden soil (Miracle-Gro, as sold)	20.0	Not printed	Not printed; label says not for containers	label: 15 lb per 0.75 cu ft
Yard mineral soil at ideal density	82.9 dry	50%	Essentially none in a 10 in pot (silty clay loam)	SDSU / NRCS; Spomer 1980
Loam, density that restricts roots	Above 112.1 dry	Below about 32%	Lower still	SDSU / NRCS Table 1

1. Potting mix (label, as sold)13
2. Bagged garden soil (label, as sold)20
3. Yard soil, ideal density (dry)82.90
4. Loam, root-restricting (dry)112.10

Source: Miracle-Gro Potting Mix and Garden Soil All Purpose labels; SDSU Extension citing USDA NRCS, checked November 2026 Bag weights include moisture in the bag; soil values are dry bulk density.

Show the numbers

	Pounds per cubic foot
Potting mix (label, as sold)	13
Bagged garden soil (label, as sold)	20
Yard soil, ideal density (dry)	82.90
Loam, root-restricting (dry)	112.10

On a balcony or deck, weight matters too: dry yard soil at 82.9 lb per cubic foot is about 6.4 times the as-sold weight of potting mix.

Can you turn garden soil into potting soil?

Yes, but not with a handful of perlite. Spomer’s threshold is the minimum amendment before aeration improves at all: about 10 volumes of sand, perlite or calcined clay plus 2.5 to 3 volumes of soil, so roughly 77 to 80 percent amendment. Below it, the fine soil fills the gaps between the coarse particles and total porosity drops. Organic amendments such as peat and bark reach the threshold with less material.

1. Screen the soil and pasteurize it: UF/IFAS says spread it in a tray and bake at 200°F for 20 minutes, stirring every 5 minutes. UConn describes sterilized commercial mixes as heated to about 180°F.
2. Mix by volume. UF/IFAS’s soil-based recipe is 2 parts soil, 1 part peat moss, 1 part perlite and 1 part coarse sand, so soil is 40 percent of the blend. Use builder’s sand; UF warns that plaster and fine sands make a dense mix.
3. Check the pH. UConn keeps soil-containing mixes at 6.0 to 6.5, against 5.5 to 6.0 for soilless ones; our guide on raising soil pH with lime covers the adjustment.
4. Use the blend in deep containers or under top-heavy plants, where weight helps; small pots do better in a bagged peat or coir mix. Reusing last year’s mix is a separate question, covered in does potting soil go bad.

How much soil does a raised bed or pot need?

Volume is length times width times depth: a 4 by 8 ft bed is 32 sq ft, so 12 inches deep is 32 cubic feet, or 1.19 cubic yards. The Miracle-Gro garden soil label’s own chart assumes you mix it 50:50 with topsoil, so its 96 sq ft, 6 in raised bed calls for 32 bags of 0.75 cubic foot, half the 48 cubic feet the bed holds.

Bed or planter area (length x width) (sq ft)FillAny bagged mixFill depth12 inches6 inches8 inches10 inches16 inches18 inches24 inches

Cubic feet

32.0

Cubic yards

1.19

1.5 cu ft bags

22

2 cu ft bags

17

Weight as potting mix, lb (13 lb/cu ft)

416

Weight as yard soil, lb dry (82.9 lb/cu ft)

2,653

Default 4 x 8 ft bed (32 sq ft) at 12 inches: 32 cu ft, 1.19 cu yd, 22 bags of 1.5 cu ft or 16 of 2 cu ft; 416 lb as potting mix vs 2,653 lb as dry yard soil. Math: sq ft x inches / 12. Weights from the Miracle-Gro Potting Mix label and SDSU/NRCS.

4 x 8 ft bed depth	Cubic feet	Cubic yards	1.5 cu ft bags	2 cu ft bags	Weight if potting mix (13 lb/cu ft)	Weight if yard soil (82.9 lb/cu ft dry)
6 in	16.0	0.59	11	8	208 lb	1,326 lb
8 in	21.3	0.79	15	11	277 lb	1,769 lb
12 in	32.0	1.19	22	16	416 lb	2,653 lb
16 in	42.7	1.58	29	22	555 lb	3,537 lb

For a bed on a hard surface, Maryland Extension sets depth by crop: at least 8 inches for leafy greens, beans and cucumbers, and 12 to 24 inches for peppers, tomatoes and squash. On open ground, roots continue into the soil below; Iowa State works the first few inches of mix into it so no distinct layer forms, and our guide on how to till soil sets the depth for that pass.

Pots are sold by gallon but mix is sold by dry quart. NIST Handbook 44, Appendix C sets a gallon at 231 cubic inches and a dry quart at 67.2006, so one cubic foot holds 25.7 dry quarts and a true gallon holds 3.44.

Container (true gallons)	Dry quarts of mix	Cubic feet	2 cu ft bags	Potting mix weight as sold
1 gal	3.4	0.13	1 fills about 15 pots	1.7 lb
3 gal	10.3	0.40	1 fills about 5 pots	5.2 lb
5 gal (bucket size)	17.2	0.67	1 fills about 3 pots	8.7 lb
10 gal	34.4	1.34	1	17.4 lb
15 gal	51.6	2.01	2	26.1 lb
25 gal	85.9	3.34	2	43.4 lb

What does each cost per cubic foot?

In Google Shopping listings captured November 12, 2026, Miracle-Gro garden soil ran $6.09 to $7.99 a cubic foot and Miracle-Gro potting mix $8.22 to $10.74, about 35 percent more.

Product, bag size as listed	Listed price	Seller	Per cu ft
Miracle-Gro Garden Soil All Purpose, 1.5 cu ft	$9.14	Supply Ontime	$6.09
Miracle-Gro 1.5 cu ft Garden Soil	$10.98	Instacart	$7.32
Miracle-Gro 1.5 cu ft Garden Soil	$11.99	Do it Best	$7.99
Miracle-Gro Potting Mix (50 qt)	$15.99	Burgaw Milling Company	$8.22
Miracle-Gro Moisture Control All Purpose Potting Mix, 50 qt	$16.99	Stones Ace	$8.74
Miracle-Gro Moisture Control Potting Mix, 50 qt	$19.11	Supply Ontime	$9.83
Miracle-Gro Potting Mix All Purpose, 50 qt	$20.88	Jamaica Hardware	$10.74

A 32 cubic foot bed costs about $195 to $256 in that garden soil, which the label cuts 1:1 with topsoil, or $263 to $344 in potting mix. Above about 1 cubic yard, bulk delivery usually wins; yard prices and the break-even are in our topsoil cost guide, and compost vs mulch covers buying the compost half.

What is the difference between Miracle-Gro potting soil and garden soil?

Read side by side, the two labels share a base of peat, processed forest products, coir or compost, sphagnum and a wetting agent. The potting mix adds perlite, which supplies the large pores, carries more fertilizer at 0.21-0.11-0.16 against 0.09-0.05-0.07, and weighs 13 lb per cubic foot against 20. The garden soil label says “for in-ground use” beside a not-for-containers icon.