Good Potting Soil - It's in the bag.

The Tucson Gardener

Chaste tree bloom.
Chaste tree, Vitex agnus-castus, bloom.

Current Cultivations

Garden Clubs

Garden Books

In the Garden Calendar

Tucson's Wildlife

Santa Rita prickly pear.

Local Garden Links

Links for Special Needs

The Archive

The Tool Shed

Gambel's quail chick.

FAQ

Glossary

Search

Site Index

You're visiting Tucsongardener.com

Good Potting Soil
By one definition soil is a portion of the earth's surface consisting of disintegrated rock and humus. Our desert soil is a bit shy of humus. Tucson's desert gardeners rely on bags of potting soil purchased from garden centers and other sources to meet their needs when relying on containers to grow their plants.

These potting mixes, without any soil in them, are usually light, able to hold moisture and allow for good drainage as well. Most are sterile so they can't introduce any diseases or unwanted weed seedlings. Many of the mixes also have added nutrients. Container growing desert gardeners rely on one or two potting soil brands that they purchase because of recommendations, what's available in the store, or cost consciousness price.

Over the years I've tried different brands and have settled on one that provided suitable results and was available at what I considered a reasonable price. I thought I'd compare price along with a sniff and a feel and maybe a water holding comparison to see how my favorite potting soil compared to others on the market.

At the left are a few of the many
all purpose potting mixes available
from garden centers and other retailers.

Seven different potting mixes were given a container and a number for the less than scientific tests.

Using less than scientific methods seven different potting mixes were purchased and each was placed in a container and given a number. Next, notes were taken on each mix as they were sniffed, touched and studied. An example of an observation: "Number 2 looks like a chipper shredder had been at work with lots of chunks of forest stuff."

My moisture test consisted of quickly pouring one cup of water into each numbered container to see what would happen. All the mixes drained rapidly but when the soil samples were allowed to draw water from the bottom up, they didn't all absorb moisture as readily. Perlite came to the surface of one and one of the mixes still had dry areas on the surface once the water had drained out of the container.

By the time I finished my analysis a few things were obvious. First, the Scotts Company name showed up a lot more times than I expected. Hyponex®, Earthgro®, and Miracle-Gro® potting mixes are part of the Scotts Company. Peters®, Osmocote®, and Ortho® brands also fall under the Scotts Company umbrella. A virtual who's who in garden product recognition.

I also learned the following:

Forest products is a popular term on potting mixes.

The bigger bags of potting soil give you added value for your money.

You usually pay more for the products with the fertilizer already in the mix.

Words like professional or premium must have been proven by the marketing departments to work as a sales enhancer.

The potting mixes in the seven containers all looked similar in appearance right out of the bag due to their moisture content. Once they started to dry out their different color and textures were more noticeable.

By the time my testing was over I had decided all these potting mixes are pretty similar in content and purpose. I assumed they would all work equally well for container plants provided the plants are given adequate nutrient and moisture. (I planted lettuce leaf basil in equal sized containers of each of the soil mixes listed here. From the results below Schultz's and Miracle Grow soils did the best. Both mixes had fertilizer in them. Two soils, Hyponex and Earthgro, not shown in the photo, had plant failures. The plants were not grown under perfect conditions but it does go to show fertilizer makes a difference. The only thing supplied to the plants was water and light.

Potting soils with fertilizer already in them did best in this grow test.

Avid container gardeners and certainly growers will purchase the needed ingredients in bulk and mix up their own special potting mix that has similar characteristics to what's available at retail. The rest of us will rely on potting mixes conveniently packaged and recommended by personnel at our favorite garden center or we'll reach for the biggest bag with the smallest price. (1999)

Editor's note: Boy have prices gone up since 1999! You could spend as much as $10 on one bag of potting soil.

A Quick Look at Seven Different All Purpose Potting Mixes
Product and purchase location	Uni-gro Premium (12 qts.) Sheldon's Nursery	Black Gold (8 qts.) Sheldon's Nursery	The Original Super Soil (25.7 qts.) The Home Depot	Earthgro All Purpose Potting Soil (20 qts.) The Home Depot	Schultz Professional Potting Soil Plus (8 qts.) Payless Cashways	Miracle-Gro Potting Mix (8 qts.) Super Kmart
Manufacturer or Distributor	Distributed by L & L Nursery Suppliers	Black Gold, Inc. Hubbard, Oregon	Rod McLellan Company San Mateo, California	Packaged by Earthgro, Inc. A Scotts Company	Schultz Company St. Louis, Missouri	Packaged by Miracle-Gro Lawn Products Port Washington, New York A Scotts Company
Purchase Price	$3.20	$3.00	$3.88	$1.98	$2.99	Advertised $3.00 price
Content	Forestry products, peat moss, vermiculite, sand, and water absorb (starch grafted copolymer potassium acrylate)	Sphagnum peat moss, earthworm castings, pumice, forest humus, oyster shell	Forest products, including fir bark and redwood. Canadian sphagnum peat and clean sand. Fertilizer (14-9-2)	(Regionally formulated from one or more of the following products: peat, forest products or compost), plus sand, perlite and wetting agent.	Formulated regionally from reed- sedge peat, sphagnum peat, horticultural vermiculite, wetting agent, and Schutz time released plant food (8-12-8)	Formulated from forest products, sphagnum peat, perlite, a wetting agent, and fertilizer (14-14-14)
Look & Feel	noticeable perlite and wood products	fine texture with traces of blue things that might have been fertilizer	fine texture with small bits of forest products	fairly fine texture, dark color, felt moist right out of the bag	noticeable vermiculite, fine texture with small chunks of forest products	lots of perlite and chunks of forest products
Moisture Holding	Good (surface material remained dry)	Good	Good	Good	Good	Good (compacted the most when watered)
Comments	If the water absorb works this might be an ideal product for Tucson's hot dry climate. Was slower to absorb moisture from bottom watering.	Pumice was pretty good size in this mix. Liked the touch and feel of the Black Gold but couldn't smell those oyster shells.	What's the big secret on content? Had a new package since the last time I'd purchased product.	Saw a "professional" variety of this mix as well.	Like the vermiculite in this product for its water holding ability.	Spotted the slow release fertilizer. Only mix to stick together in a clump when pinched. Perlite floated to surface when watered.