What’s the best soil to use? Whether you’re gardening with containers, in raised beds or digging holes in the ground, you can’t go wrong with organic potting soil. With its loamy texture, water-absorbing amendments, lots of nutrients and beneficial fungi, it mimics a healthy soil.
That’s the quick fix, but if you want a successful garden, start by building your soil.
“The old saying is, ‘Feed the soil, not the plant,’” said Yvonne Savio, creator of the Gardening in LA blog and the retired coordinator of the UC Cooperative Extension’s Master Gardener program in Los Angeles.
Much of the “soil” around our homes is often compacted, nutrient-starved dirt, Savio said. Yards generally are built on dirt that remains after the builders scrape away the top soil to install pipes, pour foundations and build, Savio said. With the remaining subsoil as a base, landscapers usually roll out a lawn, install a few shrubs and plump everything up with chemical fertilizers that give the plants a jolt of energy but leave the land depleted.
“When you just use chemical fertilizers, you’re not establishing a long-lasting base of nutrition for the plant,” Savio said. “It’s just giving it a huge piece of cake on Sunday, and then by Thursday it’s nutritionally starving.”
When you continually add organic amendments to the soil, the dirt comes alive as the amendments decompose, creating the beneficial bacteria, fungi and nutrients that plants need. “It’s really like a cafeteria where your plants can pick and choose what they really like,” Savio said.
More questions about outdoor plants
Compost and other organic amendments, such as aged manure, coconut fiber (called coir), worm castings (earthworm excrement) and seaweed, also improve the texture of the soil, Savio said. That makes sandy soils loamy and helps them retain moisture and nutrients and improves drainage in clay soils where water pools instead of percolating into the ground.
“That’s why organic matter is the perfect ingredient, whether your soil is sandy or ‘clay-ey,’” she said. “When you have a good soil, it’s going to be crumbly, not stick together in a glop like clay or filter away through your fingers like sand.”
(Unsure what kind of soil you have? Check out the handy illustrated “quick squeeze test” on the UC Cooperative Extension Master Gardeners of Orange County website.)
Organic amendments also are a buffer against deficiencies such as high pH or alkalinity in the soil, said garden consultant Steve Masley of Grow it Organically in Petaluma, Calif., whose website offers detailed suggestions for improving garden soil.
As Masley’s website explains, soil pH is a measurement of soil acidity on a scale of 1 to 14, with 7.0 being neutral and anything lower considered acidic. Southern California is known for having more alkaline soils, which have a pH over more than 7.0.
The acidity of your soil limits the minerals and nutrients available to your plants, Masley said. Minerals like phosphorus, iron and zinc become more available in acidic (lower pH) soils, but get bound up and less available in alkaline soils, he said.
You can have your soil professionally tested or you can check it yourself using a pH tester. (Some cost less than $10 at online retailers or garden stores.) Masley, who builds and maintains organic gardens, says he almost never tests for pH because adding organic matter to the soil seems to smooth out most problems.
“Plants grown in soil with lots of organic matter have healthier roots,” he said. “If you’re growing organically and put in good-quality compost, the nutrient availability is so much higher you never have to worry about pH.”
Some SoCal gardeners add about 50% sphagnum peat moss to their soil when planting acid-loving plants such as blueberries and azaleas, because it helps lower acidity. But using peat moss has become controversial, Savio said, because people are worried about depleting the natural bogs from which it comes.
Peat moss is also used to help soils retain moisture and improve drainage, but for that use Masley said he prefers coconut coir because if peat moss ever dries out, it will repel water.
“Coconut coir almost always will soak [up] moisture from the air, but peat moss has to be watered frequently or it will dry out,” Masley said. “People buy these little six-packs of plants mixed with peat moss, and if they dry out, they can never get enough water after that. So if you’re going to use peat moss, make sure it’s never dried out and that it’s buried toward the bottom of the hole. Then use coconut coir on top, as a mulch, because it always stays moist.”
Here are three steps to building better soil.