It’s warming up — at last! — so of course Southern California gardeners are eagerly roaming plant sales and nurseries in search of African basil, tomato seedlings and a billion other flower or vegetable starts.
But hold up, people.
If you really want a great garden this year, set your seedlings aside for a couple of weeks and feed your soil.
We know, we know, organic amendments like manure, compost and mulch can be expensive. Most gardeners finish their spring shopping with a big dent in their wallet, and that already is likely to include a bag or two of some kind of fertilizer. So why put more money and time into adding amendments to the soil?
Because much of the “soil” around our homes is just nutrient-starved dirt, 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.
“You know the difference?” she said. “Dirt is what you sweep under the carpet. Soil is what you want in the garden.”
Many of our yards are built on the dirt left over after the builders scraped up the top soil to install pipes, pour foundations and build, Savio said. With the subsoil that was left, landscapers usually rolled out a lawn, installed a few shrubs and plumped everything up with chemical fertilizers that gave the plants a jolt of energy but left the land depleted.
“The old saying is, ‘Feed the soil, not the plant,’ ” said Savio.
“When you just use chemical fertilizers, you’re not establishing a long-lasting base of nutrition for the plant. 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 the nutrients plants need to grow strong and healthy, Savio said. “It’s really like a cafeteria where your plants can pick and choose what they really like.”
Organic amendments also improve the texture of the soil, Savio said, giving a loamy substance to sandy soils to help them retain moisture and nutrients, and improving drainage in clay soils where the water pools instead of percolating into the ground.
“That’s why organic matter is the perfect ingredient, whether your soil is sandy or clayey,” 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.)
Finally, organic amendments serve as a buffer against deficiencies such as high pH or alkalinity in the soil, said garden consultant Steve Masely of Grow it Organically in Petaluma, whose website offers detailed suggestions for improving garden soil.
As Masely’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, with a pH over 7.0.
The acidity of your soil limits the minerals and nutrients available to your plants, Masely said. Minerals like phosphorus, iron and zinc become more available in acidic (lower pH) soils, he said, but they get bound up, and less available, in alkaline soils.
You can have your soil tested or buy pH testers (like this $11 best-seller on Amazon) to check it yourself, but Masely, 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 like blueberries and azaleas, because it helps lower the acidity. Using peat moss has become controversial though, Savio said, because people are worried about depleting these natural bogs of decaying plant matter that have taken hundreds of years to create.
Peat moss is also used to help soils retain moisture and improve drainage, but for that use, Masely said he prefers coconut coir, because if peat moss ever dries out, it will actually repel water.
“Coconut coir almost always will soak moisture from the air, but peat moss has to be watered frequently or it will dry out,” Masely 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:
1. What to add
Unless you’re making your own compost and aged manure (fresh manure will kill your plants), you’ll be buying bags at your nursery or hardware store, generally sized at 1 cubic foot.
For a new 4-by-10-foot garden space (40 square feet), Savio recommends three bags of organic compost, three bags of composted steer manure (chicken manure can be too strong) and one bag of super-premium compost, such as Bu’s Blend by Malibu Compost or Bumper Crop by Coast of Maine Organic Products.
These premium composts are usually inoculated with beneficial mycorrhizal fungi and other additives designed to build strong roots, and a little goes a long way, Savio said.
2. Spade it in, water well — then wait
Your organic amendments should make up at least 30% of your garden plot, Savio said. Evenly spread your bags of amendments and then spade or fork them into the soil, to at least one spade’s depth. The idea is to mix them with the native soil. Then water well, and — attention! — wait to plant for at least two weeks.
“Many people try to do this over a weekend, add their amendments, plant their seedlings and then wonder why everything is dying,” Savio said. “The water is going to activate everything, and the soil is going to heat up, to the point that you can’t put your hand in it without being uncomfortable. It will cool down in a couple weeks’ time, but don’t plant anything until you can stick your hand fully into the soil, at least 4 inches down, and be comfortable.”
3. Remember the mulch
Once you plant, add some organic mulch around the plants to retain moisture, keep down weeds and continue feeding the soil. Mulch doesn’t have to be expensive. Bark and leaves from most trees provide excellent cover, but avoid walnut leaves, which are toxic to many plants, and eucalyptus, which takes too long to break down, Masely said. And stay away from wood products, like sawdust, which suck nitrogen from the soil.
Savio has had great success with coffee grounds, which she collects from coffee shops around her Pasadena home. She separates the paper filters into her compost pile and thinly spreads the grounds around her plants. Don’t go much deeper than a half-inch, she said, because thick grounds will form a crust that keeps water from seeping through.