My son Liam has acquired a green thumb and has put in several raised beds, to boot. Now he wants to fill them.

My first call went to Sanctuary Soil and Feed (877-751-3935; sanctuarysoil.com). Though they’re not based in San Diego — they actually get their soil from Washington — you can buy their organic Empire Builder indoor-outdoor grower’s mix at the San Marcos, Lakeside, and Pacific Beach locations of San Diego Hydroponics (888-994-2228; sdhydroponics.com). They sell it by the Super Sack, which is 2.5 yards of soil ($500, special order).

“If you have a pickup truck,” said Sanctuary Soil owner Mitchell Davis, “they can just set the sack in the back. Or, if your garden isn’t too big, you can buy two-cubic-foot bags of soil [$22]. We have a soil calculator on our website. You can enter the height, width, and depth of your bed, and it will help you figure out how much soil you need.”

Davis granted that his soil was more expensive than others. “Generally, potting soils or grower’s mixes are made from green-waste compost or ground wood. Many are made with redwood, which becomes more tannic and acidic over time. But the compost really should be like woody forest material — branches and grasses, with a more neutral pH. Also, soils full of sphagnum or wood break down and shrink. So if you fill your raised bed with 12 inches of that sort of soil, the next year you’ll have to add another 4 to 5 inches because of shrinkage.”

Empire Builder soil avoids these problems through the use of ground coconut husks. “It’s neutral, it takes water well, it has more capacity to hold air, and better drainage. And you don’t have breakdown — it lasts for years.”

Another thing Sanctuary Soil adds is worm castings. “Darwin said that the worm is most responsible for our success on the planet. You can tell if your garden is good by digging a six-inch hole — if you don’t see any worms, then your soil is undernourished. Worm castings are nature’s all-in-one soil amendment and fertilizer. Compost that has been eaten and turned into worm poop has ten times the concentration of microingredients and microbes. Typically, a bag of soil has little to no worm-casting content. We put 150 pounds of worm castings into every yard of soil. We can do this because we have the largest worm farm in California.”

Besides worm castings, “We add another 20 micronutrients, things such as rock phosphate, alfalfa, and bone meal. If you have a garden that’s not great — say, a four-by-eight bed — and you put in six bags of Empire Builder and till it into the top six inches of your existing soil, you will vastly improve what you have.”

David at Walter Andersen Nursery in Poway (858-513-4900; walterandersen.com) told me that he fills raised beds with Edna’s Best Potting Mix ($8.99 for 1.5 cubic feet), “and then we mix in four handfuls of Grow Power All-Organic Soil Conditioner [$30 for a 50-pound bag] and Grow Power Flower and Bloom [$47.99 for a 50-pound bag]. Vegetables turn out fantastic.”

Evergreen Nursery in Carmel Valley (858-481-0622; evergreennursery.com) has a five-yard minimum on bulk purchases, but most products are also available by the bag. Employee Chris suggests the canning mix for raised beds, $35 a yard. “It’s made from sandy loam, naturalized wood shavings, iron sulfate, and calcium carbonate. Plant and then fertilize in a month or two.” They also carry worm castings: $14.99 for a 20-quart bag.

Mission Hills Nursery (619-295-2808; missionhillsnursery.com) says that buying by the bag is nearly the same as buying in bulk if you add in delivery charges and suggested planting in EB Stone’s Organic Soil Booster ($7.99 for a 1.5 cubic-foot bag). It contains fir bark, pumice, worm castings, mushroom soil, bat guano, and kelp.

City Farmers Nursery in Islenair (619-284-6358; cityfarmersnursery.com) sells an organic topsoil mix for $49.99 a yard made from one-third compost, one-third sand, and one-third topsoil, plus a touch of chicken manure. The clerk suggested adding worm castings before planting. They get theirs from Sharon’s Worm World in Ramona ($12.99 for a half-cubic-foot bag, enough for two yards of soil).