Controversy alert: pulling is no longer the default. It tears the soil open, brings buried weed seeds up to germinate, and disturbs the fungal network. Protecting soil structure is one of the fundamentals of ecological maintenance. Cutting weeds keeps the soil intact and starves the root by denying it leaves.
Most weeds
Cut them at the soil line, young, before they seed. If a weed persists after being cut, or it is one of the stubborn ones, use a method specific to the plant's habit.
The stubborn ones
Bermudagrass has runners that root at every joint. Never chop or pull it in moist soil; every piece roots. Mulch alone will not hold it. Smother it with cardboard under thick mulch, or solarize it under clear plastic for four to six weeks: June to August inland, August to September on the coast. That timing is from UC IPM.
Oxalis has three heart-shaped leaflets like a shamrock. Pulling leaves the bulbs or stolons behind. Get it before it flowers, and smother it with cardboard under thick mulch.
Dandelion and dock have a fat taproot under a flat rosette. Dig the whole root out. Cutting only prunes it.
Nutsedge has a triangular stem. Pull it before it has five or six leaves, and again every two or three weeks through summer. The tubers sit too deep to dig out.
Bindweed has arrowhead leaves on a twining vine. According to UC IPM, a two-inch root fragment makes a new plant, so digging spreads it. Cut the top growth every two or three weeks, or smother it.
Sidewalks, driveways and other hardscape
There is no soil structure or fungal network to protect here, so the cut-don't-pull rule doesn't apply. Pull these by hand, root and all, while they're young, or use a joint knife while the weed is small, before it seeds.
Sweep cracks and joints clear of soil and debris. Weed seeds need that buildup to sprout, and a swept joint stays bare longer than a dirty one.
Flame torches kill small emerging weeds fast, but only use one off-season and never near dry brush, mulch or wood. Hot water and vinegar-based sprays only burn what they touch, the leaf, not the root, so anything with a taproot or a runner grows back. For bermudagrass, nutsedge, bindweed or oxalis in a crack, treat it the way you would in a bed.
Prevention, and herbicides
Mulch and living ground cover shade weeds out before they start, which is less work than cutting or spraying.
With cutting, smothering and mulch, a garden should not need herbicides. Keep them for a stubborn perennial weed. Spot-treat on a calm day, never broadcast, and follow the label. Many weed killers are sold for licensed applicators only.
The full rule, with illustrations of each stubborn weed, is in Southern California Landscape Maintenance: Ecological Maintenance, Simplified, at rootandbranchdesign.com/book. The first chapters are free to read at rootandbranchdesign.com/book/sample.
Cutting weeds keeps the soil intact and starves the root by denying it leaves.