Growing Guide: Companion Planting in the Bay Area (USDA 9–10)
- Garden Nerd
- Aug 22
- 3 min read
What companion planting really is
It’s not plant “friendships.” It’s smart mixing of vegetables, herbs, and flowers so you:
Attract and feed beneficial insects (hoverflies, lady beetles, parasitic wasps).
Distract or corral pests with trap crops.
Use space better (shade, living mulch, vertical layers).
Make scouting and harvest easier.
Plain English rule: add flower power near your veggies and use sacrificial bait plants when a pest loves something even more than your crop.
Microclimate quick guide (USDA 9–10)
Coast / Fog belt: Cooler summers; flowers must bloom in cool weather. Pick sweet alyssum, cilantro/coriander, calendula, yarrow.
Bay flats: Most mixes work; succession sow trap crops so timing lines up with pests.
Inland / Hills: Hotter spells; keep even moisture and give young flowers light afternoon shade so they keep blooming.
Combos that actually work (and why)
1) Anti-aphid “hoverfly buffet”
Do this: Edge beds or tuck clumps of sweet alyssum and cilantro/coriander around lettuce, kale, peppers, and tomatoes.
Why it works: The flowers feed hoverflies; their larvae devour aphids.
How to place: One small clump every 2–3 ft along a bed edge; trim alyssum lightly to keep it blooming.
2) Mustard trap crop for flea beetles (brassicas)
Do this: Plant a row or border of glossy-leaf mustard (e.g., ‘Southern Giant’) 1–2 weeks before broccoli/kale.
Why it works: Flea beetles prefer mustard. You watch the trap, then remove/compost it before beetles spread to your crop.
Coast: sow at the same time as your brassicas; beetles arrive slower.
Inland: sow the trap earlier—it’ll load up fast in heat.
3) Marigolds vs. root-knot nematodes (the
right way)
Do this: Grow French/African marigolds as a short pre-plant cover crop in the same spot for 6–8+ weeks, then chop-and-drop or dig in before planting a susceptible crop.
Why it works: Certain marigolds suppress some nematodes.
Important: Interplanting marigolds next to tomatoes usually doesn’t fix nematodes—use the rotation method above.
4) Tomato + herb + flower (container or bed)
Do this: Tomato with basil or chives as a living mulch, and a potted alyssum nearby.
Why it works: Herbs shade soil and bring pollinators/beneficials; alyssum feeds hoverflies.
Tip: Don’t overpack the root zone—tomatoes still need elbow room.
What to avoid
Fennel inside veggie beds. It releases compounds that inhibit nearby plants (tomato/pepper/eggplant especially). Keep fennel separate.
Tomatoes + corn as tight neighbors. They share the same caterpillar pest (fruitworm/earworm). It makes scouting and control harder.
Expecting one magic partner to fix pests. Use companion planting as part of integrated pest management: healthy soil, right spacing, steady water, scouting, and timely harvests.
Letting trap crops sit too long. If you don’t remove them, you’ll raise pests, not protect crops.
Mint roaming free. Great insectary, but invasive — container only.
Simple layouts
Raised bed (4′×8′, spring–fall)
Front 12″ edge: sweet alyssum + cilantro/coriander in alternating clumps.
Center rows: 2 rows of broccoli or kale, 18″ apart.
Back edge (trap): 1 row mustard as a sacrificial strip. Remove it once beetles stack up.
Optional corners: calendula or yarrow for long bloom.
Patio container combo
15–20 gal tomato with cage.
Underplant: basil or chives (thin so air flows).
Nearby pot: sweet alyssum you can keep snipping to re-bloom.
Water: drip spike or saucer check daily in heat.
How to start this weekend (quick steps)
Buy a six-pack of alyssum and a bunch of cilantro starts (or sow seed).
If you grow brassicas, sow a strip of mustard today as your trap.
Put a reminder in your phone for “remove trap crop” in 2–4 weeks (check for beetles first).
Keep flowers tidy—shear alyssum lightly when it slows to kick off new blooms.
GrowBot did some digging… Flowers are your garden’s cafeteria. If you keep the cafeteria stocked, your tiny bodyguards (hoverflies, lady beetles, lacewings) stick around and go to work.
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