Companion Planting Basics for Beginners

What companion planting is (and is not)

The four ways good pairings actually help

When a companion pair works, it is for one of four concrete reasons. Any pairing you cannot explain using these four is probably folklore.

• Pest confusion or repellence: One crop's scent or shape masks or deters a pest the other suffers from. Example: onions planted near carrots confuse the carrot fly, which hunts by smell.
• Pollinator and predator attraction: Flowering companions bring bees, hoverflies, and parasitic wasps that either pollinate the crop or eat its pests. Example: calendula, dill, and sweet alyssum pull in hoverflies that eat aphids.
• Physical support or shelter: A taller crop gives structure or shade to a lower crop. Example: pole beans climb a corn stalk; lettuce grows in the cooler shade of summer tomatoes.
• Complementary root zones: Shallow and deep-rooted crops share space without competing. Example: carrots (deep tap) and lettuce (shallow mat) happily share a row.

The pairings that reliably work

Backed by field trials or strong traditional use. Each one is listed with the pest, pollinator, or structural role it plays, scan for a problem you actually have, not a chart to memorize.

• Tomatoes and basil: Basil repels some tomato pests and its flowers pull in pollinators. The flavor pairing is a bonus.
• Carrots and onions (or leeks, chives): Alliums mask the carrot scent that the carrot rust fly tracks. Carrots return the favor for the onion fly.
• The Three Sisters (corn, pole beans, squash): Corn gives the beans a pole, beans fix nitrogen for the corn, squash shades the soil to lock in moisture and deter weeds. A classic with real mechanics behind it.
• Cucumbers and dill or nasturtium: Dill pulls in predatory wasps that eat cucumber beetles. Nasturtium acts as a trap crop for aphids and squash bugs.
• Brassicas (broccoli, cabbage, kale) and aromatic herbs: Dill, thyme, sage, and rosemary mask the scent that draws cabbage moths. A ring of them around the bed is the easiest setup.
• Lettuce and tall summer crops: Tomatoes and pole beans shade lettuce through the hot months and keep it from bolting.
• Marigolds (French type) along bed edges: Some nematodes are suppressed by French marigold roots. The effect is modest but real and flowers attract pollinators.

Plan your beds and spacing with the Garden Planner Sheet (printable).

The pairings that reliably hurt

Most "bad companion" warnings online are folklore, but a handful are real and worth respecting. These combinations either compete for the same nutrients, share pests, or release chemicals that stunt a neighbor.

• Beans or peas + onions, garlic, or leeks: Alliums suppress nitrogen-fixing bacteria on legume roots. Legumes grow slower and fix less nitrogen. Keep them two to three feet apart.
• Tomatoes + brassicas (broccoli, cabbage, kale): Both are heavy feeders that share pests (aphids, cutworms) and crowd root zones. Put them in different beds or opposite corners.
• Fennel next to almost anything: Bulb fennel releases compounds that suppress most garden crops. Grow it in its own corner, a container, or an outer border.
• Tomatoes and corn: They share the corn earworm (the tomato fruitworm). Keeping them at opposite ends of the garden reduces shared pest pressure.
• Potatoes and tomatoes: Same family, same diseases (especially late blight). Never plant them in the same bed or rotate one into last year's spot of the other.
• Sunflowers near beans or potatoes: Sunflower roots release allelopathic compounds that slow some neighbors. Grow them along a fence or in a cut-flower strip instead.

Simple method, four steps to plan a bed

1. Choose your main crop. Start with what you actually want to eat most, tomatoes, carrots, lettuce, or brassicas. This is the anchor everything else is planned around.
2. Add one beneficial companion. Pick a single partner that targets the anchor's main pest or brings in pollinators: basil for tomatoes, onions or chives for carrots, dill or thyme for brassicas, nasturtium for cucumbers and squash.
3. Avoid the known conflicts. Scan the "pairings that reliably hurt" list above. Keep beans and peas away from onions, tomatoes away from brassicas and potatoes, and fennel in its own corner.
4. Add flowers at the edges. A ring of French marigolds, calendula, sweet alyssum, or zinnias feeds beneficial insects. One plant every few feet is enough to shift the bug population.

Common scenarios

Three beginner setups that cover most situations. Match the one closest to your space and copy the combination.

• Small raised bed (4×4 or 4×8): Two staked tomatoes with basil at the base, a row of carrots interplanted with bunching onions or chives, bush beans in the middle (kept away from the alliums), French marigolds at the corners.
• Container garden (pots or planter boxes): One container per crop plus its partner. Cherry tomato + basil in a 15-gallon pot. Lettuce + chives in a window box. Cucumber + dill on a trellis. Add one small pot of sweet alyssum nearby to pull in hoverflies.
• Pest-prone garden (cabbage moths, aphids, cucumber beetles): Ring brassicas with dill and thyme, interplant nasturtium with cucumbers and squash, and plant a short calendula + sweet alyssum strip along one bed edge to feed hoverflies and parasitic wasps.

Trap crops and insectary strips

The most reliable "companion planting" is not a specific pair of vegetables. It is adding a few flowering and sacrificial plants that change the insect population in your garden. Two simple setups cover most bases.

• Insectary strip (the big win): A short row or border of sweet alyssum, calendula, dill, cilantro, zinnia, or borage. Lets flowers open across the season to feed beneficials.
• Trap crops (the specific fix): Nasturtium pulls aphids and squash bugs off cucumbers and squash. Blue Hubbard squash draws cucumber beetles away from zucchini. Collards or mustard lure flea beetles off brassicas.
• Where to put them: At bed ends, as edging, or in every fourth row. You do not need a lot. One zinnia per four feet is enough to shift the bug population.

A simple beginner companion layout

You do not need to memorize a matrix. A beginner 4 x 8 bed can use this template and get 80% of the benefit.

• North edge (tallest): Two staked tomatoes with basil tucked at their feet.
• Middle row: A row of bush beans with dill or nasturtium at each end. Skip the alliums here.
• South-middle row: Carrots interplanted with bunching onions or chives.
• South edge (lowest): Lettuce and spinach (bolt-tolerant in the shade of the tomatoes in summer).
• Bed corners or edging: French marigolds, calendula, or zinnias.

What to ignore from the old companion charts

• Long lists of "enemy" pairings with no explanation. Most have never been tested and come from a single 1970s book.
• Specific "distance in inches" folklore. Nothing in the garden is that precise.
• Claims that a single companion plant will eliminate a pest. Real pest reduction is 20 to 40%, not 100%.
• Recommendations that require rare herbs or flowers. Stick with plants you can actually source locally.
• Anything that contradicts sun, spacing, or water needs. A companion in the wrong sun or wrong spacing is a dead plant, not a helper.

FAQ

Bottom line

Companion planting is useful but oversold. Stick with the handful of pairings that work for a clear reason, keep the known enemies apart, edge your beds with flowers to feed beneficials, and get sun, water, and spacing right first. That combination will beat any complicated chart.