Petunias repay a little planning around what grows beside them. Petunias are a trailing annual flower grown in beds, pots and baskets. They need full sun, soil with a pH of 6.0–7.0, 12–18 inches of space and 70–90 days to reach maturity, so their neighbours need to suit the same bed and the same season. This guide lists the companions for petunias from our crop data, how each one is thought to help, and which close relatives to keep apart.
There are 4 companions listed for petunias here: Lavender, Marigolds, Garlic and Chives. Companion planting is traditional garden practice rather than proven science, so benefits below are described in those terms — what gardeners have long said and done. Petunias are in the Solanaceae family, need moderate water, and are started indoors and transplanted out once the weather warms; they are tender, so frost will kill them and they should only go outside once all danger of frost has passed. Expect germination in 7–14 days when the soil is warm and moist. Check any pairing first with the companion-planting finder.
Best companion plants for petunias
| Companion | Why it is grown with petunias |
|---|---|
| Lavender | A scented perennial that draws pollinators and is traditionally said to deter some pests. |
| Marigolds | Grown as a border or dotted through the bed; its roots are traditionally said to discourage some soil pests, and its flowers attract beneficial insects. |
| Garlic | Its strong scent is traditionally said to deter pests, and it fits neatly at the bed edge. |
| Chives | A small, clumping herb for the bed edge; its onion scent is traditionally said to confuse pests. |
Lavender is the first companion to reach for with petunias. Its scented flowers draw pollinators through the whole season and it is traditionally said to deter some pests, so it earns its place at the bed edge. It likes the same sunny, well-drained spot and needs little feeding once established.
How companion planting works
Companion planting works through four overlapping mechanisms.
Pest confusion. Many pests find their host plant by scent. Strong-smelling companions such as Lavender, Marigolds, Garlic, Chives are traditionally said to mask that scent, so the pest passes by. It is a delaying effect, not a barrier.
Pollinator and beneficial-insect attraction. Several companions here flower — Lavender, Marigolds — drawing pollinators and beneficial insects in. Let a few flower, and leave some blooms standing rather than deadheading everything.
Nitrogen fixing. Nitrogen fixing does not apply here — none of the listed companions is a legume.
Ground cover and root layers. No companion here is a ground-cover plant, so mulch does that job instead. Deep roots beside shallow ones also compete less for water and nutrients.
None of this replaces the basics. Spacing, watering, rotation and weekly inspection matter more than any pairing.
Plants to avoid near petunias
The plants to keep away from petunias are its own relatives. Petunias belong to the Solanaceae family, and plants in the same family share the same pests and diseases — here, aphids, hornworms, flea beetles and whiteflies — so problems pass easily between them and build up in the soil.
| Plant to avoid | Why |
|---|---|
| Tomatoes | Same Solanaceae family; shares pests such as aphids, hornworms, flea beetles and whiteflies. |
| Bell Peppers | Same Solanaceae family; shares pests such as aphids, hornworms, flea beetles and whiteflies. |
| Hot Peppers | Same Solanaceae family; shares pests such as aphids, hornworms, flea beetles and whiteflies. |
| Eggplant | Same Solanaceae family; shares pests such as aphids, hornworms, flea beetles and whiteflies. |
| Potatoes | Same Solanaceae family; shares pests such as aphids, hornworms, flea beetles and whiteflies. |
Keep these relatives in a different bed and rotate the Solanaceae family to fresh ground each year. If you are unsure whether a plant is a relative, check your local extension service before planting it beside petunias.
Planting layout and spacing
One plant needs 12–18 inches and a spot that suits its needs; in cold zones it is grown as an annual and lifted or replaced each year.
Give petunias their full spacing of 12–18 inches between plants. Crowded petunias mean poor airflow, more disease and smaller harvests, and no companion plant compensates for it. Work out how many plants fit your bed with the plant-spacing calculator or the square-foot garden planner.
Plant companions in the spaces the spacing leaves, not instead of it. Low companions go in the gaps and along the bed edges; taller ones go at the north side so they do not shade the petunias; scented herbs go closest to the crop, dotted through the row.
Petunias are started indoors and transplanted out once the weather warms; they are tender, so frost will kill them and they should only go outside once all danger of frost has passed. Expect germination in 7–14 days when the soil is warm and moist. The watering calculator gives a starting point for your bed size. Expect 70–90 days from sowing to maturity. Work backwards from your last frost date with the seed-starting calculator. If growth is poor despite good care, check your local extension service for advice specific to your area and soil.
Common problems and fixes
The pests most often reported on petunias are aphids, hornworms, flea beetles and whiteflies. Companions may reduce pressure, but they do not prevent them — inspect leaf undersides and new growth weekly and act while numbers are low.
| Problem | What you see | First fix |
|---|---|---|
| Aphids | Sap-sucking insects on new growth; leaves curl. | Wash off with water; encourage ladybirds. |
| Hornworms | Large green caterpillars that strip leaves quickly. | Hand-pick them off; encourage birds. |
| Flea beetles | Tiny beetles that leave small shot-holes in leaves. | Row cover; mulch to keep soil covered. |
| Whiteflies | Tiny white flies under leaves; sticky honeydew on foliage. | Yellow sticky traps; wash leaves with water. |
Aphids
Wash them off with a strong jet of water and leave ladybirds and lacewings alone to eat them. Check the undersides of young leaves, where colonies start.
Hornworms
Hornworms are big green caterpillars that can strip a plant fast. Hand-pick them off in the evening when they are easiest to see, and leave birds alone to hunt them.
Flea beetles
Flea beetles jump when disturbed and chew small holes in young leaves. Cover young plants with row cover until they are established, and mulch to keep the soil surface covered.
Whiteflies
Whiteflies gather on leaf undersides and fly up in a cloud when disturbed. Hang yellow sticky traps nearby and wash the leaves with water to knock numbers down.
Unsure what you are seeing? Try the pest-identifier helper or the plant-disease checker. Remove badly affected leaves and rotate the Solanaceae family next year.
Frequently asked questions
What is the best companion plant for petunias?
The most widely recommended companions are lavender. A scented perennial that draws pollinators and is traditionally said to deter some pests.
What should not be planted near petunias?
Avoid other members of the Solanaceae family, including Tomatoes, Bell Peppers, Hot Peppers, Eggplant, Potatoes. They share the same pests and diseases as petunias, so problems move easily between them. Rotate the family to a fresh bed each season.
Can I plant petunias with marigolds?
Yes. Marigolds is on the companion list for petunias. Grown as a border or dotted through the bed; its roots are traditionally said to discourage some soil pests, and its flowers attract beneficial insects.
How far apart should petunias and their companions be planted?
Space petunias plants 12–18 inches apart, and put companions in the gaps, along the edges and at the ends of rows. The seed-spacing calculator and the plant-spacing calculator work out how many plants fit your bed.
Does companion planting replace pest control?
No. It may reduce pest pressure, but it does not replace inspection, spacing, watering, rotation and good airflow. Check plants weekly and act early, and check your local extension service for advice on pest problems that keep coming back in your area.