Companion planting is the old idea that some plants grow better together than apart, and for flowers it is mostly true — not because of magic, but because of pollinators, predators, and the simple fact that a mixed planting confuses pests and feeds the soil better than a monoculture. A rose bed edged with lavender and garlic chives has fewer aphids than a rose bed alone. A vegetable garden ringed with marigolds and nasturtiums has more pollinators and fewer pests. A border of mixed flowers supports the ladybirds and hoverflies that eat the aphids on everything else.
This guide covers the companion combinations that actually work for flowers, the flowers that help vegetables, and the combinations to avoid. It is honest about the limits: companion planting helps, but it does not replace good soil, spacing, and inspection. If a combination does not work in your garden, your local extension service can advise on what grows well together in your climate.
Flowers that protect vegetables
Several flowers are genuinely useful in the vegetable garden. Marigolds are the best known: their roots release compounds that suppress root-knot nematodes, and their strong scent confuses some pests. Plant French marigolds among tomatoes, peppers, and beans — our growing marigolds guide covers the varieties, and the marigolds companion plants guide gives the full list. Nasturtiums are a trap crop for aphids and cabbage white butterflies: the pests prefer the nasturtium to the crop, so plant nasturtiums at the edge of the vegetable bed and sacrifice them, removing and binning the infested plants before the pests move on. Calendula attracts hoverflies, whose larvae eat aphids, and its petals are edible. Borage attracts bees and is said to improve the flavour and growth of tomatoes and strawberries grown nearby, and its blue flowers are a magnet for pollinators. None of these is a substitute for inspection, but all of them make the vegetable garden work better.
Flowers that protect other flowers
Flowers protect each other too. Lavender planted at the foot of roses is the classic combination: its scent is said to confuse aphids, and it attracts bees that pollinate the whole garden. Garlic chives and alliums planted among roses are reported to reduce black spot and aphid problems, and their purple flower heads look good with the roses as well. Calendula among dahlias attracts hoverflies that eat the aphids on the dahlias. Sweet alyssum, a low, white-flowered annual, is one of the best insectary plants there is: its tiny flowers feed hoverflies, lacewings, and parasitic wasps, all of which eat flower pests, and it can be sown as a living edging around any flower bed. Our growing roses and growing dahlias guides both benefit from these companions. The principle is simple: a flower bed that contains small, open, nectar-rich flowers will have more predators than a bed of showy doubles alone, because the predators need small flowers to feed from.
Pollinators: planting for bees and butterflies
A flower garden that feeds pollinators is a healthier garden, because pollinators are also the reason many flowers set seed and many vegetables set fruit. Single flowers — one row of petals, with the centre open — feed pollinators far better than double flowers, whose extra petals hide the nectar and pollen. Choose single dahlias, single zinnias, and open roses rather than the most double varieties, and plant in drifts of one kind rather than single plants scattered about, so a bee can work a patch efficiently. Include flowers for every season: crocus and hellebores in early spring, lavender and buddleia in summer, asters and sedum in autumn. Leave a few herbs to flower — oregano, thyme, and mint in flower are among the best bee plants in any garden. Avoid spraying flowering plants, and if you must spray, do it in the evening when the bees have gone home. A garden full of pollinators is also a garden full of the predators that eat flower pests, so this is pest control as well as kindness.
Combinations to avoid
Not every combination works. Tall, vigorous flowers such as sunflowers and Jerusalem artichokes cast shade and compete hard for water, so do not plant them close to smaller flowers that need full sun. Sunflowers also release compounds from their roots that can suppress the growth of some neighbours, so give them their own space at the back of the bed or in a separate patch. Fennel is famously unfriendly to most neighbours and is best grown on its own. Mint spreads aggressively by underground runners and will take over a flower bed if it is not contained in a pot sunk into the ground. And do not plant roses too close to a hedge or a tree, which will compete with them for water and nutrients and shade them — a rose needs its own space, as our flowers spacing guide explains. The general rule is to match plants by their needs: do not put a flower that wants dry, lean soil, such as lavender, next to one that wants rich, moist soil, such as a dahlia, because one of them will always be unhappy.
Designing a mixed border that works
A good mixed border is a companion planting in itself. Put tall flowers at the back, medium ones in the middle, and low edging plants at the front, so every plant gets light and air. Repeat a few key plants through the border rather than planting one of everything — repetition looks better and gives pollinators a patch to work. Mix in herbs and a few vegetables among the flowers: chives, parsley, and lettuce all look good in a border and use the space between the flowers. Leave gaps for access, so you can deadhead and inspect without trampling the bed. And keep a note of what worked: a combination that thrives in your soil and climate is worth repeating, and one that fails is worth dropping. Companion planting is best treated as an experiment that you refine over years, not a set of rules to follow blindly. If you are unsure about a diagnosis, a product, or a local rule, check your local extension service — its advice is tailored to your soil, climate, and the pests and diseases active in your area.
Frequently asked questions
What flowers should I plant with roses?
Lavender, garlic chives, and alliums are the classic rose companions — they are said to confuse aphids and look good together. Sweet alyssum nearby feeds the predators that eat aphids.
Do marigolds really keep pests away?
French marigolds suppress root-knot nematodes and their scent confuses some pests. They help, but they do not replace inspection and hand-picking.
What is a trap crop?
A plant grown to attract pests away from the crop — nasturtiums for aphids and cabbage white butterflies. Plant them at the edge of the bed and remove them before the pests move on.
Which flowers are best for bees?
Single, open flowers in drifts: single dahlias and zinnias, lavender, borage, calendula, asters, and sedum. Double flowers often hide the nectar and pollen.
What should I not plant next to flowers?
Sunflowers and fennel can suppress neighbours, mint spreads aggressively, and tall vigorous plants shade smaller ones. Match plants by their water and soil needs.