Leek Companion Plants
Allium ampeloprasum (Porrum Group) · onion family family · rotation group: allium
The best companion plants for leek are Carrot, Celery, Cabbage, Tomato, and Lettuce. Avoid planting leek near Bush bean, Pea, Onion. Of the 9 pairings recorded here, 2 are supported by published research and 7 are traditional practice with no controlled evidence behind them.
What to plant with leek
| Plant | Claimed benefit | Evidence | What the evidence actually shows |
|---|---|---|---|
| Carrot | Interplanting leeks with carrots is said to cut carrot rust fly on the carrots and thrips on the leeks. | Research-backed | Uvah & Coaker (1984) showed mixed cropping carrots with ONIONS reduced both carrot fly attack on carrots and Thrips tabaci on onions versus monoculture, attributed to allium volatiles disrupting host-plant finding — but leek itself was not the tested species, the protection was strongest only while the alliums were young, and the effect is density-dependent, so a few leeks scattered among carrots should not be expected to reproduce it. |
| Celery | Row-by-row intercropping with celery suppresses weeds in leek and raises total yield from the bed. | Research-backed | In replicated Swiss field experiments the leek-celery intercrop reduced weed soil cover about 41% and weed biomass about 58% against leek alone, shortened the critical weed-control period, and gave a relative yield total about 10% above pure stands — but leek quality was measurably reduced, so this is a weed-management trade-off, not a free gain. |
| Beet | Beets and leeks are said to grow well together because their roots occupy different depths. | Traditional | Widely repeated with no controlled evidence; UMN Extension notes that plants with contrasting root habits can share a bed efficiently, but no measured advantage has been published for this specific combination. |
| Cabbage | Leeks planted among cabbage-family crops are said to reduce caterpillar damage. | Traditional | UMN Extension summarizes research in which thyme, ONION and nasturtium reduced cabbage looper and imported cabbageworm damage in broccoli; leek has not been tested, so this pairing rests on substituting one allium for another rather than on direct evidence. |
| Lettuce | Quick lettuce fills the gaps between leek transplants during the long establishment period. | Traditional | A space-and-timing use of the bed, not a biological interaction; extension charts pair onions with lettuce, but no trial has measured a pest, disease, or yield benefit from leek plus lettuce. |
| Tomato | Leeks are commonly listed as a good neighbor for tomatoes. | Traditional | Chart folklore with no measured pest or yield effect; leeks are slow, upright and shallow-rooted, so the pairing is mainly a spacing convenience and the tomato will eventually shade the leeks. |
What not to plant with leek
| Plant | Claimed problem | Evidence | What the evidence actually shows |
|---|---|---|---|
| Bush bean | Alliums such as leek are said to stunt the growth of beans. | Traditional | WVU Extension's chart states plainly that 'onion plants stunt the growth of beans', but no controlled trial demonstrating allium suppression of legume growth or nodulation could be found; treat this as untested folklore rather than a proven interaction. |
| Onion | Leeks should not be planted where onions or garlic have just grown. | Traditional | This is rotation guidance, not a same-season antagonism: UC IPM lists white rot, pink root, Fusarium basal rot and onion maggot among the shared problems of onion, garlic and leek, and white rot in particular persists in soil for many years once introduced. |
| Pea | Peas are said to grow poorly near leeks and other alliums. | Traditional | Same untested claim as for beans, repeated on extension and garden charts with no measurement behind it; UMN Extension cautions that these repellent and antagonist lists are frequently not backed by research. |
The honest verdict
Of everything gardeners recommend planting alongside leek, 2 pairings have been tested properly: Carrot, Celery. Those are the ones worth planning your bed around.
The remaining 4 pairings on this page are traditional practice. They circulate on every companion planting chart online, but we could not find controlled evidence testing them. They are not wrong so much as unverified — most cost nothing to try, and interplanting flowers and herbs has its own well-documented benefit of pulling pollinators and predatory insects into the garden.
Every row above links to the publication it came from. See how we grade evidence.
Growing leek: the numbers
| Sun | Full sun (6+ hours) |
|---|---|
| Water | Moderate |
| Spacing | 6 in apart · 15 in between rows · 9 per square foot |
| Mature size | about 30 in tall |
| Soil pH | 6–7 |
| Days to maturity | 90–150 days |
| Frost tolerance | Hardy — takes hard frost |
| Containers | Yes — 5 gallon minimum |
| Typical yield | 1 shank |
| Common pests | onion maggot, thrips, leafminers, bulb mites, nematodes |
| Common diseases | white rot, rust, purple blotch, downy mildew, botrytis leaf blight, fusarium basal rot |
When to plant leek
Zone 6b shownStart seeds indoors: Jan 16 – Feb 13 — 8–12 weeks before your last frost
Transplant outdoors: Mar 13 – Mar 26 — 4 weeks before last frost
Direct sow outdoors: Mar 20 – Apr 2 — 3 weeks before last frost
Expected harvest: Jun 11 – Aug 10 — 90–150 days from planting
Those dates are for zone 6b. Get your own dates by ZIP code →
Varieties worth knowing
seeds- King Richard — Early open-pollinated leek, 75 days from transplanting, white shank over a foot long; tolerates frost to about 20 degrees F but is not hardy enough to overwinter.
- Oslo — Organic F1 fall leek that can be overwintered in temperate regions; grown for late harvest rather than speed.
- Rally — Organic F1 leek; Johnny's leek seed and plants are tested and certified free of white rot and parasitic nematodes.
- Carentan — Long, thick open-pollinated leek recommended by UC Master Gardeners; roughly 100-120 days, spaced 4-6 inches apart.
Variety names link to seeds on Amazon. As an Amazon Associate we earn from qualifying purchases. These are the varieties named in the extension sources for this crop, not a paid placement — where a source recommended a variety for a specific reason, that reason is the note beside it.
Put it in a bed
The garden planner checks every square against this ledger as you place crops — if you drop leek next to something recorded as a bad neighbour, the square turns red and tells you why.
Records for the plants named above:
Same rotation group (allium) — don't follow one with another:
Leek companion planting questions
What should not be planted next to leek?
How far apart should leek be planted?
Does companion planting with leek actually work?
When should I plant leek?
Sources for this record
- University of Minnesota Extension — Growing leeks in home gardens
- Penn State Extension (York County Master Gardeners) — Vegetable Seed Planting Guide
- UGA Extension Bulletin C852 — Production and Management of Garlic, Elephant Garlic and Leek
- Johnny's Selected Seeds — King Richard Leek (days to maturity, frost tolerance)
- UC Master Gardeners of Santa Clara County — Leeks
Record compiled 2026-07. Spot an error or a study we missed? Tell us and we'll correct the entry.