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Entire healthy mature collards plant in a real garden bed, showing growth habit and scale.Primary identification image. 60–90 cm tall, 45–60 cm wide at maturity.

Collards

Brassica oleracea var. viridis L.

Also called: Collard greens

Family
Brassicaceae
Season
Cool-season biennial grown as an annual
Best grown in
Portland, Oregon

A heat- and cold-tolerant non-heading cabbage, and a documented perimeter trap crop for diamondback moth in cabbage.

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Life cycle & growth stages

  1. 1. SeedSow indoors or direct.
  2. 2. SeedlingEmerges in 5–8 days.
  3. 3. TransplantSet out 45 cm apart.
  4. 4. Mid-growthBroad blue-green leaves.
  5. 5. Harvest readyLeaves 20 cm.
  6. 6. HarvestPick from the bottom up.
  7. 7. OverwinteringStands through frost.

Growth stages are ordered chronologically; timing varies with cultivar, temperature, light and care.

Planting calendar for Portland, Oregon

Start indoors 4–6 weeks before last frost; transplant 0–4 weeks before last frost; direct sow 2 weeks before to 2 weeks after last frost; 55–75 days to maturity from transplant. Windows are derived from the region's average frost dates (last Apr 5, first Nov 5) and are estimates until you confirm your own dates in the calendar.

CollardsBrassica oleracea var. viridis
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
CollardsFeb 22–Mar 8 (estimate)Mar 22–Apr 19 (estimate)Aug 13–Sep 10 (estimate)Mar 8–Apr 5 (estimate)Apr 19–May 2 (estimate)May 2–Sep 11 (estimate)
  • Start seeds indoors: Feb 22 – Mar 8
  • Transplant outdoors: Mar 8 – Apr 5
  • Direct sow: Mar 22 – Apr 19
  • Tend and monitor: Apr 19 – May 2
  • Harvest: May 2 – Sep 11
  • Autumn sowing: Aug 13 – Sep 10

Spacing & support

In-row 45–45 cm; rows 60–90 cm. Planner footprint: 2 cells of 30 cm.

Side-profile diagram of mature collards: canopy 60–90 cm tall, 45–60 cm wide, medium root zone, support and harvest-access envelope.

Soil & water

Soil
Fertile loam
pH
6–7
Fertility
high
Water
Regular water for tender leaves.
Frost
very hardy; tolerates frost

Support & training

No support structure needed.

Collards mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Harvest signs

  • Leaves 20–25 cm long
  • Pick lower leaves; leave the crown
Collards at harvest readiness, showing the visual cues: leaves 20–25 cm long; pick lower leaves; leave the crown.

Common problems

Pests: diamondback moth, cabbage white caterpillars, cabbage aphid, harlequin bug

Diseases: clubroot, black rot

Appearance alone is not a diagnosis; confirm with a regional extension guide.

Side-by-side: healthy collards leaf or fruit and an example of clubroot.

Container growing

  • Minimum 15 L (25 cm deep)
  • Use quality potting mix and water more frequently
Mature collards in a correctly sized container (15 L or more) with drainage visible.

Companion overview

2 reviewed relationship records (evidence: medium).

Supported or conditional

Cabbage

Avoid or separate

None with evidence

1 popular pairing reviewed with no verified relationship.

Full companion profile

Crop rotation

Avoid planting collards or other cabbage family crops in the same spot for 3 years. Rotation is about previous seasons, not about live neighbours.

Year 1Year 2Year 3BrassicaceaeOther familyOther familyback after 3+ years

Shared risks in Brassicaceae: clubroot, cabbage root fly, cabbage white caterpillars.

Crop rotation hub

Sources, reviewer & update

Sources

Reviewer: Garden Planner editorial team (pending independent horticultural review)

Last reviewed: August 15, 2026 · version 1

Found an error or have feedback? Let us know.

Growing collards

Collards tolerate more heat than other brassicas and stand through frost, making them a long-season leaf crop in both warm and cool regions. Pick lower leaves as needed; plants reach 60–90 cm.

Collards seed beside a ruler or coin for scale.
Collards seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Collards mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

In Florida field trials, collards planted around cabbage attracted diamondback moth egg-laying and reduced the need to spray the cabbage. The trap rows had to be maintained and treated, which is the part of trap cropping that popular charts leave out.

Two or more mature collards plants with a tape measure showing in-row spacing (45–45 cm).
Collards flower detail or bolting stage.
Immature leaves of collards developing on the plant.

Pests and rotation match the rest of the brassica group.

Edible parts and safety

Edible: leaves.

Hands or tool harvesting collards correctly (cut, pull, twist or pick) without damaging the plant.

Pests and diseases

Common pests: diamondback moth, cabbage white caterpillars, cabbage aphid, harlequin bug. Common diseases: clubroot, black rot. These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

diamondback moth on collards, with a wider damage-context view.

Timeline

Season timeline for collards: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Start seeds indoors Feb 22–Mar 8; Transplant outdoors Mar 8–Apr 5; Direct sow Mar 22–Apr 19; Tend and monitor Apr 19–May 2; Harvest May 2–Sep 11; Autumn sowing Aug 13–Sep 10.

Related plants

See also: Brassicaceae family page · crop rotation · regional calendar · guides

Our Methodology & Sources

We synthesize peer-reviewed research, university extension publications, and trusted horticulture resources. Our evidence levels help you understand how strong the science is behind the guidance.

Evidence tiers

Supported evidenceConsistent results from multiple robust studies
Traditional claimHistorical use reported, limited scientific support
Context dependentMixed or variable results across conditions
No verified relationshipNo reliable evidence identified

Primary source types

  • Peer-reviewed journal articles
  • University extension publications
  • Government & research institute reports
  • Systematic reviews & meta-analyses

Last updated

August 24, 2026

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