Collard greens are tough, productive, and famously unfussy — they take heat better than most brassicas and sweeten after frost. Starting them indoors gives you sturdy transplants for a long harvest season that can run from summer into winter.
Collard Greens belong to the Brassicaceae family, need full sun, and take 60–80 days to mature, with seed germinating in 7–10 days. That combination — a moderate season and fairly quick germination — shapes every decision in this guide, from when you sow to whether indoor starting is even worth it. Collards are one of the easiest brassicas to start indoors: the seed germinates in 7–10 days, the seedlings are sturdy, and the plants tolerate both heat and frost. They work as a spring crop and, even better, as a fall crop sown in summer and harvested after frost. Direct sowing works too, but indoor-started plants get a head start that matters in a short season.
Collard Greens at a glance
| Growing factor | What collard greens need |
|---|---|
| Days to germination | 7–10 |
| Sowing method | both |
| Days to maturity | 60–80 |
| Soil pH | 6.0–7.5 |
| Spacing | 12–18 inches |
| Sun | full sun |
| Cold tolerance | frost-tolerant |
| Water needs | moderate |
| Family | Brassicaceae |
When to start collard greens seeds indoors
For a spring crop in Zones 3–6, start collards indoors 6–8 weeks before your last frost. For a fall crop, start 10–12 weeks before your first autumn frost. In Zones 7–9, collards are a fall-through-winter crop — start in late summer. In Zones 10–13, grow them through the cool season.
Timing in brief: start indoors 6–8 weeks before your last frost, or 10–12 weeks before your first autumn frost for a fall crop. Work backwards from your last frost date using our seed-starting calculator and the frost-date calculator, and confirm the timing with your local extension service. Zones 11–13 are frost-free, so never plan around a frost date there — the calendar in those zones is about heat and rain instead. If you are unsure of your zone, the hardiness-zone finder will confirm it.
What you need
- Fresh collard greens seed — check the packet date, and test old seed before you rely on it
- Seed trays or cells, plus peat pots or soil blocks if you are starting a crop that dislikes root disturbance
- Fine, sterile seed-starting mix — not garden soil, which is too heavy and carries disease
- A spray bottle or a tray for bottom watering
- Labels and a marker — collard greens seedlings all look alike at first
- A grow light, or the brightest windowsill you have
- A heat mat, if you are starting a warmth-loving crop or your room runs cool
- Clean water, and a small fan for air circulation once seedlings emerge
Keep the seed packet as your reference for variety, sowing depth, and days to maturity. Wash reused trays in hot soapy water first — old compost is where damping-off fungi live.
Step by step: starting collard greens seeds indoors
Sow collard seed 1/4 inch deep in cells or trays. Germination takes 7–10 days. Grow seedlings on until they have three or four true leaves, then plant out. Keep seedlings cool and bright — heat makes brassica seedlings leggy.
- Fill your containers. Fill trays, cells, or peat pots with moist seed-starting mix, damp like a wrung-out sponge. Water dry mix before you sow, not after.
- Sow at the right depth. Sow at the depth on the packet and no deeper — seed sown too deep runs out of energy before it reaches the surface.
- Label everything. Write the variety and sowing date on every tray.
- Water gently. Mist the surface or water from below so seed is not washed away. Cover the tray to hold moisture in, and remove the cover the moment seedlings appear.
- Keep it warm and bright. Seed germinates in 7–10 days in suitable conditions — check daily, and move the tray into light the moment green appears.
- Thin to the strongest. If two seedlings share a cell, snip the weaker one at soil level — pulling disturbs the roots of the one you keep.
- Pot on when ready. Move seedlings into individual pots once they have two or three true leaves, handling them by a leaf, never the stem.
- Feed lightly. Seed mix has almost no nutrients, so once seedlings have true leaves, feed at half strength with a balanced liquid feed every week or so.
For direct-sown crops, the outdoor version is simpler: sow where the plant will grow, keep the bed moist until germination, and thin to 12–18 inches apart. The soil pH for collard greens should be 6.0–7.5.
Light for seedlings
Collard seedlings need strong light from emergence. A grow light a few inches above the leaves for 14–16 hours a day keeps them stocky; a dim windowsill gives you leggy plants.
Give seedlings 14–16 hours of light a day. A south-facing windowsill can work in spring, but most seedlings do better under a grow light hung a few inches above the leaves and raised as they grow — if the light is too far away, seedlings stretch and go leggy, and leggy seedlings rarely recover. Our grow-light calculator can help with hanging height and hours. Give them a dark night too; do not leave lights on around the clock.
Watering seedlings
Keep compost evenly moist during the 7–10 day germination window. Collards need moderate, steady water — drought makes leaves tough and bitter.
Water seedlings from below whenever you can: stand the tray in a shallow dish for ten minutes, let the mix soak it up, then drain it away. Top watering washes seed around and keeps the surface wet, which invites damping off. Keep the mix evenly moist — never soggy, never dry — and check daily, because a small cell dries fast under lights and a dry spell during the 7–10-day germination window can stall the seed. Once seedlings have true leaves, let the surface dry slightly between waterings. Our watering calculator gives a starting point. Use room-temperature water — cold water shocks young roots.
Hardening off
Harden collards off over 7–10 days. They are frost-tolerant, so they can go out while nights are still cool, but harden gradually so the move does not check growth.
Hardening off means getting indoor seedlings used to the outdoors gradually, over 7–10 days. Start with a few hours in a sheltered, shady spot, then lengthen the time outside each day and introduce more sun and wind. Bring trays in at night for the first few days, especially if frost threatens. Seedlings put straight outside without hardening off wilt, scorch, or stop growing for weeks — the shock undoes all the careful indoor work.
Transplanting outdoors
Set collards 12–18 inches apart in rich, well-drained soil in full sun. Plant at the same depth as in the pot, firm the soil, water in, and mulch. Harvest outer leaves as needed — the plant keeps producing from the centre.
Collard Greens grow best in full sun and a soil pH of 6.0–7.5, so choose the sunniest suitable spot and test the soil before you plant. Good companions nearby include marigolds, basil, onions. Space plants 12–18 inches apart — crowding is one of the commonest causes of small harvests. Our plant-spacing calculator works out how many plants fit your bed. Plant on a cloudy day or in the evening, water in thoroughly, and mulch to hold moisture.
Common problems and fixes
| Problem | Fix |
|---|---|
| Cabbage Worms | Check plants regularly, remove by hand, and cover young plants with insect mesh. |
| Aphids | Spray off with water and encourage beneficial insects. |
| Damping off | Use fresh sterile seed mix, water from below, and give seedlings good air circulation. |
| Leggy seedlings | Move grow lights closer — a few inches above the leaves — and give 14–16 hours of light a day. |
| Seed not germinating | Check the seed is fresh and the compost is moist; collard greens seed takes 7–10 days to germinate. |
Leggy seedlings
Too warm and too dark. Grow seedlings on cool and bright, with lights close above them.
Cabbage worms
Green caterpillars chew holes in leaves. Check undersides, pick them off, and cover with insect mesh.
Tough, bitter leaves
Drought or heat stress. Keep water steady and mulch to hold moisture.
Frequently asked questions
When should I start collard greens indoors?
For spring, 6–8 weeks before your last frost. For fall, 10–12 weeks before your first autumn frost — the fall crop is often the better one, since frost sweetens the leaves.
Are collards easier than other brassicas?
Yes — they tolerate heat better than cabbage or broccoli and are less bothered by pests. They are a good first brassica.
How do I harvest collards?
Pick outer leaves as needed, leaving the centre to keep growing. A few plants give a steady supply for months.
How long do collard greens seeds take to germinate?
Collard Greens seed takes 7–10 days to germinate in suitable conditions. Keep the compost moist and at room temperature, and use fresh seed — old seed germinates slowly or not at all. Our germination-time calculator can help you work out the timing for your sowing.
Can I use old collard greens seed?
Check it first. Seed viability falls with age and poor storage, so test a few seeds on damp kitchen paper before sowing a whole tray. Our seed-viability checker walks you through the test.