Arugula is the fastest leafy green you can grow — 30–45 days from seed to salad — and it is a direct-sown crop by nature. Indoor starting buys you a week at most, and arugula dislikes being moved, so this guide is honest about when the tray is worth it.
Arugula belong to the Brassicaceae family, need full sun, and take 30–45 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. Arugula germinates in 7–10 days in cool soil and is ready to eat in 30–45 days, which makes indoor starting almost redundant. The plants bolt in heat and dislike root disturbance, so the best arugula comes from seed sown where it will grow, in cool weather, with regular water. Start a tray indoors only for the very first leaves of spring.
Arugula at a glance
| Growing factor | What arugula need |
|---|---|
| Days to germination | 7–10 |
| Sowing method | direct sow |
| Days to maturity | 30–45 |
| Soil pH | 6.0–7.0 |
| Spacing | 6–8 inches |
| Sun | full sun |
| Cold tolerance | hardy |
| Water needs | moderate |
| Family | Brassicaceae |
When to start arugula seeds indoors
Direct-sow arugula from 2–3 weeks before your last frost in Zones 3–6, and sow again every two weeks through spring. In Zones 7–9, sow in fall and winter. In Zones 10–13, sow through the cool season. Arugula bolts in summer heat, so cool-season sowing is everything.
Timing in brief: direct sow from 2–3 weeks before your last frost; indoors only for the earliest leaves. 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 arugula 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 — arugula 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 arugula seeds indoors
Sow arugula seed 1/4 inch deep, thickly, directly in the bed or in a tray for the earliest crop. Germination takes 7–10 days. Thin to 6–8 inches apart for full-size leaves, or leave thick for baby leaves. If starting indoors, transplant young and handle the root ball gently.
- 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 6–8 inches apart. The soil pH for arugula should be 6.0–7.0.
Light for seedlings
Arugula seedlings need strong light to stay compact. A bright spot or a grow light a few inches above the leaves works; a dim windowsill gives you stretched, pale seedlings.
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 the seedbed evenly moist during the 7–10 day germination window. Arugula needs moderate, steady water — drought makes leaves hot and quick to bolt.
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 off over a few days. Arugula is hardy and tolerates cool nights, so the move outside is gentle — just avoid strong sun on the first day.
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 arugula 6–8 inches apart in fertile, well-drained soil in full sun or part shade — afternoon shade helps in warm zones. Water in and mulch lightly. Start picking outer leaves when they are a few inches long.
Arugula grow best in full sun and a soil pH of 6.0–7.0, so choose the sunniest suitable spot and test the soil before you plant. Good companions nearby include marigolds, basil, onions. Space plants 6–8 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; arugula seed takes 7–10 days to germinate. |
Bolting in heat
Arugula bolts fast in warm weather. Sow in cool seasons, give afternoon shade, and succession-sow.
Flea beetles
Tiny beetles make shot-holes in leaves. Cover young plants with insect mesh.
Bitter, hot leaves
Drought or heat. Keep water steady and harvest young.
Frequently asked questions
Should I start arugula indoors?
Usually not. It germinates in 7–10 days and matures in 30–45 days, so direct sowing is faster and simpler. A tray indoors only helps for the very first leaves of spring.
Why did my arugula bolt?
Heat is the usual cause — arugula is a cool-season crop. Sow in spring and fall, give afternoon shade, and pick often.
How do I get mild arugula?
Grow it fast in cool weather with steady water, and pick young leaves. Slow, hot, dry arugula is always peppery.
How long do arugula seeds take to germinate?
Arugula 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 arugula 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.