Indoors or outdoors: the simplest way to decide where to start seeds
In cool, short-season climates, the main question is not “can this crop grow here?” but “will it have enough time?” In the table below we provide advice about when to sow your seeds based on your area’s “last frost date”, and where to plant them first:
- Starting seeds indoors gives you warm soil, steady moisture, and a head start while it is still cold outside.
- Starting outdoors is easier and often produces stronger root systems for crops that dislike being moved.
A practical rule:
- Start indoors when the crop is slow, needs warmth, or benefits from a long season (tomatoes, peppers, celery, many brassicas).
- Start outdoors when the crop grows fast, tolerates cool soil, or hates transplanting (carrots, parsnips, peas, radishes, dill).
| Crop | Start (Indoors/Outdoors) | When to start | Brief sowing notes |
|---|---|---|---|
| asparagus | Indoors | 10–12 weeks before last frost | Slow from seed; many gardeners plant crowns outdoors for faster results. |
| basil | Indoors | 4–6 weeks before last frost | Needs warmth and light; plant out only when nights are warm. |
| beans | Outdoors | 1–2 weeks after last frost | Warm soil matters; direct sow. Soaking is optional, but not required. |
| beetroot | Outdoors | 0–2 weeks after last frost | Direct sow; thin seedlings for proper roots. |
| broccoli | Indoors | 6–8 weeks before last frost | Transplant out when sturdy; protect from pests early. |
| brussels sprouts | Indoors | 8–10 weeks before last frost | Long season crop; transplant out early for best size. |
| cabbage | Indoors | 6–8 weeks before last frost | Transplants handle cool weather; keep growth steady. |
| carrots | Outdoors | 0–4 weeks after last frost | Do not transplant; keep seedbed evenly moist for germination. |
| cauliflower | Indoors | 6–8 weeks before last frost | Sensitive to stress; transplant gently and avoid setbacks. |
| celery | Indoors | 10–12 weeks before last frost | Tiny seed; sow on surface, keep moist, needs long indoor time. |
| chives | Indoors | 6–8 weeks before last frost | Easy; clumps up over time. Can also be divided later. |
| coriander (cilantro) | Outdoors | 2–4 weeks before last frost | Best direct sown; bolts in heat, so sow in waves. |
| cucumbers | Indoors | 2–4 weeks before last frost | Fast; don’t start too early. Plant out only when warm. |
| dill | Outdoors | 0–4 weeks after last frost | Dislikes transplanting; direct sow and repeat sowings. |
| fennel | Outdoors | 2-4 weeks after last frost | Many types dislike transplanting; direct sow for best roots. |
| garlic | Outdoors | Best in autumn; or early spring | Plant cloves, not seed. Autumn planting gives bigger bulbs. |
| kale | Indoors | 4–6 weeks before last frost | Very hardy; transplant out early or direct sow later. |
| lavender | Indoors | 10–12 weeks before last frost | Slow; keep warm and bright. Some seeds benefit from cold time. |
| leeks | Indoors | 10–12 weeks before last frost | Long season; transplant out while still pencil-thin. |
| lettuce | Outdoors | 4–6 weeks before last frost | Cool-loving; sow small batches often for steady harvest. |
| marjoram | Indoors | 6–8 weeks before last frost | Small seed; warmth and light help. |
| melons | Indoors | 3–5 weeks before last frost | Needs heat; plant out late and use shelter if possible. |
| mint | Outdoors | Plant as a plant (spring/summer) | Usually propagated from plants; spreads aggressively—contain it. |
| onions | Indoors | 10–12 weeks before last frost | From seed: start early indoors; from sets: plant outdoors in spring. |
| oregano | Indoors | 8–10 weeks before last frost | Small seed; slow start, then becomes hardy once established. |
| pak choi | Outdoors | 2–6 weeks before last frost | Fast; sow in cool periods to reduce bolting. |
| parsnips | Outdoors | 0–2 weeks after last frost | Slow to germinate; do not transplant; use fresh seed. |
| parsley | Indoors | 8–10 weeks before last frost | Slow germination; keep evenly moist and be patient. |
| peas | Outdoors | 2–6 weeks before last frost | Likes cool soil; direct sow early. Support for climbing types. |
| peppers | Indoors | 10–12 weeks before last frost | Needs warmth and strong light; transplant out late. |
| potatoes | Outdoors | 2–4 weeks after last frost | Plant tubers; “chit” (pre-sprout) indoors for earlier growth. |
| pumpkins | Indoors | 3–4 weeks before last frost | Fast; transplant after warm nights; protect from cold wind. |
| radishes | Outdoors | 0–6 weeks after last frost | Very fast; sow often. Best in cool weather. |
| rhubarb | Outdoors | Plant crowns in spring or autumn | Usually planted as crowns/plants; seed is uncommon for home gardens. |
| rosemary | Indoors | 10–12 weeks before last frost | Slow and heat-loving; many people prefer cuttings over seed. |
| sage | Indoors | 8–10 weeks before last frost | Start indoors; transplant once strong; drought-tolerant later. |
| shallots | Outdoors | 2–6 weeks after last frost (or autumn) | Usually planted as sets/bulbs; needs a long season to size up. |
| spinach | Outdoors | 2–6 weeks before last frost | Cold-tolerant; sow early and repeat sowings for steady leaves. |
| spring onions | Outdoors | 0–4 weeks after last frost | Direct sow; thin for size; can also start indoors for extra-early. |
| squash | Indoors | 3–4 weeks before last frost | Same approach as pumpkins; do not let seedlings get root-bound. |
| stevia | Indoors | 8–10 weeks before last frost | Small seed; warmth + light; plant out only in warm weather. |
| sweetcorn | Outdoors | 2–4 weeks after last frost | Indoor start helps in cool climates; transplant carefully when warm. |
| swedes (rutabaga) | Outdoors | 0–4 weeks after last frost | Direct sow; thin well; steady growth gives best roots. |
| tarragon | Outdoors | Plant as a plant (spring/summer) | French tarragon is usually a plant, not seed; grow in a warm spot. |
| thyme | Indoors | 8–10 weeks before last frost | Tiny seed; slow start; needs light and patience. |
| tomatoes | Indoors | 6–8 weeks before last frost | Warm germination and strong light; plant out after frost and cold nights. |
| turnips | Outdoors | 0–6 weeks after last frost | Fast; direct sow; best in cool weather. |
How to use this in real life
If you only remember one thing: Start indoors for long-season warmth lovers and slow growers; sow outdoors for quick cool-season crops and anything that dislikes transplanting. Add simple protection (fleece, cloches, low tunnel) and you can often shift outdoor sowing earlier without risking everything.