Successful seed starting begins before sowing. This guide shows you how to check old seed, test germination, calculate how much to sow, build a seed starting schedule, and move healthy seedlings into the garden with less transplant shock.
Overview
Knowing when to start seeds indoors depends on three variables: the crop, the intended transplant date, and the time seedlings need to reach a useful size. A packet date is a helpful starting point, but it does not guarantee that every seed will germinate. Storage conditions, seed age, moisture, temperature, and light can all affect results.
Use this workflow at the beginning of each sowing batch:
- Check the crop, variety, packet date, and storage history.
- Run a germination test when seed is old, poorly stored, or especially important to your plan.
- Calculate how many seeds to sow based on the test result and the number of plants you need.
- Count backward from your regional transplant window to set an indoor sowing date.
- Track actual emergence, seedling growth, and transplant performance for next season.
For a broader seasonal plan, connect seed starting with your crop rotation, soil preparation, and succession planting. A soil health plan can help determine where transplants will go, while a composting guide can help you prepare mature organic matter without relying on unfinished compost around young roots.
What to track
Seed age and storage
Record the crop, variety, source, lot or packet date if available, and the date the packet was opened. Seeds generally last longer when kept cool, dry, and protected from temperature swings. A packet stored in a warm, damp shed should be tested sooner than one kept sealed in a consistently dry indoor location.
Do not discard seed solely because it is past the packet date. Test it first, especially when the seed is valuable, uncommon, or easy to store. Different crops age at different rates, so treat longevity charts as planning guidance rather than a guarantee.
How to test seed germination
A paper-towel test is simple and requires no special equipment.
- Count out 10, 25, or 50 seeds. A larger sample gives a more useful estimate.
- Dampen a clean paper towel so it is moist but not dripping.
- Place the seeds on the towel, fold or roll it, and put it in a labeled bag or container that is not completely airtight.
- Keep the test at a temperature appropriate for that crop. Avoid direct sun and do not let the towel dry out.
- Check at the crop's expected germination time. Count seeds with a healthy root or shoot, and continue checking for several more days if germination is uneven.
Calculate the germination rate with this formula:
Germination rate = (number of seeds that germinated ÷ number tested) × 100
For example, if 18 of 25 seeds germinate, the rate is 72 percent. A test result is not a promise for every tray, but it is a better basis for sowing decisions than an assumption about seed age.
Germination-rate worksheet
| Crop and variety | Seeds tested | Seeds germinated | Rate | Decision |
|---|---|---|---|---|
| % | Use, sow extra, or replace | |||
| % | Use, sow extra, or replace | |||
| % | Use, sow extra, or replace |
To estimate how many seeds to sow, divide the number of plants you need by the germination rate expressed as a decimal. If you need 20 plants and your test rate is 80 percent, sow at least 25 seeds before allowing for handling losses, pests, or weak seedlings. For a small farm, add a separate allowance for unmarketable plants and missed harvest timing.
Crop-by-crop seed-starting reference
The ranges below are planning estimates. Confirm the preferred temperature and transplant sensitivity for your variety, then adjust for your local frost dates and growing conditions.
| Crop | Typical germination time | Approximate indoor lead time | Useful planning note |
|---|---|---|---|
| Tomato | 5–10 days | 6–8 weeks | Transplant after cold conditions have passed; provide strong light. |
| Pepper | 7–21 days | 8–10 weeks | Often benefits from consistently warm media and an early start. |
| Eggplant | 5–14 days | 8–10 weeks | Grow warm and avoid setting out into cool soil. |
| Broccoli and cabbage | 4–10 days | 4–6 weeks | Schedule for the cool-season window rather than only the last frost. |
| Lettuce | 2–10 days | 3–5 weeks | Use succession sowing for a steadier harvest. |
| Onion | 7–14 days | 8–12 weeks | Allow extra time for slow early growth. |
| Cucumber | 3–10 days | 2–4 weeks | Sow close to transplanting because roots dislike disturbance. |
| Squash | 3–10 days | 2–4 weeks | Use larger cells and transplant before plants become root-bound. |
| Basil | 5–10 days | 4–6 weeks | Wait for warm conditions and protect from cold nights. |
For crops that are usually direct-sown, such as carrots, beans, peas, and many root vegetables, compare the risk of transplant shock with the benefit of an earlier start. A greenhouse, protected bed, or short-season climate may change that decision.
Cadence and checkpoints
Count backward from transplanting
First identify a realistic outdoor planting window using local frost information, soil temperature, crop tolerance, and the forecast. Then subtract the crop's indoor lead time. Add several days for germination and a short buffer for slow growth. For example, a crop requiring six weeks of indoor growth should usually be sown about six to eight weeks before the planned transplant date, not automatically on a fixed calendar date.
Use a separate schedule for cool-season and warm-season crops. The last frost date is only one reference point; soil temperature, wind exposure, raised-bed conditions, and overnight temperatures also matter. Renters and urban growers can use container exposure and balcony microclimates as additional variables, but should still protect seedlings from sudden cold.
Checkpoints after sowing
- Day of sowing: Label crop, variety, date, cell count, seed lot, and planned transplant location.
- Expected emergence: Check moisture, temperature, and whether seedlings are appearing evenly.
- First true leaves: Begin assessing light, spacing, root development, and nutrient needs.
- One week before transplanting: Confirm weather, bed preparation, irrigation, row cover, and pest protection.
- After transplanting: Record survival, growth, and any signs of stress.
Strong light is essential. A sunny window may be sufficient for some short-term starts, but seedlings often become thin when light is weak or distant. Adjustable grow lights placed close enough to provide bright, even coverage can improve consistency. Follow the light manufacturer's guidance and monitor plant response rather than assuming that more intensity is always better.
Reusable sowing and transplant log
| Crop and variety | Sown | Emergence | Plants kept | Transplanted | Survival after one week | Notes |
|---|---|---|---|---|---|---|
How to interpret changes
Uneven results are useful information when you separate the possible causes. Use this troubleshooting chart before changing several variables at once.
| Symptom | Likely causes to check | Practical response |
|---|---|---|
| Few or no seedlings emerge | Old seed, incorrect temperature, buried too deeply, dry media, or excessive moisture | Check the packet instructions, test remaining seed, improve moisture control, and resow if timing allows. |
| Seedlings are tall and pale | Insufficient light, lights too far away, or crowded plants | Increase light coverage, move lights closer according to guidance, and provide spacing and airflow. |
| Stems collapse at the soil line | Persistently wet media, poor airflow, contaminated containers, or crowded sowing | Improve drainage and airflow, clean reused equipment, and avoid keeping the surface constantly wet. |
| Leaves turn pale after the first true leaves | Low fertility, root restriction, water stress, or unsuitable light | Check roots and moisture first, then use a mild, appropriate fertility program if needed. |
| Plants wilt after transplanting | Insufficient hardening off, root disturbance, heat, wind, or dry soil | Harden gradually, transplant in calm conditions, water the root zone, and provide temporary protection. |
Hardening off seedlings
Hardening off is the gradual transition from protected indoor conditions to outdoor sun, wind, and temperature variation. Begin about a week before transplanting, placing seedlings outdoors in a sheltered, shaded location for a limited period. Increase outdoor time and light exposure gradually, while bringing plants inside or protecting them when conditions are harsh. Reduce neither water nor care abruptly; the goal is acclimation, not deliberate stress. Delay transplanting if seedlings are wilting, weather is unusually cold, or the soil is unworkable.
When to revisit
Revisit this guide whenever you open a new packet, begin a new sowing batch, or prepare to transplant. A monthly check during active propagation is useful for home gardens; small farms may benefit from reviewing the log weekly while trays are in production and quarterly when building the next crop plan.
Update your schedule when local frost assumptions, protected growing conditions, crop varieties, lighting, or seed storage conditions change. At the end of each season, compare planned and actual dates: germination, first true leaves, hardening off, transplanting, survival, and first harvest. If a batch performed poorly, change one factor at a time where possible and record the result.
Before the next sowing, take these five actions:
- Inventory seed and mark packets that need testing.
- Run a germination test for questionable or valuable seed.
- Calculate sowing quantities from the test rate and your target plant count.
- Count backward from the intended transplant window and add a modest buffer.
- Prepare clean containers, suitable growing media, labels, light, airflow, and a transplant protection plan.
Keep the completed logs with your seed inventory. Over time, they become a practical record of which varieties, dates, and growing conditions work in your space. If you grow for sale, use the results alongside a small farm break-even analysis and a market garden crop profitability guide so propagation decisions reflect both plant performance and the crop plan.
