Calculate your seed starting schedule by finding your last frost date and counting backwards using each crop's "weeks to transplant" timing. Tomatoes need 6-8 weeks indoors, peppers need 8-10 weeks, and lettuce needs just 4-6 weeks. Starting too early is as problematic as starting too late—oversized seedlings are difficult to manage.
How to Calculate Your Schedule
Step 1: Find Your Last Frost Date
Your average last frost date determines everything:
- USDA provides estimates by zip code
- Local extension offices have accurate data
- Ask experienced local gardeners
Step 2: Count Backwards
Formula: Last Frost Date - Weeks to Transplant = Start Date
Example (Last frost May 15):
- Tomatoes (6-8 weeks): Start March 20 - April 3
- Peppers (8-10 weeks): Start March 6 - March 20
- Lettuce (4-6 weeks): Start April 3 - April 17
Step 3: Adjust for Transplant Timing
Some crops go out before last frost (cool-season), some after (warm-season):
| Crop Type | When to Transplant |
|---|
| Cool-season | 2-4 weeks BEFORE last frost |
| Warm-season | 1-2 weeks AFTER last frost |
Complete Seed Starting Schedule
Very Early (10-12 weeks before last frost)
| Crop | Notes |
|---|
| Onions | Need long growing time |
| Leeks | Slow growers |
| Celery | Slow to establish |
Early (8-10 weeks before last frost)
| Crop | Notes |
|---|
| Peppers | Slow to germinate and grow |
| Eggplant | Similar to peppers |
| Artichokes | Need vernalization |
Standard (6-8 weeks before last frost)
| Crop | Notes |
|---|
| Tomatoes | Most common start time |
| Basil | Can start with tomatoes |
| Perennial herbs | Head start on establishment |
Late (4-6 weeks before last frost)
| Crop | Notes |
|---|
| Broccoli | Fast growers |
| Cabbage | Fast growers |
| Cauliflower | Fast growers |
| Kale | Fast growers |
| Lettuce | Bolts if started too early |
| Kohlrabi | Fast growers |
Very Late (3-4 weeks before last frost)
| Crop | Notes |
|---|
| Cucumbers | Don't like root disturbance |
| Squash | Fast growers, sensitive |
| Melons | Fast growers, sensitive |
| Pumpkins | Fast growers |
Or Direct Sow
| Crop | Why Not Transplant |
|---|
| Carrots | Taproot doesn't transplant |
| Beans | Fast, don't need head start |
| Corn | Fast, doesn't transplant well |
| Radishes | Too fast, no benefit |
| Peas | Fast, cool-season direct sow |
Detailed Crop Schedule
Tomatoes
| Timing | Detail |
|---|
| Weeks before last frost | 6-8 |
| Germination time | 5-10 days |
| Transplant size | 6-8" tall, sturdy stem |
| Transplant timing | 1-2 weeks after last frost |
Example (May 15 last frost):
- Start seeds: March 20 - April 3
- Germination: March 27 - April 10
- Pot up to 4": April 10 - April 24
- Harden off: May 8 - May 18
- Transplant: May 22 - May 29
Peppers
| Timing | Detail |
|---|
| Weeks before last frost | 8-10 |
| Germination time | 7-14 days |
| Transplant size | 4-6" tall |
| Transplant timing | 2 weeks after last frost |
Example (May 15 last frost):
- Start seeds: March 6 - March 20
- Germination: March 13 - April 3
- Pot up: March 27 - April 17
- Harden off: May 15 - May 25
- Transplant: May 29 - June 5
Brassicas (Broccoli, Cabbage, etc.)
| Timing | Detail |
|---|
| Weeks before last frost | 4-6 |
| Germination time | 4-7 days |
| Transplant size | 4-6 true leaves |
| Transplant timing | 2-4 weeks before last frost |
Example (May 15 last frost):
- Start seeds: April 3 - April 17
- Germination: April 7 - April 24
- Harden off: April 14 - May 1
- Transplant: April 17 - May 1
Lettuce
| Timing | Detail |
|---|
| Weeks before last frost | 4-6 |
| Germination time | 2-7 days |
| Transplant size | 4-6 true leaves |
| Transplant timing | 2-4 weeks before last frost |
Note: Can also direct sow or start multiple successions.
Cucurbits (Cucumber, Squash, Melon)
| Timing | Detail |
|---|
| Weeks before last frost | 3-4 |
| Germination time | 3-7 days |
| Transplant size | 2-3 true leaves |
| Transplant timing | 1-2 weeks after last frost |
Important: Don't start too early—they grow fast and hate root disturbance. Many gardeners direct sow these.
Sample Schedule by Last Frost Date
Last Frost: April 15
| Crop | Start Date |
|---|
| Onions | January 21 - February 4 |
| Peppers | February 4 - February 18 |
| Tomatoes | February 18 - March 4 |
| Broccoli/Cabbage | March 4 - March 18 |
| Lettuce | March 4 - March 18 |
| Cucumbers/Squash | March 18 - March 25 |
Last Frost: May 15
| Crop | Start Date |
|---|
| Onions | February 18 - March 4 |
| Peppers | March 6 - March 20 |
| Tomatoes | March 20 - April 3 |
| Broccoli/Cabbage | April 3 - April 17 |
| Lettuce | April 3 - April 17 |
| Cucumbers/Squash | April 17 - April 24 |
Last Frost: June 1
| Crop | Start Date |
|---|
| Onions | March 6 - March 20 |
| Peppers | March 20 - April 3 |
| Tomatoes | April 3 - April 17 |
| Broccoli/Cabbage | April 17 - May 1 |
| Lettuce | April 17 - May 1 |
| Cucumbers/Squash | May 1 - May 8 |
Common Timing Mistakes
Starting Too Early
Problems:
- Seedlings outgrow containers
- Leggy, weak plants
- Root-bound before transplant
- Plants stressed while waiting
Signs you started too early:
- Seedlings flowering indoors
- Pot-up after pot-up
- Waiting weeks for weather
Starting Too Late
Problems:
- Transplants too small
- Late harvest
- Not enough production time
- May miss optimal growing window
Signs you started too late:
- Buying transplants because yours aren't ready
- Harvesting after neighbors
Solution: The Range
Most timing guides give ranges (e.g., 6-8 weeks):
- Later end of range: Shorter seasons, faster-growing varieties
- Earlier end of range: Longer seasons, slower varieties, want earlier harvest
Adjustments
For Extended Harvest
Stagger plantings:
- Start some at 8 weeks, some at 6 weeks
- Get longer harvest window
- Reduces risk
For Cool Summers
Start earlier within the range:
- Plants need more time in cooler conditions
- Maximize growing season
For Hot Summers
Start later within the range:
- Get transplants out before peak heat
- Avoid starting too early (plant stress)
For Fall Planting
Count backwards from first fall frost:
- Determine days to maturity
- Add 2 weeks for fall slowdown
- Start accordingly
Succession Planting Schedule
Lettuce (Every 2-3 Weeks)
| Planting | Start Date | Harvest |
|---|
| 1 | 6 weeks before LF | Early |
| 2 | 4 weeks before LF | Mid |
| 3 | 2 weeks before LF | Late spring |
| 4 | At last frost | Early summer |
| Continue | Every 2-3 weeks | Until heat |
Cucumbers (2-3 Plantings)
| Planting | Start | Purpose |
|---|
| 1 | 3-4 weeks before LF | Main crop |
| 2 | 2 weeks after LF | Extend harvest |
| 3 | 6 weeks after LF | Fall crop (if time) |
FAQ
How do I find my last frost date?
Search "last frost date [your zip code]" or check with your local cooperative extension. The date is an average—actual frost can occur earlier or later.
What happens if I start seeds too early?
Seedlings become overgrown, leggy, and root-bound while waiting for appropriate outdoor weather. Stressed plants don't transplant as well.
Can I start all my seeds at the same time?
No. Different crops have different indoor growing times. Peppers need 8-10 weeks while lettuce only needs 4-6 weeks. Starting all at once means some will be wrong.
Should I use the early or late end of the timing range?
If your growing season is short, use the earlier end. If you have a long season, the later end gives you less time managing seedlings indoors.
What if I miss my start date?
You can still start late (better than not at all) or buy transplants. Late starts mean later harvests but are often still worthwhile.
How accurate does the timing need to be?
Within a week or two is usually fine. The ranges account for some variability. Focus on not being drastically early or late.
The Bottom Line
Seed starting schedule basics:
- Find your last frost date — Everything derives from this
- Count backwards — Use weeks-to-transplant for each crop
- Consider transplant timing — Before or after last frost
- Don't start too early — Oversized seedlings are problematic
- Give yourself a range — Flexibility reduces stress
A simple spreadsheet or calendar with your dates makes the whole season smoother.
Related: Seed Starting Indoors Guide | When to Transplant Seedlings
