What month should you start seeds indoors?
Written by
Olivia Mitchell
Reviewed by
Prof. Charles Hartman, Ph.D.Knowing when to start seeds indoors sets you up for gardening success. Getting the timing right will make the difference between having leggy seedlings and wasted effort. Your last frost date serves as a starting guide. Work backwards for each plant type. This ensures vigorous transplants.
Frost Date Calculations
- Tomatoes: Start 6 weeks before last frost
- Peppers: Begin 8 weeks prior for best results
- Broccoli: Cold-tolerant crops need 6-8 weeks head start
- Cucumbers: Wait until 3-4 weeks before transplant
Zone-Specific Adjustments
- Zone 5: Start tomatoes mid-March for April 30 frost
- Zone 7: Begin peppers early February for March frost
- Urban gardens: Start 7 days earlier due to heat islands
- Coastal areas: Add 7-10 days for cooler springs
Your seed packets offer important advice. Be sure to note the specific temperature requirements. Tomatoes require soil temperature of 75-85°F (24-29°C). Peppers require warmer temperatures of 80-85°F (27-29°C). Cool-season crops such as lettuce prefer soil temperatures of 60-70°F (15-21°C). Use thermometers to ensure you have the correct conditions.
Microclimates can greatly affect your timing. South-facing slopes accumulate extra heat, valleys harbor frost pockets, and elevation changes will also alter timing. Additionally, for every 1,000 feet (305 meters) above 2,000 feet (610 meters), subtract one week. Pay attention to your specific garden microclimate.
Soil temperature is more important. Measure at a depth of 4 inches (10 cm) in mid-morning. Cool crops, such as peas, require a minimum temperature of at least 45°F (7°C). Warm crops need a minimum of 60°F (15°C). Tropical plants require a minimum temperature of 70°F (21°C). Plant accordingly.
Maintain thorough documentation every season. Record dates when you have success. Follow weather patterns. Take note of success and when to adjust future plantings. All of this is a valuable learning experience that your garden grants you. Continue experimenting and following the principles of when to plant.
Read the full article: When to Start Seeds Indoors: Ultimate Guide
