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Calcimator

Seed Starting Calculator

Find out when to start seeds indoors, when to transplant, and when to expect your harvest based on plant type and last frost date.

Inputs

weeks

Results

Start Seeds Indoors

Mar 19

Transplant OutdoorsMay 14
Expected HarvestJul 23
Days to Germinate7 days
Ideal Soil Temp65-85°F
Days to Harvest (from transplant)70 days
Total Growing Days126 days
How to Use This Calculator
  1. Select your plant type (tomatoes, peppers, lettuce, squash, herbs, melons, broccoli, or annual flowers).
  2. Enter your last spring frost date as a day of the year — for example, April 30 = day 120, May 15 = day 135.
  3. Enter the number of weeks you plan to grow seedlings indoors before transplanting (typically 6-8 weeks for tomatoes).
  4. Review the Start Seeds Indoors date to know exactly when to sow your seeds.
  5. Note the Transplant Outdoors date and Expected Harvest date to plan your entire season.
  6. Use the Ideal Soil Temperature and Days to Germinate to optimize your germination setup.

What each input means

Plant Type
Select the type of plant to determine transplant timing and harvest estimates.
Last Frost Date (Day of Year)
Day of the year for your average last spring frost. Apr 30 = 120, May 15 = 135. Check your USDA zone.
Weeks to Start Indoors
Number of weeks to grow seedlings indoors before transplanting.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    Plant Type = 1, Last Frost Date (Day of Year) = 120, Weeks to Start Indoors = 6 = 3 input(s) provided
  2. Calculate Start Seeds Indoors
    Start Seeds Indoors = dayToDate(startDay)
    Mar 19 = Mar 19
  3. Calculate Transplant Outdoors
    Transplant Outdoors = dayToDate(transplantDay)
    May 14 = May 14
  4. Calculate Expected Harvest
    Expected Harvest = dayToDate(harvestDay)
    Jul 23 = Jul 23

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