Halton region Master Gardeners

Elisa Bernier – Halton Master Gardener

February 13, 2025

Winter is the ideal time for gardeners to plan their vegetable garden, organize a planting schedule, sow seeds, and prepare for a successful harvest. As store-bought produce loses its appeal, many look for ways to start seeds indoors and accelerate the growing season. A digital sowing calendar is a game-changer, helping gardeners track planting dates, optimize germination, and maximize crop yields. Sowing your own seeds allows you to control growing conditions, experiment with new vegetable varieties, and enjoy an earlier, healthier harvest. Get ahead this season with a well-planned vegetable planting schedule on your very own digital calendar!

Timing is Everything:

Sowing seeds at the right time is key to a successful garden. Plant too early, and seedlings become weak and leggy; plant too late, and they may not thrive. We often jump between resources to check which seeds need to be started indoors and which can be direct-sown outdoors. Instead of juggling multiple sources, imagine having all this information in one place—accessible on your smartphone or tablet while selecting seeds at the nursery. A digital sowing calendar makes planting easier and more efficient! 

The Digital Sowing Calendar

Wonder no more! Ferrin Brook Farm created a great blog on how to solve this simple problem! We’ve adapted it to the Halton region (including the cities of Georgetown, Milton, Oakville, Burlington and Hamilton). There’s now a calendar available that you can import into your Google Calendar available on the Halton Region Master Gardeners website.

The Parameters Used to Create This Calendar

• The last official frost for the Hamilton Royal Botanical Gardens is May 10th. These dates are available on Environment Canada’s website. For more information on determining the appropriate last and first frost dates check out A Gardener’s Guide to Weather Prediction.
• The list of plants and the growing span were collected from various sources and represent general ranges for the species listed. The sources do not represent endorsement of any particular seed company. The sources are provided below. 

Will this Calendar Apply to my Garden? 

The short answer is not necessarily. The following parameters may skew the planting time for your garden:

• The variety of the plant may require narrower or longer sowing periods prior to the first frost date. Make sure to read the labels. 
• The duration of time it will take for plants to germinate will depend on the growing conditions (e.g., whether you have grow lights and heat mats, where you start the plants outside under cold frames, etc.).

Can I add this Garden Calendar to my Personal Online Calendar? 

Yes, simply follow these steps for your Google Calendar:

Step 1: Go to Halton Master Gardener “Event” page. Scroll to the “Calendar to Schedule Sowing Seeds Indoors” 

Step 2: Below the calendar select the Add to Google Calendar. This should automatically open your Google Calendar and ask you to confirm that you would like to subscribe to the calendar.

Step 3: Under Other Calendars you should be able to see Sowing Seeds Indoors.

Step 4: Ta da! You should have access to the calendar. You can toggle it on and off when you’d like to reference. 

There you have it!

Customize your Sowing Calendar in YOUR Google Calendar

As you may know, not all gardens and plants are created equally. The geographic area, topography and microclimate will all affect when it’s safe to start your seeds outdoors. If you know or suspect that May 10th is not the first frost free date for your area, or you would like to include different plants in your calendar, you can make your own! 

The examples below use Google Spreadsheets. 

Step 1a: Create an electronic spreadsheet. Give it a title of your choosing (e.g., “Sowing Calendar). 

Enter in the following headings in the top row of a spreadsheet.

Subject

Start Date

Start Time

End Date

End Time

All Day Event

Description

Sow Span End

Sow Span Beginning

Step 2a:

• Populate the spreadsheet with the crops of your preference. 
• Use your trusted sources to help you populate the fields of the spreadsheet
• Note: you must enter an end date. An example of a row might look like this: 

• Populate the spreadsheet as follows and in the following order: 
• Subject: the plant of your choosing (e.g., Brussel Sprout)
• Start Date: A formula is required for this value. This entry represents the earliest week prior to the first frost free date that seeds can be sown indoors. Enter in the following formula: 

= DATE(2025,5,10)-(I2*7)

• The date value (YYYY,MM,DD) represents the first frost free date of May, 10th, 2025. Change the date highlighted in red according to your first free date. 
• The “I2” value shown in purple represents the beginning of the sow span. 
• Start Time: Leave the  “Start Time” and “End Time” columns blank.
• End Date:A formula is required for this value. This value represents the last week prior to the first frost free date that seeds can be sown indoors. Enter in the following formula: 
  

= DATE(2025,5,10)-(I2*7)

The date value (YYYY,MM,DD) represents the first frost free date of May, 10th, 2025. Change the date highlighted in red according to your first frost free date. 

The “I2” value shown in purple represents the sow span  end value.

End Time:There is no need to fill in the “Start Time” and “End Time” columns.

All Day Event: Write “True.” “True” represents that the entire day will show up in the calendar. 

Sow Span End: The shortest sowing span to start sowing seeds indoors prior to the first frost free date (e.g., enter in “3” for 3 weeks prior to the first frost free date). This value is taken from the seed packet.  

Sow Span Beginning: The shortest sowing span to start sowing seeds indoors prior to the first frost free date (e.g., enter in “5” for 5 weeks prior to the first frost free date). This value is taken from the seed packet.  

Step 3a: Once your spreadsheet is complete. Save it as a “CSV” File. If using Google Spreadsheets,  select “File” followed by “Download” and then “Comma Separated Values.” This will automatically save the file to your downloads. 

Launch Google Calendar

Step 1b: Log into your Gmail account and open the calendar application. 

Step 2b: Select the “+” beside the Other Calendars” and click on “Create a new Calendar”

Step 3b: Label it as you wish (e.g., Starting Seeds Inside). Press “Create Calendar”. Navigate back to your Calendar page. You should now see a new calendar listed under “My Calendars.” 

Step 4b:  Select the “+” beside the Other Calendars” and click on “Import.”

Step 5b:  Select the cvs file that you created and add it to the new calendar “Starting Seeds Inside” you just created under “Add to Calendar.” Press Import. 

Step 6b: Ta da! You will receive a notice that says the data has been imported. Return to your Google calendar page. You can toggle it on and off when you’d like to reference the seed sowing calendar. 

Now think of all the possibilities you can use for this calendar tool! You can customize it to your liking for your garden bounty. You could also make a calendar to remind you when to transplant the indoor seeds outside. You could also make a calendar to prompt you to direct sow to maximize your yield. 

Wishing you a smooth growing season and hopefully this proves to be a tool that can help take the guesswork out of sowing. Your administrative work is done and it’s time to get sowing!