How to Calculate When to Plant Seeds

You’ve poured over the seed catalogs and placed orders for cute little heirloom vegetables. The mail finally delivers the nice thick envelope. You have your up-cycled seed trays ready and a space cleared out by a sunny window. You, my friend, are a master gardener—protector of the environment and organic superhero.

Now you just need to plant. This is the easy part of the process. Right?

Do you know how to calculate when to start seeds? Here's a comprehensive way to figure it all out.

Getting started

If you have seeds in their packets finding out the basic information that you need is actually quite simple. First, you will need to identify which seeds need to be started indoors. I order almost all my new seeds from High Mowing, which provides this handy planting chart (I also like this garden calculator). High Mowing uses the abbreviations “DS,” (direct sow), meaning plant directly outdoors and “TP,” (transplant), or start your plants indoors. Identify what your particular seed company uses for this information.

The seeds that require transplanting will also have a number beside them on the packets or charts. This is the number of weeks that you will want to get planting started before the last frost. (If you live in a warm climate that doesn’t experience frost, congratulations. Close your computer and go plant your seeds in your garden now.) You can also check out 6 Vegetable Plants to Start Indoors for more ideas.

I recommend making a list of all the crops you plan to grow that will require transplanting. Beside each listing write down the amount of time needed for your seedling indoors. Set aside this list along with a calendar—you’ll be needing it later.

Do you know when to start your seedlings? This guide helps you calculate last frost and planting date.

Finding the last frost

Now, let’s identify the date of the last frost. The Farmer’s Almanac is a well-considered resource for both the USA and Canada. Americans also have access to the very good frost calculator provided by Dave’s Garden. However, I find that the list of Canadian cities listed is simply not thorough. Canadian areas are not included unless they are major metropolises (not terribly helpful for many serious gardeners). The best suggestion I have is that gardeners can visit Plant Maps (that link will lead to the interactive BC last-frost map. I will include a link to each province at the bottom of this article as the website is difficult to navigate). These maps allow gardeners to zoom into their exact regions and identify the average last-frost from the bar on the side.

So, we have identified the average last frost. Take a look at your calendar and mark a date that is two weeks later than the average you have come up with. You want to make sure that you are not planning to move your seedlings outdoors too early, and two weeks allows a nice safety cushion.

Do you know when to start your seedlings? This guide helps you calculate last frost and planting date.

All ready to grow

It’s time to go back to your list. Refer to the numbers you have written down and mark the planting date of each variety on your calendar by counting back from the “last frost” date you have down.

Also think about…

There  are a few things that you might want to consider before you truly write your planting dates in stone. If you are planting in more sizable containers (yogurt tubs, etc.), you can consider starting them up to several weeks earlier. Your plants will just be more fully grown when you move them outdoors, and will start producing sooner.

You will also want to adjust your dates if the area where you will be growing your seedlings is particularly warm or cool, as this will affect the growing time. Warmer seeds grow faster, and may need to move outside before it is safe to do so. Your seeds will also get “leggy” (long and spindly) if they are in an area that doesn’t afford them enough light.

The sun will be shining on your warm garden soil before you know it. These few simple steps will help ensure that you have bright, peppy looking plants to put out and watch thrive. You are now ready to plant and to rock that organic superhero cape that you’ve been hiding in the back of your closet.

Links to last-frost map for each province: BC, AB, SK, MB, ON, QC, NB, NS, NL, PEI

Pin: Do you know when to plant seeds? This simple method can help.
This post has been shared on the following link ups: The Homesteader Hop, Going Green, and Waste Less Wednesdays.

3 thoughts on “How to Calculate When to Plant Seeds”

  1. This is such a difficult time for me to calculate as our Springs here in Normandy, France seem to be getting colder … but then plants catch up in the warmer autumns we are having now. This year we had frosts until early May and I have known them as late as May 28th but in other years all frost has finished by early April! Thank you for linking up to the #GoingGreenLinky and the next one opens on June 5th if you have anything new to add.

    1. Thanks for the comment. Of course it does help to be familiar with your local weather habits. 🙂 I’m off to see if your new linkup is open now.

  2. It would be awesome if every seed packet contained the information about if it needs to be transplanted and for how long! Thanks for sharing on the Waste Less Wednesday Blog Hop!

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