• Krista Green

When to Start Seeds Indoors - With Free Printable Seeding Guide

Updated: Mar 26

If you are like me, you are anxiously anticipating and counting down the days to when you can start seeds for your 2022 garden! For fellow Albertans, or others with similar frost dates, I will share with you when to start seeds indoors. If you live in a warmer climate these dates can be adjusted according to your last expected frost date. Starting plants from seed indoors is not only fun but it ends up costing a fraction of the price that it would to buy these plants already started at a greenhouse!


Vegetable seeds with a seed tray for the seeds to be started indoors in Calgary Alberta, Canada zone 3 growing zone.

To begin with I will discuss what supplies I use for starting plants and then I will share with you the dates I like to plant my seeds indoors for my zone 3 garden near Calgary Alberta.


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The best soil for starting plants indoors


It is helpful to have a good quality potting soil mix. Pro-mix and Sunshine mix are good brands in my experience. If you attempt to use any compost or soil from outdoors you will most likely end up with soil gnats, aphids and possibly more problems. I do not suggest this rout for growing indoors. (Trust me, I have learned this the hard way!) The last few years I have been using Sungro potting soil and have been very happy with it.


Sungro soil used for starting seeds indoors in Alberta to plant in my zone 3 garden near Calgary.

Surprisingly, good quality potting soil mixes are actually soilless, containing no natural soil. They are great for retaining moisture but also not becoming waterlogged (which can cause seed and/or root rot). Potting soil is not good for vegetable garden beds (unless mixed with 1/3 compost and 1/3 top soil) but is wonderful for growing plants in containers! Be mindful of the fact that although this soil can retain nutrients, it does not contain many nutrients. Your plants will benefit greatly from fertilizing once every week or so. Check out your local garden center or hardware store for more potting soil options.



The best grow lights for staring seeds indoors


It is not necessary to use grow lights if you have a sunny window but you will end up with less leggy, stronger and all around healthier plants by using grow lights. I started my seedlings indoors without grow lights in a sunny window for 2 years before I made the leap and purchased grow lights.


5000 lumen LED shop lights also work well as grow lights and can often be found for a much lower cost.


Using an indoor greenhouse for starting seeds indoors


An Indoor greenhouse set up is also not necessary but does make germination quicker and the layered shelves enable you to grow more in a smaller space. I purchased one three years ago and love it! I use a plastic tray underneath to catch water and soil.



Plug trays and plant pots for starting seeds indoors


You will also need a variety of plant plug trays or plant pots. You can get creative here if you would like. Some people use things like toilet paper rolls, egg shells, disposable cups or clear clamshell containers (the ones things like lettuce and grapes come in) to grow their plants. The type of container is not important as long as you have water drainage. If you use disposable cups, make sure you put holes in the bottom of them to allow for sufficient water drainage.

Make sure you label your seedlings!


Use popsicle sticks, re-write on old plant labels or purchase blank labels so that you can keep track of what you are growing. I like to include the seed brand on my labels so I can make notes on what ones grow best. I bought these ones from Amazon and have enough to share with all my friends and to last me years to come!


Use a timer for your grow lights


Ideally you will have your grow lights on for 14 to 16 hours a day. I am not very consistent with turning my lights on and off manually and just purchased these programmable timers from Amazon to help me out! This way I can set the timer and forget about the lights.



Dates for Starting Seeds Indoors in Southern Alberta


Now that you have your supplies we get to the big question, when do we plant our seeds? I will share dates with you for when I start different varieties of seeds indoors for my zone 3 growing location in Alberta. Our last hard frost in the spring tends to be around the 3rd week in May but we often get one last light frost in early to mid June. I try to keep an eye on overnight forecasted low temperatures and cover sensitive plants during any dips near freezing. (Check out what plants are most sensitive and need to be covered here.)


It is important to realize that seeding dates can vary based on your lighting and growing environment. Adjust for how much sooner or later your last expected frost date is to make this list work for your location. (Find out frost dates for your location here.) Take notes on how your plants fare and whether you think it would be beneficial to start them sooner or later for next year. By doing this you will end up with your own perfected seeding dates.


I have designed a printable garden journal to make keeping track of your garden notes much easier! Simply fill in the blanks to keep track of your seedlings and all your other gardening notes.


Use this planner to record dates you start seeds indoors in Alberta, zone 3.

Seed packages often state how many weeks before the last frost you should start your seeds indoors. This is a great guideline, but something you will want to adjust depending how big you want the plants to be by the time you plant them outside and how quickly they grow in your house. This is especially the case for flowers. Professional greenhouses likely seed earlier than my dates, but they have more space to pot plants up as they grow. If you have less space you may need to seed a few weeks later so you plants don't outgrow their smaller pots prior to moving outdoors.


I have included some of the flowers I like to start myself in this list. I find I am able to save so much money by growing my own flowers from seed!


Basil seedlings being grown from seed in a plant pot started indoors in Alberta, Canada growing zone 3.


Enter your email here to get your free printable zone 3 vegetable indoor seed starting guide sent right to your inbox!


Indoor Seeding Dates for a Last Expected Frost Date of May 24th to June 10th


January 14th - 21st

  • Lavender

  • Leeks

  • Mint

  • Onions

  • Pansies

  • Rosemary

  • Thyme

  • Sage

(If planting herbs in January, expect them to be in full sized pots by June. I like to start my herbs early so that I can begin harvesting them sooner, even while they are still indoors!)


February 14th - 21st

  • Celery

  • Gazanias

  • Lobelia (Tip: Seed in a seeding tray and transplant when half an inch. Place 3 - 5 plants in each hole with holes 1.5 inches apart.)

  • Oregano

  • Parsley

  • Peppers

  • Rudbeckia

March 1st - 7th

  • Marigolds

  • Tomatoes (If you don't have space to pot these into bigger pots, wait 3 more weeks to seed them.)

  • Snapdragons

March 7th - 14th

  • Coleus

  • Cosmos

  • Salvia

  • Stocks

March 21st - 28th

  • Bok choy

  • Broccoli

  • Brussel Sprouts

  • Cabbage

  • Cauliflower

April 1st - 7th

  • Basil

  • Cilantro

  • Fennel

  • Nasturtiums

  • Zinnias (These can be direct seeded in early May as well.)


April 21st - 28th

  • Corn (Can also be direct sewn at the beginning of June.)

  • Cucumbers (Plant in fiber pots that can be planted into soil with the bottom of the pot removed. They do not like their roots disturbed during transplant.)

  • Sunflowers (Can also be direct sewn around May 21st.)

  • Squash (Plant in fiber pots that can be planted into soil with the bottom of the pot removed. They do not like their roots disturbed during transplant.)




Not all seeds need to be started indoors


Make sure you know what seed should be started in advance and what seeds you can plant directly into your garden.


If you live in a warmer climate and are looking for start dates more applicable to the warmer zones, I recommend checking out these lists by West Coast Seeds.


Make sure you harden off your plants prior to transplanting to prevent them dying from shock.


To find out when I direct seed my garden, read When to Plant Your Vegetable Garden.

Flowers started indoors from seed in zone 3 Calgary Alberta, Canada.

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Planting dates for starting seeds indoors in Alberta showing seedlings growing in peat pots.

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