When to plant your Edmonton Garden, Raised vegetable garden bed.

When to Plant Your Edmonton Garden

Stop Waiting Until May Frost Day to Plant Your Garden

Are you wondering when to plant your garden? Historically, you would plant your Edmonton Garden the third weekend in May, but is that the best time to plant? I’d argue that you can plant your garden much early.

Waiting Until After the Last Frost Date

In cooler climates, it’s long been a tradition to plant our vegetable gardens after the threat of frost has passed. In Alberta, we’ve historically outwaited the frost by the long weekend in May (Victoria Day). The thinking is that small tender plants can be killed by a hard frost, so waiting until after the last threat of frost will protect us from an early-season catastrophe. Make sense, right? Not necessary.

When to plant your Edmonton Garden, Raised vegetable garden bed.
When should you plant your Edmonton garden?

Edmoton’s Climate is Shifting

Even if necessary to wait until the last frost date, the average last frost date has been shifting over the last hundred years. A century ago, Edmonton’s last frost date was May 27th, which is probably where we get the third week in May habit. But according to Edmonton Weather Nerdery, Edmonton’s last frost date is now around May 7th. Our last frost day comes twenty days sooner, but we’re still planting at the end of the month.

Furthermore, these average dates are determined by weather stations at nearby airports, often standing in unprotected open areas much colder than locations sheltered by trees and buildings. It’s very likely that your garden is in a protected microclimate and has a much earlier last frost date.

What’s Your Garden’s Last Frost Date?

A microclimate is the average weather conditions of a small, localized space; our cities, yards, and gardens are full of them. Your garden will likely have multiple microclimates. Gardeners instinctively exploit temperature differences when planting heat-loving tomatoes and peppers against a south-facing wall.

The best way to take advantage of your microclimates is to observe them. Purchase a max-min thermometer and take readings in the shoulder seasons to determine your first and last frost dates. You might be surprised to learn that your average last frost date is widely different from that of your city or town. I’ve recorded my yard’s first and last frost dates since 2017.

My Backyard Last Frost Dates Between 2017 and 2023
  • Last Frost 2017 – April 28
  • Last Frost 2018 – April 30
  • Last Frost 2020 – April 15
  • Last Frost 2021 – May 2
  • Last Frost 2022 – April 24
  • Last Front 2023 – April 11

In the last six years, my backyard has averaged a last frost date of April 24th, which looks to be earlier every year. So why am I waiting until the third week in May to plant my Edmonton garden? Based on my observations, planting my garden by the third week in April should be safe – but your yard may be different.

Soil Protects Germinating Seeds From Frost

Remember that most seeds are planted within the soil and are protected until they sprout. Even after sprouting, the temperature near the soil will be a few degrees warmer than the surrounding air. Considering that most seeds take a week or two to sprout, you can safely plant your garden a week or two before your last frost date.

Seeds aren’t passive participants, either. Seeds generally know when to germinate. As long as the soil isn’t too wet, they can lay dormant during cold periods and germinate when the soil warms up. A good rule of thumb is that if you see weeds germinating in your yard, it’s warm enough to plant your garden. In fact, sprouting weeds might be a better indicator than the last frost date.

Most Seedlings Can Handle Some Frost

If a plant evolved in a cool climate, its seedlings can handle some frost. In nature, seeds fall from their parent plants in the fall, lay dormant throughout the winter, and germinate when conditions are right in the spring. Take advantage of evolution and plant your garden when the ground thaws enough to work. If you can work the soil, you can plant your garden.

While there’s always a risk of late hard frost, seeds don’t germinate until the soil is sufficiently warm and can handle mild frost. So get a jump on the growing season and plant your seeds early! If you’re still nervous, buy a roll of inexpensive floating reemay cloth from your local garden centre and drape it over your row and young plants. Reemay fabric lets light and water through while retaining warmth near the soil. This trick alone could push your planting time back a few weeks.

In an extreme example, try sowing your seeds in the fall when daytime temperatures are cold enough to prevent germination, but the ground is still workable. The seeds will lay dormant until conditions are right in the spring.

Exceptions – What Shouldn’t I Plant Early?

Exceptions include anything that evolved in warmer climates that don’t have winter. Examples include beans (Central/South America), corn (Central America), squash (Central America), tomatoes (Central America), and melons (Africa/SE Asia).

Tomatoes, peppers, and squash are subtropical plants that don’t do well with frost. The one time I would wait to plant until after the fear of frost is when transplanting these subtropicals directly into the garden,

When to Plant Your Garden

The Old Rule: Plant your Edmonton Garden the third weekend in May

The Old Rule Revised: Plant your Edmonton Garden two weeks before your garden’s last frost date. (Mid to Late April).

The New Rule: Plant your Edmonton Garden two weeks before the weeds germinate or when the ground is workable.

Advanced Rule: Prepare and plant your garden in the fall

This advice could help you get your plants into the group a month earlier. May lang long weekend, when everyone else is sowing their gardens, you’ll have little plants well on their way.