There are a few rule-of-thumb planting dates among the gardening community that we enjoy repeating every year. One is to sow your peas on President’s Day. Another is to plant potatoes on St. Patrick’s Day. These are general rules though which will not apply to you if you happen to live in sunny southern California or frigid Canada. To properly time your planting, it really depends on your hardiness zone and first/last frost dates.
What is a first and last frost date, you ask? The first frost date signifies the end of winter, in a sense. Typically the ground will not freeze past this average date. The last frost date signifies the beginning of winter. The weather at this date will become too cold for most vegetables and will likely kill of those last tomatoes.
Knowing these dates will help you understand when different vegetables want to be planted. Some like to be in the ground when it’s still really cold. Others will need to be sown or transplanted after all danger of frost has passed. Find the average first/last frost dates for your location at the Old Farmer’s Almanac.
What does a hardiness zone mean? A hardiness zone tells you what plants will thrive and what plants will struggle in your location, based on climate factors. Zones reflect how severe the temperature changes are, how cold winter is or how hot summer will be. There are a couple sources for zone information: the USDA and Sunset. Sunset can sometimes be more accurate, as they often take into account microclimates in the area. Talking to your local nursery is another option to find out from locals what zone you fit into.
Let’s take Portland for an example. We have a pretty long growing season because our last average frost date is April 3rd and first is November 7th. That gives us roughly seven months to grow things outside of freezing temperatures. Our zone though is six, which means it doesn’t get really hot here. Growing things that need hot heat will most likely not do well here.
When it comes to planting vegetables, consider both your frost dates and zones. If Portland doesn’t get super hot, you might want to help heat-loving plants like tomatoes, peppers and melons. Consider growing them in black containers that will absorb heat. Pick fast-ripening varieties that require fewer hot days to mature. Another option is to cover your crops with plastic to raise the temperature level for your plants. You can do this to start vegetables outside sooner than they would otherwise prefer, or do this in the summer to get heat-loving vegetables extra warm.
I love referring locals in the Pacific Northwest to the vegetables calendar produced by Portland Nursery. They will tell you the best method to grow vegetables – either seeding indoor or direct sowing – and they tell you in what month to plant them. Easy-peasy.
If you live outside the NW, check out this great Excel spreadsheet from You Grow Girl. You enter in your first and last frost dates and the Excel form calculates when exactly you need to start seeding. Happy planting!