When Do I Plant Annual Flowers in Minnesota?

Minnesota is a very mercurial weather state, which makes it difficult to know when to plant annuals. It is incredibly hard to predict when the weather will turn warm for good. Just look at the current spring versus spring last year. Last spring’s warm weather did not really start until June because we had our last snowstorm in early May. This year was a much more drawn-out spring where the last snowfall was in early April. However, the temperatures have fluctuated all over the place.

The last frost date is crucial when planting annual flowers and plants. These “one season” plants are not as hardy as perennials or shrubs so they are affected much more by cold temperatures. They are also not buried as deeply in the ground and do not have the same established root systems that perennials and shrubs have. When the weather turns cold, the water in and around the plants can freeze and harm growth or even kill it. For this reason, it’s really important to know when the last frost date occurs.

The average last frost date for the Twin Cities is May 21. It gets up to June 15 in the northern regions of Minnesota. Keep in mind that that’s an average, so it can fluctuate between earlier and later. However, if at all possible, we try to plant our annuals in pots or displays after this date.

This year is a perfect example of why you should be patient and not overzealous with your annual plantings. Just this week (writing this on May 20, 2015), the temperature will get down to 35° F in the Twin Cities and even colder in other parts of Minnesota. That spells doom for many annuals. Patience is a virtue, especially when it comes to annual planting.

Another type of annual is the half-hardy annual . These annuals can tolerate weather into the 30s F. There are a ton of plants that fit into this category, including marigolds, dusty miller, ageratum, petunias, cleome, and nicotiana. The most spectacular (and popular) annuals are the tropical or exotic annuals like begonias and impatiens. Unfortunately, these are also the most tender type of annuals. You would not want these plants to hit any weather below 40°F. Make sure to wait until June to plant these, if at all possible.