When talking about safe planting days for vegetables we need to consider the type of crops that can be grown not just based on the ambient temperature but also the soil temperature.
Things to consider
As the spring days become warmer so does the soil. Some cold weather crop varieties, like peas and radishes, have now been bred to germinate in colder soils and be can easily withstand frost. Thus, reading the seed package is your best chance of success.
Most cold weather crops require a minimum of 40F soil temperature to thrive, preferably higher, which you can achieve by covering your garden bed, pots, or garden area to allow heat to build and warm the soil.
Cold weather crops can be planted as early as mid-march, keeping an eye on drastic temperature drops and covering them when it dips below 26F. These crops include brassicas (cauliflower, broccoli, kale, etc.) radish seeds, lettuce seeds or seedlings. Onions can be sown as early as February!
For warm weather crops we must way until the danger of frost has passed. On average we will see our last frost somewhere between May 15th and May 25th. However, in Colorado it can snow in June or September, so keep an eye on the weather forecast.
Most warm weather crops, like tomatoes, peppers, eggplants, squashes, etc., prefer a soil temperature above 55F, and night time temperatures above 50F. They’ll perform best and get stronger when the temperatures are favorable rather than struggle to settle and become defenseless to pests and disease.
The table below lists the approximate dates for safe planting of vegetable seeds and pre-started vegetable plants.
|Vegetable||Approximate Safe Date|
|Artichokes||May 15 to May 25|
|Asparagus from Seed
Asparagus from Crowns
|May 15 to May 25
April 1 to April 30
|Beans – Bush & Pole||May 15 to May 25|
|Beans – Lima & Butter||May 15 to May 25|
|Beets||May 4 to May 18|
|Broccoli||April 20 to May 5|
|Brussels Sprouts||April 20 to May 5|
|Cabbage from pre-starts||April 20 to May 5|
|Cantaloupe||May 15 to May 25|
|Carrots||May 4 to May 18|
|Cauliflower||April 20 to May 5|
|Celery from pre-starts||May 4 to May 18|
|Collard Greens||April 20 to May 5|
|Corn||May 15 to May 25|
|Cucumbers||May 15 to May 25|
|Eggplant||May 15 to May 25|
|Kohlrabi||April 20 to May 5|
|Leek||April 20 to May 5|
|Lettuce||April 20 to May 5|
|Mustard Greens||April 20 to May 5|
|Okra||May 15 to May 25|
|Onions for sets||April 1 to April 30|
|Peas||April 20 to May 5|
|Peppers||May 15 to May 25|
Potatoes – Sweet
|April 1 to April 30
May 15 to May 25
|Pumpkins||May 15 to May 25|
|Radishes||May 4 to May 18|
|Rhubarb||April 1 to April 30|
|Rutabaga||April 20 to May 5|
|Shallots||Plant in fall or April 20 to May 5|
|Spinach||April 20 to May 5|
|Strawberries from crowns||April 1 to April 30|
|Squash||May 15 to May 25|
|Tomatoes||May 15 to May 25|
|Turnips||April 20 to May 5|
|Watermelons||May 15 to May 25|