LawnWeather

Boulder, CO Planting Calendar

The last spring frost in Boulder usually comes around Apr 25 and the first fall frost around Oct 17, a growing season of about 175 days. Start tomatoes indoors Mar 14 – Mar 28 and plant them outside May 9 – May 23.

Last spring frostApr 25
First fall frostOct 17
Growing season175 days

When to plant vegetables in Boulder

VegetableStart seeds indoorsPlant outsideFall crop
TomatoesMar 14 – Mar 28May 9 – May 23—
PeppersMar 7 – Mar 21May 16 – May 30—
EggplantMar 7 – Mar 21May 16 – May 30—
Cucumbers—May 9 – May 23—
Zucchini & summer squash—May 9 – May 23—
Pumpkins & winter squash—May 16 – May 30—
Green beans—May 9 – May 23Jul 25 – Aug 8
Sweet corn—May 9 – May 23—
BasilMar 28 – Apr 11May 9 – May 23—
LettuceFeb 28 – Mar 14Mar 28 – May 9Aug 22 – Sep 5
Spinach—Mar 14 – Apr 4Aug 22 – Sep 5
Peas—Mar 14 – Apr 4Aug 8 – Aug 22
Carrots—Mar 28 – May 2Jul 25 – Aug 8
Radishes—Mar 21 – May 9Sep 5 – Sep 19
BroccoliFeb 14 – Feb 28Mar 28 – Apr 11Jul 25 – Aug 8
KaleFeb 28 – Mar 14Mar 21 – Apr 4Aug 8 – Aug 22
Onions—Mar 28 – Apr 11—
Potatoes—Apr 4 – May 2—
Garlic——Oct 3 – Nov 7

Dates count from the median frost dates (2016–2025) for Boulder. In a cold spring, wait a week; in a warm one you can go a week early.

Month-by-month planting in Boulder

  1. JanuaryPlan, order seeds and prepare beds.
  2. FebruaryStart indoors: Lettuce, Broccoli, Kale
  3. MarchStart indoors: Tomatoes, Peppers, Eggplant, Basil, Lettuce, KalePlant outside: Lettuce, Spinach, Peas, Carrots, Radishes, Broccoli, Kale, Onions
  4. AprilStart indoors: BasilPlant outside: Lettuce, Spinach, Peas, Carrots, Radishes, Broccoli, Kale, Onions, Potatoes
  5. MayPlant outside: Tomatoes, Peppers, Eggplant, Cucumbers, Zucchini & summer squash, Pumpkins & winter squash, Green beans, Sweet corn, Basil, Lettuce, Carrots, Radishes, Potatoes
  6. JunePlan, order seeds and prepare beds.
  7. JulyPlant outside: Green beans, Carrots, Broccoli
  8. AugustPlant outside: Green beans, Lettuce, Spinach, Peas, Carrots, Broccoli, Kale
  9. SeptemberPlant outside: Lettuce, Spinach, Radishes
  10. OctoberPlant outside: Garlic
  11. NovemberPlant outside: Garlic
  12. DecemberPlan, order seeds and prepare beds.

Tools for this season

Seed starting kitTrays with humidity domes for starting seeds indoors.See options on AmazonLED grow lightKeeps indoor seedlings short and sturdy.See options on AmazonFrost clothCovers tender plants on a surprise frost night.See options on AmazonSoil thermometerCheck the soil at 4 inches before you spread anything.See options on Amazon

We may earn a commission when you buy through these links, at no extra cost to you. How this works

Frequently asked questions

When is the last frost in Boulder?

The median last spring frost is Apr 25 and the median first fall frost is Oct 17, based on 2016–2025 weather data.

When should I plant tomatoes in Boulder?

Start seeds indoors Mar 14 – Mar 28 and set plants outside May 9 – May 23, once nights stay above 50°F.

When should I plant a fall garden in Boulder?

Sow or transplant cool-season crops 6 to 12 weeks before the first fall frost (around Oct 17): broccoli and carrots first, lettuce, spinach and radishes last.

More from Boulder