Planting Calendar for Longmont, CO

For the Almanac's fall and spring planting calendars, we've calculated the best time to start seeds indoors, when to transplant young plants outside, and when to direct seed into the ground.

Planting Dates for Fall

On average, your first fall frost occurs on September 23 (at LONGMONT 2 ESE, CO climate station).
Crop Based on Frost Dates
Start Seeds Indoors by...Plant Seedlings Outdoors by...Start Seeds Outdoors by...
ArugulaN/AN/A Aug 19
BeetsN/AN/A Aug 9
Bell Peppers Apr 10 June 6N/A
Broccoli Jun 12 Jul 10N/A
Cabbage Jun 2 Jun 30N/A
CantaloupesN/AN/A June 13
CarrotsN/AN/A Aug 4
Cauliflower Jun 12 Jul 10N/A
Celery Apr 1 Jun 10N/A
CornN/AN/A Jun 15
CucumbersN/AN/A Jun 20
Eggplants Apr 10 June 13N/A
Green BeansN/AN/A Jun 20
Kale Jul 2 Jul 30N/A
KohlrabiN/AN/A Aug 4
LettuceN/AN/A Aug 14
OkraN/AN/A Jun 15
ParsnipsN/AN/A Jun 20
PeasN/AN/A Jul 20
PotatoesN/AN/A Jul 10
PumpkinsN/AN/A June 13
RadishesN/AN/A Aug 19
SpinachN/AN/A Aug 29
Swiss ChardN/AN/A Aug 14
Tomatoes Apr 15 June 13N/A
TurnipsN/AN/A Aug 14
WatermelonsN/AN/A June 13
ZucchiniN/AN/A Jun 25

Planting Dates for Spring

On average, your last spring frost occurs on May 16 (at LONGMONT 2 ESE, CO climate station).
Crop Based on Frost Dates   Based on Moon Dates
Start Seeds IndoorsPlant Seedlings
or Transplants
Start Seeds Outdoors
ArugulaN/AN/A May 2-16
May 11-16
Basil Mar 21-Apr 4
Mar 21-28
May 16-Jun 6
May 16-26
N/A
BeetsN/AN/A May 2-23
May 2-10
Bell Peppers Mar 6-21
Mar 13-21
May 23-Jun 6
May 23-26
N/A
Broccoli Mar 21-Apr 4
Mar 21-28
Apr 18-May 9
Apr 18-26
N/A
Cabbage Mar 21-Apr 4
Mar 21-28
Apr 18-May 2
Apr 18-26
N/A
Cantaloupes Apr 18-25
Apr 18-25
May 30-Jun 13
Jun 10-13
N/A
CarrotsN/AN/A Apr 11-25
Cauliflower Mar 21-Apr 4
Mar 21-28
Apr 18-May 9
Apr 18-26
N/A
Celery Mar 6-21
Mar 13-21
May 23-Jun 6
May 23-26
N/A
ChivesN/AN/A Apr 18-25
Apr 18-25
Cilantro (Coriander)N/AN/A May 16-30
May 16-26
CornN/AN/A May 16-30
May 16-26
Cucumbers Apr 18-25
Apr 18-25
May 30-Jun 13
Jun 10-13
N/A
DillN/AN/A Apr 11-25
Apr 11-25
Eggplants Mar 6-21
Mar 13-21
May 30-Jun 13
Jun 10-13
N/A
Green BeansN/AN/A May 23-Jun 13
May 23-26, Jun 10-13
Kale Mar 21-Apr 4
Mar 21-28
Apr 18-May 9
Apr 18-26
N/A
Kohlrabi Apr 4-18
Apr 11-18
Apr 25-May 2
Apr 25-26
N/A
Lettuce Apr 4-18
Apr 11-18
May 2-30
May 11-26
N/A
OkraN/AN/A May 30-Jun 13
Jun 10-13
OnionsN/AN/A Apr 18-May 9
Apr 27-May 9
Oregano Mar 6-Apr 4
Mar 13-28
May 16-Jun 6
May 16-26
N/A
ParsleyN/AN/A Apr 18-May 2
Apr 18-26
ParsnipsN/AN/A Apr 25-May 16
Apr 27-May 10
PeasN/AN/A Apr 4-25
Apr 11-25
PotatoesN/AN/A May 9-30
May 9-10, May 27-30
Pumpkins Apr 25-May 9
Apr 25-26
May 30-Jun 13
Jun 10-13
N/A
RadishesN/AN/A Mar 21-Apr 11
Mar 29-Apr 10
Rosemary Mar 6-21
Mar 13-21
May 23-Jun 13
May 23-26, Jun 10-13
N/A
Sage Mar 21-Apr 4
Mar 21-28
May 16-30
May 16-26
N/A
SpinachN/AN/A Apr 4-25
Apr 11-25
Sweet Potatoes Apr 18-25
May 30-Jun 13
May 30-Jun 9
N/A
Swiss Chard Apr 4-18
Apr 11-18
Apr 25-May 2
Apr 25-26
N/A
Thyme Mar 6-Apr 4
Mar 13-28
May 16-Jun 6
May 16-26
N/A
Tomatoes Mar 21-Apr 4
Mar 21-28
May 23-Jun 13
May 23-26, Jun 10-13
N/A
TurnipsN/AN/A Apr 18-May 9
Apr 27-May 9
Watermelons Apr 18-25
Apr 18-25
May 30-Jun 13
Jun 10-13
N/A
Zucchini Apr 18-May 2
Apr 18-26
May 30-Jun 13
Jun 10-13
N/A

How to Use the Planting Calendar

This planting calendar is a guide that tells you the best time to start planting your garden based on frost dates. Our planting calendar is customized to your nearest weather station in order to give you the most accurate information possible. Please note:

  • The "Frost Dates" indicate the best planting dates based on your local average frost dates. Average frost dates are based on historical weather data and are the planting guideline used by most gardeners. Although frost dates are a good way to know approximately when to start gardening, always check a local forecast before planting outdoors!
  • The "Plant Seedlings or Transplants" dates indicate the best time to plant young plants outdoors. This includes plants grown from seed indoors at home and small starter plants bought from a nursery.
  • When no dates ("N/A") appear in the chart, that starting method is typically not recommended for that particular plant, although it likely still possible. See each plant's individual Growing Guide for more specific planting information. 
  • The "Moon Dates" indicate the best planting dates based on your local frost dates and Moon phases. Planting by the Moon is considered a more traditional technique. We use Moon-favorable dates at the very start of the gardening season. It's a little complex for a fall planting.

To plan your garden more accurately in the future, keep a record of your garden's conditions each year, including frost dates and seed-starting dates!

Frequently Asked Questions

Why Do You Start Seeds Indoors?

Starting seeds indoors (in seed trays or starter pots) gives your crops a head start on the growing season, which is especially important in regions with a short growing season. Starting seeds indoors also provides young, tender plants a chance to grow in a stable, controlled environment. Outdoors, the unpredictability of rain, drought, frost, low and high temperatures, sunlight, and pests and diseases can take a toll on young plants, especially when they're just getting started. Indoors, you can control these elements to maximize your plants' early growth and give them the best shot at thriving when they are eventually transplanted outdoors. 

For most crops that can be started indoors, seeds should be started about 6-8 weeks before your last spring frost date. This gives the plants plenty of time to grow large and healthy enough to survive their eventual transplanting to the garden. Read more about starting seeds indoors here

Which Seeds Should Be Started Indoors?

Not all vegetables should be started indoors! In fact, most are better off being started directly in the garden (aka "direct-sown"). The crops that should be started indoors are those that are particularly susceptible to cold temperatures or that have a very long growing season and need a head start. These include tender vegetables such as tomatoes, peppers, and eggplant, as well as crops with a long growing season, like broccoli, cauliflower, and brussels sprouts. 

Most other crops do best when sown directly into the garden soil. Root crops, including carrots, radishes, and beets, are especially well-suited to being started directly in the garden, since they do not like having their roots disturbed after planting. The same is true for squash and watermelon, though care must be taken to plant them when the soil is warm enough. Read more about direct-sowing seeds here!

How Is Planting for a Fall Harvest Different? 

Planting in late summer for a fall harvest has many benefits (soil is already warm, temperatures are cooler, fewer pests). However, the challenge is getting your crops harvested before the winter frosts begin. When we calculate fall planting dates (which are really in the summer), we must account for several factors, such as the time to harvest once the crop is mature and whether a crop is tender or hardy when it comes to frost. The "days to maturity" of a crop and the length of your growing season also factor into whether you start seeds early indoors or directly sow seeds into the ground outside. Note:

  • Warm-weather veggies like beans, corn, squashes, pumpkins, cucumbers, cantaloupe, and watermelons are all sown directly into the ground.
  • Tender heat-loving plants such as tomatoes, peppers, and eggplants take a long time to mature and have a lengthy harvesting period, so we generally don't plant a second round of these crops for fall, as they won't ripen in time. (In regions with mild winters, this may not be the case.) These crops are typically started indoors early in the season and transplanted.
  • Root vegetables (beets, carrots) do not transplant well, so start seeds directly in the soil outside.
  • Peas are also best seeded into the ground; do not transplant.
  • Cole crops like broccoli, cauliflower, kale, and cabbage could be direct seeded, but because of the heat of mid- and late summer, it's better to start them indoors and then transplant them into the garden.
  • We tend to direct-sow leafy greens such as lettuce, chard, and spinach, though some gardeners will also sow indoors. It depends on your climate.
  • Note that garlic is not included in our planting chart. It's a popular fall crop, but the dates vary wildly based on location and it's really best to gauge garlic planting dates with a soil thermometer. When the soil temperature is 60°F (15.6°C) at a depth of 4 inches, then plant your garlic. We'd advise checking our Garlic Growing Guide for more information. 

Read more about the "Best Vegetables to Plant in the Fall."

When Should You Transplant Seedlings?

When seedlings have grown too large for their seed trays or starter pots, it's time to transplant. If it's not yet warm enough to plant outdoors, transplant the seedlings to larger plastic or peat pots indoors and continue care. If outdoor conditions allow, start hardening off your seedlings approximately one week before your last frost date, then transplant them into the garden. Get more tips for transplanting seedlings.

What Is Planting by the Moon?

Planting by the Moon (also called "Gardening by the Moon") is a traditional way to plant your above- and below-ground crops, especially at the start of the season. Here's how it works:

  • Plant annual flowers and vegetables that bear crops above ground during the light, or waxing, of the Moon. In other words, plant from the day the Moon is new until the day it is full.
  • Plant flowering bulbs, biennial and perennial flowers, and vegetables that bear crops below ground during the dark, or waning, of the Moon. In other words, plant from the day after the Moon is full until the day before it is new again.

Old-time farmers swear that this practice results in a larger, tastier harvest, so we've included planting by the Moon dates in our planting calendar, too. Learn more about Planting and Gardening by the Moon.