When to Plant in Longmont, CO

In Longmont, gardeners can expect a median last spring frost date of May 5 and a first fall frost on September 28, resulting in approximately 146 frost-free days each year. This time frame is crucial for planning your planting schedule and selecting the right crops to ensure a successful growing season.

The microclimate in Longmont is characterized as continental mountain, which means gardeners often experience cold nights and intense daytime sun. This environment is ideal for crops like tomatoes, peppers, and squash, which thrive in warmer temperatures and appreciate the long growing season. However, crops such as lettuce and peas may struggle due to the extreme temperature fluctuations and intense heat during the day, which can cause bolting or wilting.

What to plant now in Longmont

Spring is the perfect time to plant hardy vegetables like peas and spinach. Begin sowing seeds outdoors from mid-March to early April, bearing in mind that the last frost date is May 5.
As we transition into summer, plant warm-season crops such as tomatoes and peppers after the last frost date of May 5. Transplant them outdoors from late May through early June for optimal growth.
In late summer, consider planting a fall crop of quick-maturing vegetables, such as radishes and turnips, ideally during the first two weeks of August to ensure a yield before the first frost on September 28.
As fall approaches, perform soil preparation and plant cover crops or bulbs. Late September is an excellent time for sowing winter rye or garlic, taking advantage of the frost-free days remaining before the first fall frost.

In Longmont (146 frost-free days, a moderate season), 37 of 56 planner crops fit outright, 18 get two plantings, 1 crop is perennial.

Month by month in Longmont

Month	What to do
January	In January, focus on planning your garden layout and ordering seeds. It’s a good time to research specific crops that thrive in Longmont’s continental mountain climate, considering the upcoming frost dates.
February	February is ideal for starting seeds indoors for early spring planting. Consider crops like tomatoes and peppers, which need a longer growing season before the last frost on May 5.
March	As March arrives, prepare your garden beds. You can start direct sowing hardy crops like lettuce, radishes, and peas by mid-March, as the last frost date of May 5 approaches.
April	In April, actively plant cool-weather crops such as kale and spinach. Keep an eye on the weather as May 5—the last frost—approaches, and be prepared to protect young plants.
May	May is crucial as it includes the last frost date on May 5. In the first week, ensure all frost-sensitive plants are saved. Transplant warm-season crops like tomatoes and peppers after this date.
June	In June, with frosts behind you, focus on maintenance. Water regularly and provide support for crops like tomatoes. Harvest early crops and keep pests under control as the sun's intensity increases.
July	July brings heat, and gardens flourish. Continue caring for warm-weather crops, and begin planting crops for fall, such as late-season carrots. Monitor for signs of stress due to the high daytime temperatures.
August	August is the time to plant quick maturing crops for fall. Sow radishes, turnips, and other short-season crops, ideally within the first two weeks as the first frost on September 28 approaches.
September	September is pivotal as it includes the first fall frost date on September 28. Harvest remaining summer crops and plant cover crops such as winter rye to prepare your soil for the coming winter.
October	As October arrives, your focus should shift to preparing for winter. Clean up your garden beds, mulch perennials, and continue maintaining any late fall crops that are still growing.
November	In November, most planting concludes. Focus on protecting plants against frost, and consider planting garlic if conditions allow. This month is about wrapping up your gardening tasks.
December	December is a time for reflection and planning for the next year. Research new varieties, read gardening books, and get ready for the upcoming seasons while enjoying the winter.

Frost dates for Longmont ZIP codes

ZIP	Last spring frost (50%)	First fall frost (50%)	Zone
80504	May 5	September 28	5b
80501	May 5	September 28	5b
80503	May 5	September 28	6a

FAQ

When is the last frost in Longmont?

The last frost in Longmont typically occurs on May 5. This date is critical for gardeners to plan their planting schedules.

What vegetables grow best in Longmont?

Vegetables that thrive in Longmont include tomatoes, peppers, and squash, thanks to the region's sunny days and long growing season.

When should I plant tomatoes in Longmont?

Tomatoes should be transplanted outdoors after the last frost date of May 5 for optimal growth and yield.

Can I garden year-round in Longmont?

While Longmont has cold winters, you can garden year-round by utilizing greenhouses or cold frames to extend the season.

How does Plan My Garden help Longmont gardeners?

Plan My Garden offers tailored advice, planting calendars, and tips specifically designed for the climate challenges and advantages present in Longmont.