When to Plant Tomatoes in Colorado? (Best Time)

Written by

William Golder


Dorian Goodwin

when to plant tomatoes in colorado

Colorado tomatoes are available year-round, but growing them yourself can be very rewarding. With a bumper crop of this nightshade plant from your home garden, it’s easy and convenient to make stews, sauces, and other dishes without visiting the supermarket.

If you’re wondering when to plant tomatoes in Colorado, growing them outdoors in late April is possible for some areas in the state, but mid-May and mid-June are the more common time for planting. Generally, people in CO will grow their crops from May 20 onwards.

Best Time to Plant Tomatoes in Colorado


Before growing tomatoes in Colorado, decide if you want to plant them early or not.

  • If you want to extend your growing season and enjoy an earlier harvest, start tomatoes six to eight weeks before the last frost.

This practice applies to both seeds and transplants. If you choose seeds, sow them indoors in pots in Colorado and move them outside after the freezing cold is gone.

As for transplants, you can put them directly in the garden, provided a product like Wall O’ Water is used. In this case, surround your tomato with water walls; the liquid inside them will warm the plant and protect it from temperatures down to 20 degrees Fahrenheit.

Moreover, use black plastic mulch to insulate the tomato further and avoid wetting the soil too much when you’re not watering. This way, the ground will be warmer and more conducive to plant growth.

  • At the end of the day, if you are fine with a shorter tomato season, simply grow seeds or transplants outside after the final frost. Make sure temperatures measure 55℉ or higher, though night temperatures may occasionally drop to 45 degrees at the lowest without harming plants.
  • Just as importantly, allow your crop to mature and harvest it before the first frost so that it won’t be killed Add your variety’s maturation period to your planting date. If the result is after the first frost where you live, it is too late to plant tomatoes.

On the whole, tomatoes typically grow in 60 to 100 days, but it’s better to look up your variety for accuracy.

For instance, the Celebrity cultivar may mature in 70 days, while the Cherokee Purple often needs 80 days. Both varieties are among the best tomatoes to grow in Colorado alongside Totem, Taxi, Big Beef, Lucid Gem, Sun Gold, San Marzano, and other cultivars.

To help you determine when to plant tomato seeds and transplants, here are the frost dates for some regions in Colorado.

Location Average Last Frost Average First Frost
Denver May 4 October 6
Colorado Springs May 8 October 3
Fort Collins May 7 October 2
Longmont May 13 October 1
Westminster May 7 October 4
Greeley May 7 October 3
Parker May 14 September 28

Tips for Planting Tomatoes in Colorado

A few months before you grow tomatoes in Colorado, test the soil and ensure it is well-drained, low in salinity, and with a pH of 6.0 to 6.8. Till the soil down to a depth of 10 inches, and pick a garden plot that did not house any other nightshade plant the previous three years.

In case a soil test is not possible, thoroughly mix 5 pounds of lime for every 100 square feet of your planting ground.

Remember to put tomatoes in a new spot every year as well.

If you use containers, clean them with a 10% bleach solution first. You should also choose virus-resistant varieties to boost your chances of success while planting.

  • Next, to plant tomatoes outside, sow the seeds at a depth of ½ inch. This seeding depth will also work for indoor containers.


If you have transplants, remove the peat pots first before setting the tomatoes into the soil. The plants should be 18 to 36 inches apart and hardened off for one to two weeks prior to being put in the ground. Simply place them under shade a few hours every day before transplanting them outside.


  • As for the trenches for your tomatoes, they should be two to three inches deep, enough to cover the root ball but not the foliage.


If you have a very tall plant, planting tomatoes deeply is recommended—just position it horizontally into the soil with the bottom leaves removed, leaving only the top two or three leaves above-ground.

  • This technique still applies if you’re growing tomatoes in pots. Remove the bottom foliage as necessary, then put the tomato in a 16-inch container by making a trough. Use potting soil instead of garden soil to minimize disease and insects.


  • Lastly, for both container and in-ground tomatoes, cage them right after planting. Use 2×4-feet cages, though you can reduce the height to 3 feet if the tomato is a determinate type.

Frequently Asked Questions

Do tomatoes grow well in Colorado?

Planting tomatoes in Colorado is slightly challenging, since the state only has around 30 to 150 days for crops to grow. This is why it makes sense to choose quick-growing tomatoes so that winter frost doesn’t harm your plant before you can harvest it.

So, start seeds indoors if you can, and opt for varieties like Early Girl and Fourth of July, which mature very quickly.

How often do you water tomatoes in Colorado?

Daily watering is not ideal, as it may cause calcium deficiency and blossom-end rot. Give tomatoes one to two inches of water per week in one or two waterings every seven days.

Be consistent with your irrigation, and complete it in the morning or early evening so that the soil has time to dry and is less susceptible to fungi.

Of course, remember to water the tomato after you seed or transplant it.

Do tomatoes grow better in pots or in the ground?

You can plant them in the ground or in pots. Either will do. That said, indeterminate tomatoes will grow better in the ground, since they are bigger. These can reach up to 20 feet tall while determinate varieties max out at four feet.

If you choose to keep tomatoes in pots, ensure the container is 24 inches wide for indeterminate varieties and 18 inches wide for determinate types.

It’s also wise to look up the mature height of your variety while determining the best month to plant tomatoes. This way, you’ll get two things done at once and avoid ending up with a transplant that’s too big for your home.


Knowing when to plant tomatoes in Colorado will help you enjoy a fruitful harvest from July to October right inside your home.

Remember: it’s best to grow tomatoes in spring before the last frost if you can garden indoors. This schedule will lengthen your gardening season and allow your crops to mature before winter arrives.

Here are some schedules for planting tomatoes in other states you can refer to:

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