Colorado Growing Zones Explained

Colorado Growing Zones Explained

The state of Colorado has a perfect climate offering endless opportunities to enjoy outdoor activities and recreation all year long. However, if you are new to the area and want to start gardening, it can be challenging to understand why some plants grow and thrive in Colorado while others fail. 

Colorado’s unique geography means that there are different microclimates throughout the state. So it should come as no surprise that there are several USDA planting or hardiness zones throughout the state. They range from the coldest 3a (-40 to-35°F) to the warmest 7a (0 to 5°F)

This guide will provide valuable information about the climate and plants that thrive in each zone. Plus, some gardening tips on getting the best out of your favorite plants and trees.

Planting Zones in Colorado

The state of Colorado has a vast area under cultivation with over 31,800,000 acres in operation by 2020. There are several growing zones in Colorado, which means that different plants do well according to the climatic conditions of each area. Knowing what to plant will save you time and money when planning your garden. Here is a guide to each of the growing zones in Colorado.

USDA plant growing zones in Colorado Minimum temperature(°Fahrenheit)
3a -40 to -35°F
3b -35 to -30°F
4a -30 to -25°F
4b -25 to -20°F
5a -20 to -15°F
5b -15 to -10°F
6a -10 to -5°F
6b   -5 to 0°F
7a   0 to 5°F

 

Colorado’s Growing Zone 3

Zone 3 is the coldest among the USDA garden zones in the US. This zone has a shorter growing window for gardening than most zones. The last frost date is May 15, and the first frost date is September 15. Zone 3 has a minimum annual temperature of -30ºF. 

Plants That Thrive in Colorado’s Growing Zone 3

Gardening in zone 3 can be a challenge due to its short growing season. However, that should not discourage you. There are different plant varieties that you can plant in this zone. Below are some vegetables, perennials, and annuals that will do well in your zone 3 gardens.

Vegetables to Grow in Colorado’s Zone 3 and When to Plant Them

Due to the short growing season in this zone, you need to plan well in advance on when to plant your vegetables. Seeds should be started in March or April and transplanted outdoors after the last frost date to get a head start on summer vegetables like tomatoes and eggplants. Here are some vegetables to grow in this zone

  • Cabbage
  • Brussel sprouts
  • Broccoli
  • Onions
  • Peas
  • Potatoes
  • Beets
  • Kohlrabi
  • Turnips
  • Carrots
  • Chinese greens
  • Radicchio
  • Collards 
  • Kales
  • Escarole
  • Basil
  • Parsley
  • Summer squash
  • Winter squash

Best Perennials to Grow in Colorado’s Zone 3 and When to Plant Them

Perennials are plants that bloom for a short time. They return every year, but they do not bloom all summer long. The best time to plant perennials in zone 3 is between August to September. Here is a list of perennials that you can grow in this zone.

  • Sedum
  • Lupins
  • Creeping flox
  • Foxglove
  • Creeping thyme
  • Heliopsis
  • Columbine
  • Hostas
  • Delphinium
  • Ligularia
  • Trollius
  • Balloon flowers
  • Campanula (bellflower)
  • Weigela
  • Jacob’s Ladder
  • Hollyhocks
  • Potentilla (flowering shrub)
  • Butterfly weed

Types of Annuals to Grow in Colorado’s Zone 3 and When to Plant Them

Zone 3 annual flowers only need to survive the area’s warm, temperate summer months instead of its freezing winter. For annuals that cannot survive this, it is best to consider cold, hardy annuals that will grow in zone 3. These plants have a relatively short growing season but are suited for zone 3. 

  • Sunflower
  • Flowering stock
  • Sweet alyssum
  • Pansy
  • Nemesia
  • Bachelor’s button
  • California poppy
  • Forget-me-not
  • Dianthus
  • Phlox
  • Petunia
  • African daisy
  • Godetia and Clarkia
  • Snapdragon

Some of the annuals that do well under a shade in zone 3 include

  • Coleus 
  • Impatiens 
  • Begonia
  • Browallia 
  • Torenia/wishbone flower 
  • Balsam 

Farmers’ Tips for Growing in Colorado’s Zone 3

  • Due to its short growing season, consider starting seeds indoors before transplanting them outside after the last frost.
  • Zinnias, dianthus, and cosmos are slow-blooming annuals, but planting them indoors early in zone 3 gives them a head start.
  • When selecting your seeds or plants for zone 3, go for the “very hardy” ones that can survive the harsh winters.

Colorado’s Growing Zone 4

Zone 4 is tough to garden, with a short growing season and a cold winter climate. It has colder weather than most of the US, with temperatures dipping below -30 °F and -20 °F most winters. The last frost date is around mid-May, with the first frost date coming around September.

Plants That Thrive in Colorado’s Zone 4

Zone 4’s cold and long winters make it difficult to grow hothouse vegetables. But growing cherries and berries in this zone is a good idea. Zone 4 is also suitable for perennials and bulbs because of the frost-free period from early June until early September.

Vegetables to Plant in Colorado’s Zone 4 and When to Plant Them

Zone 4 gardening can be challenging because the growing season is so short. The best way to maximize time in the garden is to start your plants indoors. You can be able to plant cold-weather vegetables as early as mid-April, such as:

  • English peas
  • Radishes
  • Spinach
  • Lettuce
  • Cabbage
  • Beets
  • Turnips
  • Kale
  • Swiss chard
  • Broccoli
  • Tomatoes
  • Turnips
  • Winter squash
  • Potatoes
  • Brussels sprouts
  • Asparagus
  • Carrots
  • Leeks
  • Collards
  • Parsnips

Best Perennials to Grow in Colorado’s Zone 4 and When to Grow Them

Perennials are reliable, durable plants that are versatile in many areas of your garden. The best time to plant perennials in zone 4 is a few weeks before the first frost. Here are a few perennials that you can grow in USDA zones 4.

  • Goat’s beard
  • Hostas 
  • Phlox 
  • Iris 
  • Coneflower 
  • Daylily
  • Gayfeather
  • Violets
  • Lamb’s ears
  • Hardy geraniums
  • Shasta daisies
  • Yarrow
  • Bleeding heart
  • Rockcress
  • Aster
  • Bellflower
  • Daylily 
  • Peonies 
  • Columbine

Types of Annuals to Grow in Colorado’s Zone 4 and When to Grow Them

Zone 4 has various last frost dates, so starting seeds in February or March is the best choice. The final frost date can be from April to mid-May, so many gardeners wait until Mother’s Day to plant annuals. Here are a few annuals that do well in this zone.

  • Calendula
  • Dianthus
  • English Daisy
  • Snapdragon
  • Marigold
  • Bachelor’s Button
  • Larkspur
  • Sunflower
  • Sweet Pea
  • Black-Eyed Susan
  • Stock
  • Sweet Alyssum
  • Sweet Pea
  • Viola
  • Wallflower
  • Forget Me Not
  • Clarkia
  • Pansy

Farmers Tips for Growing in Colorado’s Zone 4

  • Due to the cold in these areas, consider growing your plants in a greenhouse and using raised beds.
  • To extend your growing time, start seeds indoors and then transplant them later after the last frost.
  • Use mulches to protect your plants from the effects of frost.

Colorado’s Growing Zone 5

Zone 5 has two sections: 5a and 5b. When planting, it is essential to remember that the date might vary depending on the section. Overall, the whole of Zone 5 has a short growing season, with a frost-free period lasting from early June to early September.

Plants That Thrive in Colorado’s Zone 5

Zone five plants need to be able to survive temperatures between -20°F and -15°F. Most of them should be hardy and withstand a late frost or early spring. Below are the vegetables, perennials, and annuals that you can grow in your garden.

Vegetables to Plant in Colorado’s Zone 5 and When to Plant Them

As a zone five gardener, you can grow most vegetables but must plant later than in other zones. The final frost typically comes as late as April or early May, and the first frost as early as October. Here are some vegetables that do best in this zone.

  • Beets
  • Bush
  • Cabbage
  • Asparagus
  • Carrots
  • Celery
  • Cucumbers
  • Lettuce
  • Onions
  • Potatoes
  • Pepper
  • Peas
  • Pumpkins
  • Radishes
  • Rhubarb
  • Summer squash
  • Winter squash

Best Perennials to Grow in Colorado’s Zone 5 and When to Grow Them

Despite the brutal winter weather, there are many perennials you can plant in zone 5. September is the latest that you should grow them to prevent getting too close to the first frost. Here are a few perennials that can do well in this area.

  • Coreopsis
  • Delphinium
  • Dianthus
  • Coneflower
  • Joe Pye weed 
  • Aster
  • Baptisia
  • Bachelor’s Button
  • Filipendula 
  • Blanket flower 
  • Daylily 
  • Catmint 
  • Poppy 
  • Penstemon 
  • Russian Sage 
  • Garden Phlox 
  • Creeping Phlox 
  • Black-Eyed Susan 
  • Salvia
  • Hibiscus 
  • Lavender 
  • Shasta 
  • Daisy 
  • Blazing Star
  • Bee balm 

Annuals to Grow in Colorado’s Zone 5 and When to Grow Them

When growing annuals in zone 5, it is important to consider weather forecasts and frost warnings. The last frost in this zone is around April 15, so you might want to wait until early or mid-May to plant your annuals. Below is a list of annuals for zone 5 gardens.

  • Geraniums
  • Lantana
  • Petunia
  • Calibrachoa
  • Begonia
  • Alyssum
  • Bacopa
  • Cosmos
  • Marigold
  • Zinnia
  • Dusty Miller
  • Snapdragon
  • Gazania
  • Nicotiana
  • Flowering Kale
  • Mums
  • Moss Roses
  • Sunflower
  • Coleus
  • Gladiolus
  • Dahlia
  • Sweet Potato Vine
  • Cannas

Farmers Tips for Growing in Colorado’s Zone 5

  • When planting vegetables, herbs, or flowers, check the zone and days on the seed packets. The number of days represents how many days it takes to harvest or bloom. 
  • Some of the fruit tree varieties in Zone 5 include Harrow Delight pear, Warren plum, and Pink Lady apple.
  • Zone 5’s nut trees include walnuts, chestnuts, hazelnuts, and hickories.
  • To get a longer growing season, you should start your seeds indoors for at least six weeks before the end of the last frost.

Colorado’s Growing Zone 6

There is a medium-length growing season in zone 6. It gets cold in the winter with an annual minimum temperature of -5ºF. Within this zone, there are probably several microclimates. Take some time to decide which microclimates you have in your yard or garden.

Vegetables that do well in Colorado’s Zone 6 and When to Plant Them

From early March, you can sow cold weather crops like lettuce, radishes, and peas. Common garden varieties of vegetables that do well in this zone include:

  • Lettuce
  • Radishes
  • Peas
  • Zucchini
  • Cabbage
  • Tomatoes
  • Squash
  • Peppers
  • Potatoes
  • Cucumbers
  • Arugula
  • Asparagus
  • Beans
  • Corns
  • Pumpkins
  • Spinach

Best Perennials to Grow in Colorado’s Zone 6 and When to Grow Them

It is vital to research a zone 6 perennial plant’s specific needs. Some plants need much more sunlight, while others require a lot of shade. Shade-loving plants may suffer in too much sun or vice versa. You can start planting these perennials in September to avoid the summer heat.

  • Hosta
  • Daisy
  • Daylily
  • Coral bells 
  • Bee balm
  • Coneflower
  • Salvia
  • Hellebore
  • Hosta
  • Ice Plant
  • Lavender
  • Penstemon
  • Salvia
  • Phlox
  • Violet
  • Yarrow
  • Dianthus
  • Foxglove
  • Gaura
  • Goat’s Beard
  • Helleborus

Annuals to plant in Colorado’s Zone 6 and When to Plant Them

While preparing to plant your annuals in zone 6, note that the last frost happens on average from April 20th-May 20th. Meaning that Mother’s Day is usually a safe time to plant your plants outdoors. Below is a list of annuals for your zone 6 garden

  • Calibrachoa
  • Cleome
  • Cockscomb
  • Cosmos
  • Impatiens
  • Lantana
  • Lobelia
  • Marigold
  • Mexican Heather
  • Moss Rose
  • Angelonia
  • Bacopa
  • Begonia
  • Four O’Clocks
  • Nasturtium
  • Strawflower
  • Sunflower
  • Sweet Alyssum 
  • Pansy
  • Petunia
  • Snapdragons
  • Torenia

Farmers Tips for Growing in Colorado’s Zone 6

  • It can be helpful to use a cold frame or greenhouse to extend your growing season. 
  • When your garden is in zone six, the typical growing season is between March and November. You will likely plant cool-weather crops in March and again in the fall when the weather cools down.
  • Lettuces, radishes, and other root vegetables are good to start within your Zone 6 garden.
  • Start your warm-season crops indoors about eight weeks before transplanting them outdoors to avoid cold weather setbacks.

Colorado’s Growing Zone 7

Zone 7 minimum average temperature is 0° to 10°F. Zone 7a has an average temperature of 0° to 5° F. In Zone 7, the last frost date comes in mid-April, although it can come as late as May. The first frost date for this zone is mid-October, but it can sometimes come in the first week in November.

Vegetables to Grow in Colorado’s Zone 7 and When to Grow Them

Early February is an excellent time to plant your cool-weather vegetables. In contrast, late August and early October are perfect for cold-weather vegetables. Here is a list of vegetables to plant in zone 7.

  • Beets 
  • Broccoli
  • Cabbage
  • Carrots
  • Lettuce
  • Onions
  • Peas
  • Potatoes
  • Radishes
  • Spinach
  • Cucumbers
  • Eggplants
  • Okra
  • Peppers
  • Squash 
  • Tomatoes

Best Perennials to Grow in Colorado’s Zone 7 and When to Plant Them

Perennials are plants that come back every year. The best time to plant perennials is in the fall. For zone 7, here are some perennial flowers that are always favorites.

  • Bee balm 
  • Aster 
  • Painted daisy 
  • Shasta daisy 
  • Black-eyed Susan 
  • Four O’clock 
  • Hosta 
  • Salvia 
  • Butterfly weed Lavender 
  • Bleeding heart 
  • Hollyhock 
  • Phlox 
  • Chrysanthemum 

Annuals to plant in Colorado’s Zone 7 and When to Plant Them

You can start your annuals eight to ten weeks before the last frost and then transplant them outside. Here is a list of hardy zone 7 annuals

  • Marigold
  • Petunia
  • Portulaca
  • Sweet potato vine
  • Geranium
  • Dahlia
  • Cypress vine
  • Cosmos
  • Coreopsis
  • Lantana
  • Salvia
  • Spider flower
  • Strawflower
  • Snapdragon
  • Dianthus
  • Pansy

Farmers Tips for Growing in Colorado’s Zone 7

  • When you want to start a garden in zone 7, plant your seedlings indoors before winter arrives. Doing this can extend the growing season and let you grow vegetables twice: in the spring and the late summer.
  • Once the last frost has passed, you can plant zone 7 perennial flowers. These can be annuals or perennials.

FAQs

Question: Can I grow zone 5 plants in zone 4b?

Answer: Zone 5 plants can survive winter temperatures no lower than -20°F. Plants hardy in zone 5 can also be grown in zones 6, 7, and 8, but not zone 4 or lower.

Question: What is the difference between hardiness zone 7a and 7b?

Answer: There are thirteen plant hardiness zones in North America. The zones are split up based on the average minimum temperature per region. Zone 7 has an average low of 5 to 10 degrees Fahrenheit, with 7a having a low of 0 to 5 degrees. Zone 7b has a low of 5 to 10 degrees Fahrenheit.

Question: How do I know my plant hardiness zone?

Answer: You can figure out your gardening zone at the USDA website. There are two ways to do it. You can either input your ZIP code or, even more precisely, use the interactive map to find your precise location.

Conclusion

Agricultural activities contribute about 40 billion US dollars to the state’s economy. Understanding Colorado’s growing zones is vital to anyone who wants to grow plants in the state. The climate is critical to the success of your garden. Knowing how it impacts your growing region is essential. 

By knowing which zone you live in, you will determine the best time to plant and how to take care of your plants. It can also help you identify plants that will thrive in your growing region and enable you to identify pests and diseases early on.

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