Colorado Growing Zones Explained

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John Hughes was a beginning gardener too. After spending years researching, reading, and experimenting with different gardening tips, he’s here to share with you. Whether you’re already a gardening expert and want to try growing something adventurous, or you’re new to the entire journey, his content will change the way you look at gardening forever. He’s here to walk you through every step of the way to developing a healthy garden.

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.