Why Colorado’s Climate Makes Perennial Timing Tricky
Colorado’s growing conditions vary widely by elevation, from warmer lower-elevation valleys to cold, short-season mountain areas, which means there isn’t one planting calendar that applies evenly across the state. If you’re still narrowing down which perennials fit your specific hardiness zone before worrying about timing, this zone-specific plant selection guide is a reasonable starting point. Combined with low precipitation in many areas and the potential for late spring frosts and early fall freezes, timing perennial planting well in Colorado generally means paying closer attention to your specific elevation and local frost dates than to a single statewide date. For more on how elevation and regional frost timing interact generally, see the planting season guide by region.
When to Plant Perennials in Colorado
Is It Too Early in Spring?
This depends heavily on your elevation and how late your last frost typically falls. In general, it’s safer to wait until the soil has thawed and warmed somewhat and the risk of a hard late freeze has passed before planting new perennials, since young, newly-installed root systems are more vulnerable to cold stress than established plants. If you’re planting in a higher-elevation area with a later average last frost, waiting longer into spring is generally the more cautious approach.
Late-Summer and Fall Planting Windows
Some sources point to late summer as a reasonable planting window for certain perennials, giving roots time to establish in warm soil before winter dormancy — though this general guidance wasn’t paired with Colorado-specific dates in the sources reviewed for this guide. As a general principle that applies across most temperate climates, including Colorado, planting in late summer or early fall (rather than right up against the first hard freeze) gives roots more time to establish before winter. Because exact windows vary by elevation and microclimate within Colorado, it’s worth checking guidance for your specific area rather than relying on one generic fall date.
Best Perennials for Colorado Gardens
Tough, Long-Lived Perennials From CSU Trial Gardens
The Associated Landscape Contractors of Colorado (ALCC) cites results from a perennial research and demonstration garden affiliated with Colorado State University in Northern Colorado, where the following perennials have shown good long-term adaptability:
- Baptisia ‘Lemon Meringue’ (Lemon Meringue False Indigo) — blue-green compound leaves with lemony-yellow blooms, reaching up to 36 inches tall and wide; has overwintered in the demonstration garden since 2014.
- Dianthus ‘Kahori Scarlet’ (Kahori Scarlet Dianthus) — a full-sun, mat-forming perennial with scarlet-pink spring blooms, up to 12 inches tall with a 12-18 inch spread; benefits from winter watering during low-precipitation months, and responds well to deadheading for repeat blooms.
- Persicaria polymorpha (Fleece Flower) — a clump-forming perennial shrub with white, paintbrush-like blooms in late summer, reaching up to 60 inches tall and wide; has overwintered at CSU since 2013 without spreading beyond a single clump, and benefits from being cut back to about 12 inches in spring.
- Salvia ‘Rose Marvel’ (Rose Marvel Salvia) — a compact, pollinator-attracting perennial with vivid fuchsia-pink spring flowers, about 14 inches tall and wide; deadheading after the first bloom can encourage later blooming.
Native, Drought-Tolerant Perennials for Xeriscaping
For lower-water landscaping, Hall Contracting (a Denver-area landscaping company) highlights several native Colorado perennials suited to dry, rocky conditions:
- Purple Poppy Mallow (Wine Cups) — 6-12 inches tall and wide, full sun, tolerant of dry soil and moderate drought; bright red-purple flowers over several months.
- Creeping Juniper — low-growing (around 18 inches high, spreading up to 10 feet wide), full sun, very drought-tolerant; useful on slopes and for erosion control, though not ideal for high foot-traffic areas.
- Mat Pentstemon (Mat-Root Beardtongue) — low-growing (2-5 inches high, spreading up to 3 feet), full sun, prefers dry, well-drained soil; suited to rocky environments and high elevations.
- Kinnikinnick — a low, hardy evergreen shrub (6-12 inches high, up to 3 feet wide), full sun to partial shade, drought-tolerant; produces white spring flowers and red berries that persist into winter.
- Prairie Verbena (Fernleaf Verbena) — 6-12 inches tall, spreading up to 3 feet, self-sowing, full sun, drought-tolerant; flowers range from white to pink to purple.
These native options are generally lower-maintenance once established, since they’re already adapted to Colorado’s typical soil and water conditions.
Perennials to Avoid or Plant With Caution in Colorado
The sources reviewed for this guide didn’t provide a specific, well-documented list of perennials to avoid in Colorado, so this is worth treating as general caution rather than a confirmed list. As a general principle, perennials bred for consistently moist, humid climates, or those rated for warmer hardiness zones than your local elevation supports, are more likely to struggle in much of Colorado’s dry, variable climate. Checking a plant’s hardiness zone rating and water needs against your specific elevation and local conditions before planting is a more reliable approach than relying on a general avoid-list.
What Is the “3 Year Rule” for Perennials?
This isn’t a term with one single, authoritative definition in the sources reviewed for this guide, so it should be treated with some caution. It’s sometimes used informally among gardeners to describe the general pattern of perennial establishment — commonly summarized as “sleep, creep, leap”: modest growth in year one, more noticeable growth in year two, and fuller, mature growth by year three. If you’re hearing this term used in a specific context, it may be worth asking for the source’s own definition rather than assuming it matches this general usage.
Planting and Establishment Tips
- Amend soil with compost where drainage is poor, since many Colorado soils are heavy clay or sandy and benefit from organic matter.
- Water newly planted perennials more frequently during their first season to support root establishment, then taper off as the plant matures — particularly for drought-tolerant natives, which generally need less supplemental water once established.
- Mulch around new plantings to help moderate soil temperature and retain moisture, which can be especially useful given Colorado’s low humidity and intense sun at higher elevations.
- Match plant choice to your specific microclimate (slope, sun exposure, wind) rather than relying solely on a general statewide recommendation.
For how perennial timing compares with the vegetable and annual planting calendars covered elsewhere in this cluster, see the seasonal planting timing guide.
FAQ
What is the 3 year rule for perennials? It’s an informal way some gardeners describe typical perennial establishment timing, often summarized as “sleep, creep, leap” — modest first-year growth, more growth in year two, and fuller growth by year three. It isn’t a strict, universally defined rule.
Is it too early to plant perennials in Colorado? It depends on your elevation and local last-frost timing. Waiting until the risk of a hard late freeze has passed is generally the more cautious approach for newly planted perennials.
What are the best perennials to grow in Colorado? Varieties proven in CSU-affiliated trial gardens, such as Baptisia ‘Lemon Meringue,’ Dianthus ‘Kahori Scarlet,’ Persicaria polymorpha, and Salvia ‘Rose Marvel,’ along with native drought-tolerant options like Purple Poppy Mallow and Creeping Juniper, are commonly recommended.
What are some perennials to avoid planting? There’s no single confirmed list for Colorado specifically, but perennials suited to consistently moist, humid climates or warmer hardiness zones than your local elevation supports are generally more likely to struggle.