In the Denver area, prune hybrid teas, floribundas, grandifloras and shrub roses from late March to mid-April, when the buds swell and before the leaves open. Roses that bloom once in early summer are the exception, and they get cut right after the flowers fade. Denver sits at 5,280 feet. Mountain towns run weeks later, and the western slope has its own calendar, so the dates shift with your address.
When to prune roses in Colorado
The calendar works backward from the last freeze. At the Denver station, the NOAA NCEI climate normals put the last spring 32°F freeze between May 1 and May 11. That range is where the odds of a freeze sit between 30 and 70 percent, so a freeze after May 11 still happens in some springs. The first fall freeze falls between September 30 and October 12.
Pruning ahead of that spring range puts the job in the window before the last spring frost. By then the deepest cold has usually passed, but the plant is still dormant. Look at the canes. Healthy ones are green to reddish-brown, and the bud eyes (the small bumps where leaves will form) are plump and starting to turn red. When the eyes are tight and flat, wait a week and look again. Watch the neighborhood plants for signs that the window is open.
The plant’s own state matters more than the date on the calendar. A rose that has not started to move can be cut at any point in the window. One that has already pushed new growth on warm days is past the best moment, and every day of delay makes the new shoots more exposed to a late freeze.
Colorado covers USDA hardiness zones 3b to 7b. That system rests on a single number, the average annual extreme minimum temperature, so it tells you how cold the worst night gets but not when buds wake up. Denver is the reference city for the dates above. In mountain towns the swelling buds may not show until later, and the safe rule there is to prune when the buds swell, whatever the date. Warm, low-elevation spots on the western slope run earlier than Denver.
If you mounded soil or mulch over the crowns for winter, pull it back gradually over a week or two before you cut. The Protecting Roses Through a Colorado Winter guide covers how to set that protection up in the first place. Fall is not a pruning season. A light trim of tall canes keeps them from whipping in the wind, but hard cuts in September or October invite new growth just as the first freeze arrives.
For the broader picture of site, soil and care, see the main guide to growing roses in Colorado.
The date is not the same for every type of rose
Roses bloom on one of two kinds of wood, and the pruning date follows from that. Wood that grew last year is old wood. Wood that grows this spring is new wood. Cut at the wrong time and you remove the flower buds along with the stems.
Hybrid teas, floribundas, grandifloras and most repeat-blooming shrub roses flower on new wood. A late March to mid-April cut gives them time to grow fresh canes that carry this summer’s blooms. Hard pruning is not just tolerated here, it encourages stronger growth. Knock Out and similar landscape shrub roses follow the same rule.
Climbers sit in between. Repeat-blooming climbers flower on side shoots that grow this season from last year’s main canes. Leave the main canes in place, tie them up, and in early spring shorten the side shoots. Removing the main framework every year leaves you with a plant that never builds height.
Ramblers and once-blooming old garden roses flower on old wood. Gallicas, albas, damasks and centifolias fall in this group, along with the single-flush climbers and species roses that put on one big show in late spring or early summer. Their flower buds formed last summer and have sat on the canes all winter. A late winter haircut takes off the buds, and you get a green shrub and no flowers. For these roses, prune right after the flowers fade, so the plant has the rest of the season to grow the canes that will bloom next year.
If you are not sure which group a rose belongs to, watch it for one season without pruning it. A plant that blooms once in early summer and never again is almost certainly on old wood. One that flowers in flushes through summer and into fall is on new wood. Even in early spring, remove only what is dead, damaged or crossing on a rose you cannot identify, and leave the live canes alone until after it blooms.
| Type of rose | Blooms on | When to prune |
|---|---|---|
| Hybrid teas, floribundas, grandifloras | New wood | Late March to mid-April, as buds swell |
| Repeat-blooming shrub roses (including Knock Out) | New wood | Late March to mid-April |
| Repeat-blooming climbers | Side shoots on older canes | Early spring for side shoots, leave main canes |
| Ramblers and once-blooming old garden roses | Old wood | Right after bloom, June to early July |
How far back to cut here
In a mild climate, a hybrid tea can be cut to a set height and every cane is alive. In Colorado, winter wind, dry air and cold snaps kill the tips of canes, and some years kill them nearly to the ground. So the rule here is to remove dieback first and cut below it.
Dead canes are brown or black, shriveled, and brittle inside. Live canes are green on the outside and white to pale cream in the center, the pith. Cut each cane a little at a time, working down from the tip, until the cut shows a white center. Make the cut above an outward-facing bud, at a slight slant, so the new shoot grows away from the middle of the plant and water runs off the cut.
After the dieback is gone, hybrid teas and floribundas typically end up shorter, though in a hard winter they may be shorter still. That is a cold-climate range, shorter than the heights you will see on packets written for warmer regions. For Knock Out and similar shrub roses, cut the whole plant back hard. They regrow quickly and bloom on the new canes.
Use the same pass to take out three kinds of wood: canes that cross and rub, thin stems, and any cane that is dead or damaged. What remains should be strong canes arranged like an open vase, so air moves through the center of the plant.
If every cane is dead to the soil line, check what grows back. Many grafted roses sit on a different rootstock, and a shoot that comes up from below the graft union will not be the rose you bought. Its leaves often have seven leaflets and the flowers are usually single and plain. A rose growing on its own roots will regrow true to type even after a total top kill. Dark, sunken lesions on canes can also signal canker, which the guide to Rose Diseases in Colorado: What the Climate Here Actually Brings explains.
What pruning too early costs in Colorado
A pruning cut tells the plant to wake up. The buds below the cut swell and push, and soon there are tender red shoots. Those shoots have no cold tolerance. A hard freeze after they emerge kills them, and in this state freezes into early May are normal, with the mean last freeze in Denver falling between May 1 and May 11.
The damage is easy to recognize. The new shoots turn limp, then dark brown or black, and the tips curl and shrivel. Leaves that had begun to open look water-soaked and then crisp. Older wood below the cut is usually fine, because it was still dormant enough to handle the cold.
The plant is set back but not lost. It spent stored energy on that first push, so the first flush of blooms may come late. Wait a week or so after the freeze, then trim off only the blackened shoots, cutting back to the next healthy bud or to green tissue. Resist cutting deeper into live wood. Dormant buds lower on the cane will break and replace what was lost.
To avoid the problem, watch the forecast. When a hard freeze is expected after the new growth has started, drape frost cloth or burlap over the plants for the night, or set an overturned bucket over a small shrub, and take it off in the morning. Plan on pruning in the last two weeks of the window, not the first, in years when March is cold and the buds are slow.
Checking this against your own county
Elevation and distance from water move the date within the state. A cold basin, a canyon mouth and a south-facing wall all warm up at different speeds, and a town higher than Denver may wait longer for its buds to swell. Colorado State University Extension has county offices staffed by people who track local conditions through the year. Call your county office and ask when roses are usually pruned in your town, and match that to what your own buds are doing.
Common questions
Can I prune roses in the fall in Colorado?
Not hard. Fall cuts push new growth, and the first freeze at the Denver station arrives between September 30 and October 12. Shorten very tall canes so wind does not whip them, then save the real pruning for spring.
Do I prune when the forsythia blooms?
It works as a rough guide for roses that flower on new wood, because forsythia blooms when the soil and air are warming. Check the rose itself, though. If the bud eyes along the canes are swelling and turning red, go ahead.
Should I deadhead roses through the summer?
Repeat-blooming roses reward it. Snip spent flowers back to a leaf with five leaflets and the plant sets new buds. Once-blooming roses are better left alone after pruning, since they will not rebloom and some form ornamental hips.
What if I already pruned and new growth has started?
Leave it and protect it. Cover the plant on nights when a freeze is forecast, and if the shoots are damaged, trim only the blackened tips after the weather settles. Pruning later than the window is a smaller problem than pruning into the middle of a freeze.