Don’t Let Rose Pruning Be a Thorn in Your Side

Southwest Yard & Garden

by Dr. Marisa Thompson

 

Figure 1. Forsythia in full bloom in 2015 (photo credit M. Renew).

Question:

I will prune my roses soon, but I’m confused about when is the best time to prune and what are the possible problems if I prune too early or too late?

-        Elizabeth T., Ruidoso, NM            

Answer:

This is a great question, and the full answer includes all kinds of cool rose physiology information that could make a riveting book (nobody steal my idea, please).

Unlike many other landscape species, many roses do not go dormant. Dormancy can be defined as a physiological condition in which growth is halted until internal switches are triggered, even if environmental conditions are otherwise perfect for growth. That is why roses may green up and start to grow in January with only a few days of warm temperatures. This is also why pruning too early in the winter can cause more harm than good.

I heard that the proper time to prune roses is when forsythia (Fig. 1) are in bloom. This week (March 12, 2018) I visited a forsythia bush at the Albuquerque BioPark to check the blooming status, and it is indeed in bloom (Fig. 2)! However, flower-loving scouts I have enlisted around Albuquerque and Las Cruces have reported that theirs have not bloomed quite yet. Cute as it may be, the idea of following the phenology (cyclical patterns, like flowering habits) of one species in order to make decisions about how to deal with other species has its flaws.

Figure 2. Forsythia flowers opening on March 14, 2018 (photo credit M. Thompson).

• Timing and techniques for pruning depend on what type of rose you are growing. Dr. Curtis Smith, retired NMSU Extension Horticulture Specialist, offers great tidbits about the hows and the whys of rose pruning in the archives for this column (http://aces.nmsu.edu/ces/yard/search.html). Here are selected tips from Dr. Smith’s columns, as well as some from another great resource, NMSU Extension Guide H-165 “Growing Roses” (http://aces.nmsu.edu/pubs/_h/H165/):
• Severe pruning may result in fewer, but higher quality, flowers.
• Large bushes, such as Harrison's Yellow, the rugosas, Austrian Copper, and other species grown for large bushy effects, need little or no pruning as long as there are no dead or weak branches.
• Never prune the hybrid perpetuals, such as Paul's Scarlet, Blaze, Silver Moon, and American Pillar, before they bloom, and even after they bloom do not prune them severely.
• ·     Prune climbers in late spring, after the first heavy crop of blooms have faded. Excessive pruning removes flower buds. This is because these plants blossom on 1- and 2-year-old wood.
• The optimal time window for most rose pruning is the period from one month to two weeks before your expected last frost. Even when pruned at this time, an abnormal late freeze can do considerable damage to your rose plants, but it is less likely.
• Roses may initiate growth too early and be damaged by freezing if they are pruned too early. Many people have pruned early and the roses have done well, but there are a lot of roses in New Mexico growing from only the root stock (flowering once each year) as a result of improper pruning timing.
• There is a good reason for waiting. Pruning can stimulate growth at the wrong time. Another consideration is that the buds you will leave after pruning are "protected" by the buds above them. These buds (that will be pruned away) will begin growth first if the weather stimulates growth too early. These early buds inhibit the growth of the lower buds. If growth begins too early, the buds that will freeze are those that you will remove anyway when you prune. However, if you prune too early and a mid-winter warm spell stimulates growth, the buds that will freeze are those that you are depending on for growth later in the spring.
• Hybrid tea roses should be pruned in late winter. Bushes pruned in late fall or early winter may be injured by cold and require further pruning in late winter, resulting in more severe pruning than desired. Early pruning also tends to induce early cane growth that is subject to spring freezes.

Many roses are impressively drought- and heat-tolerant. There are also flowering shrubs in the Rosaceae family that are native to New Mexico and are great options for low-water landscaping. Native or not, now is a great time to add mulch under your bushes and around trees (keep mulch back 1–2 inches from the trunk), and as a moisture-holding layer on the tops of your veggie beds.

The Albuquerque Rose Society offers free pruning demos each year, and several are still upcoming this season: March 17, 18, 24, and 25 from 10 am–3 pm (http://www.albuquerquerose.com/). Do you know of rose pruning workshops in your area? Send me the event details! As long as they are free and open to the public, I’ll add them to my blog and share them on social media (https://nmsudesertblooms.blogspot.com/).

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.