English lavender (Lavandula angustifolia). This plant thrives in the Monterey Bay area, growing mounds of silvery gray foliage at least 3 feet high and wide, and producing long-lasting dusky blue-violet spikes or flowers in midsummer. After the spent flowers are pruned back to soft green foliage (not to woody stems), the plants continue to be attractive. (Courtesy Tom Karwin)
Scarlet bermuda squid (Lobelia aguana). This vigorous plant grows throughout the year. We control its size with the Chelsea Chop, done in late May, and again with hard pruning down to 6 to 12 inches from the ground in the autumn. It regrows readily. (Courtesy Tom Karwin)
Rambling rose (Rosa mulliganii). Another vigorous plant, this rambler can easily extend along 40 feet of fence or climb to an equal height. No pruning is required except to control size. This should be done soon after blooms fade. This image shows an immediate need to deadhead the blooms and remove or train the newer canes. (Courtesy Tom Karwin)
Blue African sage (Salvia africana-caerulea). This South African native has outgrown its space and intruded into the adjacent pathway. After producing many small blue flowers from late spring through the summer, it finished blooming a while ago. According to Flowers by the Sea (ftbs.com), “At any time, you can perform cosmetic pruning — shaping, controlling height and width, and removing the oldest wood. Some gardeners periodically remove the oldest stems to encourage fresh new growth.” (Courtesy Tom Karwin)
Coast rosemary (Westringia fruticosa ‘Morning Light’). Although we had learned that this Australian native would grow 3 feet high and wide, it has outgrown its allotted space, invaded a garden pathway and crowded a white Australian fuchsia (Correa ‘Ivory Bells’). We will need careful pruning to reduce it into a compatible form. (Courtesy Tom Karwin)
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English lavender (Lavandula angustifolia). This plant thrives in the Monterey Bay area, growing mounds of silvery gray foliage at least 3 feet high and wide, and producing long-lasting dusky blue-violet spikes or flowers in midsummer. After the spent flowers are pruned back to soft green foliage (not to woody stems), the plants continue to be attractive. (Courtesy Tom Karwin)
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As we enter autumn, the transition from summer to winter, gardeners should plan on cutting back their spent perennials. This column focuses on seasonal pruning of herbaceous shrubs, with a review of year-round management for these plants.
Today’s image gallery
Typically, our column’s images feature plants in bloom. While we appreciate flowers and foliage at their peaks, this column addresses a practical realism of gardening: pruning. The accompanying images illustrate current pruning projects in my garden. As gardeners prune their flowering shrubs, they prepare the plants for future blooms and take satisfaction in a job well done.
Pruning goals
Herbaceous shrubs are woody at the base and vigorously produce soft new growth each year.
The annual pruning strategy for herbaceous shrubs keeps them compact, floriferous and well-suited to growing in the Monterey Bay’s climate of cool, wet winters and dry summers, and ensures year-round interest without missing future blooms.
Year-round pruning maintains a herbaceous shrub’s shape, vigor, flowering and air circulation, while preventing the plant from becoming leggy or overgrown.
In this column, we will first address the pruning objectives for the autumn months (September through November) and then summarize pruning tasks for other periods of the garden year.
Pruning shrubs in the autumn
Many herbaceous shrubs have finished blooming during the fall. While the timing of the season’s final blooms varies by the plant’s growth cycle, bloom period and climate conditions, the gardener can schedule pruning based on inspiration and convenience.
Some shrubs flower on old wood and others flower on new wood. Shrubs that flower on old wood include hydrangeas, mock oranges (Philadelphus), currants (Ribes) and others. These plants bloom from buds set the previous year, so they should be pruned early in the autumn, after flowering, not later in the winter.
My garden includes a cluster of heat-tolerant Descanso lilacs (hybrids of Syringa vulgaris), which flower on old wood. They bloom early in the spring, so we completed the pruning early in the autumn to remove spent blooms and protect the next season’s buds.
In the autumn, gardeners might discover the need to prune herbaceous shrubs to manage their size after they have grown larger than anticipated, crowding adjacent plants or intruding into garden pathways. Ideally, the gardener should install a new plant in the right place, having learned about its mature size, but some plants thrive in their new site and exceed expectations.
When reducing the size of an overgrown plant, the gardener should strive to maintain the plant’s natural shape, rather than to convert it into a hedge. This goal requires studying the plant and proceeding in phases. Removing lower branches first can help to retain the plant’s attractive overall form.
The subsequent work to reduce the size of longer branches can be done by pruning at nodes. These are points on a stem where leaves, branches or buds originate. Nodes are sites of active cell division and are capable of generating new shoots and leaves.
This pruning practice involves making cuts just above nodes, removing part of the branch or stem while leaving the node intact. This encourages dormant buds near the node to activate and produce new growth, effectively revitalizing the plant.
Pruning shrubs during the year
The gardener should plan year-round pruning practices based on the targeted plants’ growth cycle and bloom period.
During the winter months, pruning includes the removal of damaged or broken stems, leaving seedheads for birds or winter interest and cutting back last season’s stems before new growth begins. For some herbaceous shrubs, cutting to a low framework of woody stems will promote new growth. This practice applies to salvias, lavenders, buddleias and many other herbaceous shrubs.
When the spring season arrives, pinch the tips of new shoots when they are 6 to 8 inches long to encourage branching and bushiness. Remove any weak shoots and thin-crowded stems to optimize air flow. Lightly prune early bloomers, such as Ceanothus, Ribes and Philadelphus, after flowering to shape the plant and limit woodiness.
During the summer months, remove spent flowers to extend the blooming season. This applies to roses, salvias, penstemons and other summer bloomers. Limit other pruning to light shaping; avoid hard pruning during hot weather.
Advance your gardening knowledge
Success in gardening depends on a balance of the gardener’s instincts and his or her knowledge of the targeted plants. You already have your instincts, hopefully. You can search online to quickly and easily gain plant-specific knowledge at no cost.
Gardeners can acquire useful information about their plants. Internet searches depend on the targeted plant’s common name or, preferably, its botanical name.
When seeking info about a particular plant, search for the plant’s name and include “-.com” to avoid marketing websites.
Gardeners can also search the internet by category of plant, drawing upon the many available online resources.
Garden columnist Margaret Roach recently published her conversation with Rebecca McMackin (another garden columnist) about online garden reference resources. See this conversation by browsing tinyurl.com/jcmxejvk and clicking on McMackin’s favorite sites.
Scroll to the end of the discussion to click on Roach’s extensive resource list: awaytogarden.com/resources.
Both McMackin and Roach list mostly East Coast-oriented resources. For West Coast-oriented resources, visit these sites:
California Native Plant Society’s “California Native Plant Destination”: Calscape.org.
University of California’s Agriculture and Natural Resources: ucanr.edu/topics/gardening.
In a future column, I will list my favorite online resources on gardening.
This week in the garden
List plants in your garden that are out of bloom or overgrown and in need of pruning. If you need pruning recommendations (you might already be prepared), search the internet for “pruning (botanical plant).”
Enjoy your garden!
Tom Karwin is a past president of Friends of the UC Santa Cruz Arboretum and the Monterey Bay Iris Society, a past president and lifetime member of the Monterey Bay Area Cactus and Succulent Society, a Lifetime UC Master Gardener (certified 1999-2009), past board member of the Santa Cruz Hostel Society and active with the Pacific Horticultural Society and other garden-related societies. To view photos from his garden, visit facebook.com/ongardeningcom-566511763375123. To review the archive of recent On Gardening columns, visit santacruzsentinel.com and search “Karwin.” Go to ongardening.com to review columns from 2012-2020 (and soon) from 2025. Send comments or questions by email to gardening@karwin.com.
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