Tuberous Begonia (Begonia x tuberhybrida pendula ‘Illumination Apricot’). This Begonia hybrid reaches 2 feet by 2 feet, with double peachy-apricot blossoms from late spring to fall. It grows best in coastal California, ideally in filtered shade with only morning sun, and requires moderately moist conditions. Begonias are native to moist subtropical and tropical climates, not summer-dry zones. (Courtesy Tom Karwin)
Chilean Lily of the Valley Tree or Evergreen Snowbell (Cirinodendron patagua). This unusual South American tree’s genus is one of 12 in the Quandong plant family (Elaeocarpaceae). It grows to 16 feet tall and eight feet wide, and from mid to late summer, it lines the stems with pure white, waxy bells resembling small bells. The bottom of the waxy bloom is deeply serrated. This small tree will be a feature in my Chilean garden bed. (Courtesy Tom Karwin)
Miniature Jade (Crassula ovata ‘Minima). The dwarf South African succulent grows to 30 inches tall and 34 inches wide, with thick trunk and branches. Its leaves are fleshy, round and glossy yellow with subtle reddish edges, and its flowers are small, star-shaped and coral-pink. It is shown in front of a Japanese Maple (Acer palmatum ‘Bloodgood’). (Courtesy Tom Karwin)
Four O’clock (Mirabilis jalapa). This tuberous-rooted tender perennial, a native of Mexico, grows to 3 feet tall and wide. From June to frost, it produces blossoms with colors ranging from pink, rose, red, magenta, yellow and white, as well as various patterns known as sectors, flakes and spots. Different combinations of flowers and patterns can occur on different flowers of the same plant. This characteristic is reflected in the generic name, which means ‘miracle’; the specific name refers to several places in Mexico. The common name refers to the flowers opening in the late afternoon and closing the following morning. (Courtesy Tom Karwin)
Shasta Daisy (Leucanthemum × superbum). This plant is an old-fashioned favorite for perennial borders and cut flowers. American horticulturist Luther Burbank introduced the original Shasta daisy in 1901 as a quadruple hybrid of the oxeye daisy (Leucanthemum vulgare), English field daisy (Leucanthemum maximum), Portuguese field daisy (Leucanthemum lacustre), and Japanese field daisy (Nipponanthemum nipponicum). Numerous single and double-flowered cultivars are currently available. (Courtesy Tom Karwin)
Red Chestnut Bromeliad (Vriesea fosteriana var. seideliana ‘Red Chestnut’). This plant, endemic to Brazil, produces glossy-green, white-striped leaves that turn a rust-red hue as they age. The base of the leaves forms a cup-like shape that collects water. Flowers, growing on a shaft, are white and green with red spots, and last only one night. It is monocarpic, flowering only once in its life. The plant is epiphytic, absorbing nutrients from the air and its water reservoir, rather than from the soil. (Courtesy Tom Karwin)
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Tuberous Begonia (Begonia x tuberhybrida pendula ‘Illumination Apricot’). This Begonia hybrid reaches 2 feet by 2 feet, with double peachy-apricot blossoms from late spring to fall. It grows best in coastal California, ideally in filtered shade with only morning sun, and requires moderately moist conditions. Begonias are native to moist subtropical and tropical climates, not summer-dry zones. (Courtesy Tom Karwin)
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Our most recent column addressed the planning of a year-round garden, including designing landscape basics and searching for (mostly) California native plants. To review that column, browse santacruzsentinel.com and search for “Karwin.”
Today’s column introduces guidelines for year-round gardening for herbaceous perennial plants that are native to a Mediterranean climate zone. This category focuses on the majority of plants commonly grown in typical gardens. It excludes trees and annual plants, which we will address in a future column.
Herbaceous perennial plants have various cultivation requirements, so an annual calendar must include exceptions. Given the large number of garden plants in this category, we can’t list all the exceptions. Therefore, to find information on specific plants of concern, gardeners can search the internet for “cultivate (botanical name).” Searching for a plant’s common name might succeed.
Today’s image gallery
My garden features beds for each of the world’s Mediterranean climate zones (also called dry-summer zones). I tend to show blooms from these plants, but today’s gallery shows current blooms from only two of these zones: Chile and South Africa. The exceptions include a Begonia, selected for my patio’s shade garden; a variation of Luther Burbank’s Shasta Daisy; a Mexican “miracle;” and a Brazilian epiphyte.
Guidelines for herbaceous perennials
Planting and Transplanting. The ideal planting period continues from October through February. Installing new plants in the garden during this period allows them time to establish strong roots in cool temperatures and with natural rainfall. New plants can be installed at any time of the year, including summer months, but require irrigation (see below). Mulching newly installed plants helps to retain moisture and suppress weeds.
Irrigation. Newly installed or transplanted plants require regular irrigation until they have established a strong root system. This is particularly important during the summer-dry period. Once established, Mediterranean plants are summer-dormant and require little or no summer irrigation. When a garden includes Mediterranean and other plants that require irrigation, the gardener should group plants by water needs to avoid overwatering the drought-adapted species. This practice is known as “hydrozoning.”
Pruning to Control Form. Dead, broken, or diseased branches can be pruned at any time. In late summer or winter (depending on their growth cycle), herbaceous perennial plants can be cut down to the ground or a basal rosette. For example, cutting back Salvias in late winter or early spring. This annual practice supports renewed growth from the plant’s base. Light pruning or pinching to shape bushy perennials can be done March through May, during their active growth period.
Pruning to Promote Blooms. Late-summer flowering perennial plants benefit from cutting their flowering stems back in late May or early June. This method is known as the Chelsea Chop, referring to the Chelsea Flower Show held in late May. Cutting back the stems of these plants by up to two-thirds produces plants that are more compact, do not slump, and do not need staking.
After early-summer flowering perennials have flowered, they can be cut back to just above ground level. Cutting back the whole plant promotes the growth of young foliage and future flowers and prevents self-seeding. This method is known as the Hampton Hack, referring to the Hampton Court Palace Flower Show, which takes place in early July.
Removing spent blossoms (deadheading) regularly prolongs bloom on herbaceous perennials. Gardeners can pursue this practice casually during blooming periods. Deadheading also applies to woody perennials, such as roses and lilacs.
Propagation by Division. Clumping perennials, such as Pacific Coast Irises (including Iris douglasiana), Yarrows (Achillea), and Blue-eyed Grass (Sisyrinchium), should be completed in the fall. Dividing other perennials should be done in either the October to November period or the February to March period, depending on when the plant is dormant or resprouting.
The basic guideline for cultivating herbaceous perennial plants is to follow nature.
Advance your gardening knowledge
Mark your garden calendar for the Native Plant Bootcamp from 10 a.m. to 1 p.m. Aug. 2 at 719 Old Stage Road, Salinas. The UC Master Gardeners of Monterey & Santa Cruz Counties will present this free event, which will include several workshops: Creating Habitats with Native Plants, Year-Round Color with Native Plants, and Replacing your Lawn with Native Plants. Also included: interactive demonstrations, observing drawing by natural history illustrator Erin Hunter, learning from selected local garden-related organizations, and purchasing plants from the Blue Moon Native Garden. There is a full schedule! For details, browse to tinyurl.com/3k4knsze.
The state of California prohibited the sale of gasoline-powered leaf blowers (and other small off-road engines) after Jan. 1, 2024, allowing localities to regulate the use of these polluting devices.
About one year ago, the city of Santa Cruz adopted an ordinance prohibiting most uses of gasoline-powered leaf blowers (only) within city limits, after Jan. 1, 2025. Then, a month before that deadline, the city extended the effective date to July 1, 2025. This change allowed city residents an additional six months to access rebates for the cost of replacing gasoline-powered landscaping equipment with new zero-emission electric alternatives. These rebates are available from the Monterey Bay Air Resources District’s Landscape Equipment Exchange Program. For details on these rebates, browse to www.mbard.org/leep.
The city of Santa Cruz has not prohibited the use of other gasoline-powered small off-road engines for landscaping equipment, such as chain saws and tillers, but rebates for the replacement of professional landscape service equipment are still available through the state’s Clean Off-Road Equipment Voucher Incentive Project. For details, commercial landscapers can browse californiacore.org/how-to-participate-professional-landscape.
This week in the garden
If you have gasoline-powered small off-road engines for landscaping, replace them with environmentally friendly electric alternatives. Corded equipment is workable, but battery-operated devices are easier to move around the garden.
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.