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Tom Karwin, On Gardening | Seasonal projects in the backyard – Santa Cruz Sentinel

Care for your garden

Today’s column compiles brief discussions on selected current topics in my own garden. While we usually focus on one topic each week, the multi-faceted nature of gardening inspired this column.

Controlling weeds. Every garden has weeds, perhaps just a few or sometimes many. They arrive through seed drops, wind gusts, imported plants, or avian flyovers. Close spacing of desired plants could be the best strategy for weed control: it denies the inevitable weed seeds the sun exposure they need to grow.

Plan B is to notice and remove weeds before their seeds mature and spread. Annual and perennial weeds must be tracked for this approach to succeed.

Then, we have mulching with the objective of blocking the sunlight from the weed seeds. Some gardeners like inorganic mulches (pebbles, plastic, weed fabric, etc.). These items can be effective, but organic mulches (shredded leaves, wood chips, etc.) are cheaper, consistent with a commitment to natural gardening, and decompose over time to add nutrients to the soil.

Sheet mulching involves covering the garden surface with recycled cardboard cartons and adding a layer of organic mulch material. This practice disposes of the boxes that are delivered to our homes and can smother weed growth. The cardboard also will decompose and enrich the soil.

I have recently learned about mulch research by Washington State University Professor Linda Chalker-Scott. A very brief summary of her findings from her is that wood chips alone are better than sheet mulching because the cardboard smothers the soil as well as the weeds. For the full story, see her talk about her, “Mulches: The Good, The Bad, and The Really, Really Ugly.” Browse to and search for “Chalker-Scott mulch.”

Controlling pond algae

My patio includes a small above-ground pond that is the home of numerous very small fish. They are likely Common Minnows (Phoxinus phoxinus). The pond sometimes has interesting pond plants, but it now has a bumper crop of Filamentous Algae, which resembles a cloud of green wet wool. This weed, which could be any of a few different plant species, grows on the bottom, attaches to rocks or other objects, or floats close to the surface.

After laboriously scooping algae from the pond, I searched for a targeted herbicide. Several products claim to be safe for fish and pond plants (that’s important!), but some safe herbicides oxygenate the water while others remove oxygen and require constant fountain action to aerate the pond and keep the fish alive.

My quick survey of available products identified Mizzen as a good option. This product is a liquid, chelated copper-based algaecide. When I tried to order it, would not ship to California! Lake Restoration, which produces Mizen, told me that California’s regulations guard against allowing chemicals to enter the natural waterways. My pond is isolated from waterways, so Lake Restoration is sending a pint for my trial uses. I’ll report my Mizzen experience in a future column.

Protecting Salvia Apiana from poaching

The California Native Plant Society’s very special Spring 2022 issue of its magazine, Flora, is dedicated to the issues surrounding White Sage (Salvia apiana), a California native plant “with which California Indigenous communities have had a relationship for thousands of generations.”

The focus on this plant is warranted by its medicinal and cultural significance and recent pop culture popularity, which raises the risk of endangerment. As it explores these issues, the California Native Plant Society invites a broader meditation on our society’s relationship to plants.

Without attempting to summarize White Sage’s rich cultural history, we move directly to today’s enthusiasm for smudging sage bundles to cleanse one’s personal energy or home. Always a good thing!

Sage smudging is a simple process: place a bundle of sage leaves in a fire-proof bowl (ideally an abalone shell, but ceramic, clay, or glass would serve), and light the end of the bundle with a match. If it catches fire, blow it out and allow the bundle to smolder. It produces an aromatic smoke that should be guided (ideally with a feather from an eagle or other large bird, but a fan will do). A nearby open window allows the smoke to escape, taking impurities with it.

You could purchase smudging kits from several online suppliers. The demand for such commerce motivates large-scale poaching of the plant from the native environment. Too often, this is done thoughtlessly by pulling plants out by their roots, interfering with natural seed propagation, and ultimately threatening the survival of the species.

You could try smudging by growing your own White Sage. It’s notoriously difficult to cultivate from seed (a friend recommends seed scarification to aid germination) but plants are often available from garden centers or online nurseries, eg, Annie’s Annuals.

If you buy a smudging kit, confirm that the sage bundle was responsibly harvested.

Thinning apples

Now is the time to thin the apples on your tree. Healthy apple trees produce a large number of attractive blossoms, each of which has the potential of becoming an apple. If it succeeds, the weight of the fruit could cause branches to break. I’ve seen the results in a friend’s small orchard, and it was not pretty.

The apple tree has natural defenses against such damage, referred to as the June drop. From mid-June to mid-July, an apple tree will release small apples for two reasons: insufficient pollination (not enough bees) and insufficient carbohydrates (not enough leaves to support the maximum crop). The June drop is an impressive demonstration of the apple tree’s self-preservation.

Still, the gardener’s thinning of the apples builds upon the tree’s natural defense to promote the development of larger fruits.

The usual thinning advice is to twist off the smaller apples and leave about 6 inches between the remaining apples. This should be done while the apples are smaller than golf balls, to provide enough time for the selected apples to reach full size.

Pruning and propagating lavender

Lavender plants need annual pruning to maintain the preferred overall shape. My English Lavenders (Lavandula angustifolia), which are currently blooming prolifically and keeping the local bee community busy, should be pruned back after the blooms fade in mid-August. Pruning away the new growth supports the next season’s blossoms while containing the plant in a compact form.

When not pruned annually, lavenders develop to grow a large, rangy, woody base that can split open and shorten the plant’s life span.

One of my lavenders, Lavandula allardii ‘Meerlo’, is an unusual variegated species that I did not prune consistently and has developed an unattractive woody base. Severe pruning of the plant is not the solution, because lavenders do not sprout from woody stems.

The better option is to grow new plants, and, once they become established, simply remove the overgrown plant.

Propagating a lavender plant from cuttings is an easy task because the cuttings develop roots readily, given reasonable care.

Either softwood or hardwood cuttings can be rooted. Hardwood cuttings take a little longer but are more successful. They can be taken in the spring or fall. We’re close to the beginning of summer (June 21), but my Merlo lavender is blossoming later than the English lavenders, so I’m speculating that it’s still springtime for the Merlo.

The cutting should be about 4 inches long, cut just below a leaf node. Stick the cutting two inches into a well-drained starting medium, firm the soil around the cutting, provide an environment that retains moisture, and let roots develop for two-to-four weeks. I’ll report back!

Advance your knowledge

Ruth Bancroft Garden has scheduled two fee-based webinars intended for gardeners who could gain useful information. To register, browse to

“Proteaceae & Pals” Troy McGregor, owner of Gondwana Flora and Waltzing Matilija, will present two lectures about plants in the Proteaceae family (such as Protea, Leucadendron, Leucospermum and Grevillea). Two online sessions on Saturdays at 10 am June 18 (overview) and June 25 (care/maintenance).

“Mitigating Fires Risks Through Garden Design & Maintenance” Jennifer de Graaf, Landscape Architect, will present a two-part series about how a multi-faceted, interconnected lifetime of decisions in your landscape can help mitigate your risks versus fire. Two online sessions at 10 am on June 22 and June 29.

The Cactus and Succulent Society of America will present its regularly scheduled webinar at 10 am June 25. This free series has consistently featured knowledgeable collectors of these intriguing plants, often with accounts of expeditions to regions with native succulent plants. As the date approaches, details and registration link will be available on the Cactus and Succulent Society of America’s Facebook page:

Enjoy your garden!

Tom Karwin is past president of Friends of the UC Santa Cruz Arboretum and the Monterey Bay Iris Society, a Lifetime Member of the Monterey Bay Area Cactus & Succulent Society, and a Lifetime UC Master Gardener (Certified 1999–2009). He is now a board member of the Santa Cruz Hostel Society, and active with the Pacific Horticultural Society. To view daily photos from his garden by him, For garden coaching info and an archive of previous On Gardening columns, visit

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