A Cautionary Tale About Ivy

 Ivy brings a combination of pleasure and pain to the garden, and the potential to surprise gardeners who do not pay attention

Forty years ago, when I moved to my current residence, the property had a generous crop of English Ivy (Hedera helix). This most common species of the genus Hedera has some appeal in the garden. The Royal Horticultural Society has honored fourteen cultivars of H. helix with its Award of Garden Merit, reflecting the plant’s apparent good behavior in England’s climate.

Despite its British credentials, H. helix grows rampantly on the west coast of the United States. Washington and Oregon have listed it as a noxious weed. California’s Department of Food and Agriculture has not yet listed this plant as a noxious weed, but hopefully is considering that action. 

This plant had covered much of my new garden, grown into some shrubs, and overwhelmed a large evergreen tree. We removed the tree, with great regret. After several months of hacking at this invasive plant and uncounted ivy hauls to the local landfill, we had it under control. During the following years, we pulled many sprouts and still do today. The more recent sprouts probably began with bird visits, but it is not impossible that dormant ivy seeds have been lurking in my garden for decades, awaiting a taste of moisture and sunlight.

More recently, perhaps five years ago, a variegated cultivar of Algerian Ivy (H. algeriensis) caught my eye, and I planted a small amount near the base of a chimney as a groundcover. All ivies grow horizontally, and are often selected for groundcover duty. My willingness to give this plant another chance in my garden reflects both short memory and persistent optimism.

In the same area, and with similar optimism, I installed a Big Mexican Scarlet Sage (Salvia gesneriiflora). This plant quickly grew well above ten feet in height (it can reach twenty feet high in the mountains of northeastern Mexico) and spread to four separate shrubs.

These beautiful but huge plants concealed the ivy’s relentless spread. The Algerian Ivy/Big Mexican Scarlet Sage collusion continued for weeks, until the enormous salvia finished blooming, and became ready for renewal pruning (i.e., cutting it to the ground).

That drastic action revealed that the ivy had discovered the chimney that rises about thirty feet beside the house, and used it aerial roots to grow to the top of the chimney and spread in both directions across the side of the house. This growth had not been impossible to observe, but the tall shrubs close to the pathway effectively screened the situation from view.

There’s a certain charm to ivy-covered walls, but the plant eventually can cause damage and rot, and harbor unwelcome wildlife. My best choice was to have the ivy pulled down, expecting that it would take down some of the thin-brick veneer, which it did.

There is no simple solution to ivy on the house and chimney.

The next steps of this project include reattaching the missing pieces of the veneer, removing the ivy and all but one specimen of the Big Mexican Scarlet Sage, and keeping it pruned to appropriate size.

Then, the project includes shopping for plants to re-landscape the area. The UCSC Arboretum’s Fall Plant Sale will be a fine opportunity to acquire California native plants for this project. The sale begins at 10:00 a.m. tomorrow (Saturday, October 13th).

Lesson learned: if you plant any variety of ivy in your garden, check occasionally to make sure that it is growing only where you want it to grow.

Managing Weeds

Garden renovation can bring multiple rewards. Re-thinking your landscape can yield opportunities to exercise one’s creativity, pursue recent insights into botanical combinations, add exciting new plants, dismiss too-familiar vignettes in favor of new horticultural frontiers, and discover excuses to “shovel-prune” under-performing plants.

The process also includes several downsides: lots of work, heavy expenses, and the frustration of waiting for the new landscape to develop into its promise.

There’s another downside to consider: enabling the germination of unwanted plants in the weed seed bank.

Experienced gardeners know that their soil harbors an inventory of weed seeds that are lurking a few inches below the surface, waiting for a little sunlight, a little moisture, and presumably a little oxygen. Given those prerequisites, they will burst into growth and the production of another generation of seeds.

The weed seed bank developed in a variety of ways. It might have come from last season’s weeds, or the careless importation of contaminated soil or potted plants, or the tireless efforts of birds, who we suspect are spending their days moving seeds into our gardens. And there’s the wind, which transports the lighter-weight seeds to gardens where they typically are unwanted.

Some itinerant seeds are actually welcome in our gardens, but they are out-numbered by the weed seeds.

Regardless of the origins of the weed seed bank, the important fact is that the seeds are not far from the surface, and they can retain their vitality for years.

Given this reality, consider what happens with a garden renovation project. In my garden, this process included cutting down fifty feet of large shrubs and grinding their roots, digging and replanting scores of native irises, relocating a large number of bearded irises, and planting dozens of new plants from one-gallon and fifteen-gallon pots.

All of this activity has churned the soil and consequently liberated my garden’s weed seed bank. A clear contrast in weed populations can be observed between the disturbed and untouched areas. This requires hours of weeding, with the optimistic goal to pull weeds before they set seeds for next season.

An activity that parallels garden renovation is the sowing of seeds for annual plants, whether for edible or ornamental gardening. The usual advice for planting seeds is to loosen the soil, scatter the seeds, rake them in, water them in, and maintain moisture while the seeds germinate. If your goal would be to activate your weed seed bank, you would go through exactly the same steps!

The Theodore Payne Foundation for Wild Flowers and Native Plants has sent the wildflower seeds I ordered and provided recommendations for leaving the weed seed bank in its dormant state. The basic strategy is to disturb the soil as little as possible and preferably not at all. The Foundation recommends digging or tilling no deeper than three or four inches. Better still, after clearing the planting area of existing weeds, rake the soil gently, scatter the seeds, and cover them with about one-eighth inch of garden soil or light potting soil.

Despite this careful effort to leave weed seeds dormant, the Foundation adds a tip for planting wildflower mixtures: plant a sample of the seed in pots in some fresh potting soil, so you could identify which seedlings in the ground are the desired wildflowers, and which are weeds to be removed. Even when the experts are most careful, weed seeds will germinate.

Battling weeds might be an unavoidable part of gardening, but it can’t deny us the joys of renovating our gardens from time to time and growing annual plants.

Weeding Ideas, Early Blooms

Gardening friends are pulling weeds that sprouted during our recent warm days and wishing for effective treatments. There are no quick and easy solutions to weed problems, but the longer view dictates “weeding before seeding.”

Ever optimistic, I am testing an organic pre-emergent herbicide that is based on corn gluten, a natural material that discourages the formation of roots. It’s neither cheap or 100% effective, but might be worth a try. For more information on a pelletized product, visit eartheasy.com and search for “corn gluten.” For a liquid version, go to amazon.com and search for “Green It.”

Another organic approach is the application of vinegar, which can kill really young weeds. Household vinegar (5% acidity) has some effect but horticultural vinegar (20-30% acidity) works better but dangerous to the user.

Other organic weed killers are based on clove oil will kill at least the top growth of mature weeds.

Still, the best, cheapest and most reliable way to kill weeds is pulling or digging them out by their roots.

Take a break from weeding to anticipate the coming spring and enjoy plants that are in bloom now in your garden. As I look around, I am pleased to see these early bloomers:

Wagner’s Sage (Salvia wagneriana), a large sub-shrub from Mexico and Central America has gorgeous hot pink or pink and white bracts that are greatly appreciated by hummingbirds as well as gardeners.

Wagner’s Sage

Salvia blossom - scarlet

Big Mexican Scarlet Sage

Big Mexican Scarlet Sage (Salvia gesneriiflora ‘Tequila’), another treasure from Mexico and Central America, produces brilliant red flowers with a striking black calyx and grows about ten feet high in California gardens. My neighbor has a stand of this plant that has grown fifty feet wide and well over fifteen feet high with support from adjacent shrubs.

 

 

 

 

Wonga Wonga Vine (Pandorea pandorana), from Australia, is a vigorous, woody vine that climbs with support from a tree or large shrub, or a trellis of some kind. Its popular varieties have differently colored blossoms: ‘Snowbells’ (white), ‘Ruby Belle’ (pinkish), ‘Ruby Heart’ (cream with ruby blotch), and ‘Golden Showers’ (yellow). My specimen grows on 2” x 2” rail attached to a fence and produces white racemes. The plant usually flowers in spring; we’re still in winter, so this is an early bloom.

Other plants now in bloom include

  • Beach Sage (Salvia africana-lutea), interesting wrinkly, golden brown flowers, from South Africa.
  • Winter Daphne (Daphne odora ‘Aureomarginata’), delicate blossoms, fine fragrance;
  • Common Hyacinth (H. orientalis), one of the earliest bloomers
  • Trumpet Daffodil (Narcissus ‘King Alfred’ probably), a cheerful yellow blossom
  • Blue Hibiscus (Alyogyne huegelii ‘Santa Cruz’), a large, frequent blooming evergreen shrub

A plant to watch is the Chinese Ground Orchid (Bletilla striata), which is now preparing for early blossoming. This hardy orchid, native to China, Japan, Taiwan, and Vietnam, is delightfully easy to grow. It is a terrestrial orchid that requires no extraordinary care and produces rose-mauve blossoms that resemble a miniature Cattleya orchid flower. An established clump will produce dozens of flower spikes. I recently moved several plants from too-shady spots into large shallow containers, anticipating the development of clumps in a couple years. They are not particularly frost-tender, but recent frost warnings encourage moving the pots under shelter.

As always, gardening involves the exercise of patience.

Controlling Annual Weeds

 

The gardener’s war on weeds cannot be ignored at this time of the year, as cool-season annual weeds respond to the current temperatures and recent rains. By popping up in our gardens.

The weeds in front of us always command immediate attention, but they also encourage a broader view of weeds. Let’s review the sources of the problem and the strategies for weed control.

The first step in control involves knowing the three broad categories of weeds: annuals, which are usually the most troublesome, and biennials and perennials, which we will consider on another day.

Annual weeds are those that grow and die in one season. This cycle begins with seed germination and ends with the dispersal of a new generation of seeds.

Annual weeds include two sub-categories: summer and winter annuals, which are also referred to as warm season and cool-season annuals. The names of weeds in each of these groups could be identified, but their botanical or common names are less important than their life cycle.

After Annual Weeds Sprout

Cool-season annual weeds germinate from seed in the late summer or early fall. They grow during the winter, flower, set seed and die from heat in the late spring or early summer. This approximate calendar guides actions to reduce weed growth in the garden. Right now, these pesky plants have already germinated, so the appropriate action is to minimize the production and dispersal of seeds. Do this by removing the flowers as soon as they appear. Depending on the circumstances and other factors, this can be done by plucking the flowers, mowing the weed batch, or pulling the entire plant.

Warm-season annual weeds germinate and grow in the spring, and thrive throughout the summer and into the early fall. They will die by frost, however, in the Monterey Bay area, where frost comes later if at all, these plants can persist for quite a while. Controlling warm-season weeds after germination uses the same techniques outlined above: minimize the spread of new seeds by removing the flowers or the entire plant before, or as soon as, the flowers appear.

Up to half the weeds that are pulled from the garden are still capable of dispersing seeds, so the safest plan is to dispose of them in the green waste. They could be added to a compost bin, but only if your compost maintains a temperature of 160 degrees Fahrenheit or more for three hours or more, the seeds won’t survive.

Before Annual Weeds Sprout

Methods to minimize the production and dispersal of seeds are highly recommended, but inevitably some seeds will make their way into in your garden. Seeds will arrive from weeds that already grow there, or are brought in by the wind, by the dropping of birds, or by hitching a ride on people’s shoes or clothing, animal’s fur, or imported plants, even plants from a garden center. The result of these several sources is the weed seed bank tat exists in all gardens.

All seeds require light and moisture to germinate, so the basic method for discouraging the germination of seeds already in the garden begins with mulch. Two or three inches of organic mulch will deny the seeds light, and most will not be able to sprout.

Viable seeds can remain in the soil for years, waiting for light and moisture. They might be surprisingly deep in the soil. The best plan is to let sleeping seeds lie. The worst plan is to dig up the soil to give the seeds access to light and moisture. If you need to dig up your garden, even to install a new plant, cover the exposed soil immediately after with mulch. Mechanical tilling of the soil will reliably produce a new crop of weeds.

In addition to mulching, close placement of desirable plants also will deny light and moisture to the dormant seeds. In many cases, a closely planted bed is also attractive.

Also, controlling access to moisture with drip irrigation, while controlling access to light with mulch and landscape plants should minimize weed growth significantly.

Finally, let a few weeds grow. You are unlikely with a goal of complete eradication of unwanted plants, and there is some value in the contribution of weeds to the flora and fauna of the garden. In any event, a casual (but systematic) approach to weed control allows you to relax in the garden.

Cold, Rain, and Buttercups

We have had welcome rains, and apparently we should expect more around the time that this column appears. That’s good, but that weather prompts some salient observations.

First, although the drought has been broken for the present, we should regard the present period as a hiatus, rather than an end to dry times. Long-term projections still indicate below average rainfall in future years,

Most importantly, our aquifers were depleted significantly during the drought years, and replenishing them will require many years of at least normal rainfall. We will have to wait for encouraging reports on that front.

Meanwhile, examine your garden for possible negative impacts from the recent cold and rainy days. The plants in my garden are nearly all native to California or other summer-dry (Mediterranean) climates, so they managed well during the dry days.

One exception was a mature Chilean Myrtle (Luma apiculata) that succumbed to the drought, and had to be removed.

That experience recalls a thoughtful comment by Alexander Graham Bell: “When one door closes, another opens; but we often look so long and so regretfully upon the closed door that we do not see the one which has opened for us.” In this case, the tree had grown larger than expected and closer to the house than wanted, so while I regretted its loss, its absence opened space for new plants.

Almost all my succulent plants shrugged off the cold spell, with the exception of a Foxtail Agave (Agave attenuata), which I had been growing in a large container. I planned to plant it in the ground eventually, to provide the space it will need to reach its full size of four feet high and eight feet wide. The plant’s rosette is quite attractive and dramatic, but its distinctiveness is based on its flower stalk, which grows five-to-ten feet, reflexes to the ground and then arches upward again. I learned too late that this plant is unusual among Mexican native succulents for its susceptibility to cold weather. I should have covered it, or brought it inside. It lost some leaves, but now appears to be coming back.

I have been taking advantage of the fine weather between rainstorms by catching up (with help!) on the seasonal weeding tasks. This work includes the annual battle with Bermuda buttercup (Oxalis pes-caprae), a South African native that thrives in California’s coastal gardens, and opens its bright yellow blossoms in late winter or early spring.

Bermuda Buttercups

Bermuda Buttercups

I have been puzzled by the relentless and random spread of this annoying plant. The explanation on UC’s Integrated Pest Management website (ipm.ucanr.edu/) has been incomplete:

“Viable seed never has been documented in California, and rarely has it been seen anywhere else in world. Foliage dies and the bulbs become dormant when temperatures rise in late spring and summer. Bermuda buttercup reproduces vegetatively by bulbs and spreads when plants are divided or soil containing the bulbs is moved to un-infested areas.”

I have learned that this plant is tristylous, an uncommon morphology meaning that it has three flower shapes (morphs). All the flowers on a given plant will have the same shape, but the pollen from a flower on one morph cannot fertilize another flower of the same morph.

Tristyly does not necessarily affect the propagation of the Bermuda buttercup, but it might explain its spread in gardens, and provide a clue to its management. The search goes on!

Meanwhile, we continue with weeding and mulching, and preparing to enjoy the garden in the spring.

Summer Priorities

 

My first summer priority in the garden centers on weeding, and my regular resolution to walk around with a weed identification book. My desire to know the names of garden plants extends to the weeds that know so well how to grow under all conditions, and without nurture.

One new arrival is the Black Nightshade (Solanum nigrum), which is a relative of several desirable plants, including potatoes, tomatoes and peppers. It is common throughout California.

7-17-15 - Solanum_nigrum

This weed grows up to four feet tall. UC’s Integrated Pest Management website describes its leaves as follows: “The first true leaves are spade shaped with smooth edges and the lower surface is often purple. Later leaves are increasingly larger, egg shaped, dark green, often purple tinged, with a smooth to slightly wavy edge, and covered with short non-glandular hairs and some glandular hairs.”

The plant produces small, star-shaped white flowers that develop in blackberries about one-quarter inch in diameter. Some varieties have edible berries, but their taste is not good enough to offset risking that you have a different variety in your garden.

To its credit, the Black Nightshade pulls up easily.

Another member of the Solanaceae, the tomato, is also flourishing in my garden. This year, I planted two cherry tomato varieties from Love Apple Farm, chosen at San Francisco Flower & Garden Show. A volunteer from last season, ‘Sweet Million’, popped up, so with minimal watering, I have an abundant harvest of cherries for salads and casual snacks outdoors.

Then, a friend gave me a seedling of a Black Krim (Solanum lycopersicum), a heirloom tomato from Russia. This plant needs consistent moisture. If the soil is allowed to dry out between watering sessions, the fruit has a tendency to crack.

Tomato fanciers relish its “rich, salty flavor,” so I’m watching for the fruits to ripen enough for a taste. When fully ripe, the tomatoes are a dark reddish purple or brown (not truly black) and with dark green around the top, or shoulder.

Screen Shot 2015-07-30 at 11.57.09 AM

Black Krim Tomato Credit: www.gardenharvestsupply.com/

Another priority for the summer is mulching, which is actually a good practice for any season, whenever the soil is uncovered. Mulching discourages weeds, slows the evaporation of moisture, creates a good environment for soil microbes, and protects the soil from erosion.

Organic mulches are available in garden centers in bags of 1.5 or 2 cubic feet. For larger gardens, chipped material from a tree service is a low-cost alternative. Such material is coarser than commercial mulches, and consequently lasts longer.

A tree service will drop a load of chips on your property without charge, if you can receive it on their schedule. Another option is load a yard or two of chips into your truck, at the service’s premises. Call ahead!

A responsible tree service will not bring or offer chips from diseased trees, but otherwise the chips will be from a randomly chosen pruning project. All chips are good in the garden, but some are more aromatic than others. Think eucalyptus!

Finally, during these warm summer months, we can anticipate significant rainfalls this winter, based on the meteorologists’ assessments of the El Niño ocean conditions. Potentially heavy rains won’t completely end our drought, but it could help a lot.

***

Gardening in July

During this hot and dry month, the avid gardener should pursue seasonal tasks to keep the garden looking good and prepare for the change of seasons.

Irrigation should be a high priority to sustain plants that must have a ration of water during the drought. Pass by Mediterranean climate plants, which are accustomed to dry summers. A little moisture will perk up even these rugged individuals and extend their best days, but a better use of scarce water resources would target the garden’s thirstier specimens.

Roses, for example, could produce another bloom cycle during July if treated to a balanced fertilizer and watered deeply. Other candidates for regular watering are plants in containers, which can dry out fast.  First confirm that your water usage is within current restrictions.

If your garden consists mostly of Mediterranean climate and succulent plants, this year’s drought should not cause alarm. On the other hand, if you have a thirsty lawn, consider replacing it with plants of the summer-dry persuasion. The same strategy would be appropriate for plants from tropical, riparian or boggy areas.

Blossoms to enjoy in July include gladiolus, agapanthus and fuchsia, and fragrant Oriental hybrid lilies, e.g., pure white ‘Casablanca’.

Casablanca Lily

I am also enjoying blossoms of Chitalpa tashkentensis ‘Pink Dawn’ trees, which are crosses of catalpa and desert willow. They put on a show reliably around Independence Day, but opened a little earlier this year.

IMG_0291

The Corsican hellebores (H. argutifolius) have finished their winter-to-spring display, and leaned down their bloom stalks to drop seeds all around. The seasonal task is to cut stalks to their bases to make room for the new growth, which has already started.

The tall bearded irises also have finished blooming for this year. They will look best after the flower stalks are cut down, the leaves fade, and the rhizomes enter dormancy. Every four years, during the period from mid-July to mid-September, dig and divide the rhizomes to promote blooming for net spring.

In July and August, plant autumn-blooming blubs, e.g., autumn crocus (C. speciosus and C. sativus), meadow saffron (Colchicum autumnale), and spider lilies: Lycoris squamigera with lilac or rose pink blooms and L. radiata with orange-red blooms.

Control cool-season annual weeds, currently going to seed: bindweed, chickweed, crab grass, knotweed, lambs-quarters, mallow, pigweed, purple deadnettle, groundsel, nettle, purslane, speedwell and spurge, as well as field grasses. Dispose of seeds in the green waste not in the compost bin! The invasive cheery yellow Bermuda buttercup (Oxalis pes-caprae) has already faded, leaving clusters of bulbs to sprout next spring.

Renovating the Garden – More Planning

Gardening and landscaping involves planning before getting your hands in the soil.

Last week’s column, which was about renovating a garden, recommended four preparatory actions:

  1. Draw a Diagram of the Property
  2. Decide on Basic Design Concepts
  3. Establish Objectives for the Finished Landscape
  4. Set Priorities for Development

Once the gardener has completed those actions, he or she still has to additional tasks to complete. Those tasks are the focus of this week’s column.

Remove Unwanted Plants

A neglected garden probably motivated the landscape renovation project. Neglect often includes trees and woody shrubs that have outgrown their space, lack a role in the new design, or are unhealthy. In some cases, this task will require contracting with an arborist or laborers. Check local ordinances before removing trees.

All herbaceous plants that are unwanted are defined as weeds. These include garden plants and grasses as well as common weeds. Pull or dig larger plants, then remove grasses and weeds efficiently with chemical-free solarization. This method covers the target area with clear plastic so that the sun raises the temperature of the soil, killing weeds, pathogens, nematodes, and insects. For details, see the University of California’s free online publication “Soil Solarization for Gardens & Landscapes.”

Removing weed plants with a do-it-yourself approach could be time-consuming and frustrating. Consider contracted services to get the job done quickly and thoroughly.

Remove Unwanted Hardscape

If your garden includes paving, e.g., sidewalk, patio, walls or outbuildings that are not included in the new design, remove them to free your progress. Again, consider contracted services to speed the work. This would be a good time to invite a disinterested friend to comment on your garden accessory collection, and to remove items that are no longer assets.

Analyze Soil Structure

The gardener should know the structure of the garden’s soil. An ideal soil would have 45% minerals (sand, clay, silt), 5% organic material (plant and animal), 25% air and 25% water.

Click to Enlarge

Soil Textural Triangle

The Soil Texture Triangle illustrates various combinations of sand, clay and silt that might be found in a garden. The mineral content of ideal garden soil, called loam, should be about 40% sand, 40% silt and 20% clay. A simple method to analyze your garden’s soil texture, involves placing a sample of your soil in a jar with water, shaking  and then letting it settle into density layers. Here are Organic Gardening’s brief instructions for a soil texture test.  Also, check out this helpful article by the Marin Master Gardeners.

Notice that these preparations do not include buying plants! For many gardeners, the primary strategy for improving the landscape is to buy plants. That approach, without an overall plan, weakens the landscape design and wastes time and money.

Enjoy your preparation! The fun stuff (selecting and installing plants) comes next.

Gardening Ideas for Fall

Recently, we have considered seasonal projects: harvesting annual seeds for planting and planting bulbs. Here are more timely garden projects.

More about bulbs: gophers avoid daffodils, which are toxic to them, so encircle a favored bed with daffodils to produce both a gopher barrier and a pleasing display for the spring. This project works best with island beds and costs least with wholesale prices (as little as 30¢ per bulb). A good source for daffodils by the hundred: Van Engelen, Inc., at www.vanengelen.com or (860) 567-8734.

Renovating Garden Beds

The fall is the ideal time to renovate a bed that has become neglected, overgrown or plain boring. First, clean out everything unwanted, reserving plants small enough to be relocated or given to friends.

Every three years, divide plants with rhizomes, tubers or bulbs. Divide overgrown plants by cutting their root balls into two or more segments, and replant.

Then, add compost, cultivate, and add fertilizer.

If the bed is larger than four feet in any dimension, install narrow paths to provide access to the plants without compressing the soil or stepping on plants.

Then, select plants that are right for your climate and the bed’s sun exposure, and that will grow to appropriate sizes. Also, choose plants that will combine well and please your eye.

Finally, plant, mulch and water. Keep watering until the rains take over.

Controlling Weeds

The early fall is also time to control both annual and perennial weeds.

Annual weeds include bindweed, chickweed, crab grass, knotweed, lambs-quarters, mallow, pigweed, purple deadnettle, groundsel, nettle (common), purslane, speedwell, spurge and yellow oxalis.

Perennial weeds include bindweed, burdock, dandelion, dock, ground ivy, horsetail, Japanese knotweed, plantain, poison ivy, purslane, quackgrass, thistle, ragweed and anything else you might have.

The primary strategy for organic weed control is to remove weed seeds before they mature and are dispersed. Hoeing weeds before they set seed can be effective with annual weeds.

This method certainly helps to reduce the spread of perennial weeds, but it leaves behind root segments that could re-grow. For this reason, perennial weed control includes removing the entire root system by pulling or digging. Persistence is the gardener’s friend!

Other organic approaches to weed control include providing a three-to-four inch layer of mulch between plants, to deny weed seeds the light and air they need to grow. Dense spacing of desirable plants also can crowd out weeds.

Finally, drip irrigation systems deliver water to desired plants and deny water to weeds.

Enjoy gardening in the fall!

More

A helpful resource for organic weed control is the website, Pests in Gardens and Landscapes: Weeds, maintained by the University of California’s Integrated Pest Management Program. This site includes weed photos, articles and fact sheets in individual weeds that are common in California gardens and landscapes.

A Seasonal Pest

For the past several days, I have been pulling oxalis seedlings from my garden. There are 800 species of oxalis, some of which are desirable ornamental plants, but the species in my garden is no prize.

The pest in my garden is Oxalis pes-caprae (Bermuda Buttercup or Sour Grass), a South African plant that has naturalized in the Monterey Bay area’s similar climate. The plant has clover-like leaves and a bright yellow flower. It’s not unattractive, but it reproduces rapidly and could take over the entire garden in time.

Leaves, root, bulblets

Ocalis-pes-caprae

It reproduces by multiplying its small bulbs, which are around one-quarter inch in diameter. One bulb can produce ten in a single season.

It’s theoretically possible to excavate 100% of the bulbs, but this is time-consuming and unlikely to be successful.

The most effective approach is “old bulb exhaustion,” which involves removing the top growth before it can flower. In this area, flowering occurs in February, with sunnier spots blossoming earlier than shadier spots. The idea is to deprive the old bulb of nutrients that would be provided by the leafy growth above ground, so that the new bulbs will die off.

It is best also to disrupt the new bulbs by cultivation, but this might be difficult if the pest has started close to desirable plants.

In any event, this process requires tilling to remove any new growth that appears in about two weeks. A Dutch hoe, which is good for shallow cultivation, would make short work of the new growth.

Several products are marketed as controls for this pest and other broadleaf plants: Weed-B-Gon Chickweed, Clover & Oxalis Weed Killer, Roundup, Finale, Oxalis X, etc. I do not use synthetic chemicals in my garden, because of concerns that they will harm plants, beneficial insects, microorganisms and perhaps myself and other mammals, in addition to the plants or pests they are intended to control.

There are less toxic concoctions for controlling this plant. For example, one foliar spray recipe calls for two cups of white vinegar, one teaspoon of baking soda, and one teaspoon of liquid detergent. Reportedly, this spray will kill the oxalis plant’s top growth but not the bulbs. It should not be sprayed on desirable plants.

Another control strategy is let chickens snack on this weed. Reportedly, they like it a lot.

The gardener engaged in weed control adventures can find confidence in the knowledge that no plant will survive the persistent removal of its top growth.

Finally, a frustrating encounter with Oxalis pes-caprae should not bias the gardener against less invasive species from the wood sorrel family. One of my favorite nurseries, Annie’s Annuals and Perennials, lists seven Oxalis species as desirable garden plants.

Enjoy your weed-free garden.

More

More information on this weed from the California Invasive Plant Council.