Plants Preferred by Other Insects

In a recent column, we described the first report of the Royal Horticultural Society’s “Plants for Bugs” study, which focused on Pollinators. In this column, we’ll look at the second report of this study, “Gardens as Habitats for Plant-Dwelling Invertebrates” (August 2017), which is about insects and invertebrates that live in our gardens, and the plants they love.

Let’s first review the related taxonomic issues.

Gardeners should appreciate the difference between “bugs” and “insects.” The title of the RHS study uses “bugs” to refer informally to a large and diverse group of invertebrates. To be precise, true bugs are members of the order Hemiptera, which is within the class Insecta. There are some 50,000 to 80,000 species of true bugs, all of which have sucking mouthparts. Examples of true bugs include cicadas, aphids, planthoppers, leafhoppers, and shield bugs. By the way, none of the true bugs are pollinators.  

The Insecta is a class within the phylum Arthropoda, which includes 6 to 10 million species, all of which are hexapod (six-legged) invertebrates.

To put the true bugs in perspective, they represent only a tiny fraction of the Insecta.

Returning now to the RHS study, the first report addressed garden insects that are Pollinators, which include bees, butterflies, and a few other insects.

The second report addresses other significant categories of garden insects, which include these groups:

  • Herbivores. Invertebrates that feed on living plants, using chewing mouthparts (e.g., caterpillars) or sucking mouthparts (aphids are a familiar example).  
  • Predators. These are invertebrates that eat other invertebrates. These include lacewings, beetles, e.g., ladybirds, some true bugs, spiders, and parasitoid wasps, which kill their hosts.
  • Omnivores. These invertebrates feed on both plants and other invertebrates. This group includes the harvestman (a spider relative), earwigs, and aphids.
  • Detritivores. Invertebrates that feed on decomposing organic matter. Examples include springtails, woodlice, and some beetles.
Common Lacewing (Chrysopa species) photo by JJ Harrison, shared via Wikimedia Commons

These groups, along with the Pollinators featured in the first report of the RHS study, constitute a vital component of the garden’s balanced ecosystem. In addition to breaking down dead plant material, these plant-dwelling invertebrates provide food for other wildlife, including birds, reptiles, and small mammals.

In their four-year Plants for Bugs study, the RHS scientists used suction samplers to collect about 18,000 of plant-dwelling invertebrates. Their samples included 18% Herbivores, 3% Omnivores, 18% Predators, and 61% Detritivores. They also collected about 4,700 uncategorized invertebrates.

They recorded these collections of invertebrates separately from plants that were native to three different areas: the United Kingdom (called ”natives”), other areas in the Northern Hemisphere (“near natives”, and Southern Hemisphere (“exotics”).

As they found with Pollinators, the scientists found that the native plants supported the largest numbers of the plant-dwelling invertebrates. By comparison with the native plants, the near-native plants supported about 10% fewer invertebrates, and the exotic plants supported 20% fewer.

Overall, these observations indicated that native plants are most important in supporting these groups of invertebrates, and the near-native and exotic plants also provide effective support at somewhat reduced levels.

The study concluded that gardens should emphasize native plants, but could include near-native and exotic plants as well. The most important consideration was to develop a dense planting scheme so that the garden could support all kinds of plant-dwelling invertebrates as part of a balanced ecosystem.

Exotic plants are important to include in the garden for Pollinators because Southern Hemisphere plants often bloom during months when Northern Hemisphere plants are dormant, and thus provide Pollinators with food sources for a longer period of the year.

Although this study was conducted in England, its findings could apply reasonably also to gardens of the Monterey Bay area. With that interpretation, we would treat California native plants as the “natives,” plants from the Mediterranean climate areas as “near natives,” and any other plants as “exotics.”

These two studies support the usual assessment that native plants are most supportive of local plant-dwelling invertebrates, while showing that near-native and exotic plants also provide effective supports for the garden’s ecosystem.

These findings might apply as well to local birds, reptiles and mammals, but demonstrating those relationships would require another study. For example, while berry-producing shrubs provide natural food for birds, separate counts of bird visits to native, near-native, and exotic berry-producing shrubs might yield interesting results.

That would be a very challenging assignment!

WInter Bloomers from Mexico

There’s a lot that I’m thankful for, including a couple fall-season bloomers in my garden.

I have recently mentioned these two plants, which are natives of Mexico, but they are blooming right now and deserving of attention.

The first is the Tree Dahlia, which produces attractive blossoms in November, and also astonishes me each year with its annual growth. The Tree Dahlia (D. Imperialis) originated in the mountains of Mexico and Guatemala. It is an historic favorite of Mexican gardeners, and an ancestor of the garden dahlia, Mexico’s national flower and a current focus of hybridizers.

Tree Dahlia in bloom

Botanists travelling with the Spanish conquistadores discovered the Tree Dahlia and brought it to the Royal Gardens of Madrid by the late 1700s. The genus became popular throughout Europe and was recorded in the United States bas early as 1821.

In one season, a Tree Dahlia with established roots will grow up to twenty feet tall, with clusters of lavender pink blossoms high in the air, to be enjoyed from below. The blossoms are free of fragrance, which is not a problem given their height.

If a Tree Dahlia were to be planted below a deck of just the right height, people could appreciate the blossoms more closely. That would be a fine deck-plant combination.

The magical nature of this plant is its annual cycle. Around March, after it finishes blooming and its leaves have faded, the canes can be cut to about six inches from the ground to stimulate new growth from the roots.

The canes can then be cut into sections and planted to start new plants. Each section should have at least four leaf nodes and still leaking liquid sap. These cuttings are then planted right side up in sandy soil or potting mix and watered from time to time, until they show new green shoots. This plant is not difficult to propagate!

I first encountered the Tree Dahlia several years at a Master Gardener workshop, when someone shared cane sections. I planted those sections at the edge of my garden, in a partially shaded area. They grew quickly.

This plant is available commercially at least occasionally from Annie’s Annuals and Perennials, and few other sources. It’s a good example of a “pass-along plant.”

Given an appropriate site, it is a spectacular seasonal addition to the landscape.

Blossoms of the Daisy Tree

A second favorite plant at this time of the year is another Mexican native, the Daisy Tree (Montanoa Grandiflora).  This is an upright, evergreen shrub that grows up to ten feet tall and wide. It develops large, deeply lobed, rather leathery tropical looking leaves.

In November, it produces clouds of daisy-like flowers, white with yellow centers, with the fragrance of chocolate or freshly baked cookies. After about a month, the blossoms are replaced with long lasting “bouquet-worthy” chartreuse seed heads.

In the early spring, the branches should be cut to the ground to stimulate a new cycle of growth. Like the Tree Dahlia, this plant grows vigorously from its roots to produce a striking new presentation each year.

My first introduction to the Daisy Tree was during a visit to the Esalen Institute on Big Sur, during a stop on a tour hosted by the Pacific Horticultural Society. I was impressed by the plant, and searched diligently for a small plant for my garden. It’s not offered widely, but I found it it eventually at Annie’s Annuals & Perennials.

This is a large shrub, so it works best in the landscape if it’s placed in a space large enough to accommodate its spread, and close enough to a walkway to enjoy its fragrance. While it is evergreen, the recommended practice for rejuvenation pruning means that the garden design should anticipate its periodic absence. When the gardener cuts down the Daisy Tree, he or she might plan to fill the void with wildflowers.

Plants like the Daisy Tree and the Tree Dahlia bring dynamic qualities to the landscape, and welcome gifts to the holiday season. 

Color Combinations in the Garden

Combining floral and foliage colors can be an enjoyable and challenging aspect of garden design. The plant kingdom offers a vast range of possible color combinations, including mixes of the various shades of green.

When planning floral color combinations in the garden, a basic consideration is to select plants that will display their colors at the same time. This issue alone can require compiling notes regarding the bloom periods of plants under consideration, drawing on reference materials such as Sunset’s Western Garden Book.

In addition, the selected plants should have similar requirements for exposure, irrigation, and drainage.

Then, it will usually be desirable to select plants of similar size, so that the blossoms will be in fairly close proximity for optimal effect.

Once the gardener has satisfied these placement and cultivation considerations and has identified a good number of candidate plants, the focus can be on deciding the actual color combinations.

Unless the gardener has a natural gift for visualizing and evaluating color combinations, a color wheel is a useful tool for combining colors in a systematic manner, presenting the spectrum of colors in the familiar sequence of red, orange, yellow, green, blue, indigo and violet (ROYGBIV). They vary primarily in the range of hues presented. A very basic wheel will show just the three primary colors: red, yellow, blue. A more advanced wheel will include the secondary colors: green, orange, purple. An even more detailed wheel will include the six tertiary colors, which are created by mixing primary and secondary colors.

A search of the Internet will produce numerous examples of color wheels for convenient reference in planning color combinations in the garden.

Color theory can be a lengthy study for visual artists and others seeking to appreciate the subtle relationships among colors.  Most gardeners will need only familiarity with the basic color relationships on the color wheel: complementary (opposite colors), analogous (adjacent colors), triadic (three colors evenly spaced), etc. For illustrations of these and other relationships, search the Internet for “color harmonies.”

Real-world combinations might be reflect one of the formal color harmonies, but are as likely to be only a rough approximation. For example, this photo shows a chance mix of a blue-purple salvia blossom and a pink/white geranium blossom. This is a roughly analogous combination, but because the color green adds to the display, it qualifies as a roughly triadic harmony. In any event, if it pleases the gardener, it’s a success!

Salvia and Geranium combine pleasing colors

Another example of a chance mix shows succulent foliage in various shades of green. This too is a roughly analogous combination based on a small sample of the many greens that appear in many gardens.

Succulents provide several green hues

Here is a brief reality check on color combinations in the garden.

  • Creating classic color harmonies requires lots of study to select plants with similar cultivation needs, compatible sizes, and the “correct” floral or foliar colors.
  • Many plants will present pleasing combinations of colors virtually by chance. While beauty is in the eye of the etcetera, it’s difficult to imagine mismatched colors in nature.
  • Garden magazines often include breathless excitement over apparently random color combinations, and describe them with verbiage about their inspired creativity,

If you discover two or more plants that would provide a good mix of colors in your eyes, move them together or keep them together, and enjoy the effect. Garden design by the book can be time-consuming and frustrating, while botanical serendipity can be a delight.

Enjoy your garden!

Strategic Use of Specimen Plants

Recently, we focused on three basic priorities for landscaping: develop a short list of plants, install significant numbers of each kind of plant, and select some unfamiliar plants that will fit into your plan.

A complementary strategy emphasizes the strategic use of specimen plants, which are “unusual or impressive plants grown as a focus of interest in a garden.” A specimen can thought of as an example of a category, but

A plant could function as a specimen plant if it is sufficiently large, especially showy, striking in form, or quite unusual. Note that a plant doesn’t qualify as a specimen plant simply by being an isolated instance of some plant. In other words, a garden of single examples of various plants does not work as a landscape of specimen plants. 

Conversely, a plant that works as a specimen because it is large, showy, striking or unusual probably would not work as a component of a mass planting. Instead, a specimen plant complements a mass planting.

Many plants could qualify as a specimen plant. Garden designers often will choose a tree of appropriate size as a specimen plant. Japanese maples, for example, are popular selections for this purpose.

The placement of a specimen plant contributes significantly to its effectiveness. In many cases, the specimen will succeed best as a contrast to a fairly large grouping of plants, especially foliage plants, e.g., hedges.

A “large, showy, striking or unusual” plant that is apart from other plants also could function as a specimen plant.

As an example from my garden, we have a Kennedia beckxiana ‘Flamboyant’, which is an evergreen climber in the Pea Family (Fabaceae), and one of the UCSC Arboretum’s Koala Blooms Australian Plant Introductions. The plant’s common name, Cape Arid Climber, refers to a region in western Australian.

Kennedia becksiana ‘Flamboyant’ climbing on a stairway

The plant’s generic name honors a British nurseryman, John Kennedy, and its specific name honors Gustav Beckx, a 19th century Belgian consulate General in Australia.

It earns the variety name ‘Flamboyant’ with its 2-inch long orange-red flowers with a showy large lime-green central spot at the base of the reflexed keel petal.

Kennedia beckxiana blossom (Wikimedia photo by Christer Johannson via Creative Commons)

I acquired a five-gallon plant about a year ago from the Arboretum, and installed it to climb on a stairway. It has grown vigorously there, and will soon reach its mature height of ten feet.

My online research into the cultivation of this robust plant suggests that it should be cut back heavily after flowering to prevent invasive growth.

Given its prominent location and showing blossoms, my Cape Arid Climber will hold its own as a botanical focal point.

Look for a spot in your garden where a specimen plant could attract the eye and add interest to your landscape. You might have a fine selection already in place, or one that could be moved to such a special location. If you have “spotted the spot” but don’t have a specimen plant in hand, you can anticipate the pleasure of choosing one for your garden.

Mark Your Calendar

The Monterey Bay Area Cactus & Succulent Society will hold its Fall Show & Sale on September 29th and 30th, in nearby San Juan Bautista, where there is enough space for Society members to fill some eighty tables with fascinating plants for sale or display. We’ll have full details about this event in next week’s Home & Garden section, so be sure to schedule the date for this opportunity to acquire succulent plants for your landscape.

Landscaping Priorities

This year’s Fall Equinox lands on September 22, marking the unofficial start of the planting season.

Installing new plants in your garden during the fall provides them time to establish roots and prepare for leafing out and blooming in the spring. Ideally, we would have our historic pattern of winter rains during this time, so that the plants will have ample moisture to work with.

An additional benefit of this planting schedule might include end-of-season plant clearance sales at your favored garden center or nursery. You can feel like a savvy garden shopper when you acquire plants at good prices in the fall, and resist the temptation to stock up in the spring, when small plants have been forced into seductive blooms with nitrogen fertilizers.

The planting season is still a couple weeks away, so right now is a good time for planning to select and install plants in your garden. Having a plan when you open a mail order catalog or walk into a garden center will prepare you to focus your targets and avoid becoming overwhelmed by the array of possibilities.

Strategies for garden planning in the Monterey Bay area include emphasizing drought-tolerant plants, or California native plants, or a particular theme of your own choosing. Earlier versions of this column have addressed such strategies.

Today’s column describes additional strategies suggested by Rochelle Greayer, author of Cultivating Garden Style (Timber Press, 2014). In her online newsletter, Pith + Vigor, Greayer recently identified three mistakes that gardeners make when designing with plants:

  • Too many different plants
  • Not enough plants
  • Planting just the plans you know.

Let’s consider positive strategies in these three areas.

First, develop your landscape around a just nine to twelve different plants. Selecting plants in this short list for specific roles will bring order and cohesion to the landscape, and avoid the chaos that too often results from impulsive additions of individual plants.

Second, once you have selected your short list of plants, install lots of them. This strategy is related to adding plants in clusters of three, five, or any other odd-numbered quantity, to present them in a natural and pleasing manner. As you reach larger numbers, install the plants in swathes or bands to provide a landscaping effect. Greayer says, “Repetition gives a scheme flow and rhythm. Repetition is a savvy designer’s best trick.” For example, I recently planted two parallel arcs of blue and yellow irises as a color statement for next spring. Over the next few seasons, these plants will increase to provide increasingly dramatic displays.

A swath of Dalmation Iris (Iris pallida ‘Variegata’) backed up with Lavender plants
A bed of hardy geraniums (Geranium × cantabrigiense ‘Biokovo’ ) with a garden art pheasant

Related to the idea of repetition planting is the installation of plants with close spacing. While you might be tempted to spread plants out to cover space in the garden, having open areas between plants reduces their visual impact and invites the growth of weeds. Close spacing reflects the natural tendency of plants to propagate and develop into colonies. It also functions as “green mulch,” denying weeds the sunlight they need to develop.

Third, explore the wonderful world of plants to find good choices for your short list of selections for the landscape. It’s always important to select plants that are suitable for the climate, soil and exposure of the locations for which you are planning, but there are always many interesting selections that are both suitable for your garden and new to your experience. Relying on common and familiar plants will doom your landscape to being (gasp!) ordinary. Discover interesting plants that will bring excitement to your garden, and invest time in learning how to cultivate them successfully.

In review, there are three strategies for planning the development of your garden during this planting season: develop a short list of plants, install significant numbers of each kind of plant, and select some unfamiliar plants that will fit into your plan and provide a fresh new look to your landscape.

Enjoy this fall’s planting season, and your garden’s coming spring!

Planning a Cutting Garden

An ornamental garden, as contrasted with an edible garden, often will yield a number of blossoms suitable for occasional floral arrangements. To produce blossoms specifically for indoor display, however, the gardener needs to develop and maintain a cutting garden.

A cutting garden can be as small or as large as the gardener chooses. Because it serves as a “blossom factory,” it need not be a landscaping feature. It could be a rectangular space with plants in orderly and efficient rows. The bed could be as short or long as desired, but should be no more than about four feet wide, with access on both sides for cultivation, maintenance and harvesting.

The bed should follow the familiar basic standards: fertile soil with good drainage, six-to-eight hours of sunlight, and convenient access to irrigation.

A grouping of Dahlia ‘Jomanda’. Image courtesy of the Monterey Bay Dahlia Society

Plant selection should reflect the gardener’s preferences, which might be based on personal favorites, intended combinations of blossom colors, or other criteria. Unless the gardener has particular plants in mind, the initial plant selection might be based on expert recommendations.

The best source I know for such recommendations is Debra Prinzing, advocate for American-grown flowers, author of The 50 Mile Bouquet and Four Seasons of Locally Grown Bouquets from the Garden, Meadow and Farm. Here are her current top ten picks for summer bouquets:

  • Dahlia — medium-sized forms
  • Zinnia — Queen series for soft colors; Persian Carpet varieties for textural accents
  • Sunflower—‘Plum’, ‘White Night’, ‘Moulin Rouge’, ‘Strawberry Blonde’, ‘Chocolate’
  • Cosmos—Double Click and Cupcake series
  • Ammi—(called false Queen Anne’s Lace) ‘Dara’, ‘White Dill’, and ‘Green Mist’
  • Yarrow—both pure colors and muted/pastel varieties
  • Shasta Daisy—especially double forms like ‘Crazy Daisy’ and ‘Sante’
  • Roses —try some in the caramel and terra cotta range: ‘Hot Cocoa’, ‘Cinco de Mayo’, ‘Pumpkin Patch
  • Herbs— purple basil and ‘Berggarten’ sage for foliage and fragrance
  • Nigella—blue blooms, unusual seedpods, and lacy greenery are eye-catching

After the gardener has selected plants for the cutting garden, the options are to buy and install small plants at a garden center, or plant seeds. Buying small plants involves paying someone for starting the plants from seed, so it’s faster and more expensive than growing your own. But choices could be limited Planting seeds requires less expense, and also provides access to a wide range of options.

Seeds should be planted at the right time of the season. Some seeds should be started indoors in early spring; others are best planted in the ground in early spring, early summer, or mid-summer/early fall. This month is still a good time to start certain seeds for a cutting garden.

An excellent source of recommendations for seasonal planting of seeds for flowering plants is local expert Renee Shepherd. For a timely list of flowers to plant now, browse to her website, click on “Gardening Resources” and search “Time to plant Renee’s Garden Seeds.” Her seeds are among those on display in garden centers.

Seed packets typically have brief instructions for successful planting of seeds.

Flowering plants that have multiple, branching stems will produce maximum yield of good quality flowers with long stems when their primary stems are cut back (“pinched”) at an early stage of growth. Examples include carnation, cosmos, dahlia, and snapdragon.

Pinching is not appropriate for plants that produce just one flower per plant. Examples of such plants include flax, stock, and single-stemmed sunflowers.

Growing your own flowers for bouquets and floral arrangements is one of the most satisfying garden activities. A good time to start your own unique cutting garden, and beginning to gain experience and enjoy the process,  is mid summer/early fall. That’s right now!