By Carolyn Melf, Butte County Master Gardener, August 12, 2016.

If you haven't trimmed and divided your iris this summer, now is the time to do it.

Bearded iris plants need to be thinned or divided every 3-5 years.  A single rhizome sprouts new rhizome offshoots many times over the years, developing into a heavy crisscross clump, often choked with old leafless rhizomes.  Eventually the mass of leaves will exclude sun and air from the roots.  This will lead to poor flowering and often weakens the plants, making them more susceptible to insects and diseases.

It is best to divide iris in July or August.  Clumps may be thinned by removing the old divisions at the center of the clump, leaving new growth in the ground.  Better yet, dig up the entire clump with a garden fork and lift it from the soil.  Separate the rhizomes with a knife or by gently pulling them apart.  Retain the younger, healthiest three- to four-inch-long rhizomes containing five leaves.  Discard the plants that have a bloom stalk as well as those that are leafless, soft or old. 

With a sharp stream of water from a garden hose, remove all soil from the roots and rhizomes.  Trim roots to about 3 inches and trim the leaf fans to 6 inches to prevent them from tipping over when you replant them.   Let them dry before replanting.

Iris are greedy plants and prefer to be placed in virgin soil, but you can fool them by amending the soil with well-composted planting mix.  Rhizomes should be placed 18 to 24 inches apart.  For each one, dig a hole, place a mound of soil in the center of the hole, then place the rhizome on the mound and spread its roots downward.  Cover with 1 inch of soil.  Don't plant them too deep!  Plant additional leaf fans in the planting bed facing the same direction. This way the rhizomes will all grow in the same direction and there will be less crowding.

Newly-set plants need moisture to help their root systems become established.  Water weekly if the weather is dry.

Iris will bloom sparsely the first year after planting but will bloom well in the second and third years. 

By Cindy Weiner, Butte County Master Gardener, July 29, 2016. 

One approach to dealing with drought conditions in the garden is to turn to native plants that are well-acclimated to our local environment.  Some gardeners new to planting natives may be concerned that these plants might require special care, but in general they need not worry. While some natives can be difficult in the garden, most are not, and many are very easy to grow. Three local landscape designers specializing in native plants offer the following suggestions for “no fail natives.” In addition to being easy to care for, these particular plants give a threefold return on one's investment:  they are attractive, versatile, and provide valuable support for wildlife in the garden.

Eve Werner, landscape architect and owner of Eve's Garden Design, likes to use coffeeberry (Frangula californica) as a screen, background or hedgerow. Its blackish berries resemble coffee beans and are very attractive to birds. This evergreen shrub can grow to six to ten feet tall and wide although the cultivar ‘Eve Case' is smaller, only reaching about five feet. It is native to Butte County and grows in Upper Bidwell Park.  Werner says, “This adaptable plant thrives in full sun to shade with monthly to no summer irrigation.”

John Whittlesey, owner of Canyon Creek Nursery and Design, is a fan of Cleveland sage (Salvia clevelandii) for its “fragrant foliage, showy flowers that attract an array of pollinators, and extreme toughness for full sun and little water.” This woody perennial blooms in early summer with spikes of blue flowers in whorls around the stem.  Whittlesey suggests planting them with the robust matillija poppy in larger gardens, or with the white-flowered native yarrow in smaller gardens.  Cleveland sage grows three to five feet tall, although the cultivar ‘Winifred Gilman' is a little smaller.

Jason Mills, owner of Ecological Solutions, suggests, “If you're looking for an evergreen shrub, why not try giving the local and less commonly used hollyleaf redberry (Rhamnus ilicifolia) a shot?” Hollyleaf redberry has small serrated leaves, resembling holly. It grows best in full sun or partial shade. The flowers are small and inconspicuous but develop into beautiful red fruit, which provide food for birds. It grows five to ten feet tall and needs no summer water once established.

Both Werner and Whittlesey recommend California buckwheat (Eriogonum fasciculatum), one of several species of buckwheat that are native to California. Werner says, “California buckwheat is an evergreen shrub with a whimsical, mopsy form, much like baby's breath on steroids. Its pom-pom-like flowers bloom white in summer and then age from dusky pink to deep russet.” Whittlesey likes growing it in a sunny dry border with California fuchsia, penstemon, yarrow, sages, flax and grasses. It attracts many native bees when blooming. California buckwheat grows to about 3 feet tall and wide and needs no summer water once established.

Mills and Whittlesey like using the large perennial bunch grass deergrass (Muhlenbergia rigens). Whittlesey says, “I use deergrass to bring a rhythm and flow into a garden. When in flower in later summer, it has a stronger architectural form which holds through the winter months. It combines readily in front of larger shrubs or as a foil for small shrubs and perennials.” Deergrass forms a dense clump to 4 feet tall and wide in full sun or light shade.

Growing natives can be easy if you give careful consideration to the plant's cultural requirements. Mills states, “In the end it all comes down to putting the right plant in the right spot. We look to nature and try to match the conditions (substrate, moisture, light exposure) found in remaining intact habitats when we create our designs and implement native landscapes. When you get it right, you'll know, as they thrive for years to come with little to no water and maintenance and provide crucial resources for wildlife along the way.”

By Barbara Ott, Butte County Master Gardener, July 15, 2016.

Most gardeners are aware of the national USDA Hardiness Zones and the Sunset Climate Zones.  The USDA zone map is primarily used to assess if a plant has the ability to survive freezes, while the Sunset zones take into consideration a number of other factors as well, includinglength of growing season, timing and amount of rainfall, humidity, wind, and summer high temperatures, as well as winter low temps.  Especially because our local Mediterranean climate experiences a great number of very hot days each year, Butte County gardeners must also pay attention to whether a plant can survive full summer sun plus excessive heat.

Most plant labels will state the lowest USDA zone in which the plant will survive in the winter.  And a label might indicate that the plant can tolerate (or even require) “full sun.”  But how many plants have been purchased because they fall within the appropriate USDA zone and seem to thrive in full sun until that “full sun” climate includes a run of days when temperatures exceed 100 degrees?  A conscientious gardener works hard at placing plants in ways that insure strong growth and survival over time.  And yet many gardeners who have turned to Mediterranean or native plants because of our prolonged drought may find that even some of these plants cannot survive full sun plus full summer heat in the Sacramento Valley. It can be frustrating to do everything in one's power to help plants survive, only to find that those carefully-chosen and maintained plants cannot handle full sun plus extremely high heat. 

Heat damage is subtle.  Plants die quickly when they freeze, but when they experience too much heat they can hang on in a sickly manner as flower buds dry up and fall off; leaves droop and are munched by insects; leaves lose their green coloring; and roots stop growing.  Plants dying from heat can linger on for years, becoming increasingly stunted and chlorotic, until finally enzymes fail and the plant dies. 

How can you find out how much heat a plant can take when placed in full sun or partial sun?  The American Horticultural Society (AHS) has developed a tool that can help us choose appropriate plants for our climate and guide us in placing those plants in optimum locations.  This is the AHS Plant Heat-Zone Map.

The AHS Plant Heat Zone Map is based on twenty years of daily high temperatures gathered from nearly 5,000 weather stations across the country by the National Climatic Data Center.  The color-coded map indicates 12 nationwide zones based on the average number of days annually that an area experiences heat days in which temperatures exceed 86 degrees Fahrenheit.  When temperatures top 86 degrees, plants begin showing signs of physiological damage caused by heat.  The AHS Heat Zones range from Zone 1 (less than one heat day) to Zone 12 (more than 210 heat days).  Chico and Oroville are in AHS Heat Zone 8 (91 to 120 days over 86 degrees); Paradise and Magalia are in AHS Heat Zone 7 (61 to 90 heat days).  The AHS Plant Heat-Zone ratings are based on the assumption that a plant is being adequately watered at all times, because heat damage is linked to an insufficient amount of available water.  The ability of a plant to survive in a Heat Zone (or even outside of its designated Heat Zone) can be affected not only by water use, but also by light exposure, day length, air circulation, and proximity to nearby structures, among other factors.

For example, placing a “full-sun” plant in a morning-sun only location might be appropriate if you are in the plant's hottest recommended heat zone.  And, because on a hot day fast-moving air can quickly dehydrate a plant, taking fences or other structures into consideration when locating a plant, or even planting hedges to cut down on rapid air flow, can be helpful strategies in our somewhat challenging climate.

Alas, at this date most nursery plant labels do not indicate their AHS Heat Zones, but that is changing.  Thousands of garden plants have been coded for heat tolerance, and more are presently being coded.  Here are some examples:

Gardenia jasminoides “Veitchii.”  This plant is listed as USDA Hardiness Zones 8 – 11, AHS Heat Zones 12 – 8, and Sunset zones H1, H2, 7-9, 12-16, and 18-24.  That Heat Zone number indicates that it may do better in the warmer valley areas of Chico and Oroville than in the higher (cooler) ranges of Paradise and Magalia.

Kerria japonica is listed as appropriate for USDA zones 5-9, AHS Heat Zones 9-1, and Sunset zones 2-23; while it falls into our local climate zones on each of these zone maps, in Chico and Oroville our AHS zone of 8 means that placing Kerria where it will get some relief from hot afternoon sun (even though it is a “full sun” plant) may be well advised.

One useful site that lists AHS Heat Zones for plants is http://www.learn2grow.com/plants.

For more information on the American Horticultural Society and its Plant Heat-Zone Map, see AHS Plant Heat Zone Map.

By Cindy Weiner, Butte County Master Gardener, July 1, 2016.

Many people think Chico has the most beautiful campus in the California State University system, due to its attractive landscaping and riparian corridor along Big Chico Creek. Because of the age of the campus (founded in 1887), much of the landscaping is traditional in style, with expansive lawns, eastern trees and an abundance of azaleas and roses. Also, as Michael Alonzo, Supervisor of Grounds and Landscape Services, says, “Nice landscaping is an important recruitment tool for the university, even during the summer, when many parents and potential students visit the campus.”

While this more traditional style is beautiful, it is not particularly well-suited to our Mediterranean climate with hot, dry summers, and therefore requires irrigation several months of the year.  But there are many areas on campus where native plants are featured in the landscaping, and these areas are multiplying in tandem with changes in the built environment of the campus.  New plantings of natives and compatible non-native, water-smart plants are generally added to complement new buildings (such as, most recently, the new Arts and Humanities Building) or where lawn has been removed. According to Alonzo, the goals for landscape remodeling projects are sustainability; bringing harmony to the campus; blending the contemporary look with the more traditional look of older plantings; clustering plantswith similar water requirements together in an effort to conserve water (an approach known as hydrozoning; and educating visitors about the “new” (sustainable, water-wise) California landscaping.

The riparian corridor along the creek contains many mature native plants. This area was overrun with invasive plants such as privet, catalpa, and Chinese trees of heaven, until members of the Chico Creek Stewardship Committee and the student Arboretum Club took on the project of clearing then replanting it with natives propagated by students. Beginning in the early 1990s, this project took more than twenty years to complete.  Some of the trees and shrubs growing here are valley oak, western sycamore, Oregon ash, box elder, black elderberry, redbud and spicebush.

The Creekside Education Garden is on the south side of Big Chico Creek just west of Sylvester's Café. Developed in the spring of 2011, it contains native species historically found adjacent to riparian zones and used by the Mechoopda and other local Indian tribes. Signs indicate the common name, scientific name and sometimes the Mechoopda name of these plants. Deergrass, California wild rose, valley gum plant, and showy milkweed are some of the plants grown here.

The Phenology Garden is located in the raised planting bed at the east entrance to Holt Hall. Phenology is the study of periodic plant and animal life events related to climate conditions, such as flower blooming or bird migration. Planted in 2014, it is used by students to participate in research involving long-term data collection. It contains primarily native plants that require no supplemental water once they become established. Foothill penstemon, alum root, snowberry, sticky monkeyflower and western dogwood are some of the plants in the Phenology Garden.

Just a short distance away, at the northeast side of Holt Hall, a new garden was planted this spring to replace a former
lawn. Designed to resemble a forest understory layer, it contains giant chain fern, bigleaf maple, western dogwood, redbud and western columbine growing under existing mature trees. 

Two large planting beds between the new Humanities building and the Performing Arts Center were also installed in the spring. These contain shade-loving natives such as coffeeberry, evergreen currant, bearberry, Oregon grape and creeping mahonia planted in long swathes.

A new planting area combining both natives and non-natives will replace some of the lawn between the Acker and Shurmer gyms and Yolo Hall and will be installed in the fall. Keep an eye on these new areas to watch these gardens grow and mature.