By Jeanne Lawrence, UC Master Gardener of Butte County, July 13, 2018

Summers are getting hotter in much of the U.S., including our local environment. One way to counteract this change in climate is by planting trees to provide more shade in the summer months. But adjusting to a shadier garden also means shifting to different plant choices. While it is true that most colorful garden flowers (like roses, zinnias, poppies, and hollyhocks) require full sun, there are still many options for blooms available to the shade gardener. White flowered gardenias and pink or blue flowering hydrangeas are common shade plants in our area. Here are some less obvious selections of shrubs that are easy to care for and can provide interest in the shade garden at different times of the year:

A great small shrub for very shady areas is Sarcococca (sweet box). It is evergreen, with dark green leaves and tiny white flowers that appear in late winter or early spring and are very fragrant. Following the flowers are red berries. Once established, Sarcococca will tolerate dry shade. It is especially lovely planted in groups or as a small hedge; several of these shrubs growing together maximizes their scent, which has been compared to that of sweet vanilla. S. ruscifolia is slow growing, but can eventually reach six feet tall and wide; S hookeriana humilis is a much shorter shrub, growing to perhaps one and a half feet. This variety will spread by underground runners to create a good ground cover over time. Sarcococca is a perfect choice for deeply shaded areas under eaves and overhangs, alongside entryways, and under low-branching evergreen trees.

For a spot in the garden that would benefit from some bright color in spring and early summer, consider Kerria japonica. This is a deciduous shrub, but its bright yellowish-green stems provide color in the winter months. Triangular bright green leaves emerge in early spring on thin arching branches, followed by golden yellow blossoms that resemble small roses about an inch in diameter. K. japonica ‘Pleniflora' is commonly found in local nurseries. It can grow eight to ten feet tall and wide, with graceful arching branches covered with double yellow blossoms. Plant K. japonica in a partially shaded spot, where it will get at least four but no more than six hours of sun each day, preferably in the morning hours, or in the early evening after the hottest time of day. After flowering is completed, cut the branches that have flowered back to the ground, allowing this shrub to retain its arching habit.

The genus Spiraea includes many species that do well in lightly shaded areas in our climate. There are two main types of Spiraea: those with long, graceful, arching branches lined with clusters of tiny white flowers (these are often referred to as the “bridal wreath type”); and those with a shrubby growth habit which produce clusters of white, pink or red blossoms at their branch ends. Both types are deciduous, and the leaves of many of these species turn bright shades of red, orange, or yellow in the fall.

Spiraea thunbergii is a bridal wreath type that can reach six feet high and wide, with many thin, arching branches. In early spring, the bare branches are lined with clusters of tiny white flowers. These are followed by very narrow, inch-and-a-half-long, blue-green leaves that turn yellow or reddish brown in the fall. Another stunning bridal wreath type is the fast-growing S. x vanhouttei. On this shrub, diamond-shaped blue-green leaves emerge first, followed by flat clusters of white blossoms covering the plant in mid to late spring.

A notable shrubby type of Spiraea is S. japonica ‘Anthony Waterer.' Reaching three to five feet high and wide, it produces two-to-three-inch wide clusters of deep pink blossoms in late spring and early summer, and will produce another crop of blossoms if spent flower clusters are reliably pruned out. While ‘Anthony Waterer' has bright green foliage, similar pink-flowering varieties have been developed with quite remarkable leaf color. For example, ‘Goldflame' and ‘Goldmound' have bright yellow-green foliage, and the leaves of ‘Limemound' emerge lemon yellow, then turn to lime green.

By planting several different species of Spiraea, you can have blooming shrubs in shadier areas of the garden from early spring into summer, with the added bonus of beautiful fall colored leaves, and often, brightly-colored bare stems in winter.

By Jeanne Lawrence, UC Master Gardener of Butte County, June 29, 2018

It may be too hot outside to even think about putting new plants in the ground, but it's always a good time to take stock of the garden. Are there aging plants that need replacing? Do you have an open area for a large, attractive shrub? Are you thinking about planting a hedge to provide privacy or screen out a less-than-desirable view? Would you like to have flowers to bring indoors for floral arrangements in the spring? If you can answer “yes” to any of these questions, you should think about planting one or more species of Viburnum.

The genus Viburnum comprises over 150 evergreen and deciduous shrubs and small trees, many of which do very well in our Butte County environment. In addition to providing structure and interest to the home garden, many viburnums are drought-tolerant and often provide fruits for birds to feed on. Some species produce highly fragrant flowers. And deciduous viburnum species can add lovely fall color to the garden before their leaves drop.

The following are just a few of the Viburnum species that do particularly well in our area.

Viburnum tinus (Laurustinus). This evergreen shrub is fast-growing in full sun or partial shade and creates a dense hedge of leathery oval, dark green, two-to-three-inch-long leaves. Allegedly only growing to 12 feet, examples have been spotted in Chico that easily reach 15 ft. or more. In early spring, tiny pink buds open up to clusters of white flowers that are long-lasting and fragrant; when the flowers finally drop, they are followed by equally long-lasting clusters of blue/black fruits that are loved by birds and may hang on until summer. V.tinus can be kept tidy by pruning, but if the possibility of a 15-foot hedge alarms you, dwarf and compact varieties are available.

Viburnum carlesii (Korean Spice Viburnum). This is a Viburnum for real lovers of scent in the garden. It has a looser growing habit than V.tinus, is considerably shorter, reaching 6 to 8 feet, and is deciduous. Its springtime blooms are similar to those of V.tinus, with the exception of being more powerfully scented, a lovely surprise in the springtime garden. V.carlesii is also a little more delicate, preferring part shade in our summer heat.

Viburnum davidii. For a lower-growing shrub that provides nice structure in front of taller plants, V.davidii is a good choice. It is evergreen, with large oval leaves of up to six inches. It prefers partial shade, and, if happy, can produce clusters of brilliantly-colored metallic blue fruit.

Viburnum opulus ‘Sterile' (Common Snowball). Deciduous in colder climates, V.opulous is nearly evergreen here. A taller Viburnum, it can reach up to 15 feet, but is easily kept in bounds. Its leaves are lighter green and maple-shaped. In spring it has snowball-like flowers clusters about two-and-a-half inches across, which start out lime green and turn to white. The flowering stems make a spectacular display as cut flowers indoors. This Viburnum bears no fruit.

Viburnum plicatum tomentosum (Doublefile Viburnum). This is perhaps saving the best for last, as the Doublefile may be the most stunning viburnum in the landscape. It is deciduous, but that is all the better for displaying its beautiful tiered growth habit – the branches move outwards in a series of almost parallel horizontal layers, clearly evident as soon as the new shoots begin to appear in spring. In late spring and early summer, white lacecap flowerheads two-to-four inches across line the upper sides of the branches. The flowers eventually give way to red fruits which turn to black. In the fall the leaves turn a pale shade of red, accented by brighter or pinker tones.

These are just a few of the interesting shrubs in this hard-working genus. If you have space for a new shrub, think about adding a viburnum to your garden.

For more information on gardening in our area, visit the Butte County Master Gardener web page at: http://ucanr.edu/sites/bcmg/. If you have a gardening question or problem, call our Hotline at (530) 538-7201 or visit ucanr.edu/p/49588.

ucanr.edu/p/49588

By Cindy Weiner, UC Master Gardener of Butte County, June 15, 2018

On our hot summer days, shady garden areas can offer welcome respite from the heat. One of the challenges of gardening in shade, though, is adding interest through color, because it can be difficult to find plants that bloom in shade. Incorporating native plants in your garden can greatly increase the choices available to you.

One plant suitable for dry shade is Catalina perfume or evergreen currant (scientific name Ribes viburnifolium). Native to Catalina Island and Baja California, it is a small evergreen shrub with glossy dark green leaves that have a spicy fragrance. The arching red stems reach 3 feet tall and spread about 6 feet. Pruning the stem tips will increase the density of the plant. Small rose-colored flowers appear from February to April. The fruit, a reddish-orange berry, isn't commonly seen in garden settings. While Catalina perfume needs no supplemental water once established, it can tolerate more, so it can be grown alongside plants with greater water requirements.

Coral bells and alum roots in the genus Heuchera are herbaceous perennials native to North America. Their large lobed leaves on long stems are evergreen, making the foliage attractive all year. They have tiny bell-shaped flowers held above the leaves in airy sprays on long stems. These plants look especially nice growing in drifts under trees. They grow well in filtered or part shade and require only occasional to moderate water. Their woody rootstocks should be divided or cut back to short stubs every 3-4 years.

Island alum root (Heuchera maxima) is native to the Channel Islands. It grows one to three feet tall and has creamy white to pinkish flowers. Crevice alumroot (Heuchera micrantha) grows on rocky mountain outcrops from central California north to Oregon. It is smaller than island alum root and its flowers are white or pink. Many cultivars of crevice alum root are available in general nurseries. These cultivars have been selected for foliage with silvery, bronze or purple tones. Three of the cultivars are “painted lady,” “Blessingham bronze,” and “purple palace.”

Many local gardeners enjoy growing azaleas for their beautiful flowers in the spring, but few grow the equally beautiful western azalea (scientific name Rhododendron occidentale). It is native to the coastal ranges and the west side of the Sierra Nevada and Cascade mountains of California and Oregon, including Butte County, where it grows along streams or in other moist areas. In fact, a dried specimen of western azalea collected in Cherokee by Annie Bidwell in 1879 is housed in the herbarium of Harvard University. Western azalea blooms in May and June, later than other azaleas, and has large white or pinkish flowers with a yellow blotch on the top petal. The long stamens extend beyond the flower. Unlike other azaleas, the flowers are fragrant. Western azalea blooms best in filtered or part shade; it will grow in full shade, but blooms will be sparse. Too much sun will burn the foliage. The leaves are deciduous, turning yellow in the fall. At maturity it can reach up to ten feet in height. Like other azaleas, it requires acid or neutral soil and routine irrigation during the dry season. Western azalea makes a worthy companion for other acid-loving plants in the garden.

For more information on gardening in our area, visit the Butte County Master Gardener web page at: http://ucanr.edu/sites/bcmg/. If you have a gardening question or problem, call our Hotline at (530) 538-7201.

By Lynnde Sharpton, UC Master Gardener of Butte County, June 1, 2018

If you notice droopy, dried-out flower clusters on your pears, Asian pears, quince, apples or crabapples, fire blight may be the cause.

Fire blight is caused by a bacterium and is a common and frequently destructive disease that shows up in April and May.  Fire blight can also affect pyracantha, ornamental pear trees, and some other landscape plants.

The first sign of fire blight is often blackening of flowers, shoots or leaves followed by a watery, light tan ooze from affected shoots.  Open flowers are the most common infection site and remain susceptible until petal fall. 

Initially, fire blight infections might be localized, affecting only a flower cluster, but then the infection grows downward, extending into twigs and branches.  These twig cankers kill more and more tissue as they advance.  Dead, blackened leaves and fruit cling to dead branches throughout the season, giving the tree a scorched appearance -- hence the name “fire blight.”  The pathogen can kill highly susceptible trees, while others may suffer significant branch dieback.  Once infected, the plant will harbor the pathogen indefinitely unless the cankers are pruned out well below the infection. 

Fire blight development is favored by warm, humid weather in spring, and is spread by splashing rain and insects.  Our recent weather, including intermittent rain and hail, has produced ideal conditions for the spread of fire blight. 

Monitoring trees regularly, a couple of times a week, will allow you to identify and deal with new fire blight strikes before they become a branch infection.  It is important to remove and destroy any new fire blight infections before they spread and affect more tissue.  Dip pruning shears in a 10-percent bleach solution after each cut. 

If fire blight strikes have been ignored, the infection will spread and infect the branch.  Once the wood is infected, the branch must be pruned out well below the infection.  In this case, you will need to remove the diseased wood in summer or winter when the bacteria are no longer spreading through the tree.  Again, dip pruning shears in a 10-percent bleach solution after each cut. 

It is critical to make your cuts in the right place.  Find the lower edge of the visible infection in the branch, trace that back to the branch's point of attachment and cut at the next branch juncture down without harming the branch collar (this is the distinct enlarged portion of woody tissue formed at the base of a branch where it attaches to the trunk).  This will remove the infected branch and the branch to which it is attached. 

If fire blight occurs on a trunk or major limb the wood may be saved by scraping away the bark down to the cambium layer in affected areas (removing both outer and inner bark).  When scraping look for long, narrow infections that can extend further down the branch or trunk.  If any are seen, remove all discolored tissue plus 6-8 inches more beyond the infection.  This procedure is best done in winter when trees are dormant and bacteria aren't active.  Don't apply any dressing to the wound.  If the limb has been girdled, scraping won't work and the entire limb must be removed. 

When selecting new fruit trees, choose those that are less susceptible to fire blight, if possible.  The most susceptible varieties are Fuji, Gala, Golden Delicious, Granny Smith, Gravenstein, Jonathan, Mutsu, Pink Lady and Yellow Newton.  Unfortunately, most pear varieties are susceptible to fire blight.

For more detailed information on identifying and controlling fire blight, see IPM Fire Blight Pest Notes.